UNITED STATES DEPARTMENT OF THE INTERIOR

Walter J. Hickel, Secretary

Leslie L. Glasgow, Assistant Secretary

for Fish and Wildlife, Parks, and Marine Resources

Charles H. Meaeham, Commissioner, U.S. FISH AND WILDLIFE SERVICE

Philip M. Roedel, Director, Bubeau of Commercial Fisheries

FISHERY BULLETIN

VOLUME 68, No. 1

PUBLISHED BY UNITED STATES FISH AND WILDLIFE SERVICE • WASHINGTON • 1970
PRINTED BY UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON, D.C.

As the Nation's principal conservation agency, the Depart-
ment of the Interior has basic responsibilities for water,
fish, wildlife, mineral, land, park, and recreational resources.
Indian and Territorial affairs are other major concerns of
America's "Department of Natural Resources."

The Department works to assure the wisest choice in
managing all our resources so each will make its full contri-
bution to a better United States — now and in the future.

V3i HQ,

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SUPERSATURATION OF NITROGEN IN THE COLUMBIA RIVER AND ITS
EFFECT ON SALMON AND STEELHEAD TROUT

BY WESLEY J. EBEL, FISHERY BIOLOGIST
BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY
SEATTLE, WASHINGTON 98102

ABSTRACT

The nitrogen gas regime in the Columbia River was
studied in 1966 (from Grand Coulee Dam, Wash., to the
estuary at Astoria, Oreg.) and in 1967 (from Priest
Rapids Dam, Wash., to the estuary). Dissolved nitrogen
was subject to considerable seasonal fluctuation and
varied with flow of water over spillways of dams; it was
normal (near 100-percent saturation) in the fall and
winter when no water was spilled, and high (above 135-
percent saturation) in the spring and summer when
large volumes of water were spilled. Some saturation

levels over large areas were high enough and lasted long
enough to be potentially dangerous to salmon
(Oncorhynchus spp.) and steelhead trout {Salmo
gairdneri).

Supersaturation of nitrogen at Priest Rapids Dam
lowered the tolerance pf juvenile fish to temperature
increases, and some showed symptoms of gas bubble
disease. Field studies to determine the effects of high
levels of dissolved nitrogen on adult salmon and steel-
head trout did not provide conclusive results.

Observations in tlie spring of 1965 by tlie Wash-
ingt.on State Department of Fisheries and the
Bureau of Commercial Fisheries showed that
saturation of dissolved nitrogen at some sites in
the Columbia River was as high as 125 percent.
Because levels of this magnitude had protluced gas
bubble disease in adult and juvenile salmon
(Rucker and Hodgeboom, 1953; Harvey and
Cooper, 1962; and Westgard, 1964), additional
surveys were made in 1966-67 to attempt to deter-
mine whether high levels of dissolved nitrogen
might be responsible for losses of adult salmon
and poor production of young fish at spawning
channels.

The first phase in tlie study of nitrogen and
oxygen concentrations (February-November
1966) was primarily to determine the cause of
supersaturation of dissolved nitrogen and to deter-
mine seasonal variations. Water samples were
taken from 26 sites between Grand Coulee Dam,
Wash., near the Canadian border, and Astoria,
Oreg., at the mouth of tlie river. The second phase
(March-October 1967) was to determine the effect
of nitrogen sujiersaturation on adult and juvenile
salmon. We suspected that gas bubble disease was
one of the factoi-s in losses of adult and juvenile

Published June 1969.

chinook salmon {O. taJiawytscha) migrating be-
tween dams. The studies in 1967 concentrated on
obtaining field evidence of such losses.

This report discusses the amounts of dissolved
nitrogen in 1966-67, the effect of dams and reser-
voirs on saturation, the seasonal variation and
duration of supersaturation, and the effect of
supersaturation of nitrogen on juvenile and adult
salmon and steelhead trout {Salmo gairdTieri) in
the Columbia River.

METHODS

Descriptions of the sampling stations, analyti-
cal tecliniques, and other experimental procedures
are given in this section.

SAMPLING STATIONS AND TECHNIQUE

Twenty-six principal sampling stations were
established along the Columbia River between the
forebay of Grand Coulee Dam and the estuary at
Astoria (fig. 1). All stations except 13, 25, and 26
were either in midreservoir, about 500 m. upstream
from the dam, or on the spillway side of the river,
about 500 m. below. Samples of water were taken
at the surface and at 10-m. depths at the forebay
stations. The spillways discharge from the surface
down to a maximum depth of about IO14 m., and

FISHERY BULLETIN: VOL. 68, NO. 1

Chief Joseph
5
Wells

Grand
Coulee

3 2-

WenatcheeiR.

Rocky Reach
7
8^^%^ Rock Island
9

Wanapum

Priest Rapids
12

.11

Yakima R.

19

15

16

14

Ice
Harbor

RIVER

22 2

20

18

McNary

17

OREGON

24

23

John Day

The Dalles

FiGiTRE 1. — Principal sampling stations on the Columbia and Snake Rivers.

the turbines withdraw water from about 8 m. down
to 20 ni. at all the dams downstream from Chief
Joseph Dam. Maximum f orebay depths at full pool
do not exceed 45 m. Because of these facts and the
fact that temjDeratures in the forebay of the reser-
voirs seldom varied more than 1° C. from the sur-
face to tlie bottom, a sample at the surface and
10-m. depth was sufficient to represent the aver-
age forebay concentration and in turn represent
the water passing through the turbines and spill-
ways. Duplicate samples were collected at the sur-
face at stations below the dams where high current
velocities made it impossible to sample at depth.
Because the amount of soluble nitrogen depends on
water temperature/ the temj^erature of each sam-
ple was recorded before it was placed in an iced
cooler for transport to the laboratory. The use of

' An iitmosphiric pressure o( 760 mm. mercury was used in
computing normal saturation (100 percent) for each sample.

two aircraft made it jwssible to obtain all samples
in 1 day ; analysis was completed on the following
day.

Water samples were obtained from additional
stations when more information was needed for a
specific dam or reservoir. For example, additional
stations were established along the reservoirs be-
hind McNary and Chief Joseph Dams to study
changes in nitrogen content of water passing
through these reservoirs. Additional stations were
also sampled when the effect of a specific dam on
saturation levels was examined. Table 1 gives a
detailed description of the principal sampling
stations and the dates when samples were obtained.

ANALYSIS

The amount of dissolved nitrogen in the sample
was determined by a modification of the technique
used by Swinnerton, Linnenbom, and Cheek
(1962). A Fisher blood gas analyzer Model

U.S. FISH AND WILDLIFE SERVICE

Table 1. — Locations and dales of sampling in the Columbia and Snake Rivers; sampling sites are shown by number in figure 1

Dates sampled

1966

1967

Feb.

Mar.

Apr.

May

June July

Aug.

Sept

Oct.

Nov.

Apr.

May

June

July

Aug.

Sept.

Oct.

9

7

9

6

11

1

6

7

3

5

3

6

18

1 15

6 27

5

19

2 23

Num-

ber

Station

1

Forebay— Grand Coulee

X

X

X

X

X

X

X

X

X

X

X

Dam.

2

Tailrace— Grand Coulee
Dam.

X

X

X

X

X

X

X

X

X

X

X

3

Forebay — Chief Joseph
Dam.

X

X

y

y

X

X

X

X

X

X

X

4

Tailrace — C hief Joseph
Dam.

X

X

X

y

X

X

X

X

X

X

X

5

Wells dantsite

Forebay — Rocky Reach
Dam.

X
X

X
X

X
X

X

y

X
X

X
X

X
X

X
X

X
X

X
X

X
X

6

7

Tailrace — Rocky Reach
Dam.

X

X

X

y

X

X

X

X

X

X

X

g

Forebay— Rock Island
Dam.

X

X

y

y

X

X

X

X

X

X

X

9

Tailrace— Rock Island

X

X

y

y

X

X

X

X

X

X

X

Dam.

10

Forebay— Wanapum
Dam.

X

X

y

y

X

X

X

X

X

X

X

11

Forebay — Priest Rapids
Dam.

X

X

X

X

X

X

X

X

X

X

X

.... X

X

X

X ....

X

12

Tailrace — Priest Rapids
Dam.

X

X

X

X

X

X

X

X

X

X

X

.... X

X

X

X ....

13

Columbia River at
Richland, Wash.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

14

Forebay— Ice Harbor
Dam.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X ....

X

X

15

Tailrace— Ice Harbor
Dam.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

16

Forebay — McNary Dam
(north sidt).

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

17

Forebay — McNary Dam
(south side).

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

18

Tailrace— McNary Dam
{south side).

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

19

Tailrace— McNary Dam
(nortli side) .

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

20

John Day damsite

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

21

Forebay— The Dalles
Dam.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

22

Taih-ace— The Dalles
Dam.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

23

Forebay — Bonneville
Dam.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

24

Tailrace— Bonneville
Dam.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

25

Columbia River at
Longview, Wash.

X

X

X

X

X

X

X

X

X

X

X

X

X X

X X

X

X

X X

X

X

26

Columbia River estuary
Astoria, Oreg.

X

X

y

y

X

X

X

X

X

X

X

X

6-390V2 - was substituted for tlieir Model 25, and
the length of the extraction chamber was increased
to 150 mm. Model G-390V2 is more sensitive than
Model 25, and the longer extraction chamber
allowed analysis of larger samples.

Saturation values quoted in this report are cor-
rect to within ±2 percent. Limitations in the
accuracy of the method and the uncertainty of the
theoretical solubilities of nitrogen precluded more
precise interpretation.

- Trade nanii's referred to in this publication do not Inipl.v
iMidorsement of coninier<'i;il products by the Unreau of Com-
iiiercinl Fisheries.

EFFECT OF DAMS AND RESERVOIRS ON
SATURATION OF DISSOLVED NITROGEN

Major causes of supersaturation of water with
gases are heavy concentrations of algae (Wood-
bury, 19i2), warming of water without adequate
circulation and exposure to the atmosphere for
equilibration, and falling of water into an en-
closed plunge basin (Harvey and Cooper, 1962).
Algae concentrations like those described by
Woodbury are not found in the Columbia River
and the river is not warmed sufficiently at any
location to account for the high concentrations
previously recorded. Spillways at dams create

SUPERSATURATION OF NITROGEN IN COLUMBIA RIVER

conditions similar to those described by Harvey
and Cooper and were suspected to be the major
cause of supersaturation ; during periods of high
flow, large volumes of water plunge from spill-
ways at all the dams on the Columbia River into
various types of basins.

OBSERVATIONS AT DAMS

Samples analyzed at individual dams to deter-
mine the effect of turbines and spillways on dis-
solved nitrogen indicated that supersaturation in
the Cohmibia River is caused primarily by spill-
ways. This was clearly demonstrated during tests
at Bonneville Dam in March 1966 when the Corps
of Engineers spilled large volumes of water at a
time when spilling normally does not occur. Vari-
ables, such as spilling at upstream dams and rapid
temperature increases, were eliminated; the only
factor which remained that could create super-
saturation was the spilling of the water. The con-
centration of dissolved nitrogen at Bonneville Dam
before and during these spillway tests is shown in
figure 2. Two replicates of samples were taken be-
fore spill and three replicates after spill at each
location. Maximum variance in analysis at each
location before spill was 4 percent; after spill, 6
percent. Concentrations in the forebay and below
the turbines and spillway before the spill tests were
near normal saturation (98-102 percent). During
the spill tests, concentrations below the spill in-
creased to 125-percent saturation, whereas concen-
trations in the forebay and below the turbines
remained near 100 percent.

Nitrogen levels at other dams (table 2) indicated
that each dam has different, characteristic effects
on nitrogen saturation. The spillways at Bonne-
ville, Grand Coulee, and Ice Harbor Dams in-
creased the concentration of nitrogen, but the
amount of the increase differed. By contrast, the
spillway at Priest Rapids decreased the concentra-
tion when the water was supersaturated above the
dam. Differences in the structural arrangement of
the dams, shape of the spillways, and depth of
tailwater are factors which could explain the
differences.

EQUILIBRATION IN RESERVOIRS

Sampling throughout the length of resei-voirs
above Chief Joseph and McNaiy Dams showed
that water supersaturated with dissolved nitrogen

Table 2. — Average nitrogen concentrations (percentage
saturalion) in ike Columbia River of samples taken at
specific dams to determine effect of dams on water passing
through turbines and over spillways (spring 1966)

- Forebay Tail- Forebay Tail-
Location and date above water above water Samples Spill

spill below turbines below volume

spill turbines

Bonneville- Percent Percent PercerU Percent Number 100 cm. a.

Mar. lOandll 102 125 94 98 8 28.3-42.6

Ths Dalles'

Feb. 27-Mar. 2 103 104 102 97 12 1-33.7

Ice Harbor: , „ „

May 16 and 18 109 118 107 106 8 .6-0.8

Priest Rapids: , „ „ ,

May26and31 131 114 121 --. 8 1.9-2.4

Orand Coulee:

Apr. 27 106 129 105 106 4 .7

does not equilibrate during transit. In McNary
Reservoir on June 8, the saturation of nitrogen
that entered the reser\oir from the Columbia River
averaged 127 percent ; samples collected in the fore-
bay of McNai7 Dam on the same day averaged 127
percent. Evidently, hu'k of circulation and warm-
ing of the surface water in the foi-ebay tended to
maintain the saturation level.

SEASONAL AND DAILY VARIATIONS IN
SATURATION OF DISSOLVED NITROGEN

As expected, variations of dissolved nitrogen
concentrations from Grand Coulee Dam to the
estuary depended largely on the volume of water
released over the spillways. Nitrogen saturation in
February, March, and April of 1966 was below 110
percent except below dams where intermittent
spilling occurred. On February 9, when no dams
were spilling (table 3), all samples had saturation
below 105 {percent (fig. 3). The concentrations in
March were nearly the same except below the Bon-
neville spillway where spilling was minimal. Satu-
ration of dissolved nitrogen i-emained below 110
percent through April except in areas of spilling.
Streams began to rise in April, and spill releases
became regular at all dams by early May. Sur-
face concentrations of nitrogen were over 110 per-
cent at all stations except in the forebay of Grand
Coulee and The Dalles Dams. The highest concen-
tration in May (132 percent) was downstream
from the spillway at Bonneville Dam. Tempera-
ture on May 9 ranged from a low of 8.5° C. (47.3°
F.) in the forebay of Chief Joseph Dam to a high
of 15.3° C. (59.5° F.) in the forebay of Grand
Coulee Dam.

U.S. FISH AND WILDLIFE SERVICE

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[23 DURING SPILL TEST

f:

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^

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y...

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FOREBAY
ABOVE
SPILLWAY

TAILWATER

BELOW
SPILLWAY

FOREBAY
ABOVE
TURBINES

TAILWATER

BELOW
TURBINES

Figure 2. — Percentage saturation of dissolved nitrogen in 32 samples taken near Bonneville Dam before and

during spill tests, March 3-11, 1966.

SUPERSATURATION OF NITROGEN IN COLUMBIA RIVER

STATION LOCATIONS

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TT

TT

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X

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JUNE 6. 1966
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AUGUST 1,1966

O

OCTOBER 3, 1966

Nitrogen gas soturation in forebay

(overage of surface + lO-mefer samples)
O Nitrogen gas saturation in lailwoters below dams
Temperoture "C. (forebay at lOmeters)

X

X

16

14
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12

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22 I

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18

16

- 20

- 14

160 320 480 640 800

DISTANCE FROK^ MOUTH OF RIVER (KM.)

960

120

Figure 3. — Saturation of dissolved nitrogen and temperature of samples in Columbia River from
Astoria to Grand Coulee Dam, February to October 1966.

U.S. FISH AND WILDLIFE SERVICE

Table 3. — Mean daily

spill (S.) and. total floiv (T.), in 100 c.tn.s. (hundreds of oubic meters per second), at different
Columbia River dams, February-November 1966

Dam

Feb. 9

Mar. 7

Apr. 6
S. T.

May 9
S. T.

June 6

July 1
S. T.

Aug. 1
S. T.

Sept. 6
S. T.

Oct. 3

Nov

.7

S.

T.

S.

T.

S. T.

S.

T.

S.

T.

Grand Coulee

0.0

21.8
23.2
23.7
24.3
24.7
25.4
7.1
31.7
33.0
33.7

0.0
.0
.0
.0
.0
.0
.0
.0
.0
.0

21.9
26.1
22.4
23.2
27.1
26.9
19.3
26.4
27.1
24.3

0.0
.0
.0
.0
.0
.0
.0
.0
.0
.0

17.5
15.1
16.5
17.4
19.4
19.4
19.3
42.8
46.4
44.9

19.4 47.2

28.8 47.5

52.0

57.7

17.1 54.3

21.9 56.2

19.3 30.9
50.7 91.4

43.4 84.1
59.6 86.5

100 c.m.a.

55.1 74.7 49.7 66.3
60.3 77.9 48.1 71.1

78.1 _ 68.5

83.5 73.3

46.0 80.8 31.9 69.2

46.8 81.4 36.3 70.3

9.7 21.0 .0 7.2

66.7 99.4 41.7 79.1
60.3 101.0 39.3 80.3

67.8 99.6 47.3 80.1

22.4 42.9

20.7 41.4

43.6

45.4

1.9 44.8

36.2 35.7

.0 6.1

11.1 54.1

11.5 57.6

23.8 56.6

0.0
.0
.0
.0
.0
.0
.0
.2
.0
.0

19.5

22.6
22.0
22.3
23.1
23.2
6.2
24.6
28.7
27.8

0.0
.0
.0
.0
.0
.0
.0
.0
.0
.7

21.0
20.6
20.1
20.5
23.5
23.6
4.5
25.3
25.3
28.1

0.0
.0
.0
.0
.0
.0
.0
.0
.0
.0

18.4

Chief Joseph

.0

16 5

Rocky Reach

17.5

.0

17.5

Wanapum

Priest Rapids

Ice Harbor

McNary.

The Dalles

Bonneville.- --

.0

22.1
21.5
6.1
25.7
26.2
26.6

The. higliest nitrogen saturation during 1966
occurred in June. Concentrations ranged from 112
to 140 percent ; most of the samples were above
120 percent (fig. S). These values remained high
tlirough August between Grand Coulee and Priest
Rapids Dams. On July 11 and August 1, however,
the river equilibrated rapidly between Priest
Rapids and McNary Dams. Concentrations in the
forebays dropped from an average of 1152 percent
at Priest Rapids Dam to an average of 109 per-
cent at McNary Dam. Spilling at Bonneville Dam
tiien increased the saturation to above 120 percent
downstream from Bonneville. The rapid equilibra-
tion of gas content between Priest Rapids and
McNary Dams during July and August was jirob-
ably caused by the increased circulation of water
in the unimpounded river area below Priest
Rapids and the lower total flow and spill volumes
at Priest Rapids and Ice Harbor Dams (table 3).

In September, Columbia River flows had de-
creased further and spilling had almost ceased at
all dams; tliis cjiange precipitated a marked reduc-
tion in the saturation of nitrogen at all stations —
only five samples were above 110 percent. Satura-
tion continued to decrease in October and was well
below 110 percent — ranging from 88.4 percent at
Rocky Reach Dam to 100.6 percent at Grand
Coulee Dam. Water temperatures in October
ranged from 16.1° to 18.6° C. (60.8-65.5° F.), and
the average temperature was about 1° C. lower
than in September. The lack of spilling and lower
water temperatures accounted for the decrease in
saturation from August to September.

In the last survey during 1966, on November 7,
the saturation was not significantly different from
that in October 1966 (or November 1965).

DIURNAL VARIATIONS

During a 24-hour period (June 30 and July 1,
1966) of moderately high saturation in the forebay
of The Dalles Dam, nitrogen concentrations
varied only 0.6 p.p.m. from a maximum of 18.6
p.p.m. (114 percent saturation). Spill volumes at
The Dalles Dam were nearly constant for the 24-
hour period.

SEASONAL VARIATIONS IN THE SNAKE RIVER

Sami^les from the tailrace below the spillway of
Ice Harbor Dam in the Snake River (station 15)
indicated a seasonal variation in amount of nitro-
gen similar to that in the Columbia River; i.e.,
normal saturation before spill releases increased
saturation as spill releases increased and de-
creased saturation as spill releases subsided. The
timing of the cycle differed from that in the
Columbia River, as spilling at Ice Harbor Dam
usually l^egan in late April, peaked about mid-
May, and ended by mid-June. Thus, the net effect
of the Snake River discharge on saturation in the
Columbia River was to increase the amount of
nitrogen in late April and May and decrease it in
June, July, and August.

COMPARISION OF 1966 AND 1967

Saturation of dissolved nitrogen in 1967 fol-
lowed the same general seasonal changes as in
1966. Values were normal in winter and early
spring before the dams began spilling, but rose as
spilling increased. Levels again were highest in
June and July when the largest volume of water
passed through the spillways. When spilling
ceased and cooling of the river began in Septem-
l)er and October, saturation decreased sharply
(fig. 4).

SUPERSATURATION OF XITROGEN IN .COLUMBIA RIVER

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70-

60-

OCTOBER 3

POTENTIALLY DANGEROUS
SATURATION LEVEL

80 160 240 320 400 480

DISTANCE FROM MOUTH OF RIVER (KM.)

560

640

Figure 4. — Saturation values of dissolved nitrogen in samples of Columbia River water taken from Long-
vievc. Wash., to Priest Uapids Dam, May 1, June 6, August 2, and October 3, 1967. (Values shown are
the averages of the surface and 10-m. sample at each location.)

Saturation in May 1967 (102-115 percent) was
considerably lower than in May 1966 (110-133
percent) because spillway releases in 1967 were not
significant on tlie main Columbia until late May.
By mid-Jmie 1967, however, extremely high spill-
way releases brought even higher saturations than
were recorded in 1966.

In 1966-67 the saturation of dissolved nitrogen
over a large area of the river was sufficiently high
and of sufficient duration (middle to late May
through mid-August) to be a potential danger to
migrating juvenile and adult salmon and trout.
Experiments by Westgard (1964) showed that
adult chinook salmon held in water with concen-
trations of dissolved nitrogen at 116 percent sat-
uration de\^lopecl definite symptoms of gas l)ul)ble
disease. Harvey and Smith (1962) indicated that
saturation as low as 108 jaercent produced gas bub-
ble disease in fingerlings at Cultus Lake Trout
Hatchery. These values were much lower than
those recorded in the Columbia River. The fish
were held in shallow ponds or raceways, however,

whereas fish in the Columbia Eiver are usually able
to move to greater (compensating) depths, except
when they are ascending fish ways. The ability of
fish to seek compensating depths must be taken into
account in the assessment of the effect of high sat-
uration of nitrogen in the Columbia River.

EFFECT OF SUPERSATURATION OF

DISSOLVED NITROGEN ON SALMON

IN THE COLUMBIA RIVER

Studies of suijersaturation of nitrogen in 1967
were made in conjunction with tagging studies
designed to determine the cause of loss of adult
fish during their migration from Bonneville to Ice
Harbor and Priest Rapids Dams.^ The primary
purpose in 1967 was to determine the effect of dis-
solved nitrogen on juvenile and adult salmon and
st«elhead known to be in the river when concen-
trations of dissolved nitrogen were high.

'■' Tagging stud.v in progress by Bureau of Commercial Fisheries,
Seattle, Wash. — James H. Johnson, Program Leader.

8

U.S. FISH AND WILDLIFE SERVICE

JUVENILE SALMON

Examination of juvenile chinook salmon that
suffered excessive mortality in holding tanks (used
for marking fish) at Priest Rapids Dam in 1966
revealed that most fisli had symptoms of gas bub-
ble disease. Although the fish otherwise appeared
to be sound, they were definitely distressed and, if
held, eventually died from gas embolism. Dissolved
nitrogen concentrations at Priest Rapids Dam
ranged from 114 to 133.9 percent saturation. Tem-
I>erature in the gatewells of the dam from which
fish were collected ranged from 13.9° C. (57° F.)
on July 7 to 17.8° C. (64.0° F.) on August 31
wlien operations ceased. The water temperature
in the holding tanks usually rose about 1° to 2° C.
before marking began. This slight increase was
sufficient to liberate enough gas from the blood of
the fish to cause embolism and death. The symp-
toms of gas bubble disease and distress were
eliminated if these fish were held in water slightly
cooler than that in the river where they were col-
lected. Usually a decrease of 1° or 2° C. was suffi-
cient to reduce the mortality.

Apparently, juvenile chinook salmon, equili-
brated to supersaturation of nitrogen in this tem-
perature range, have considerably less tolerance
to increases in temperature than fish that are
equililirated to normal saturation. Brett (1952) in
his studies of the tolerance range of juvenile salm-
on to temperature changes showed that spring
chinook salmon acclimated to 10° C. (50° F.)
could tolerate temperatures up to 24.6° C. (76.1°
F.) before mortalities began. The fish at Priest
Rapids Dam, which were acclimated to higlier
temperatures (13.9-17.8° C), could not tolerate
increases of 1° to 2° C.

It was apparent from observations at Priest
Rapids Dam that juvenile migrants were in a pre-
carious situation in July and August. If they did
not remain at sufficient depth to compensate for
the supei-saturation of dissolved nitrogen, they
died of gas bubble disease. Their tolerance to tem-
perature increases was also lowered; conceivably
sudden temperature increases of only a few de-
grees centigrade would have caused mortality.

We conducted an experiment in the forebay of
Priest Rapids Dam to determine the depth at
which juvenile fish must remain to avoid gas bub-
ble disease wlien subjected to supersaturation of
nitrogen. Juvenile coho (0. Msutch) and chinook

salmon were held in i^ens submerged at different
depths in the forebay and then observed by
SCUBA divers at various intervals for symptoms
of gas bubble disease. Three tests from 200-280
hours' duration were conducted from May 28 to
August 14, 1967, a period when saturation of dis-
solved nitrogen changed from a high of 143 per-
cent in late May and June to 118 percent in Au-
gust. Hatchery-reared coho salmon were used in
tests 1 and 2 and wild chinook in test 3. One
hundred fish were placed in each test cage and in
a control cage held in river water of normal sat-
uration at the dam. Tlie first observation was made
about 12 hours after placing the cages at the
selected depths in the forebay. Other observations
were made at 24-hour intervals for the first 4 days ;
the time between observations was increased
thereafter, depending on rate of mortality. Dead
fish were brought to the surface by divers and
examined for symptoms of gas bubble disease.
Neither test nor control fish were fed during the
tests. In one test 100 percent of the coho salmon
in a surface pen and 70 percent in a pen lowered
to a depth of 2 to 3 m. died from gas bubble dis-
ease (fig. 5) . Three percent was the maximum mor-
tality for control fish held during the test. The
experiment showed that at 130 to 140 percent sat-
uration fish must remain below 2.5 m. if they are
to be free of symptoms of gas bubble disease. From

TEST I
COHO

TEST 3
CHINOOK

0.5- 2 2 5
1,5 3 3 5

DEPTH OF CAGES

2.0 2 5 0-
3 3 5 GO

(M.)

05- 20 25- 0-
I 5 3.0 3 5 6.0

Figure .5. — Percentage mortalit.v caused by gas bubble
disease during holding exixriment in forebay of Priest
Rapids Dam May 28 to August 14, 1967. Saturation of
dissolved nitrogen ranged from 14.3 iiereent in test 1
to lis i>ercent in test 3 ; flsli were held about 200 hours
in tests 1 and 2,280 hours in test 3.

SUPERSATURATION OP NITROGEN IN COLUMBIA RIVER

6 to 16 percent of the coho and chinook salmon died
in a pen whicli allowed the fish to seek any depth
from the surface to 6 m., which suggested that
some mortality may also have occurred to naturally
migrating fingerlings even though they could move
to any depth.

These field observations of juvenile migrants,
though limited, indicate that naturally migrating
juvenile fish in the Priest Rapids Dam area ai*e
under stress from supersaturation of dissolved
nitrogen; it is highly probable that a significant
percentage of the fish is lost. The Hanford area of
the ri\ier downstream from Priest Rapids is of
particular concern. Juvenile and adult salmon al-
ready under stress must pass areas where thennal
reactors emit large volumes of water with tem-
peratures 10° to 15° C. higher than the river
temperatures, ()b^•iously, fish under stress from
supersaturation of gases have less tolerance to
rapid temperature increases, and losses of fish
which inadvertently enter the thermal plumes are
inevitably high. Further investigation seems im-
perative on the effect of supersaturation of dis-
solved nitrogen on the tolerance of salmon to
temperature increases.

ADULT SALMON AND STEELHEAD TROUT

About 2,300 adult chinook salmon, 1,600 .steel-
head trout {tSalmo gainhieri), and 1,000 sockeye
salmon {Oncorhynclms nerha) were examined at
Bonneville and McNary Dams from mid-April
through mid-October 1967 for external symptoms
of gas bubble disease. The external symptoms that
were used to indicate gas bubble disease were (1)
gas bubbles under skin, in roof of mouth, and in
fin membranes and (2) hemorrhaging inside the
eye and the associated "pop eye" condition of the
eyeball. Nitrogen saturation was measured at both
dams so that the incidence of disease symptoms
could be correlated with the saturation of nitrogen.

Examination of the adult salmon and steelhead
trout began on April 11 when saturation was about
106 percent and continued until May 25 when sat-
uration was near 120 percent. Because nitrogen
saturation did not exceed 110 percent until May
10, little incidence of gas bubble disease -was ex-
pected; 1 of 125 steelhead trout examined showed
symptoms of the disease (on May 25).

Observations of adult fish at McNary Dam be-
gan on June 23 and ended October 11. Nitrogen

saturation ranged from 131 percent in June to 104
percent in October. Saturation was high (above
120 percent) from June 23 to July 19 but began
to drop sharply after July 19 ; by August 22, val-
ues were below 110 percent. In July, symptoms of
gas bubble disease were noted in 10 of 1,000 sock-
eye salmon, but none were observed in 1,762
chinook salmon and 1,461 steelhead trout. Ap-
parently, chinook salmon and steelhead trout in
this area either compensated for the high satura-
tion by remaining at a sufficient depth or the
symptoms of the disease had not progressed suffi-
ciently to be evident.

Surveys for carcasses of adult fish were made
from April to October during each flight made to
obtain water samples. Four additional aerial sur-
veys for carcasses were made during June and
July when saturation was highest. Carcasses of
eight dead salmon (and a few unidentified fish)
were deserved; however, it could not be positively
verified that any of these fish had died from gas
bubble disease. Generally, the fish were too decom-
posed for determination of cause of death.

Steelhead trout and chinook salmon were ob-
served (June 15 to September 19) congregating in
the Columbia River at its confluence with the
Snake River. Saturation of dissolved nitrogen in
the Columbia ranged from 110 to 130 percent, and
temperatures in the Snake River were as much as
5.7° C. (10.3° F.) higher than in the Columbia
(table 4). Fish equilibrated to supersaturation of
dissolved nitrogen in the Columbia could have died
fi-om gas embolism if they had entered the Snake
River at this time. A concentrated search on the
surface by boat and on the bottom with SCUBA
did not yield carcasses of any salmon whose death

Table 4. — Temperature (° C.) and percentage saturation of
dissolved nitrogen in the Columbia and Snake Rivers at
the mouth of the Snake River — June 6 to Sept. 5, 1967

Date

Columbia River at mouth
of Snake River

Snake River at mouth

Tempera-
ture

Saturation

of dissolved

nitrogen

Tempera-
ture

Saturation

of dissolved

nitrogen

June 6

June 27...

13.2
14.2

Percent
130
129
129
126
120
119
118
118
118
110

°C.
12.2
16.3
19.4
22.2
23.0
23.7
26.0
24.7
23. S
23.3

Percent
126
123

Julys

July 19

16.6
17

113

July 27

18.4

109

Aug. 2-

Aug. 9

Aug. 15

Aug. 30

Sept. 5

19.1
19.3
21.0
20.3
21.2

111
108
106
103

105

10

U.S. FISH AND WILDLIFE SERVICE

could be attributed to gas bubble disease or gas
embolism. A study of the movement of these fish
indicated that many did not reach Ice Harbor
Dam.^ The destination or fate of these fish was
not determined.

We have no positive evidence to indicate that the
high nitrogen saturation in the Columbia River in
1907 caused serious mortality of adult salmon, but
tlie possibility cannot be discounted. From the sur-
veys and searches made in 1967 it was obvious that
it would be difficult to detect a continuous low rate
of mortality in a river the size of the Columbia
even witli continuous surveillance. Various reports
of mortality were received from local residents,
but again it could not be established that fish had
died from gas l)ublile di-sease.

SUMMARY AND CONCLUSIONS

A seasonal cycle of supersaturation of dissolved
nitrogen occurs each year in the Columbia River.
Degi-ee of supersaturation varies with flow of wa-
ter over spillways of dams. levels are normal
(near 100-percent saturation) in the fall and win-
ter when little or no spilling takes place and high
(above 120 percent) in the spring and summer
when large volumes of water are being spilled.
Water plunging over spillways is the primary
cause of supersaturation in the Columbia River.

Water supersaturated with nitrogen does not
equilibrate rapidly in reservoirs. Lack of circula-
tion and increases in surface Avater temperature
tend to slow the rate of equilibration. Saturation
of dissolved nitrogen in the Columbia River is
sufficiently high and occurs over a large area over
a sufficiently long time to be potentially dangerous
to salmon and steelhead trout. Observations of
juvenile salmon at Priest Rapids Dam indicate
tliat supersaturation of nitrogen otfers a definite
problem; further study is needed to determine its
extent.

Field observations to determine the effect of
high levels of dissolved nitrogen on adult salmon
and steelliead trout were not conclusive. Some

' PereentaKp of tng rPtiinis from fish Mihjpctfc] to tliesn coiidi-
tloiis was lUiont TiO iicn-iTit lownr than ri-turns from other Krmipx
passing over Icp Harbor Dam. (Verbal conimnnic'ation. Gerald
Monan, BCP Biolopioal Laboratory. Seattle. Wash.)

sockeye salmon and steelhead trout were observed
with symptoms of gas bubble disease, but no
Chinook salmon had symptoms. A potential prob-
lem exists for adult salmon and trout migrating
from the Columbia River into the Snake River in
July and August. Fish equilibrated to supersatura-
tion of nitrogen from the Columbia River encoun-
ter an increase of 5° to 6° C. in temperature on
entering the Snake River. The tolerance of the
salmon to this temperature change under those
conditions is unknown.

ACKNOWLEDGMENTS

I thank Richard Westgard of the Washington
Department of Fisheries for providing photos of
external symptoms of gas bubble disease in adult
chinook salmon and for his advice on analytical
techniques for dissolved nitrogen. I also thank
Richard Krcma of the Bureau of Commercial
Fisheries, Pasco, Wash., for his help in conducting
the holding experiment at Priest Rapids Dam.

LITERATURE CITED

Brett, J. R.

19.52. Temperature tolerance in young Pacific salmon,
genns Oncorhynchi/g. J. Fish. Res. Bd. Can. 9 : 265-
.323.
Harvey, H. H., and A. C. Cooper.

1962. Origin and treatment of a supersaturated river
water. Int Pac. Salmon Fish. Comm., Progr. Rep.
9, 19 pp. [Processed.]
Harvey. H. H., and S. B. Smith.

1962. Supersaturation of the water supply and oc-
currence of gas bubble disease at Cultus Lake trout
hatchery. Can. Fish Cult. .30: .39-17.
RucKER, R. R., and K. Hodgeboom.

195.3. Observations on gas-bubble disease of fish.
Progr. Fish-Cult. 15 : 24-26.
SwiNNERTON, J. W., V. J. LiNNENBOM, and C. H. Cheek.
1962. Determination of dissolved gases in aqueous
solutions l)y gas chromatography. Anal. Chem.
34 ; 483-485.
Westgard. Richard L.

1964. Physical and biological aspects of gas-bubble
disease in impounded adult chinook salmon at Mc-
Nary spawning channel. Trans. Amer. Fish. Soc.
93 : 306-309.
Woodbury, Lowell A.

1942. A sudden mortality of fishes accompanying a
supersaturation of oxygen in Lake Waubesa, Wis-
consin. Trans. Amer. Fish. Soc. 71 : 112-117.

SUPERSATURATION OF NITROGEN IN COLUMBIA RIVER

11

U. S. GOVERNMENT PRINTING OFFICE : 1969 O - 329-409

ADDITIONS TO A REVISION OF ARGENTININE FISHES

BY DANIEL M. COHEN, Zoologist, AND SAMUEL P. ATSAIDES,' Biological Technician
BUREAU OF COMMERCIAL FISHERIES SYSTEMATICS LABORATORY, U.S. NATIONAL MUSEUM

WASHINGTON, D.C. 20560

ABSTRACT

Four new species of the genus Argentina are de-
scribed, three from the western Atlantic and one from
Peru. Range extensions are presented for A. euchus from
the western Indian Ocean and A. sialis from the north-
eastern Pacific. Speciation in the genus is discussed,
and a l(ey is presented to the 12 species recognized.

Pigmentation of the swimbladder and its significance
as a systematic character are discussed.

A new species of Glossanodon from the western Indian
Ocean is described, and additional material of G. polli
from the tropical eastern Atlantic is noted.

Argentinine fishes are taken in commercial
quantities in the temperate western North Atlantic
(Emery and McCracken, 1966) and are forage
fishes in Australia (Fairbi-idge, 1951). Species
found in tropical waters are usually associated
with shrimp grounds and are available to shrimp
fishing gear. This paper su^jplements the revision
of argentinine fishes published by Cohen in 1958.
Since then, additional material has accumulated
comprising undescribed species, additional ma-
terial of poorly known forms, and range exten-
sions. In this paper we reassess the status of pop-
ulations in the genus Argentina. We discuss
speciation, comment on swimbladders, and de-
scribe one new species from Peru and three from
the tropical western Atlantic. Range extensions
are recorded for A. euchxi^ from the western In-
dian Ocean and A. sialis from the northeastern
Pacific. A new species of Glossanodon from the
western Indian Ocean is described, and additional
material of G. polli from tropical West Africa is
noted.

MATERIALS AND ACKNOWLEDGMENTS

We have received material from the Smithsonian
Oceanographic Sorting Center ; the U.S. Progi-am
in Biology of the International Indian Ocean Ex-
pedition; the Guinean Trawling Survey; the

Southeastern Pacific Biological and Oceano-
graphic Program; the Bui'eau of Commercial
Fisheries Exploratory Fishing and Gear Research
Bases at Pascagoula, Miss., and Seattle, Wash.;
and Scripps Institution of Oceanogi-aphy.

Specimens stored in the following collections
have been examined : U.S. National Museum,
Wash., D.C. (USNM) ; Harvard Museum of Com-
parative Zoology, Cambridge, Mass. (MCZ) ;
Field Museum of Natural History, Cliicago, 111.
(FMNH) ; Stanford University Division of Sys-
tematic Biology, Stanford, Calif. (SU) ; Scripps
Institution of Oceanogi-aphy, La Jolla, Calif.
(SIO) ; British Museum, Natural History, Lon-
don (BMNH) ; Museum National d'Histoire
Naturelle, Paris (MNHN) ; Universitetets Zoo-
logiske Museum, Copenhagen (UZMC) ; Univer-
sity of Miami Marine Laboratory, Miami, Fla.
(UMML) ; Bureau of Commercial Fisheries
Tropical Atlantic Biological Laboratory, Miami,
Fla. (TABL) ; Academy of Natural Sciences,
Philadelphia, Pa. (ANs'P) ; Tulane University,
New Orleans, La. (TU) ; University of Florida,
Gainesville, Fla. (UF) ; Gulf Coast Research
Laboratory, Ocean Springs, Miss. (GCRL) ; and
California Academy of Sciences, San Francisco,
Calif. (CAS).

'Also Department of Zoology, University of Maryland, College Park,
Md. 20740.

Published June 1969.
FISHERY BULLETIN: VOL. 68, NO. 1

13

We thank the curators of the collections listed
above for allowing us to examine specimens in their
care and providing X-ray photographs. We also
thank the many individuals in the field programs
listed above who have helped us.

METHODS

Methods and definitions follow Cohen (1958).
We note in particular that the split posterior ray
of the dorsal and anal fins is counted as two rays
and that the vertebral count does not include the
urostyle or the hypural fan. The method of count-
ing gill rakers is shown in figure 1. Meristic
characters are given as the mode followed by the
range in parentheses. Where the range includes
data for more than one species, no mode is given.
Measurements are given as the mean followed by
the range in parentheses.

FIOUEE 1.— Argentina striata, USNM 203001. First gill
arch from left side ; rakers on lower arm are counted as
six. Gill filaments are not shown. Drawn by Mildred H.
Carrington.

GENUS ARGENTINA LINNAEUS

For this genus, we divide the species into two
groups and discuss sympatry and its significance,
taxonomic significance of the swimbladder, and
present a key to the species of Argentina.

SPECIES GROUPS

The 12 species of Argentvna are divided into two
groups.
Species Group 1

Four species are in this group. They are silus
and sphyraena from the North Atlantic and Med-
iterranean and .^ialis and aliceae from the eastern
Pacific. This group is distinguished by its larger
jaw, almost always greater than 21.5 percent of
head length (fig. 2), and usually more gill rakers
(7-21 on the lower arm of the first gill arch ; one

species, A. sphyraena, has few gill rakers, 7-10,
but the other three species have 11-21 ; see table 1) .
The species in this group are allopatric (although
the gross geographical ranges of sphyra^ma and
silus overlap, they are ecologically separate,
mainly living and certainly spawning at different
depths), and are very distinct morphologically.

Species Group 2

Eight species are in this group. They are striata,
brucei, georgei, and stewarti, all from the western
Atlantic; euchus, from the western Indian Ocean;
and elongata, australiae, and kagoshimae from the
western Pacific. This group is distinguished by its
shorter jaw, almost always less than 20 percent of
head length, and generally fewer gill rakers (5-10,
but one species, A. elongata, has more gill rakers,
8-10 ; the other species have 5-8) . At least some of
the species in this group are sympatric.

SYMPATRY AND ITS SIGNIFICANCE

Cohen (1958) treated the forms (then three, a
fourth is described in this paper) constituting the
silus group as full species. However, the three
western Pacific forms of the striata group,
austraUae, elongata, and kagosMmae, were recog-
nized as subspecies because these disjunct popula-
tions (Australia, New Zealand, and Japan, respec-
tively) are very similar to each other, far more so
than are the species in the silm group (see key).
A. striata was recognized as a full species, but
could just as easily have been ranked as a sub-
species. A. euchus (Cohen, 1961) was given full
species rank because it was described from only
two specimens.

Subsequent study of hundreds of specimens from
the western Atlantic has shown that what was
formerly considered to be a single species, A.
striata, clearly comprises four forms. These forms
are similar to each other and separated by few
characters. In fact, they are distinguished, one
from the other, by characters which both qualita-
tively and quantitatively resemble those that
separate the western Pacific forms.

We recognize the four closely related western
Atlantic forms as full species because at least some
of them are sympatric. A striata and hrucei have
been taken together in trawl hauls off Venezuela
{Atlantis sta. 2700; Oregon sta. 1989, 4410, and
4465). A. hrucei and steivarti were taken together
off Nicaragua {Oregon sta. 3574 and 3610). A.

14

U.S. FISH AND WILDLIFE SERVICE

SPHYRAENA

N = 68

SILUS

N = 34

■— t— >

SIALIS

N = 45

ALICEAE

ELONGATA

AU5TRALIAE

KAGOSHIMAE

N=15

N=10

N«n

r-M

N = 50

H

rti

I , I I

EUCHUS

N=16

r-H

STRIATA

GEORGEI

N = 53

N-35

J±l.

J±L

BRUCEI

STEWA8T1

N = 69

N=18

r— h-i

XtL

13 14 15 16 17 18 19 20 21 22 23 24

MAXILLARY LENGTH AS PERCENT OF HEAD LENGTH

25

26

27

28

FiouBE 2. — Two species groups of Argentina as shown by maxillary length as percent of head length. Horizontal lines are
ranges ; bars are two standard errors on each side of means ; vertical lines are means.

georgei and bnu;ei have been taken together off
Honduras {Oregon 3626) and at closely adjacent
localities at similar depths off the south coast of
Jamaica [Oregon 3549 and 3548). A. georgei and
stewarti were caught in the same trawl off the
Virgin Islands {Orego-n sta. 2606). A. striata and
georgei were caught at approximate, localities and
depths off' the east coast of Florida, south of Dry
Tortugas, and on the north coast of Cuba.

Figure 3 shows the distribution and figure 4
sununarizes the co-occurrence of the four species.
A. hrucei and georgei each live with three other
western Atlantic species; .striata and stewarti each
with two others. Only A. striata and stewarti are
not so far known to co-occur.

We treat the four tropical western Atlantic
forms as full species because they are sympatric,
even though the magnitude of differences between

them is less than the magnitude of differences
separating species of the situs group. Although the
western Pacific forms are not known to be sjTn-
patric, we recognize them also as full species. It is
obvious that in the genus Argentina, characters of
the magnitude of those separating elongata,
austraiia-e, and kagoshiniae can signal the existence
of full species.

SWIMBLADDER

The occurrence of silver}^ pigment in the outer
layers of the SAvimbladded of some species of
Argentina has l>een noted many times in the litera-
ture. Cohen (1958) added the observation that
some species of Argentina lack this silvery pig-
ment. He commented that presence or absence of
silvery pigment did not seem to be a function of
age, size, time of year, or method of preservation,

ADDITIONS TO A REVISION OF AEGENTININE FISHES

15

379-242 O - 70 -

FioTjBE 3. — Distribution of four species of Argentina in the western Atlantic.

16

U.S. FISH AND WILDLIFE SERVICE

STRIATA

GEORGE I

BRUCEI

STEWARTI

Figure 4. — Co-occurrence of four species of Argentina in
the western Atlantic. Solid lines connect species talien
from the same trawl. A clotted line connects species
taken In different trawls at the same or closely adjacent
localities.

and he, tlierefore, used the character taxonomi-
cally, although always in company with other
characters. We here point out errors in Cohen's
observations and comment on the variability of
this character. In his key to the species of Argen-
tina and in his diagnosis of A. striata Cohen stated
that A. striata lacked a silvery-pigmented swim-
bladder. We have exammed the swimbladders of
150 specimens of A. striata from tliroughout the
range of the species and find that most, though not
all of them, have definite silvery pigment. Cohen
probably based his 1958 statement on examples of
one or more of the other three species of Argentina
from the -western Atlantic.

The swimbladder of A. striata may have any
one of four patterns of pigmentation. In one, the
entire out«r part of the organ is heavily coated
with guanine (fig. 5) ; in the second, the anterior
and posterior quarters of the bladders are pig-
mented with guanine, but the intervening segment
lacks silvery pigment (fig. 5) ; in the third, only
the posterior segment is pigmented with guanine;
in the fourth and rarest type, the outer layer is

faintly iridescent or appears to lack any impregna-
tion of guanine.

In all but two instances, all specimens of A.
brucei lack silvery pigment on the swimbladder
(fig. 5). In a collection of six specimens from
Venezuela (UF 5237), five individuals have irides-
cent to silvery pigment on each swimbladder, and
a single individual lacks pigment completely. Also,
one of three specimens from Honduras (FMNH
74571) has a silvery swimbladder.

All specimens examined of A. stewarti lack
definite silvery pigment (fig. 5) ; however, one
had a slightly iridescent swimbladder. A few
examples of A. georgei have slightly iridescent
swimbladders.

The specimens of A. australiae^ eloivgata, and
hagosMmae listed by Cohen (1958) were reex-
amined. The bladders were iridescent in australiae;
pigment was lacking in the other two species.

The swimbladder pigmentation patterns dis-
cussed in this paper are valid only in preserved
specimens.

Fiinge (1958) has suggested that guanine might
help to keep gases in the bladder. It would be in-
teresting to test the diffusion rate of gases through
the swimbladder walls of pigmented and unpig-
mented species of Argentina. In this respect we
note that the small posterior chamber of the
Argentina swimbladder, first described by Cohen
(1958) and shown by Fahlen (1965) to have a re-
sorbent function, invariably lacks silvery pigment.

According to Cohen (1958), argentinine fishes
are physoclists that lack a rete mirabile. Such
a condition is, of course, highly improbable unless
there is some unknown methofl of gas being se-
creted into and maintained in the swimbladder.
Argentina does in fact have a rete, which has been
described for A. silus by Fiinge (1958). He noted
that it is a unique stnicture, different from the
rete of other kinds of fishes. Marshall (1960)
named it a micro-rete and described it in several
other genera of argentinoid fishes.

KEY TO SPECIES OF ARGENTINA

la. Branchiostegal rays 6, scales with spines ^_

lb. Branchiostegal rays 5, scales lacking spines S.

2a. Lateral line scales 52 (50-54); gill rakers on lower arm of first arch 8 (7-10) A. sphyraena.

2b. Lateral line scales 67 (64-69); gill rakers on lower arm of first arch 13 (11-17).. A. sUm.
3a. Gill rakers on lower arm of first arch 14-21; jaw relatively large, snout to max-
illary tip distance usually less than 5 in head 4.

ADDITIONS TO A REVISION OF ARGENTININE FISHES

17

1 ^ '* tun

Pi j/f.ato c/ia;/^ i0o>ii6

« c/eo'de ji^"^ '**^^

ft. btucei uF S3il

FiQUBE 5. — Swimbladders from four species of western Atlantic Argentina. See text for explanation.

3b. Gill rakers on lower arm of first arch 5-10; jaw relatively small, snout to max-
illary tip distance usually more than 5 in head 5.

4a. Head 3.0 (2.7-3.1) in standard length; eye 11.5 (10.5-12.7) in standard length;

vertebrae 44 (43-45) ; lateral Une scales 47 (45-48) A. aliceae p. 19.

4b. Head 3.5 (3.2-3.7) in standard length; eye 14.3 (12.7-16.4) in standard length;

vertebrae 48 (47-50) ; lateral line scales 49 (48-51) A. sialic p. 22.

5a. Gill rakers on lower arm of first arch 9 (8-10) A. elongata.

5b. Gill rakers on lower arm of first arch 5-7 6.

6a. Pectoral fin rays 13-14 A. australiae.

18

U.S. FISH AND WILDLIFE SERVICE

6b. Pectoral fin rays 15 or more 7.

7a. Ventral fin rays 10-12 8.

7b. Ventral fin rays 12-15, usually 13 or more.. 9.

8a. Lateral line scale rows 54 (51-54) ; ventral fin rays 1 1-12, usually 12 ; anal fin rays

11-13, usually 12 or fewer; vertebrae 50-51 A. kagoshimae.

8b. Lateral line scale rows 49 (47-50); ventral fin rays 10-11, usually 10; anal fin rays

13 or more; vertebrae 47-48 A. euchus p. 33.

9a. Gill rakers on lower arm of first arch usually 7 ; vertebrae 45 (44-46) A. brucei p. 31.

9b. Gill rakers on lower arm of first arch usually 6 ; vertebrae 47-54 10.

10a. Swimbladder usually with definite silvery pigment or iridescence; pectoral fin
rays 19 (18-21); body depth in standard length 8.2 (6.4-10.3); caudal peduncle

depth in head length 5.2 (4.4-6.0); vertebrae 49 (47-51) A. striata p. 22.

10b. Swimbladder lacking silvery pigment, sometimes U'idescent; pectoral fin rays 17
(16-19); body depth in standard length 9.5 (7.4-12.0); caudal peduncle depth

in head length 6.4 (5.6-7.3) ; vertebrae 48 (47-50) A. georgei p. 27.

10c. Swimbladder lacking silvery pigment, sometimes iridescent; pectoral fin rays 20
(19-21); body depth in standard length 11.8 (9.1-13.6); caudal peduncle
length in head length 6.0 (5.5-7.1); vertebrae 52-53 A. stewartip.29.

ARGENTINA ALICEAE, NEW SPECIES Counts

Figures 2, 6 See tables 1 to 7.

Measurements
Diagnosis g^^g^^j ^^ ^^^^ ^qq specimens, 83.2 to 143 mm.

This species can be separated from ^. s;;%raewz standard length, given as percent of standard

and sj?us by its smooth instead of spiny scales and length. Predorsal 48.6 (46.0-50.6); head length

by its five instead of six branchiostegals. J.. afo"ceae 33.7 (32.3-36.7); snout 10.5 (9.7-11.6); eye 8.7

differs from sialis in having a longer head, 33.7 (7.9-9.5) ; maxillary length 7.8 (7.0-9.1) ; depth

(32.3-36.7) percent of standard length, in sialis a^t dorsal fin 17.3 (15.1-20.0) ; depth caudal pe-

28.8 (27.3-31.2); a larger eye, 8.7 (7.9-9.5), in duncle 7.5 (6.9-8.7).

sialis 7.0 (6.1-7.9) ; fewer vertebrae, 44 (43-45), in Description

si<ilis 48 (47-50) ; and fewer lateral line scales, 47 Greatest depth at dorsal origin, tapering to

(45^8), m sialis 49 (48-51). It differs from all caudal peduncle. Body in cross section deeper than

other species of ^7Ve?ii!^w^ in having 16 to 21 gill wide; belly rounded. The head, when viewed

rakers on the lower ai-m of the first arch rather laterally, has its dorsal profile slightly broken by

than 5 to 10. the margin of the eye ; the ventral profile rises to

Figure &.— Argentina aliceae, USNM 202462, holotype, 147 mm. standard length. All scales not shown. Cross section from

in front of dorsal fin. Drawn by Mildred H. Oarrington.

ADDITIONS TO A REVISION OF ARGENTININB FISHES

19

Table 1. — Gill rakers on lower arm of first arch in species of Argentina

Species

sphyraena..

silus

sialis

aliceae

elongata

australiae..,
kagoshimae.

euchus _

striata

georgei

brucei

stewarti

Gill rakers

S 6

10 11 12 13 14 15 16 17 18 19 20 21

2 27 17

Number offish

.... 9 1

2 14

... 17

... 76 2

... 41 1

... 1 87

... 21 1

6 13 12

3 13 23 10 1 ■""

1 2 9 22 6 4 i

1 8 29 13 3 i

Species

sphyraetia..

silus.

sialis

aliceae

elongata

australiae...
kagoshimae -

euchus

striata

georgei

6rucei

stewarti

Table 2. — Vertebral counts in species of Argentina

Number of vertebrae

43 44 45 46

48 49 50 51 62 53 54 — 64 65 66 67

1 47 27

1 3

■4 "'67" "is

Number offish
1 1

1

1 6 10

2 2 3 1

2 5

11 5

3 22 111 13 2

4 31 8 4

17

Table 3.— Dorsal fin ray counts in species of Argentina Table b.— Pectoral fin ray counts in species of Argentina

Species

Dorsal fin rays

9 10

11

12

13 14

15

16

17

sphyraena

12

46
2
5

11

12
6

10

Numbt

3 .

•32
35

85

4 .

1 .

2 .
15 .
18 .

1 .

5 .

6 .

r of fish

silus

23

sialis

8

aliceae

5

elongata

3

australiae

5

kagoshimae... .

4

euchus

striata

1

39

38
67
14

georgei

1

brucei

1

stewarti. . .

1

Species

sphyraena. .

silus.

sialis

aliceae

elongata

australiae. _
kagoshimae.

euchus

striata

georgei

brucei

stewarti

Pectoral fin rays

11 12 13 14 15 16 17 18 19 20 21

Number offish

5
'35"

24 42

9 9

28
"26'

2
10

24

1

3 26

13 4 ....

30 80 4

1 7 8

Table 4.-Anal fin ray counts in species of Argentina Table &.-Ventral fin ray counts in species of Argentina

Species

Anal fin

rays

9 10

11

12

13

14

15

16

17

sphyraena ..

1

Num
12

ber of

33

1

9
23

7

8

1

9
34

2
27
10

fish

23
4

26
33
4

1

32

6

3

silus

12

3

sialis

aliceae

elongata

4

5
3
6

australiae

kagoshimae

6

euchus

5

1

striata

3

20

9

20

8

36

11

georgei

brucei

stewarti

Species

Ventral fln rays

10

11

12

13

14

15

sphyraena

6

49

Number

6
44

5 .
7 .

6 .
5

14 .

offish

silus

13 .

sialis

3
4

40
84
13
6
3
2

aliceae

australiae

13 .

euchus

14

striata

4
4

9
22
43

9

40
8

21
9

3

stewarti

3

20

U.S. FISH AND WILDLIFE SERVICE

Table 7. — Lateral line scales in three species of Argentina

Lateral line scales

Species

45

46

47 48 49

60

51

»iali>

Number offish
7 20

18

1

1

21

58 16

1 4 11

euchus

the snout in a gentle curve; the interoi-bital space
between the supraocular canals is broadly concave.
The frontals laterad to the canals arch upward
slightly. The dorsal portion of the maxillary is
hidden under the lacrimal and the jugal bones. The
distal end of the maxillary is closer to the anterior
margin of the eye than to the snout. Some speci-
mens have a slight, bony knob at the symphysis of
the lower jaw. The jaws are subequal ; the upper
broadly rounded, the lower less so. The palatine
and the head of the vomer bear a continuous band
2 to 4 teeth wide composed of small, closely spaced,
conical teeth; about 50 on the vomer and 25 to 30
on each palatine; dentary teeth are lacking. The
ceratobranchial of the fifth gill arch bears 7 to 10
small, conical teeth ; two patches of similar teeth,
5 to 10 on the anterior i^atch and 10 to 15 on the
posterior patch, are found at the anterior end of
the fourth suprabranchial. The tongue bears 6
strong recurved teeth (description of dentition
based on a single alizarin-stained specimen). The
gill rakers are elongate, compressed, and relatively
widely spaced; the longest gill rakers are equal
to about one-third of the interorbital distance.

The pectoral fin originates slightly ahead of a
vertical through the posterior tip of the opercle.
The anterior end of the pectoral fin base is elevated
from the horizontal by an angle of 30 to 45 degrees.
The distance between the bases of the innermost
rays of the pectoral fins is less than the least depth
of the caudal peduncle. The gi-eatest height of the
dorsal fin is usually greater than the maximum
depth of the body. The greatest height of the anal
fin is greater than the least depth of the caudal
peduncle. The pectoral fins extend more than one-
half the distance between the bases of the pectoral
and ventral fins; the ventral fins are slightly
shorter.

The scales lack spines. The lateral line scale
count is summarized in table 7.

The peritoneum is colored with large, dark
chromatophores, which are most densely dis-
tributed in the antero-dorsal section of the body
cavity; the gut is immaculate. Ten to 14 pyloric
caeca are present in 12 specimens. The body cavi-
ties of all specimens examined contained consider-
able amounts of fat.

The elongate swimbl adder extends from about
the level of the curve of the stomach to about the
midlength of the ventral fin. The anterior tip of
the swimbladder bears some silvery pigment, and
the posterior one-third to one-half of the organ is
strongly impregnated with silvei-y pigment.

Pigmentation in alcohol of adult specimens is
light straw-colored on the lower two-thirds of the
fish ; the dorsum is darker ; the muzzle is dusky, as
are the nape and the upper portion of the opercle.
Many specimens have the remnants of an irides-
cent band along the midline. In fishes less than
about 95 mm. standard length, there is a series of
8 to 10 dusky blotches along the upper third of
the body. In life the fish is a bright silvery color
(H. A. Fehlmann, Smithsonian Oceanographic
Sorting Center, personal communication).
Teratology

A single specimen from Anton Brnmn sta. 640-B
(USNM 202472) lacks pectoral fins. An X-ray
photograph shows that a pectoral girdle is present
Distribution

A. aliceae is known from nine localities along
the northern coast of Peru, where it has been
trawled at depths of 50 to 54 fm. (91-99 m.) to
105 to 170 fm. (192-311 m.) ; most specimens were
taken between 55 and 88 fm. (100-161 m.).
Habits

This species has been taken only in bottom
trawls and like most other Argentina apparently
travels in schools a short distance above the bot-
tom. The largest catch recorded was from Anton
Bruun sta. 641-A, where 1,440 individuals weigh-
ing 44 kg. were taken. Several specimens examined
had their stomachs tightly packed with partially
digested crustaceans. Annotated station data from
Anton Bruun cruise 16, which collected most of
the study material, are presented by Chin (1966).
Name

Named for Alice Holland, former Secretary of
this Laboratory, in recognition of her devoted
services to ichthyology.

ADDITIONS TO A REVISION OF ARGENTININE FISHES

21

Study Material

All study material from Peru. Holotype: USNM
202462, 147 mm. standard length; R.V. Anton
Bruun cruise 16, station 641-A, 6°54' S., 80°44' W.,
97 to 110 m.; 6 June 1966; otter trawl. Paratypes:
USNM 202459 (84 specimens, 1 cleared and
stained); data as for holotype; from the same
station MCZ (5); SIO (5). Paratypes: USNM
202460 (97); Bruun 640-B, 7°01' S., 80°44' W.,
105 m.; otter trawl; from the same station USNM
202472 (1 lacking pectoral fins); FMNH (5);
CAS (3). USNM 202463 (18); Bruun 639-A,
6°47' S., 80°43' W., 100 to 91 m.; otter trawl.
USNM 202465 (1); Bruun 635-A, 6°27' S.,
80°56' W., 160 m.; otter trawl. USNM 202464
(3); Bruun 631-A, 5°59' S., 81°12' W., 100 m.;
otter trawl. USNM 202461 (320), Bruun 630-A,
6°02' S., 81°12' W., 160 m.; otter trawl; from the
same station BMNH (5) ; UZMC (4) ; MNHN (3) ;
ANSP (3). USNM 202466 (4); Bruun 627-A,
5°02' S., 81°24' W., 192 to 311 m.; otter trawl.
USNM 202467 (2); Bruun 625-A, 4°57' S., 81°23'
W., 118 to 133 m.; otter trawl. USNM 199802
(4); SW. of Lobos de Afuera Islands, Peru, 110
m.; trawl.

ARGENTINA SIALIS GILBERT

Figure 2

The heretofore northernmost locality for A.
sialis is Monterey Bay, Calif. (Follett, 1945). An
extension of the known range of about 1,120 km. is
provided by a single specimen ( 147 mm. standard
length) taken by the John N. Coll off the coast of
Oregon on 3 March 1962 : USNM 188126, 46°04'
N., 124°39' W., 100 to 102 fm. (183-187 m.), otter
trawl, bottom temperature 8.3° C. The specimen
agrees well with the description given by Cohen
(1958).

Additional vertebral counts based on specimens
from southern California listed by Cohen (1958)
are presented in table 2.

ARGENTINA STRIATA GOODE AND BEAN

Figures 1, 2, 3, 4, 5, 7, 8, 9, lOA

Argentina striata Goode and Bean, 1896, p. 52,
pi. 17, fig. 62 (original description; type-locality:
Allatross station 2402, 28°36' N. 85°33' "W., Gulf
of Mexico, 111 fm. Holotype: USNM 43858, not
designated in text of original description, but on
p. 4 of the Atlas in the caption for pi. 17, fig. 62).
Diagnosis

This species can be separated from A. sfhyraena
and sillies by its smooth instead of spiny scales and
by its five instead of six branchiostegals. It differs
from sllu.'i, sialis, aliceae, and elongate, in having
6 (occasionally 7) gill rakers on the lower arm of
the first arch, whereas the four species list«d above
have 8 to 21. It also differs in gill raker count from
A. Irucei, wliich has 7 (occasionally 6) rakers;
also striata has 47 to 51 vertebrae; Irucei has 44
to 46. It differs from euchus in having 12 to 15
ventral rays rather than 10 or 11. It differs from
kagoshiTnae, australiae, elongata, sialis, and
sph.yrae7xa in having 18 to 21 rather than 11 to 17
pectoral rays. It differs from georgei and stewarti
in usually having silvery pigment on the swim-
bladder, whereas the others lack it; from stewarti
in having 47 to 51 vertebrae rather than 52 or 53;
from georgei in having caudal peduncle depth in
head length usually less than 5.7 rather than
usually more than 5.7.
Counts

See tables 1 to 6.
Measurements

Based on about 55 specimens, 88.0 to 173 mm.
standard length, given as percent of standard

FiGTJKE 1.— Argentina striata, USNM 203003, 154 mm. standard length. Cross section from In front of dorsal fin. Scales not

drawn. Drawn by Mildred H. Carrington.

22

U.S. FISH AND WILDLIFE SERVICE

23 •

22 •

21 '

20 •

i
5

19 •

2

18 •

I
1-
Q.
LLI
Q

17 .
16 •

O

CO

15
14 •

13

12

11
in

• STRIATA

* GEORGEI
O STEWARTI

160

STANDARD LENGTH IN MM.

Figure 8. — Regressions of body depth (mm.) on standard length (mm.) for three closely related species

of Argentina. See,text for equations.

length. Preanal 83.5 (80.8-85.9) ; preventral 55.5
(52.2-58.0) ; predorsal 46.6 (44.2-48.6) ; head
length 30.1 (26.1-32.0) ; snout 9.6 (8.5-10.6) ; eye
9.8 (7.8-10.9) ; maxillary length 5.4 (4.2-6.1) ;
depth at dorsal fin 12.3 (9.7-15.7) ; depth caudal
peduncle 5.8 (5.2-6.5).

Description

Body not very elongate. Greatest depth at dorsal
origin, tapering to caudal peduncle. Figure 8
shows a regi'ession of body depth on standard
length (Y = .150X — 3.50) compared with two
closely related species. The caudal peduncle is also
relatively deep. Figui'e 9 shows a regression of
caudal peduncle depth on head length (Y=.180X
+ .524) compared with two closely related species.
Body in cross section deeper than wide, dorsum
and venter broadly rounded. The head, when
viewed laterally, has its dorsal profile barely if at
all broken by the upper margin of the eye; the
ventral profile rises to the snout in a gentle curve ;

many specimens are preserved with the mouth
open and the basibranchial projecting into the
ventral profile. The interorbital space between the
supraocular canals is flat or only slightly concave.
The dorsal portion of the maxillary lies under the
lachi-ymal. The distal end of the maxillary is
usually about midway between the tip of the snout
and the anterior margin of the eye. The jaws are
broadly rounded, the lower slightly included. The
palatine and the head of the vomer bear small,
closely spaced, needlelike teeth in a continuous
band from 2 to 5 teeth wide, about 30 on the vomer
and 40 on each palatine; dentary teeth are lacking.
The ceratobranchial of the fifth gill arch bears 9
small, conical teeth ; two patches of similar teeth,
10 on the anterior patch and 14 on the posterior
patch are at the anterior end of the fourth supra-
branchial ; there are also a few teeth on the tliird
suprabranchial. The tongue bears eight strong re-
curved teeth (description of dentition based on a

ADDITIONS TO A REVISIOX OF ARGENTININE FISHES

23

2
S

0.
UJ

Q

O

Z
3
Q

UJ

a.

<
Q

<

•

o

STRIATA

GEORGEI

STEWARTI

HEAD LENGTH IN MM.

FiQDBB 9. — Regressions of caudal peduncle depth (mm.) on head length (mm.) for three closely related species of

Argentina. See text for equations.

single alizarin specimen). The gill rakei-s (fig. 1)
are medium-sized, compressed, and widely spaced.
The longest gill rakers are equal to one-fifth to
one-sixth of the interorbital distance.

The pectoral fin originates close to the posterior
margin of the opercle. The anterior end of the
pectoral fin base is elevated from the horizontal
by an angle of about 45 degrees ; the distance be-

tween the innermost rays of the pectoral fins is
about equal to or slightly less than the least depth
of the caudal peduncle. In almost all of our speci-
mens the pectoral and ventral fins are broken off
short; however, in a few specimens, the pectorals
appear to extend at least half the distance from
the pectoral base to the ventral base. The ventral
fins are probably shorter.

24

U.S. FISH AND WILDLIFE SERVICE

Scales and scale pockets are deciduous ; however,
the few scales we have seen lack spmes. Lateral
line counts of scale pockets in several specimens
are about 50.

The peritoneum is black or almost so ventrally,
grading to a less dense distribution of chro-
matophores laterally, then a darker band along
the kidneys. The gut is immaculate. Nine to 14
pyloric caeca are present in 12 specimens. Most
specimens have considerable fat in the body cavity.
The swimbladder begins slightly anterior to the
hind cun^e of the stomach and extends posteriorly
to about the tip of the ventral fin. In 137 swim-
bladders examined, only 6 lacked any silvery pig-
ment and several of these were iridescent. About
one-half of the specimens having swimbladders
that were completely impregnated with silvery
guanine also had silverj' pigment on the head, sug-
gesting that strong formaldehyde solution that
dissolves the silvery pigment on the body may also
dissolve away pigment from the middle part of
the swimbladder.

Pigmentation of adult specimens preserved in
fonnaldehyde solution is variable, but in general
the ventral two-thirds of the body is light. There
is often a brown band above the lateral line; in
some examples the band is barely discernible (fig.
7), in others quite distinct. Although the dark pig-
ment of the j^eritoneum may show through the
thin belly musculature, there is no extenially pig-
mented band along the niidventral line. Some
specimens have the throat peppered with brown
chromatophores (fig. 10 A) ; in many, however,
this region is immaculate. Specimens less than
about 100 mm. standard length may have a row
of eight or nine dusky blotches along the upper
third of the body, but not all do. Alcohol-pre-
served specimens are silvei-y below the lateral line
and on most, of the head.
Distribution

A. striata is widely distributed in the western
Atlantic, ranging from the offing of Nova Scotia
(Schroeder, 1955), along the east coast of the
United States, the north coast of Cuba, around the
Gulf of Mexico, in the northwesteni and southern
Caribbean, and off the mouths of the Orinoco.
There are two records, however, from much far-
ther south off Brazil. Carvalho (1950) described
specimens from Banco Sao Tome at about lat. 22°
S., and Miranda Eibeiro (1961) described and

FiQUBE 10. — Pigmentation on venters of four
western Atlantic species of Argentina: A.
striata, USNM 203001; B. steicarti, USNM
187834; C. georgei, USNM 186356; D. hrucei,
USNM 187793. Drawn by Mildred H. Carring-
ton.

figured specimens from 24° 14' S., 44°49' W. We
have not examinefl material from either locality,
but the descriptions fit our material of A. striata.

ADDITIONS TO A REVISION OF ARGENTININE FISHES

25

In the West Indies, A. striata has been taken
only off the northern coast of Cuba and around
the southern end of the Lesser Antilles; the rec-
ords of striata given by Cohen (1958, 1964),
Springer and Bullis (1956), and Bullis and
Thompson (1965) from Hispaniola and the Lesser
Antilles are of striata, steivarti, georgei, or brnicei,
or of combinations of these four.

Depth distribution ranges from 80 to 260 fm.
(146^76 m.), but most records are from between
100 and 240 fm. (183-439 m.).

Habits

A. striata is taken with a bottom trawl, usually
over a mud bottom at bottom temperatures rang-
ing from 48° to 59° F. (8.9-15° C). Specimens are
caught singly and also in aggregations of as many
as 100 individuals. Mixed collections of A. striata
and A. hrucei have been taken in the same haul.
Study Material

All from the Atlantic.

Bahama Banks. — MCZ 38476 (1 specimen),
22°45' N., 78°45' W., 150 to 180 fm. (274-329 m.).
MCZ 40614 (1), 22°46' N., 78°45' W., 195 to 225
fm. (357-412 m.). UMML 11689 (10), 27°08' N.,
79°53' W., 110 fm. (201 m.).

U.S. Atlantic— VMMh 12127 (21), 27°10' N.,
79°55' W., 100 fm. (183 m.). MCZ 39817 (2),
27°17' N., 79°49' W., 200 fm. (366 m.). USNM
158082 0), Pelican 25, 2S°03' N., 79°52' W., 150 to
175 fm. (274-320 m. ). TU 14774 (1), Pelican 60, 28°
29' N., 79°54' W., 160 to 190 fm. (293-348 m.). TABL
100559 (1), Combat 319, 28°31' N., 79°52' W., 180
fm. (329 m.). USNM 156659 (1), Pelican 204-4,
28°59' N., 80°01.5' W., 100 fm. (183 m.). USNM
188905 (1), Oregon 5094, 29°31' N., 80°09' W.,
210 fm. (384 m.). TABL 100564 (11); Silver Bay
217, 29°41' N., 80°08' W., 180 to 200 fm. (329-
366 m.). SU 49755 (1), 29°47' N., 80°12' W.
TABL 100558 (1), Silver Bay 212, 29°59' N.,
80°07' W., 200 fm. (366 m.). UMML 1461 (2)
and UMML 529 (1), NE. coast of Florida,
ESE. St. John's River Entrance, 105 fm. (192
m.). MCZ 38305 (4), 37°00' N., 74°00' W., 150
fm. (274 m.). MCZ 34568 (1), 37°36' N., 74°17' W.,
100 fm. (183 m.). MCZ 38213 (9), 37°38' N.,
74°15' W., 120 to 130 fm. (220-238 m.). USNM
186300 (1), Delaware 15-B, 37°42' N., 74°12' W.,
150 to 225 fm. (274-412 m.). MCZ 39778 (6),
38°36' N., 73°10' W. MCZ 38341 (1), 38°38' N.,
73°10' W., 190 to 200 fm. (348-366 m.). MCZ

37947 (1), 39°58' N., 69°28' W., 105 to 140 fm.
(192-256 m.). MCZ 39973 (1),39°59' N., 69°35' W ,
82 to 85 fm. (150-155 m.). MCZ 37419 (1),
Captain Bill II 35, 40°02' N., 70°24' W., 105 to
llOfm. (192-201 m.).

U.S. Gulf of Mexico.— UMML 16905 (1);
24°18' N. 82°52' W., 190 fm. (348 m.). UMML
16651 (1); 24°19' N., 82°29' W., 103 fm. (188
m.). TU 10901 (5); Oregon 1005, 24°20' N.,
83°20' W., 190 fm. (348 m.). TU 12695 (12);
Oregon 1548, 24°25' N., 83°00' W., 210 fm.
(384 m.). TU 10917 (4); Oregon 1007, 24°26' N.,
83°24' W., 180 fm. (329 m.). FMNH 66231
(1); Oregon 2671, 24°26' N., 83°24' W., 212
fm. (388 m.). FMNH 66230 (10); Oregon 2670,
24°27' N., 83°26' W., 210 fm. (384 m.). UMML
13289 (5); Oregon 4362, 24°30' N., 83°33' W.,
190 fm. (348 m.). SU 49753 (1); Oregon 1009,
24°34' N., 83°34' W., 200 fm. (366 m.). SU
49726 (1); FMNH 59880 (19); Oregon 1026,
25°08' N., 84°19' W., 163 fm. (298 m.). TU
12669 (9); Oregon 1556, 26°24' N., 98°45' W.,
210 fm. (384 m.). UMML 4441 (1); 28°07' N.,
85°13' W., 150 fm. (274 m.). USNM 158687 (1);
Oregon 953, 28°23' N., 85°51' W., 180 fm. (329
m.). SU 49724 (1); Oregon 1276, 28°30' N.,
86°11' W., 240 fm. (439 m.). USNM 158686
(2); GCRL V60:119 (6); Oregon 36, 28°30' N.,
85°36' W., 120 fm. (220 m.). USNM 4385S,
holotype and USNM 83864, paratype (1) ; Albatross
2402, 28°36' N., 85°33' W., Ill fm. (203 m.).
FMNH 46270 (12); Oregon 277, 28°48' N., 85°40'
W., 104 fm. (190 m.). TU 11698 (2); Oregon
1520-30, 29°00' N., 88°00' W., 200 to 250 fm.
(366-457 m.). GCRL V62:731 (1); Oregon 3697,
29°00' N., 88°36.5' W., 190 to 200 fm. (348-366).
USNM 203086 (1); Oregon 3725, 29°00.5' N.,
88°35.5' W., 220 fm. (402 m.). USNM 156658
(2); Pelican 9, 29°02' N., 88°41.5' W., 120 to
169 1/2 fm. (220-310 m.). USNM 203087 (1);
Oregon 3763, 29°03' N., 88°34' W., 190 fm. (348
m.). USNM 159349 (7); Silver Bay 156, 29°04'
N., 85°49' W., 100 to 102 fm. (183-187 m.) . USNM
188212 (18), TABL 100557 (2) and USNM
187836 (3); Oregon 3646, 29°07' N., 88°34' W.,
125 fm. (229 m.). SU 49725 (1); Oregon 273,
29°09' N., 85°59' W., 110 fm. (201 m.). GCRL
V63:933 (1); Oregon 60, 29°09' N., 88°33' W.,
110 fm. (201 m.). GCRL V63: 932 (2); Oregon 32,
29°10' N., 85°55' W., 95 fm. (174 m.). USNM
188387 (1); GCRL V62: 730 (1); Oregon 3676,

26

U.S. FISH AND WILDLIFE SERVICE

29°10' N., 88°10' W., 200 fm. (366 m.). UMML
1508 (1); 29°10' N., 88°20' W., 150 fm. (274 m.).
USNM 188389 (3); Oregon 3677, 29°11' N.,
88°06' W., 200 fm. (366 m.). USNM 158127 (1);
SU 49727 (1); Oregon 1246, 29°15' N., 88°11' W.,
200 to 210 fm. (366-384 m.). SU 17441 (1);
29°15.5' N., 87°53' W. FMNH 45932 (2);
Oregon 864, 29°19' N., 86°04' W., 82 fm. (150
m.). FMNH 46269 (5); Oregon 265, 29°20' N.,
87°42' W., 101 fm. (185 m.). USNM 159013 (1);
Oregon 1260, 29°23' N., 86°48' W., 250 fm.
(457 m.). SU 49723 (1) and FMNH 46268 (2);
Oregon 269, 29°27.5' N., 87°26.5' W., 150 fm.
(274 m.). USNM 158842 (1); Oregon 1400, 29°30'
N., 87°08' W., 210 fm. (384 m.). TU 11761 (2);
Oregon 946, 29°41' N., 86°44' W., 100 fm. (183
m.). TU 2716 (7); Oregon 278, 29°49' N., 85°45'
W., 112 fm. (205 m.).

Mexico.— SU 49721 (1); Oregon 1054, 19°37' N.,
92°40' W., 200 fm. (366 m.). FMNH 45728 (1);
Oregon 726, 22°41.9' N., 86°41.2' W., 225 fm.
(412 m.). USNM 186068 (2); Silver Bay 1184,
23°56' N., 87°32' W., 150 fm. (274 m.). TU 12939
(7) ; UF 1316 (2) ; Oregon 1091, 26°46' N., 96°20' W.,
200 to 210 fm. (366-384 m.). FMNH 46266 (2);
Oregon 550, 26°55' N., 96°25.5' W., 125 fm. (229
m.). TU 10998 (4); Oregon 1094, 27°10'N., 96°20'
W., 150 fm. (274 m.). FMNH 45050 (1) ; 27°15' N.,
ge'lS' W., 200 fm. (366 m.). TU 2770 (4); Oregon
164, 27°21' N., 96°06' W., 160 fm. (293 m.).
USNM 203000 (1); Oregon 4617, 27°48' N., 94°37'
W., 200 fm. (366 m.).

Central ylrnerico..— USNM 187835 (1); Oregon
3634, 16°44' N., 87°55' W., 190 fm. (348 m.).

South America.— \JY 8026 (2); FMNH 66223
(11); Oregon 1989, 9°45' N., 59°45' W. USNM
203046 (1); Oregon 4465, 10°45' N., '66°37' W.,
125 fm. (229 m.). USNM 203003 (5); Albatross
2700, 10°59' N., 66°00' W., 140 fm. (256 m.).

TABL 100556 (4); Oregon 5037, 11°36' N., 62°46'
W., 200 to 240 fm. (366-439 m.). USNM 203002
(1); Oregon 4410, 11°52' N., 69''27' W., 230 fm.
(421 m.). USNM 200430 (1); Oregon 5690, 12°30'
N., 72°08' W., 257 fm. (470 m.).

Antilles.— yiCZ 40617 (1); Albatross 3422,
22°48' N., 79''09' W., 235 fm. (430 m.). MCZ
40010 (1); 22°49' N., 79°07' W., 235 fm. (430 m.).
MCZ 40618 (1); 22°52' N., 79''22' W., 240 fm.
(439 m.).

ARGENTINA GEORGEI, NEW SPECIES

Figures 2, 3, 4, 5, 8, 9, IOC, 11

Diagnosis

This species can be separated from A. sphyraena
and silus by its smooth instead of spiny scales and
by its five rather than six branchiostegals. It dif-
fers from siliis, sialis, aliceae, and elongata in hav-
ing 6 (occasionally 7) gill rakers on the lower arm
of the first arch — the four species listed above have
8 to 21. It differs in gill raker count from A.
brucei, which has 7 (occasionally 6) rakers; also
georgei has 47 to 50 vertebrae, brucei has 44 to 46.
It differs from euchus in having 12 to 14 ventral
rays rather than 10 or 11. It differs from
sphyraena, sialis., elongata, and a.usiraliae in hav-
ing 16 to 19 pectoral rays rather than 11 to 16. It
differs from kagoshimae in having vertebrae
usually less than 50 rather than usually more than
50 ; pectoral rays 16 to 19 rather than usually less
than 17 ; ventral rays usually 13 or 14 rather than
11 or 12. It differs from striata in lacking silvery
pigment on the swimbladder ; in having anal rays
usually 10 or 11 rather than 12 or 13, pectoral rays
usually 17 or 18 rather than 19 or 20, and caudal
peduncle depth in head length usually more than
6 rather than 6 or less. It differs from stewarti in
having 47 to 50 vertebrae rather than 52 or 53, in

FiQUBE 11. — Argentina georgei, USNM 18S224, paratype, 109 mm. standard length. Scales not shown. Cross section from

In front of dorsal fin. Drawn by Mildred H. Carrington.

ADDITIONS TO A REVISION OF ARGENTININE FISHES

27

having usually 10 or 11 anal rays rather than 12
or 13, and in having pectoral rays usually 17 or 18
rather than 19 to 21.
Counts

See tables 1 to 6.
Measurements

Based on 37 specimens, 102 to 146 mm. standard
length given as percent of standard length. Preanal
85.1 (83.3-86.3) ; preventral 55.6 (53.7-58.6) ;
predorsal 46.4 (44.9-48.6) ; head length 30.6 (28.5-
32.4) ; snout 10.0 (8.7-11.2) ; eye 9.4 (8.2-10.9) ;
maxillaiy length 5.8 (5.2-6.6) ; depth at dorsal fin
10.6 (8.3-13.4) ; depth caudal peduncle 4.8
(4.3-5.6).
Description

Body of medium length. Figure 8 shows a
regression of body depth on standard length
(Y=.120X-.504) compared with two closely re-
lated species. Greatest depth behind head, tapering
to the relatively narrow caudal peduncle. Figure 9
shows a regression of caudal peduncle depth on
head length (Y = . 123X4- 1.28) compared with two
closely related species. Body in front of dorsal fin
almost square in cross section or somewhat wider
than deep; compressed posteriorly. Dorsum and
venter flat, not rounded. The head, when viewed
laterally, as deep or deeper than the body, its dor-
.sal profile barely or not at all broken by the upper
margin of the eye; the dorsal and ventral profiles
of the head converge at about equal angles on the
snout. The interorbital space between the supra-
ocular canals is broadly concave. The dorsal por-
tion of the maxillary lies under the lachrymal. The
distal end of the maxillary reaches to at least the
midpoint of the distance from the tip of the snout
to the anterior margin of the orbit and usually
farther. The jaws are broadly rounded, the lower
included; there is a slight, bony protuberance be-
hind the symphysis of the lower jaw. The palatine
and the head of the vomer bear small, closely
spaced, needlelike teeth in a continuous band 2 to
5 teeth wide, about 40 on the vomer and 50 on each
palatine; no dentary teeth. The ceratobranchial of
the fifth gill arch bears 8 small, conical teeth ; two
patches of similar teeth, 5 on the anterior patch
and 15 on the posterior patch, are at the anterior
end of the fourth suprabranchial. The third su-
prabranchial lacks teeth. The tongue bears eight
strong, recurved teeth (description of dentition

based on a single alizarin-stained specimen). The
gill rakers are medium-sized, compressed, and
widely spaced. The longest rakers equal one-
seventh to one-eighth of the interorbital distance.

The pectoral fin originates on the ventral surface
of the fish anterior to a vertical through the rear
margin of the opercle; the distance between the
innermost rays of the pectoral fins is equal to or,
more often, greater than the least depth of the
caudal peduncle. The fin rays of all specimens are
broken off short.

Scales deciduous, the few we have seen lack
spines. Lateral counts of scale pockets in several
specimens are about 50.

The peritoneum is dark. The gut is immaculate.
Eight or nine pyloi'ic caeca are present in eight
specimens. The swimbladder begins close to the
hind curve of the stomach and extends posteriorly
to slightly beyond the origin of the ventral fin.
Swimbladder lacking silvery pigment (fig. 5),
however, we have seen several specimens with
slightly iridescent bladders.

Pigmentation of adult specimens preserved in
formaldehyde is distinctive and consists of a dark
brown band extending along the upper quarter of
the side; it is not continuous over the dorsum;
however, there is a dark, middorsal streak. The
venter and throat of most specimens are pig-
mented with large, dark chromatophores which
form a wide dark band extending to the pelvics
(fig. IOC), and in many specimens all the way to
the vent. In some specimens the superficial pig-
mentation of the belly is poorly developed, and in
these the darkly pigmented peritoneum shows
through the thin ventral musculature.

Distribution

A. georgei is found off the east coast of Florida
and barely enters the Gulf of Mexico south of Dry
Tortugas. It has also be«n taken at several locali-
ties along the western side of the Bahama Banks
and on the north coast of Cuba. In the Caribbean
and along the Antilles, A. georgei has been trawled
off Honduras, NicaragTia, and Jamaica and near
Puerto Eico and the Virgin Islands (fig. 4).

Depth distribution ranges from 120 to 250 fm.
(220-457 m.), but the fish has been most often
caught between 150 and 220 fm. (274-402 m.).

Habits

A. georgei has been taken only in bottom trawls
over mud and shell bottoms at bottom tempera-

28

U.S. FISH AND WILDLIFE SERVICE

tures of 48, 58, 61, and 62° F. (8.9, 14.4, 16.1, and
16.7° C). Specimens are most often taken singly.
Our largest sample has six individuals. A. georgei
has been taken with hi'ucei and with steivarti.

Name

Named for George Clipper, to whom we are in-
debted for efficient assistance in this Laboratory.

Study Material

All from the Atlantic. Holotype: USNM 203016,
125 mm. standard length, Oregon 3622, 16°01' N.,
81°08' W., 145 to 150 fm. (265-274 m.), June 6,
1962. Paratypes:

Bahama Batiks. — FMNH 65791 (1 specimen),
Oregon 1343, 22°59' N., 79°17' W., 250 fm.
(457 m.). TABL 100575 (1), Silver Bay 2457,
23°43' N., 79°07' W., 250 fm. (457 m.). FMNH
66217, Combat 446, 25°10' N., 79°13' W., 250 fm.
(457 m.). UF 1350 (1), Combat 235, 27°27' N.,
78°58' W., 180 fm. (329 m.). USNM 158689 (1),
Combat 237, 27°28' N., 78°44' W., 215 fm. (393 m.).

U.S. Atlantic.— TABL 100563 (4), Combat 441,
25°16' N., 80''00' W., 185 fm. (338 m.). TABL
100569 (1), Silver Bay 2482, 26°07' N., 79°12' W.,
200 fm. (366 m.). TABL 100567 (1), Silver Bay
218, 29°38' N., 80°11' W., 220 fm. (402 m.).
TABL 100573 (5), Combat 491, 29°30' N., 80°10'
W., 125 fm. (229 m.).

U.S. Gulf of Mexico.— UMML 2882 and 2545
(1 each) ; Combat 281, 24°17' N., 82°47' W., 215 fm.
(393 m.).

Central America.— USNM 187841 (5), Oregon
3579, 12°26' N., 82°26' W., 125 fm. (229 m.).
USNM 203017 (4) and MCZ (2), Oregon 6423,
13°28' N., 82°01' W., 150 to 158 fm. (274-289 m.).
USNM 187839 (6), Oregon 3566, 14°10' N.,
81°58' W., 150 to 160 fm. (274-293 m.). USNM
188224 (4), Oregon 3622, data as for holotype.
USNM 187834 (3, 1 cleared and stained), Oregon
3625, 16°26' N., 8r35' W., 120 fm. (220 m.).
ANSP 98604 (4), Oregon 3626, 16°45' N., 81°27'
W., 150 fm. (274 m.).

>*a-^'

Antilles.— VSNM 187816 (2); Oregon 3548,
17°53' N., 77°56' W., 150 fm. (274 m.). TABL
100572 (S); Silver Bay 5193, 18°16' N., 67°22' W.,
150 fm. (274 m.). FMNH 66224 (1); Oregon 2606,
18°37.5' N., 65°04' W., 210 fm. (384 m.). USNM
157980 (1); Oregon 1344, 22°50' N., 79°08' W.,
200 to 225 fm. (366-412 m.). USNM 157976 (1);
Oregon 1343, 22°59' N., 79°17' W., 250 fm.
(457 m.).

ARGENTINA STEWARTI, NEW SPECIES

Figures 2, 3, 4, 5, 8, 9, lOB, 12
Diagnosis

This species can be separated from A. sphyraena
and sihis by its smooth instead of spiny scales and
by its five instead of six branchiostegal rays. It
differs fi'om silu.s, siaUs, aliceae, and elongata in
having 6 (occasionally 7) gill rakers on the lower
arm of the first arch — the four species listed above
have 8 to 21. It differs in gill raker count from A.
hnicei which has 7 (occasionally 6) rakers. A.
steioarti differs from siall.^, aliceae, kagoshimae,
eucJvm, striata, georgei, and bnwei in having 52
or 53 vertebrae — the others have 43 to 51. It dif-
fers from sphyraena, sialis, elongata, australiae,
and kagoshimae in having 18 to 21 pectoral rays
rather than 11 to 17. It diffei-s from sphyraena,
sialis, aliceae, elongata, kagoshimae, and euchus
in having 13 to 15 ventral rays rather than 10 to 12.
It differs from striata in lacking silvery pigment
on the swimbladder (occasionally lacking in stri-
ata) and in its more slender body, depth usually
10 or more times in standard length rather than
usually less than 9 in standard length in striata.
It differs from georgei in having anal rays 12 or
13 rather than usually 10 or 11 and in liaving pec-
toral rays usually 19 or more, rather than usually
18 or fewer.
Counts

See tables 1 to 6.

'^^^"

FiQUBE 12. — Ai-gentina stewarti, USNM 202998, para type, 148 mm standard length. Scales not shown. Cross section from

in front of dorsal fin. Drawn by Mildred H. Carrlngton.

ADDITIONS TO A REVISION OF ARGENTININE FISHES

29

Measurements

Based on 18 specimens, 121 to 166 mm. standard
length, given as percent of standard lengtli.
Preanal 85.0 (83.5-86.7) ; preventral 55.8 (53.8-
57.3) ; predorsal 47.7 (46.4-49.1) ; head length 30.6
(28.8-33.0) ; snout 10.3 (10.1-10.5) ; eye 9.7 (8.7-
10.7) ; maxillary length 5.3 (3.8-5.9) ; depth at
dorsal fin 8.6 (7.3-11.0) ; depth caudal peduncle
5.1 (4.5-5.5).
Description

Body elongate. Figure 8 shows a regression of
body depth on standard length (Y=.069X + 2.43)
compared with two closely related species. Great-
est depth behind head, tapering little to the caudal
peduncle. Figure 9 shows a regression of caudal
peduncle depth on head length (Y=.112X + 2.44)
compared with two closely related species. Body
in cross section in front of dorsal fin usually wider
than deep, approximately rectangular. The head,
when ^dewed laterally, has its dorsal profile
slightly interrupted by the upper margin of the
eye; the ventral profile of the head rises gently to
the snout. The interorbital space between the
supraocular canals flat or barely concave. The
dorsal portion of the maxillary lies under the
lachrymal. The distal end of the maxillary is mid-
way between the tip of the snout and the anterior
margin of the orbit. The jaws are broadly rounded,
the lower included. The palatine and the head of
the vomer bear small, closely spaced, needlelike
teeth in a continuous band 2 to 5 teeth wide, about
30 on the vomer and 45 on each palatine; no
dentary teeth. The ceratobranchial of the fifth gill
arch bears 14 small, conical teeth ; two patches of
similar teeth, with about 18 on each are found at
the anterior end of the fourth suprabranchial. The
tongue bears eight strong recurved teeth (descrip-
tion of dentition based on a single alizarin speci-
men) . The gill rakers are widely spaced triangular
flaps ; the longest ones are equal to one-seventh to
one-eighth of the interorbital distance.

The pectoral fin originates on the ventral surface
of the body anterior to a line through the hind
margin of the opercle. The distance between the
inner rays of the pectoral fins is equal to or greater
than the least depth of the caudal peduncle. The
rays of all fins ai'e broken off short.

Scales deciduous; the few we have seen lack
spines. Lateral scale pockets about 55.

The peritoneum is densely punctulate with small

dark chroniatophores. Several specimens have the
gut lightly peppered with chroniatophores. Seven
to nine pyloric caeca are present in eight speci-
mens. The swimbladder begins close to the hind
curve of the stomach and extends posteriorly to
beyond the origin of the ventral fin. Swimbladder
lacking silvery pigment (fig. 5) ; however, we
have seen one specimen with an iridescent swim-
bladder.

Pigmentation of adult specimens preserved in
formaldehyde solution consists of a dark brown
band extending along the upper one-fourth of the
body; ventral and parallel to the band is a less
darkly pigmented area. These two pigment bands
color the entire upper one-half of the body. The
dorsum is unpigmented with the exception of a
narrow middorsal streak. The throat and breast
are peppered with chromatophores, which in some
specimens are also scattered at the bases of the ven-
tral fins (fig. lOB). In some specimens the peri-
toneum shows through the belly as a dark, mid-
ventral streak. Some specimens also have some of
the scale pockets of the venter outlined in dark
pigment.

Distribution

A. stewarti has been taken off Nicaragua in the
western Caribbean and from Mona Island to Do-
minica in the Antilles (fig. 4) . It seems likely that
it is widespread in the southern Caribbean.

Depth distribution ranges from 200 to 310 fm.
(366-567 m.) — deeper than the other three Gulf
and Caribbean species. A. stewarti does overlap the
lower half of the depth distributions of the other
three ; however, iit is the only species that has not
been taken shoaler than 200 fm. (366 m.).
Habits

We have little information on this species. It
has been taken only with a bottom trawl ; however,
we have no information on bottom type or tem-
perature. Specimens are most often taken singly;
however, we have one collection with six fishes. A.
stewarti has been taken with georgei and ht'ucei.
Name

Xamed for Stewart Springer in recognition of
his numerous contributions to the ichthyology of
tlie tropical western Atlantic.
Study Material

All from the Atlantic. Holotype; USNM 202996,
144 mm. standard length; Oregon 3565, 14°10' N.,

30

U.S. FISH AND WILDLIFE SERVICE

Sl'SS' W., 240 to 250 fm. (439-457 m.), May 21,
1962. Paratypes:

Central America. — USNM 203572 (1 specimen);
Oregon 3610, 12°23' N., 82°29' W., 200 fm. (366
m.). USNM 202998 (4); Oregon 3574, 12°31' N.,
82''21' W., 200 fm. (366 m.). USNM 188223 (1);
Oregon 3614, 14°00' N., 81°50' W., 200 fm. (366
m.). USNM 202997 (1); USNM 187790 (6);
Oregon 3565, data as for holotype.

Antilles.— MCZ (1); Oregon 5925, 15°38' N.,
61°15' W., 245 fm. (448 m.). FMNH 66225 (1);
Oregon 2636, 17°37' N., 63°36' W., 280 fm. (512
m.). USNM 202999 (2, 1 cleared and stained);
Oregon 6695, 17°41' N., 62°50.5' W., 300 to 320
fm. (549-585 m.). USNM 186356 (1); Oregon
2645, 18°12' N., 67°42' W., 260 fm. (476 m.).
FMNH 66226 (1); Oregon 2651, 18°16.5' N.,
67°17' W., 250 fm. (457 m.). USNM 108374 (1);
Caroline, 18°32' N., 68°21' W., 260 fm. (476 m.).
FMNH 66224 (2); Oregon 2606, 18°37.5' N.,
65°04' W., 210 fm. (384 m.).

ARGENTINA BRUCEI, NEW SPECIES

Figures 2, 3, 4, 5, 8, 9, lOD, 13

Argentina striata not of Goode and Bean, 1896 ;
Cohen, 1964 (fig. 5).

Diagnosis

A. hrucei differs from sphyraena and silus in
having smooth instead of spiny scales and five in-
stead of six brancliiostegal rays. It differs from
sUus, sialis, aliceae, and elongata in having seven
(sometimes six) gill rakers on the lower arm of
the first arch rather than eight or more. It differs
from all Argentina except sphyraena and aliceae

in its low vertebral count, 44 to 46 rather than 47
or more. It differs from sphyraena, sialis, elongata,
australiae, and kagoshimae in having 18 to 20
pectoral rays rather than 19 or fewer. It differs
from elongata, kagosKirrme, and euchus in having
13 or 14 ventral rays rather than 12 or fewer. It
differs from australiae, kagoshimae, eiichus,
stnata, georgei, and stewarti in having usually
seven gill rakers rather than usually six gill rakers.
It differs from stnata in usually lacking silvery
pigment on the swimbladder.

Counts

See tables 1 to 6.
Measurements

Based on about 72 specimens, 68.4 to 132 mm.
standard length, given as percent of standard
length: Preanal 84.5 (74.6-87.9); preventral 56.2
(52.9-58.8); predorsal 48.3 (44.4-50.7); head
length 31.2 (27.7-33.1) ; snout 10.1 (8.7-11.2) ; eye
10.0 (7.9-11.6); maxillary length 5.9 (4.6-6.6);
depth at dorsal fin 13.0 (10.9-15.4) ; depth at cau-
dal peduncle 5.9 (5.0-6.5).

Description

A relatively short-bodied species with greatest
depth at dorsal origin tapering to caudal peduncle.
Body in cross section deeper than wide, the ventei-
broadly rounded. Body in preserved specimens
notably soft. The head, when viewed laterally,
usually has its dorsal profile broken by the upper
margin of the eye. The dorsal and ventral profiles
of the head converge on the snout at about equal
angles. The interorbital space between the supra-
ocular canals is flat. Tlie dorsal portion of the

^sihi!-^.^u.x:A.i.^,*.vt,Z-jS,.i<;i^i.<^^

FiouKE IZ.— Argentina hrucei, USNM 159357, paratype, 128 mm. standard length. Scales not shown. Cross section from in

front of dorsal fln. From Cohen, 1964, as A. stnata.

ADDITION'S TO A REVISION OF ARGENTININE FISHES

31

379-242 O - 70 - 3

maxillary lies under the lachrymal. The distal end
of the maxillai-y extends at least to the midpoint
of the snout and in some specimens farther. The
jaws are bi'oadly rounded; the lower, which often
has a slightly bony protuberance at the symphy-
sis, is included. The palatine and the head of the
vomer bear small, closely spaced, needlelike teeth,
in a continuous band 2 to 5 teeth wide, about
55 on the head of the vomer and 70 on each pala-
tine; no dentary teeth. The ceratobranchial of the
fifth gill arch bears 8 small, conical teeth; two
patches of similar teeth, 10 on the anterior patch
and l-i on the posterior patch, are found at the
anterior end of the fourth suprabranchial. The
tongue bears eight strong, recurved teetli (descrip-
tion of dentition based on a single alizarin speci-
men). The gill rakers are medium-sized, widely
spaced, and compressed at the base. The longest
gill rakers are equal to one-seventh to one-eighth
of the interorbital distance.

The pectoral fin originates on the dorso-lateral
curve of the body close to the level of the posterior
margin of the opercle. The distance between the
innermost rays of the pectoral fins is generally
less than the least dei^tli of the caudal peduncle.
The pectoral fin extends at least half the distance
from the pectoral origin to the ventral fin origin.

The scales are deciduous and lack spines. Scale
pocket counts are difficult on this soft-bodied fish ;
however, we estimate about 48 lateral line scales.

The peritoneum is pepi^ered with large, dark
chromatophores ; however, they are not so densely
distributed that they give the peritoneum a com-
pletely black appearance. The gut is immaculate.
Eight to 10 pyloric caeca are present in 12 speci-
mens; many body cavities are heavily invested
with fat. The swimbladder usually begins slightly
anterior to the hind curve of the stomach and
terminates slightly beyond the origin of the ventral
fins. Six specimens of about one hundred had
silvery swimbladders; otherwise, bladders lack
pigment.

Pigmentation of adult specimens preserved in
formaldehyde solution is a light straw color below
the lateral line, somewhat dai'ker along the upper
third of the body. The duskiness is not contiiuious
over the dorsum. Many examples cany 8 to 12 in-
distinct dusky blotches on tlie upper part of the
body. The throat, breast, and belly are unpig-
mented (fig. 10), although a few specimens have

a light sprinkling of chromatophores at the bases
of the i>ectoral and ventral fins. The i^eritoneum
shows through the midventral line in some
specimens.

Distribution

A. bnicel has been taken on the north coasts of
Hispaniola and Puerto Eico; off Jamaica, Hon-
duras, Nicaragua, Costa Rica, and Panama; and
along the north coast of South America. It has also
been trawled at several localities off the mouths of
the Orinoco.

Depth distribution ranges from 100 to 300 fm.
(183-549 m.) ; however, the fish has been most
often caught between 100 and 230 fm. (183^21
m.).

Habits

A. brucei has been taken only with a bottom
trawl, over a mud bottom, at bottom temperatures
ranging from 50° to 64° F. (10°-17.8° C). The
fish is caught more often in aggregations than
singly. A. bnicei has been taken in mixed collec-
tions with all three of the other tropical western
Atlantic sjDecies, striata, georgei, and stewarti,
though with only one at a time.

Name

Named for the well-known ichthyologist Bruce
B. Collette, who helped collect many of the speci-
mens upon which this description is based.

Study Material

All from the Atlantic. Holotype: USNM 203029,
117 mm. standard length; Oregon 3584, 9°13' N.,
81°30' W., 200 fm. (366 m.). May 25, 1962.
Paratypes:

Central America.— V?>^M. 187817 (3 specimens),
Oregon 3595, 9°02' N., 81°26' W., 100 fm. (183 m.).
USNM 187789 (16) and TABL 100571 {&); Oregon
3598, 9°03' N., 81°22' W., 200 to 220 fm. (366-402
m.). USNM 203047 (5); Oregon 3597, 9°04' N.,
81°25' W., 150 to 160 fm. (274-293 m.). USNM
187833 (7); Oregon 3585, 9°12' N., 81°30' W., 135
to 140 fm. (247-256 m.). USNM 187837 (1);
Oregon 3584, data as for holotype. USNM 187753
(1); Oregon 3590, 9°1S' N., 80°22' W., 125 fm.
(229 m.). USNM 200429 (5, 1 cleared and stained) ;
Oregon 5738, 9°14' N., 79°07' W., 120 fm. (220 m.).
USNM 188016 (b); Oregon 3610, 12°23' N., S2°29'
W., 200 fm. (366 m.). USNM 203031 (4); Oregon
3574, 12°31' N., 82°21' W., 200 fm. (366 m.).
USNM 187793 (7); Oregon 3570, 14°08' N.,

32

U.S. FISH AND WILDLIFE SERVICE

81°55' W., 200 to 240 fm. (366-439 m.)- TABL
100566 (1); Oregon 3615, 14°16' N., 81°55' W.,
200 fm. (366 m.). USNM 185093 (1) and FMNH
74571 (3); Oregon 1868, 16°36' N., 82°37' W., 175
fm. (320 m.). USNM 159353 (1); Oregon 1871,
16°39' N., 82°26' W., 250 fm. (457 m.). ANSP
98604 (14); Oregon 3626, 16°45' N., 81°27' W.,
150 fm. (274 m.). TABL 100562 (3); Oregon 3627,
16°50' N., 81°21' W., 200 fm. (366 m.). FMNH
66218 (2); Oregon 1883, 16°52' N., Sl°30' W., 200
fm. (366 m.).

South America.— USNM 159356 (3); FMNH
66222 (2); Oregon 1985, 9°41' N., 59°47' W.,
150 fm. (274 m.). USNM 159357 (9) and UF 8026
(4); Oregon 1989, 9°45' N., 59°45' W. UF 5237 (6)
and FMNH 66221 (6); Oregon 1983, 9°43' N.,
59°53' W., 125 fm. (229 m.). USNM 203049 (1);
Oregon 4465, 10°45' N., 66°37' W., 125 fm. (229
m.). USNM 203032 {1); Albatross 2700, 10°59' N.,
66°00' W., 140+ fm. (256+ m.). MCZ 45937 (6);
Oregon 4838, 11°09.5' N., 74°24.5' W., 170 to 180
fm. (311-329 m.). TABL 100568 (1); Oregon 4858,
11°09' N., 74°25' W., 160 fm. (293 m.). USNM
188973 (2); Oregon 4860, 11°09' N., 74°26' W.,
155 to 160 fm. (284-293 m.). USNM 203033 (1);
Oregon 4410, 11°52' N., 69°27' W., 230 fm.
(421 m.). USNM 203048 (2); Oregm 4408, 11°53'
N., 69°28' W., 230 fm. (421 m.). USNM 203030
(2); Oregon 4407, 11°59' N., 69°30' W., 230 fm.
(421 m.).

Antilles.— TABL 100570 (4); USNM 187838
(14); Oregon 3549, 17°50' N., 77°52' W., 170 fm.
(311 m.). USNM 186355 (1) and FMNH 66227
(1); Oregon 2653, 18°18' N., 67°18.5' W., 300 fm.
(549 m.). USNM 186354 (1); Oregon 2656, 18°24'
N., 67°15' W., 100 fm. (183 m.). MCZ 40588 (4);
FMNH 66228 (5) ; Oregon 2658, 18°26' N., 67°11.5'
W., 175 fm. (320 m.). USNM 186352 (2); Oregon
2664, 18°31.5' N., 66°46.5' W., 160 fm. (293 m.).
USNM 186353 (1); Oregon 2665, 18°31.5' N.,
66°50' W., 180 fm. (329 m.). USNM 186357 (1)
and FMNH 66229 (1); Oregon 2666, 18°32' N.,
66°46.5' W.,200 fm. (366 m.).TABL 100565 (2);
Silver Bay 5161, 19°57' N., 71°05' W., 190 fm.
348 m.).

ARGENTINA EUCHUS COHEN
Figure -2

A. exichius was originally described from only
two specimens (Cohen, 1961). On the basis of an
additional 15, we here present a new diagnosis and

counts and measurements as well as a range ex-
tension.

Diagnosis

A. euchus differs from sphyraena and silus in
its smooth instead of spiny scales and by its five
instead of six branchiostegals. It diffei-s from spJiy-
raemt., dlus, siaiis, aliceae, elongata, and hriKei in
havintr six gill rakeis on the lower arm of the firet
arch rather than seven or more. It has 47 or 48 ver-
tebrae, more than aliceae and hrucei, which have
43 to 46 ; and fewer than silits., elongata. aii-sfraliae,
kagoshimae, and stewarti, which have 49 to 67. It
difi'ei-s from siaiis and att-straliae in having 16 to 18
pectoral rays rather than 11 to 14. It differs from
silus, striata-, georgei, hntcei, and stewarti in hav-
ing 10 or 11 ventral rays rather than 12 or more.

Counts

See tables 1 to 7.
Measurements

Based on 14 specimens, 123 to 154 mm. standard
length, given as percent of standard length. Pre-
anal 82.4 (81.2-83.6); maxillary width 1.6 (1.4-
1.8) ; depth at dorsal fin 13.5 (11.9-15.3) ; head
depth 12.9 (11.7-13.8).
Discussion

The measurements given above were used, on
the basis of the two types, to help separate A.
euchus from A. elongata. austraJiae, and kago-
shimae (Cohen, 1961). The additional material
herein reported upon shows that with the excep-
tion of body depth and head depth in separating
euckus from au-straliae, morphometric data are un-
satisfactoi-y in diagnosing A. euchus.

Four specimens examined lacked silvery pig-
ment or iridescence on their swimbladders.

Distribution

A. euchus has been taken off Natal, southern
Mozambique, and Kenya at depths ranging from
131 to 322 fm. (240-589 m.).
Study Material

All from the western Indian Ocean. USNM
203160 (1 specimen), Anton Bmun cruise 8, sta.
421 G, 02°56' S., 40°28' E. 240 m. USNM 203159
(11), MCZ (1), FMNH (1), and BMNH (1);
Anton Brunn cruise 8, sta. 396 B, 25°32' S., 33°24'
E., 450 to 455 m.

ADDITIONS TO A REVISION OF ARGENTININE PISHES

33

GENUS GLOSSANODON GUICHENOT

We have received material of GJossanodon jJoUi
from West Africa and five small fishes from the
Arabian Sea that represent a species close to but
distinct from G. polli.

GLOSSANODON MILDRED AE, NEW SPECIES

Figure 14
Diagnosis

(r. mildredae differs from pygmaeus in having
its vent immediately anterior to the anal fin base
rather than farther forward, in having teeth on
the dentary, and in having 23 ratlier than 12 to 14
pectoral rays. It ditfei's from Jeiogloss-us and scmi-
fasciatus in having dentary teeth along more than
half tlie distance from the symphysis to the angle
of the gape. It differs from Jineatus in liaving 5
instead of 4 branchiostegal rays, 13 instead of 15
anal rays, and 23 instead of 20 pectoral rays. It
differs from polli in having at least 55 lateral line
scales rather than 48 to 51. Also, G. mildredae has
dusky blotches mainly alxjve the midline of the
body; in similar-sized polli, the ventral half of
the side bears continuations of the dorsal blotches.
Counts and Measurements

See table 8.
Description

Greatest depth behind head, tapering little to
caudal peduncle. The dorsal profile of the head
is slightly interrupted by the dorsal rim of the or-
bit. The ventral profile of the head rises more
abruptly from a point below the anterior margin
of the eye. The interorbital space between the su-
praocular canals is flat.

The dorsal margin of the maxillary lies under

the lachiymal and extends to the joint between
the lachi7mal and the jugal ; its distal end is closer
to the anterior margin of the orbit than to the
snout. Lower jaw projecting slightly; both jaws
are rounded, the lower less broadly.

Table 8. — Counts and measuremenls in millimelers on type
specitnens of Glossanodon mildredae

Holo- Para-
type type
USNM USNM
203235 203234

Para-
type

USNM
203234

Para-
type
USNM
203234

Para-
type

USNM
203233

Afeasurements:

Standard length _

Preanal.

Preventral

PredorsaL_

Head length

Snout

Eye

Maxillary length

Maxillary width

Body depth at dorsal-..
Body width behhid

head _ _

Caudal peduncle depth.
Counts:

Dorsal fin rays

Anal fin rays

Pectoral fin rays

Ventral fin rays _ _

Vertebrae.

Gill rakers on lower

arm first arch

Lateral line scales

Branchiostegal rays

64.9
64.1
33.6
30.7
20.8

6.2

6.2

6.3

1.2 .

7.1 .

7.0 .
4.1

13
13
23
13
51

68.1
48.6
29.5
28.4
16.6
5.1
6.4
4.0
1.0

6.3
3.8

13
13

56-1-

12
50

23

12

50

23

"i'

65.7
63.6
34.1
31.3
19.2

4.7

6.4

4.6

1.2 .

7.7

6.5
4.2

13
13
23
12

51

41.6
32.2
22.7
20.7
13.7
4.1
3.9
3.1

6.4

4.2
3.1

23
13
49

Each palatine bears 15 to 20 short, conical,
widely spaced teeth, arranged in an irregular
series. The head of the vomer has 10 to 12 similar
teetli. The tongue lacks teeth. About 10 teeth are
widely spaced in a single irregular row on each
dentary, extending from the symphysis to the
angle of the gape. The gill rakers are elongate,
lathlike structures and are closely spaced on the
gill arch. The longest rakers equal about one-half
the interorbital distance.

Figure 14.~Glossatwdon mildredae, USNM 20323.5, holotype, &i.9 mm. standard length. Scales not shown. Drawn

by Mildred H. Carrington.

34

U.S. FISH AND WILDLIFE SERVICE

The posterior end of the pectoral fin base forms
an angle of 35 to 40 degrees with the horizontal.
The tip of the pectoral fin extends at least one-
third of the distance from the pectoral fin origin
to the ventral fin origin. The ventral may be some-
what longer. The longest rays of the dorsal fin are
longer than body depth.

Scales are lost from all four specimens; how-
ever, on the holotype we have been able to count
at least 55 scale pockets along the lateral line and
there are possibly 4 or 5 more.

The peritoneum is dusky. The gut is immaculate.
The swimbladder lacks silvery pigment. Nine py-
loric caeca are present in a single specimen.

The largest paratype (69.8 mm. standard
length) has gonads containing minute, transparent
eggs. We camiot say wheither this fish is an im-
mature female or a matui'e female with unripe
gonads. If tlie latter, then G. mildredae matures at
a smaller size than does G. polli.

The body is straw-colored, with a narrow brown
band extending along the side above the midline.
Spaced along the band, and broader but less well
defined is a series of 8 to 10 dusky blotches, which
are less distinct anteriorly. The blotches extend
barely below the midline of the body. In our small-
est specimen (41.6 mm. s.l.) the blotches are made
of large, widely spaced chromatophores and the
lateral band is very indistinct. G. polJi of sizes
comparable with our mildredae specimens (See
fig. 8 in Cohen, 1958, taken from Poll, 1953, of a
specimen 8.3 cm., probably fork length. Also
USNM 203244, 61.5 mm. standard length and
USNM -203243, 65.8 mm. standard lengtli) have
blotches or bands over the ventral as well as the
dorsal half of the side.
Discussion

G. mildredae is closest to G. poJll. from which it
is not easily distinguished. Unfortunately, our ma-
terial of G. mildredae is limited in quantity, size,
and quality, and we have but few specimens of
G. polli of comparable size. We doubt that one and
the same species of Glossanodon lives in the tropi-
cal western Indian Ocean and off tropical West
Africa, and we believe tliat at least the characters
in our diagnosis serve to indicate the existence of
two distinct populations.

Distribution

Known only from two localities in the tropical
western Indian Ocean.

Name

Named for Mildred H. Carrington, whose taste-
ful and accurate drawings have contributed
greatly to the progress of ichthyology.

Study Material

Holotype: USNM 203235, 64.9 mm. standard
length, Anton Bruiin cruise 9, sta. 422, 6°51' S.,
39°54' E., 54 fm. (99 m.) ; 19 Nov. 1964; bottom
trawl. Paratypes: USNM 203234 (3 specimens);
data as for holotype. USNM 203233 (1) ; Anton
Bruun cruise 9, sta. 463, 11°24' N., 51°35' E., 41 to
95 fm. (75-174 m.), 17 Dec. 1964, bottom trawl.

GLOSSANODON POLLI COHEN

G. polli has not been recorded since its original
description (Cohen, 1958). We have examined the
18 recently collected specimens listed below and
find that they agi'ee well with the description. The
two Geronimo specimens listed below are juveniles
of 61.5 and 65.8 mm. standard lengths and show
the barred pattern illustrated in the original
description.

Study Material

USNM 203236 (12 specimens), MNHN (2),
MCZ (1), and FMNH (1); Guinean Trawling
Survey, La Rafale, transect 8, sta. 6, 8°28' N.,
14°21' W., 55 fm. (100 m.). USNM 203244 (1),
Geronimo cruise 2, sta. 213, 2°31' S., 8°51' E., 110
fm. (201 m.). USNM 203243 {I), Geronimo cruise
2, sta. 214, 2°01' S., 8°50.5' E., 110 fm. (201 m.)

LITERATURE CITED

BuLLis, Harvey R., and John R. Thompson.

1965. Collections by the exploratory fishing vessels
Oregon, Silver Bay, Cotribat, and Pelican made dur-
ing 1956-1960 in the southwestern North Atlantic.
U.S. Fish Wildl. Serv.. Spec. Sci. Rep. Fish. 510,
130 pp.

Carvalho, ,T. Paiva.

19.50. Resultados pientificos do cruzeiro do "Bae-

pendi'' e do "Vega" Ji I. da Trindade, Bol. Inst.

Paulista Oceanogr. 1 : 97-133.
Chin, Edwabd.

1966. Cruise report, re.search vessel Anton Bruun,
cruise 16. Texas A M Univ. Mar. Lab., Spec. Rep.
6, 36 pp. 4- 10 appendices. [Processed report,
Texas A M Univ. Mar. Lab., Galveston, Tex.]

Cohen, Daniel M.

19.58. A revision of the fishes of tlie subfamily Ar-

gentininae. Bull. Fla. State Mus. 3(3) : 93-173.
1961. On the identity of tlie species of the fish genus

Argentina in the Indian Ocean. Galathea Rep. 5:

19-21.

ADDITIONS TO A REVISION OF ARGENTININE FISHES

35

1964. Suborder Argentinoidea. In Henry B. Bigelow
(editor-in-chief), Fislies of the western North At-
lantic, pp. 1-70. Sears Found. Mar. Res., Mem.
1(4).

Emery, A. R., and F. D. McCracken.

1966. Biology of the Atlantic argentine (Argentina

silus Ascanius) on the Scotian Shelf. .T. Fish. Res.

Bd. Can. 23: 114.5-1160.
Fahlen, Goran.

1965. Histology of the posterior chamber of the
swimbladder of Arsrcnfma. Nature (London) 207:
94-95.

Fairbridge, W. S.

1951. The New South "Wales flathead, Ncoplatyccph-
alus macrodon (Ogilby). Aust. J. Mar. Fresh-
water Res. 2 : 118-178.
Fange, Ragnar.

1958. The structure and function of the gas bladder
in Argentina silus. Quart. J. Microsc. Sci. 99:
95-102.

FOLLETT, W. I.

1945. Notes on Argentina sialis Gilbert, an isospon-
dylous fish of western North America. Copeia
1945: 143-145.
GooDE, George B., and Tarleton H. Bean.

1896. Oceanic ichthyology : A treatise on the deep-

sea and pelagic fishes of the world. U.S. Nat. Mus.,
Spec. Bull. 2, XXV + 529 pp. Atlas, xxii -f 26
pp. -f 123 pis.
Marshall, N. B.

1960. Swimbladder structure of deep-sea fishes in
relation to tlieir systematics and biology. Discov-
ery Rep. 31: 1-122.

Miranda Ribeiro, Paulo De.

1961. Alguns peixes pouco conhecidos ocorrendo na
costa Brasileira. Bol. Mus. Nac. Rio de Janeiro,
nov. ser., Zool. 224, 11 pp.

Poll, Max.

19.53. Poissons, III.-TS16ost^ens Malacopt^rygiens.
Expedition Octenographique Beige dans les Eaux
Cotieres Africaines de I'Atlantique Slid (1948-1949)
4(2), 258 pp., 8 pis.

Schroeder, William C.

1955. Report on the results of exploratory otter-
trawling along the continental shelf and slope be-
tween Nova Scotia and Virginia during the sum-
mers of 1952 and 1953. Pap. Mar. Biol. Oceanogr.,
Deep-Sea Res., suppl. vol. 3 : 358-372.

Springer, Stewart, and Harvey R. Bullis.

1956. Collections by the Oregon in tlie Gulf of Mex-
ico. [U.S.] Fish Wildl. Serv., Spec. Sci. Rep. Fish.
196, 134 pp.

36

U.S. FISH AND WILDLIFE SERVICE

U.S. GOVERNMENT PRINTJNG OFFICE: 1969 O — 326-935

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF THE MIDDLE ATLANTIC

CONTINENTAL SHELF

BY FRANKLIN STEARNS, RESEARCH OCEANOGRAPHER

BUREAU OF COMMERCIAL FISHERIES ENVIRONMENTAL OCEANOGRAPHIC RESEARCH PROGRAM

WASHINGTON, D.C. 20242

ABSTRACT

Large-scale bathymetric maps covering the northern
two-thirds of the Middle Atlantic Continental Shelf
have recently been published. They were compiled at
a scale of 1:125,000 from 39 smooth sheets and are
contoured in 1-fm. (1.8 m.) intervals on the shelf and
in 10-fm. (18.3 m.) intervals on the upper slope.

Part 1 of this report discusses the construction and
reliability of these maps. In addition, a short review
of surveys made in the mapped area is given, a few uses

for the maps are suggested, and the reliability diagrams
(which appear on each map) are explained.

Part 2 discusses the past geologic history, the general
distribution of sediments, and the major geomorphic
processes at work in the area. In addition, the several
physiographic regions and features on the Middle At-
lantic Shelf are described in terms of their topography
and sediments.

The Middle Atlantic Continental Shelf is one
of the world's most studied shelf areas. The 60,000
square nautical miles ^ of drowned coastal low-
land making up its surface have long been of in-
terest to mariners, commercial fishermen, and
scientists. Numerous nautical chart surveys,
ooeanographic studies, and geophysical, geolog-
ical, and biological investigations have been made
in the area (Geyer, 1948; Drake, Ewing, and Sut-
ton, 1959 ; Heezen, Tharp, and Ewing, 1959 ; Mur-
ray, 1961 ; Drake, Heirtzler, and Hirsliman, 1963 ;
Stearns, 1963; Uchupi, 1963; Livingstone, 1965;
and Emery, 1966b) .

The Middle Atlantic Continental Shelf borders
one of the world's largest concentrations of hu-
man activity. Called Megalopolis by Gottmann
(1961), this region contains almost one-fifth of
'the population of the United States and is a
vast market for marine resources of all kinds.
The shelf supplies Megalopolis with commercial
and sport fisheries, recreation on the seashores,

^I use Engllsb fathoms and nautical miles throuKhout the
paper because aJl the data -n-cre collected in English rather than
metric units. For conversion, 1 fm. equals 1.83 m.. and 1
nautical mile equals 1.85 km.

Published June 1969.

FISHERY BULLETIN: VOL. 68, NO. 1

mineral resources, and space for waste disposal.
The need for detailed bathymetric maps in the
study of Continental Shelf geology, geomorphol-
ogy, and mineral resources is well known (Veatch
and Smith, 1939; Emery and Schlee, 1963;
Emery, 1966b). Less widely appreciated, but
equally important, are the uses of such maps in
the synthesis and study of physical and biological
data.

The shape of the sea floor can influence the
movement of water masses on the shelf, and this
movement can affect the distribution of such
oceanographic properties as temperature, salin-
ity, and nutrient elements (Bigelow, 1931; Hach-
ey, Lauzier, and Bailey, 1956; Trites, 1956). Al-
though only a few benthonic animals are known to
respond directly to the shape of the bottom (e.g.,
see Yonge, 1962), all marine animals respond to
tiie distribution of water-mass properties, which
are affected by the bottom. Hence, definite cor-
relations exist between the shajje of the Ixjttom
and the locations of marine animals (see Parker
and Curray, 1956), and detailed studies of en-
vironmental relations on the shelf require a de-
tailed knowledge of bathymetry.

37

Large-scale bathymetrio maps covering the
northern two-thirds of the Middle Atlantic Con-
tinental Shelf (fig. 1) have recently been pub-
lished by Stearns and Garrison (1967). These
maps are contoured in 1-fm. intervals from the
shore to 100 fm. and in 10-fm. intervals from 100
to 500 fm. and ai-e drawn on a Meroator projection
at a nominal scale of 1 : 125,000.

The present maps can be used in a variety of
ways, such as (1) interpolation aids when map-
ping physical data, (2) foundations for the
analysis of relations between physical features and

biological distributions, and (3) sources of infor-
mation for the efficient planning of stratified
sampling programs and surveys.

The purpose of this paper is to describe these
maps, their construction and reliability, and to
discuss the geomorphology of the mapped region.

PART 1. BATHYMETRIC MAPS

The proper use of bathymetric maps requires
some knowledge of how they were made, as well as
an estimate of their reliability. These topics are
discussed in this part of the report.

FiGUKE 1. — Generalized bathymetry of the Middle Atlantic Continental Shelf and locations of major features dis-
cussed in the text. Depth contours in fathom.s. Sources: USCGS Chart 1000 (13th ed., 1949) and Stearns and
Garrison (1967).

38

U.S. FISH AND WILDLIFE SERVICE

CONSTRUCTION OF THE MAPS

Construction of the maps is discussed from
three aspects: (1) history of past surveys, (2)
study of present surve3's, and (3) methods of
construction.

Past Bathymetric Surveys

The first systematic bathymetric survey of the
entire width of tlie Middle Atlantic Continental
Shelf was made by the U.S. Coast Survey in 1842
(USCGS Hydrographic Survey no. 100, scale
1 : 400,000) . Previously, only some inshore ai-eas

had been systematically surveyed, and charts of
the offshore regions were based on a few isolated
soundings. The 1842 survey covered the area be-
tween Rhode Island Sound and Cape May and
from near shore to a little over 100 fm. It was
supplemented in 1844 by a survey covering much
the same area (no. 101, scale 1 ; 400,000) and again
in 1859 by a survey extending fi-om Mart.ha's
Vineyard to sliglitly south of Cape Henlopen,
Del. ( no. 670, scale 1 : 400,000) .

No surveys were made during the Civil War,
but in the 1870's and 1880's much sounding was

BATHYMETRIC MAPS AND GEOMOEPHOLOGY OF MIDDLE ATLANTIC CONTINENTAL SHELF

39

done on the Continental Slope and in the adjacent
ocean basins, largely as a result of (1) an increased
interest in the life of abyssal regions, (2) increas-
ing activity in the laying of submarine telegraph
cables, and (3) the development of deep sea wire-
sounding machines (Agassiz, 1888; Tanner, 1897).
From 1877 to 1880 Alexander Agassiz (1888) di-
rected surveys aboard the Coast Survey ship Blake
along the Atlantic Continental Slope, but it was
not until 1882 that the shelf itself was again sur-
veyed, this time from Montauk Point, Long Island,
to Cape Henlopen, Del. (no. 1558, scale 1 : 300,-
000). This survey was extended south to Cape
Charles in 1886 (no. 1720, scale 1:200,000) and
to the east as far as Georges Bank during 1887-
1889 (nos. 1782, scale 1:300,000; and 1837, scale
1:400,000). In all of these early surveys, the
soundings were by lead line and the navigation
was by shore sightings, astronomical fixes, and
dead reckoning.

Except for a few isolated investigations of shoal
areas, the Middle Atlantic Shelf was not again
systematically surveyed until the 1930's, when
new sounding and navigational methods had been
developed. These surveys, from Georges Bank to
Cape Henry and from the shore to the Continental
Slope and Rise, are the principal sources used for
constructing the maps discussed in this paper.

Several earlier bathymetric maps -were based on
the surveys of the 1930's. Tlie first and most fa-
mous are the maps of Veatch and Smith (1939) —
see also Smith (1939). These authors compiled a
series of charts of the Continental Slope fi'om
Georges Bank to Chesapeake Bay and of the Hud-
son Channel region of the shelf (scale 1 : 120,000) .
Uchupi (1965), in cooperative work by the Woods
Hole Oceanographic Institution and the U.S.
Geological Survey, used the sui'veys to compile a
1 : 1,000,000 scale map of the shelf, slope, and rise
from southern Canada to the Straits of Florida.
In addition, the USCGS has used tlie surveys to
construct nautical charts of the region at scales
of 1 : 80,000 and 1 : 400,000 (see the 1100 and 1200
series of nautical charts). The surveys have also
been used for small maps, published as text illus-
trations (e.g., Elliott, Myers, and Tressler, 1955;
Garrison and McMaster, 1966) .

Present Data Sources

The data from 39 USCGS hydrographic sur-
veys, made between 1932 and 1961, were used for

making the present maps. (The smooth sheets of
these surveys vary in scale from 1 : 20,000 to
1 : 120,000.) In addition, 25 published USCGS nau-
tical charts (scales 1:10,000 to 1:80,000) were
used for some nearsliore areas, bays, sounds, and
harbors. The land contours which appear on some
sheets were compiled from U.S. Geological Sur-
vey and Army Map Service topographic quad-
rangle maps (scales 1 : 24,000 and 1 : 62,500). The
Long Island contours are from a topographic map
of the Island, scale 1 : 125,000, appearing in Fuller
(1914).

More bathymetric information exists than was
used in the present compilation. Many miles of
sounding lines have been run on the Middle Atlan-
tic Continental Shelf by the research ships of
\'arious government agencies, private research in-
stitutions, and universities. Many of these data ai-e
equal in quality to those used, but most have not
been reduced and plotted in a form that can be
readily contoured.

The new developments in the surveys of the
1930's were ecliosounding and radio-acoustic rang-
ing. Echosounding was developed in both the
United States and Europe during the first part
of this century, and by 1923 the USCGS had in-
stalled their first echosounder. This method of
measuring depths was rapidly improved and soon
rejolaced tlie older lead line and wire-sounding
machine. Before the 1930's, positions were deter-
mined in much the same manner as they were in
1842 and before. During the early 1920's, offshore
positioning had developed into an elaborate system
of precise dead reckoning, but it was not until the
USCGS introduced radio-acoustic ranging in 1924
that methods of navigation were changed funda-
mentally (Adams, 1942). This new method was
continually improved througliout ihe surveys of
the 1930's and was replaced by wholly electronic
systems during the 1940's.

Methods of Construction

Bathymetric contour lines were drawn directly
on either (1) full-scale, corrected copies of the
original surveys (smooth sheets), or (2) on nauti-
cal charts of nearshore areas. Louis E. Garrison
contoured the area between about long. 69°25' and
72°00' W. and shallower than about 100 fm. (US
CGS Hydrographic Surveys 6331, 6347, 6440,
6441, and 6447). I contoured the rest of the area.

This contoured source material was transferred

40

U.S. FISH AND WILDLIFE SEEVICE

by pantograph to dimensionally stable plastic
compilation sheets at a uniform scale of 1 : 125,000
(Mercator projection, scale of 1 : 125,000 at lat. 40°
X.) ; each sheet covered 1° of latitude and longi-
tude. Transfer was done in stages for each piece
of source material ; small quadrangles were trans-
ferred independently to minimize distortion of
scale and paper. Adjustment and matching be-
tween surveys, corrections, and final smoothing
of the isobaths were done on the compilation
sheets. The USCGS made the final map layout
and design.

RELIABILITY OF THE MAPS

Present technology makes it impractical to ob-
serve large areas of the sea floor directly; thus,
bathymetric maps are necessarily interpretive
drawings of an invisible surface (for discussions
of this subjective element in bathymetric mapping
see Veatch and Smith, 1939; Jones, 1941; and
Shepard, 1943) . Such maps are usually made from
discrete soundings, between which assumed depths
must be interpolated before contour lines of con-
stant depth (isobaths) can be drawn. The uncer-
tainty of these assumed dejjths, j^lus observational
and positional errors in the original soundings,
makes exact correspondence between a bathymetric
map and the real sea floor an impossibility. The
user of a map, however, should know what accu-
racy to expect.

The following paragraphs of this section discuss
the evaluation of the reliability of the maps, the
reliability diagrams which appear on each map,
and the spatial distribution of the map errors.

A general method for quantitative estunate of
the reliability of isoline maps has been presented
by Stearns (1968). In this general method the
reliability of isolines (expressed as a variance) is
related to (1) observational errors, (2) positional
errors, (3) interpolation errors, (4) errors in the
time of an observation, (5) synopticity errors (er-
rors due to lack of simultaneity in the observa-
tions), and (6) the space-time rates-of-change and
the directions of the gradients of the mapped
variable.

In applying the method to the present bathy-
metric maps, I considered all the above factors,
with the exception of time and synopticity errors.
I omitted the time-dependent errors, first, because
little exact information is available on the rates-
of-change of bottom topography, and, second, be-

cause such clianges, except in limited areas, are
likely to be very small during the period of useful
life of the maps.

The reliability equations (Stearns, 1968), witli
the time-dependent terms omitted, are as follows :

e3 = io+epPp Cos yp+eiQi Cos yi+^i'g,' Cos 7/

(1)

which expresses the expected bias of the values of
the isobaths at any point on the map or within
any subarea of the map, and

T%=T/„-f F,^(T/,^+^|) (Fc„. .,+C^^7;

+ Ve,{V,^ + gl) (Fcoa .,+ C^=T,) (2)

+ e?C^^.,[1^Cos 7, + C^= 7,]+^?Fcos y,)

+V,;{V,/+gr-)(Vcosy,'+C^"-y,')

+ '^ :HV,^'[Vaosy/ + C^' y/] + 9r-Vc.,sy/)

which expresses the variance of the values of the
isobaths at any point, or within any subarea, on
the map.

These equations may be evaluated for a map as a
whole (in which case a single average reliability
value would be obtained), or for any arbitrarily
selected small portion of a map. For the present
maps, the equations were evaluated for each ad-
jacent unit area of 5 geographical minutes to a
side. This unit area was selected as a compromise
between the geogi'aphic divei"sity of the map's reli-
ability and the time available for manual compu-
tation. Over 1,600 unit areas were involved in the
evaluation.

Evaluation of the Reliability

The evaluation of the terms in equations 1 and 2
are discussed in this section.

Ohsermtional errors (e„). — The echosoundings
made during the sm-veys of the 1930's and used
as the basis for constructing most areas of the
present maps were evaluated by Veatch and
Smith (1939)— see also Adams (1942). They con-
cluded (p. 60) that the accuracy of these sound-
ings was within 1 part in 100 for areas deeper than
100 fm. and witliin 1 part in 200 for areas shallower
than 100 fm. To approximate maximum errors on
the shelf proper, I used their larger estimate, 1

BATHYMETRIC MAPS AND GEOMORPHOLOGY OP MIDDLE ATLANTIC CONTINENTAL SHELF

41

part in 100, for all depths (0 to 500 fm.) and for all
surveys and nautical charts used in the compilation.
Because of lack of data on bias in the soundings,
I assumed unbiased work; hence, e^ was taken to
be zero. The variance of the observational errors
was estimated by assummg that the errors are
normally distributed and that the value, 1 part
in 100, represents 99 percent of the total distri-
bution (this assumption implies that systematic
and personal errors have been removed from the
data and that any reduction errors have a ran-
dom distribution). Therefore,

±c?/100= ±2.576 VK7; ^^"^® K„=0.000015c?2

where the variable d equals the maximum depth,
in fathoms, within each 5-minute unit area.

To account for round-off errors, I added a con-
stant factor to eacli variance value. This factor was
0.083 fm. when the soundings were recorded to the
nearest fathom and 0.0023 fm. wlicn recorded to
the nearest foot. I assmued a rectangular, or uni-
form, distribution of these errors ; hence, the vari-
ance equals E~/Z (see Weatherburn, 1961, p. 14),
where E equals one half of the round-off interval.

Positional' errors (cp). — Veatch and Smith
(1939) discussed the accuracy of positioning for
the radio-acoustic ranging methods used in the sur-
veys of the 1930's (see also Adams, 1942). They
concluded (p. 65) that the accuracy was 1 part in
200 for distances less than 100 nautical miles from
the control (reference) points used in a sm^vey.
To approximate a maximum estimate of positional
errors, I used 1 part in 100 for all of the surveys
(except for a few recent ones which cover a large
part of Nantucket Shoals) and all the nautical
charts.

Again, because, of lack of data, I assumed un-
biased work; hence ij, was taken to be zero. The
variance of the positional errors was determined
in the same way as described above for observa-
tional errors; hence Fep=0.000015Z>% where the
variable D equals the maximum distance in nauti-
cal miles between each 5-minute unit area and the
nearest control point (sonobuoy or station vessel)
used in a survey. For nearshore nautical charts
the distance D was measured to the nearest promi-
nent shore feature.

To each vai'iance value 1 added a constant fac-
tor — 0.0045 nautical mile, to account for such car-
tographic errors as paper distortion and misalign-

ments in tracing and printing. Tliis factor was cal-
culated by assuming a normal distribution of car-
tographic errors with a 99 percent limit of ±0.1
inch or ±0.17 nautical mile at a scale of 1 : 125,000.

For the recent sui'veys on Nantucket Shoals
(1959-61), during which electronic positioning
systems were used, I assumed a 99 percent error
of ±0.066 nautical mile (±400 feet) and a normal
error distribution; hence F(3;, = 0.0007 nautical
mile. To this was added the cartographic error
variance of 0.0045 nautical mile giving a constant
total error variance of 0.0052 nautical mile for
these surveys.

Ivferpolatioii errors (ei and e/). — If we were
concerned with maps showing only the depths of
soundings, the total error would be a simple com-
bination of the positional and observational errors
discussed above. Because, however, we are dealing
with isobatli maps, interpolation erroi's must also
be considered. These errors are of two kinds: (1)
those associated with depths interpolated along
axes between actual soundings (primary interpola-
tion error, ei) and (2) those associated witii depths
interpolated between the primary interpolation
axes (secondary interpolation error, e/).

The equations for computing these interpolation
errors are (Stearns, 1968) :

e,= er = Q

(3)
(4)
(5)

These are based on a simple two-point linear
interpolation scheme.

The evaluation of F,, and F,,, depends on the
particular survey pattern used. The quantity
(F|-|-7^) in equation 4 is the mean sum of the
squares of the distances between the soundings.
For a rectangular array of discrete soundings
along more or less parallel track lines, as is the
situation for most of the hydrographic surveys
of the Middle Atlantic Continental Shelf, this
quantity equals }i(a^+b-), where a is the distance
between track lines and b is the distance between
soundings on each line. By taking the mean of five
systematic samples of the two distances, I esti-
mated the quantities a and b for each 5-minute
unit area.

42

U.S. FISH AND WILDLIFE SERVICE

The quantity {Vi'-\-l'^) in equation 5 is tlie
mean sum of the squares of the distances between
the primary interpolation axes. Several choices
are possible for secondary interpolation axes
(Stearns, 1968). The correct choices are those axes
actually used by the cartographer in drawing the
map. A human being, however, in his subjective
approach to contouring, is seldom fully aware of
just what axes he has used. Therefore, in com-
puting the reliability of the present maps, I
assumed that the shortest axes were used, which,
in the rectangular trackline siu-veys of the Middle
Atlantic Continental Shelf, equaled the distance
between soundings. These distances are usually
equal within any unit area, so the quantity
(V,. + l") equals 61

The topographic slopes. — Positional and inter-
polation errors (which are expressed in distance
units) are converted into depth errors, by multi-
plying them by g Cos y, where g is the positive
topographic slope in the vicinity of the soundings
(or the interpolated point) and y is the angle
between the errors and the local slope.

The slopes g,,, g,, and g^ were assumed to be
equal and were estimated from five systematic
samples taken in each 5-minute imit area. Each
sample consisted of the maximum slope measured
in a circle 1 nautical mile in diameter. The mean
slope, g, was taken as the mean of the five samples,
and the variance of the slopes, Vg, was approxi-
mated by (0.43 ci))-, where w was the range of the
five samples. This estimate of the variance assumed
that the slopes have a normal distribution within
each 5-minute unit area and was used as a com-
putational expedient (see Dixon and Massey,
1957, pp. 273, 404).

The cosines. — In estimating the cosines in
equations 1 and 2, I assumed that all angles had
an equal probability of occurrence; thus yp, 7;,
and 7;/ range from zero to ir radians (from 0° to
180°), and the probability functions of the angles
equal l/ir. Hence,

Cos-

-r

Cos7d7=0

and

Vc.

i7 — - <-

tJo

0S=7d7=}^

This assumption may be true for positional errors,
because I assumed that these errors are unbiased.
It is not strictly true, however, for interpolation

errors, and a more accurate, although more time-
consuming method could have been used ; i.e., the
final map could have been matched with the inter-
polation networks actually used and the angles
measured.

The Source Diagram

The source diagram on each map shows the
number, scale, and date of the USCGS hydro-
graphic surveys and nautical charts used in the
construction of tlie maps.

The maps depict the sea floor at the dates of the
\'arious surveys, and the user must draw his own
conclusions as to changes that may have taken
place since then. Significant changes are likely
only along some portions of the coast above about
10 fm., in offshore shoal areas, and along the
upper Continental Slope where slumping may
have occurred (see Lucke, 1934a, 1934b; Howard,
1939; Heezen, 1963; Miller and Zeigler, 1964;
Stewart and Jordan, 1964; Uchupi, 1967). In
such areas the maps and their reliability diagrams
sliould be used with caution.

Those who wish to study the actual soundings
may examine or purchase copies of the original
hydrographic survey sheets from the USCGS,
Washington, D.C.

Diagram of the Mean Distance Between Track Lines

The mean distance between track lines is a
common device for indicating the reliability of
bathymetric maps. Reliability is usually assumed
to be better where the lines are closely spaced.
Trackline spacing also indicates the resolution of
a survey; i.e., the minimum size of features con-
sistently discoverable from the survey. Surveys
with many different trackline spacings were used
in drawing the maps. Consequently, the isobaths
are more detailed in some areas than in others.

Diagram of the Standard Deviation
of the Isobath Depth Error

The standard deviations in the isobath depth
error diagram are estimates of liow much and how
frequently the depths indicated on the maps may
depart from the true depths. Tlie diagram is based
on the square root of the variance given by equa-
tion 2 and shows the average standard deviation
in unit areas of 5 geographical minutes to a side.
It applies to depths as indicated on the maps, not
to the original soundings. A more detailed dia-
gram of the entire mapped area is reproduced in
figure 2.

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF JIIDDLE ATLANTIC CONTINENTAL SHELF

43

Js,

O'tJo

Figure 2.— Standard deviatiou of the isobath depth error. (1) Less than 0.25 fm. (2) 0.25-0.49 fm. (3) 0.50-0.99 fm.
(4) 1.00-1.99 fm. (5) 2.00-3.99 fm. (6) 4.00-7.99 fm. (7) 8.0O-15.99 fm. (8) 16.00-31.99 fm. (9) 32.00-63.99 fm.
(10) 64.00-127.99 fm. (11) 128.00 fm. and more.

The figures in the diagram may be used to esti-
mate the expected correspondence between the
mapped depths and the true depths. This expected
correspondence is expressed as a probability that
the true depth falls between certain limits. For
example, if we assume a normal distribution of
depth errors in an area where the standard devia-
tion of the depth error is 1 fm., then the probabil-
ity is 99 percent that the indicated depth is correct
to within ±2.6 fm., 90 percent tliat the dei)th is
correct to within ±1.6 fm., or 50 percent tliat tlie
depth is correct to within ±0.7 fm. Tlie depth of
any isobath as shown on tlie maps should be

thought of as representing a probable range of
depths rather than as a single exact depth.

The above limits were computed by the formula
r=Zi(T, where r is the expected range of depths,
0- is the standard deviation taken from the depth
error diagram (fig. 2), and Z, is a number that
depends upon the probability i and upon the kind
of error distribution (see Dixon and Massey, 1957,
or other statistics textbooks).

The above formula gives the expected range
due only to errors in the map. To find the expected
range when the maps are being used aboard a ship
to search for a given bathyraetric feature, the

M

U.S. FISH AND WILDLIFE SERVICE

10

10

II 10

^O'

standard deviation would have to include the

is the

sliip's errors; i.e., a-

--^ij.

r+o-/, where

map standard deviation taken from the depth error
diagram, and a^ is the ship standard deviation.
The ship standard deviation may be estimated as
the square root of the first three terms on the
ri2;ht-hand side of equation 2.

Diagram of the Standard Deviation of the Isobath
Position Error

The standard deviations in the isobath position
error diagram are estimates of how much and how
frequently the positions of the depths as indicated
on the maps may depart from the true positions.

This diagram is also based on the square root of
equation 2; it shows the average standard devia-
tion in 5-minute unit areas and applies only to
indicated depths — not to the original soundings.
The values in the diagram were computed by
dividing the standard deviations of the isobath
depth error (fig. 2) by vFe+^', where ^ is the mean
topographic slope of the sea floor in a given 5-
minute unit area, and V^ is the variance of the
topographic slope within the same 5-minute unit
area. A more detailed diagram of the entire
mapped area is reproduced in figure 3.

The figures in this diagram may be used to esti-

BATHYMETRIC MAPS AND GEOMORPHOLOGY OP MIDDLE ATLANiTIC CONTINENTAL SHELF

45

mate the expected correspondence between the
mapped positions of the depths and their true posi-
tions. This expected correspondence is expressed
as a probability that the true position falls be-
tween certain limits. For example, if we assume a
normal distribution of position errors in an area
where the standard deviation of the position error
is 0.2 nautical mile then the probability is 99 per-
cent that a given depth will be found within ±0.5
nautical mile of its indicated position (i.e., will be
found within a circle 1.0 nautical mile in diameter
centered on the given depth), 90 percent that it
will be found within ±0.3 nautical mile of its

indicated position, or 50 percent that it will be
found within ±0.1 nautical mile of its indicated
position. The position of any isobath as shown
on the maps should be thought of as the center of
a probable range of positions rather than as a
single exact position.

The above limits were computed by the same
formula as was the probable range of depths, ex-
cept that here /■ is the expected range of positions,
and (T is the standard deviation taken from the
position error diagram (fig. 3).

This computation also applies only to map
errors. To find the expected range when the

Figure 3.— Standard deviation of tlie isobath position error. (1) 0.a>-0.09 nautical mile. (2) 0.10-0.14 nautical mile.
(3) O.lfi-0.19 nautical mile. (-1) 0.20-0.24 nautical mile. (.5) 0.2.5-0.2!> nautical mile. ((>) O..30-0..39 nautical mile.
(7) 0.40-0.49 nautical mile. (8) 0.50-0.59 nautical mile. (9) 0.60-0.09 nautical mile. (10) 0.70-0.79 nautical mile.
(11) 0.80-0.89 nauUcal mile.

46

U.S. FISH AND WILDLIFE SERVICE

maps are being used aboard a ship, a must be
equated to Va-m^+c/, where 0-^ is taken from the
position error diagi-am, and o-j is computed by
dividing the first three terms on the right-liand
side of equation 2 by Vg-\-'g-, for the area in which
the ship is working, and then taking the square
root of the quotient.
Distribution of the Map Errors

The standard deviations of the isobath depth
error (fig. 2) generally increase in an offshore
direction. Most of this increase is due to the steeper
topographic slope on the outer shelf and upper
slope which makes interpolation of depths between

soundings less certain in these regions. A part of
the increase is also due to a wider spacing between
tracklines offshore.

Most of the large inshore standard deviations
are also caused by locally steep topographic
slopes (e.g., the Hudson Channel, Long Island
Sound, Delaware Bay, and Nantucket Shoals);
however, the large deviations east of Cape Cod
are due both to wide trackline spacing and to steep
slopes.

Figure 4 shows the percentage of the total vari-
ance of the dejjth error which can be attributed to
observational, positional, and interpolation errors.

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLANTIC CONTINENTAL SHELF

47

379-242 O - 70 - 4

Figure 4. — Percentage of tbe variance of the isobath depth
error that can be attributed to observational errors
(OBS), positional errors (POS), and interpolation
errors (INT).

The figure is based on the variance in 100 repre-
sentative 5-miniite unit areas. In most of these unit
areas more than half of the total variance results
from uncertainty in interpolations of assumed
depths between the original soundings.

Interpolation errors are \ery sensitive to topo-
graphic slope and spacing between soundings. To
achieve the same reliability of isobath depths, the
spacing of soundings must be much closer in areas
of steep slopes than in areas of gentle slopes. For
many surveys, not only of bathymetry but of other
variables as well, the observations are so widely
spaced (usually for reasons of economy) that ordi-
nary positional and observational errors have little
effect on the reliability of the final isolines.

Figure 5 shows the relation of the standard
deviation of the isobath depth error to the meau
topographic slope in a few selected unit areas. The
dispersion of the points results largely from varia-
tions in the spacing between tracklines.

The standard deviations of the isobath position
error (fig. 3) also increase offshore, mostly because
of wider spacing between tracklines. Figure 6
shows the relation of these standard deviations to
the mean spacing between tracklines. The disper-
sion of the points is due mainly to variations in the
observational and positional errors of the original
soundings.

PART 2. GEOMORPHOLOGY

A description of the configuration of the Middle
Atlantic Continental Shelf, along with a general
discussion of its evolution, of the processes invoh-ed
in its formation, and of its sediments, is presented
in this part of the report.

GENERAL CONSIDERATIONS

The general appearance, geological history, sedi-
ment distribution, and geomorphic processes of the
Middle Atlantic Shelf are discussed in this section.

General Appearance and Past Geologic History

The present continental border of eastern North
America can be divided into five geomorphic zones
which roughly parallel the present shoreline (fig.
7 ) : ( 1 ) a hilly to mountainous system of parallel
valleys and ridges (the Newer, or Folded, Appa-
lachian Mountains), (2) a fiat to hilly upland re-
gion (the Older Appalachian Mountains), (3)
a coastal lowland, in places submerged below pres-
ent sea-level (the Atlantic Coastal Plain and Con-
tinental Shelf), (4) a .submerged slope about 1,500
fm. high (the Continental Slope), and (5) a very
gently sloping surface merging seaward with the
deep ocean floor (the Continental Kise) . For a dis-
cussion of these geomorphic divisions see Fenne-
man (1938), Heezan et al. (1959), and Hammond
(1964).

Before the Cretaceous Period (some 136 million
years ago) a succession of evolving highlands oc-
cupied the present sites of the Older Appalachians
and the Coastal Plain. According to Dietz and
Holden ( 1966) , these highlands were formed when
material uplifted from an ancient Continental
Slope and Rise and from the adjacent deep-sea
floor was added to a then smaller continent. This
process of accretion is supposed to have started in
the late Ordovician Period (about 445 million
years ago) and to have continued until the end of
the Permian Period (about 225 million years ago) ,
eventually adding some 150 to 400 or more miles
to the continent. (Dates are from Kulp, 1961, and
Harland, Smith, and Wilcock, 1964.) The eroded
remnants of tliese old highlands now underlie
Cretaceous and younger sediments on the present
Coastal Plain; they outcrop in a belt of greatly
deformed and altered rocks throughout tlie Older
Appalachian Mountains.

The region west of the Older Appalachians was
occupied in pre-Ordovician times by an ancient

48

U.S. FISH AND WILDLIFE SERVICE

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MEAN TOPOGRAPHIC SLOPE (TM./N.MI.)

FiGUKE 5.- — Variation of the standard deviation of the isobath depth error with respect to

the mean topographic slope.

BATHYMETRIC MAPS AND GEOMORPHOLOGY OP MIDDLE ATLANTIC CONTINENTAL SHELF

49

0.6

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MEAH DISTANCE BETWEEN TRACKLINES
(NAUTICAL MILES)

Figure 6. — Variation of tlie standard deviation of the
isobath position error with resiject to the mean distance
between tracklines.

coastal plain and continental shelf. This plain be-
came an epicontinental inland sea in post-Ordo-
vician times, and its bottom was progressively
folded mitil the Appalachian Eevolution of middle
and late Permian times finally forced it and its
sediments into the present Folded Appalachian
Moimtains. The above sequence of events is only
one recent inference from available evidence; for
other interpretations of the geologic history of the
region see Schuchert (1923), Kay (1951), Drake
etal. (1959), Wilson (1966), and Harland (1967);
seealso the criticism by Hsu (1965) of earlier ideas
of Dietz (1963a) and the reply by Dietz (1965).

-^.S v''-^ '

Figure 7. — Physiographic regions of the Middle Atlantic Coast. (1) Appalachian Plateaus and Interior Lowlands.
(2) Folded Appalachian Mountain-s. (3) Older Apiwlachian Moimtain.s, including (3A) Blue Ridge Mountains,
(3B) New England-Acadian Mountains, (3C) Piedmont-Xew England Hills, (3D) Piedmont Plain, and (3E) Xew
England Plain. (4) Emerged and Submerged Coast.al Plain, including (4A) Emerged Coastal Plain, (4B) Sub-
merged Coastal Plain or Continental Shelf, and (4C) Gulf of Maine Basin. (5) Continental Sloi>e. (6) Continental
Rise. Boundaries are approximate. Sources: Femieman (1938) ; Heezen et al. (1959) ; and Hammond (19<>4). Tlie
heavy solid line is the boiuidary of the mapped area.

50

U.S. FISH AND WILDLIFE SERVICE

Since the Cretaceous Period, tlie eroded roots of
the old coastal highlands have experienced suc-
cessive invasions of the sea, and a large wedge of
sediment has been deposited on their surfaces.
The most recent submergence was between about
4,000 and 20,000 years ago. (For discussions of
terrestrial conditions on the shelf in the recent
past see Emery, 1966a ; Emery, Wigley, and Rubin,
1966 ; and Wigley. 1966) . The presently submerged
surface of this sedimentary wedge is the Conti-
nental Shelf of eastern North America.

General Sediment Distribution

The surface of the Middle Atlantic Continental
Shelf is covered only in part by contemporary
sediments. These are mainly in a narrow near-
shore zone (Emery, 1961; Uchupi, 1963). The
largest part of the shelf is covered by relict de-
posits formed during lower stands of sea level in
the Ice Age.

Relict shelf features and sediments were recog-
nized as early as 1850 by Austen who suggested
that the English Channel was once a subaerial
river valley. Dana (1863) extended Austen's idea
to the Middle Atlantic Continental Shelf by his
discovery on an 1852 Coast Survey chart of both
the Hudson and Block submarine channels which,
he concluded, were once occupied by the Hudson
and Connectidut Rivers. Taylor (1872) later sug-
gested that evidence of dry land, rivers, and shore-
line features should be found within the 100-fm.
line, and during the same period Louis Agassiz
taught his Harvard classes that the offshore fish-
ing banks consisted superficially of glacial drift
(Upham, 1894). Most recent authors accept the
idea of relict deposits, although emphasis shifted
somewhat after Gulliver (1899) and Jolmson
(1919) introduced the concept of an inner shelf
which had been cut by waves and an outer shelf
which had been built up by wave deposition (for
a discussion of this concept see Dietz, 1963b, 1964 ;
and Moore and Curray. 1964).

The Middle Atlantic Shelf is covered by modi-
fied glacial outwash and moraines, river channel
and flood plain deposits, ancient deltas, offshore
bars, and old coastal beach-lagoon complexes
(Uchupi, 1968). Some smaller areas may contain
materials formed in place by submarine chemical
processes (Uchupi, 1963; Emery, 1966b). Super-
imposed on these primai'y sediments are patches
of both contemporary and ancient shell debris

(Merrill, Emery, and Rubin, 1965; Emery, Mer-
rill, and Trumbull, 1965).

The subsurface sediments of the Shelf and
Coastal Plain consist of layer after layer of much
the same type of deposit that occurs today on their
surface (with additions of other types such as
peat and limestone). These sediments have been
accumulating at least since the Cretaceous Period
and now form a thick prism which ranges from
a few feet at the landward border of the Coastal
Plain to over 15,000 feet (4.6 km.) thick at the
edge of the shelf. An even greater thickness has
accumulated at the foot of the Continental Slope,
and some 25,000 feet (7.6 km.) of sediments now
lie under the Continental Rise (for a discussion of
this deeper structure see Dietz, 1952 ; Drake et al.,
1959; Heezen et al, 1959; Murray, 1961; Emery,
1966b ; Krause, 1966 ; Hoskins, 1967 ; and Uchupi
and Emery, 1967).

Geomorphic Processes

The nearshore breaking of waves is the most
important cause of erosion on the landward edge
of the shelf, but is apparently effective only above
about 5 to 10 fm. (Dietz, 1963b; see also the dis-
cussion by Moore and Curray, 1964 and the answer
Ijy Dietz, 1964). Some controversy exists, however,
concerning the ability of contemporary processes
to alter significantly the relict terrains and sedi-
ments seaward of the surf-zone. Several authors
have thought that present waves and currents can
scour the shelf intensely to great depths (Dana,
1890; Gulliver, 1899; Johnson, 1919; Alexander,
1934; and Jones, 1941). Other workers have sug-
gested that the preseiat shelf surface is drowned
and entirely out of adjustment with present condi-
tions (Lindenkohl, 1891; Dietz, 1963b, 1964). Still
others have believed that a thin surface layer
(6-24 inches, or 15-60 cm.) is in adjustment with
contemporary sea level (Donahue, Allen, and
Heezen, 1966), or that fine sediments are being
either moved across the shelf or dejiosited in cer-
tain restricted areas (Shaler, 1881; Shepard and
Cohee, 1936; Stetson, 1938b; and Emery, 1966b).
Uchupi (1968) suggested that some linear sand
bodies on the inner shelf may ha^-e been formed
by large modern storm waves. It is also possible
that with a long-continued stand of the sea at its
present level, the shoreline would build out over
a large portion of the inner shelf (Curray, 1964;
Emery, 1966b) or that existing bottom sediments

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLAN/TIC CONTINENTAL SHELF

51

and relict land forms would eventually become
completely adjusted to present sea level (Stetson,
1938b, 1939; Moore and Curray, 1964).

A distinction must be made between gross land
forms and surficial sediments. All of the relict sur-
face sediments above the late Wisconsin low stand
of the sea (about 66 or 70 fm.) have been modi-
fied during the last 20,000 years or so by the ac-
tive surf-zone, as this zone migrated shoreward
across the shelf with the latest postglacial (or
Holocene) rise of sea level. Thus, the surface sedi-
ment layer is a direct product of the Holocene
marine transgression. Large terrain features, how-
ever, are not likely to have been obliterated by the
Holocene rise; hence, much of the present gross
morphology on the shelf is probably related to
pre-Holocene events.

Between the nearshore surf-zone and the land
a complex of barrier beaches, lagoons, and coastal
marshes has developed along most of the Middle
Atlantic Coast. This complex traps much of the
sediment load now brought to the ocean by rivers
and other runoff. A large volume of recent sedi-
ment is also deposited in bays or sounds, and the
small amount of suspended fine material that
escapes is often removed from the shelf by cur-
rents or deposited in such depressions as the Hud-
son and Block Channels (Stetson, 1955; Curray,
1964).

As changes have occurred in sea level, the shore-
line (along with a complex of barrier beaches,
lagoons, coastal marshes, and estuaries) has mi-
grated scores of miles back and forth across what
is now the shelf and the emerged coastal plain
(Emery, 1967). As early as 1881 Shaler suggested
that the net effect of this repeated migration,
combined with a slow subsidence of the conti-
nental margin, has been the deposition of the series
of layers that now form the thick sedimentary
wedge of the Continental Shelf.

REGIONAL PHYSIOGRAPHY

The physiographic regions and features on the
Middle Atlantic Shelf are described in terms of
their topography and sediments in the following
paragraphs. The major regions and features dis-
cussed are (1) nearshore terrains, (2) terrains
southwest of the Hudson Channel, (3) the Hudson
Channel, (4) terrains northeast and east of the
Hudson Channel, and (5) terraces and ancient
shore features on both the inner and outer shelf.

52

The baithymetric maps of Stearns and Garrison
(1967) serve as illustrations for this section and
should be available ; features mentioned in the text
are keyed to these maps by chart number. The loca-
tions of some of the larger features are also shown
in figure 1.

Nearshore Terrains

Nearshore terrains are easily accessible and have
been much studied (see, for example, Shaler, 1893,
1895; Johnson, 1919, 1925; Shepard, 1948; and
Guilcher, 1958). In the mapped area they may be
divided into three types.

Tlie s\i,rf-2on£. — Parallel to the shoreline is a
relatively smooth concave slope, in some places
interriipted by one or more offshore bars, extend-
ing from the beach to a dei>th of 5 or 10 fm. The
width of the surf-zone rarely exceeds 2 nautical
miles (its average width is about one-half mile)
and it appears to be deepest off New Jersey and
eastern Long Island. The sediments of the surf-
zone are mostly clean, coarse to fine sand, with a
few patches of gravel and rock. Some black mud
that lies between 4 and 11 fm. off New Jersey and
Long Island may indicate places where the surf-
zone has exposed old coastal marsh deposits
such as underlie the present barrier beaches (see
Fischer, 1961).

The harrier heach-lagoon complex. — Shoreward
of and parallel to the surf-zone, throughout most
of the mapped area, are extensive linear barrier
beaches forming the seaward margin of shallow
bays, lagoons, and coasital marshes. This terrain
is especially well develofjed along the whole of the
Maryland, Delaware, New Jersey, and southern
Long Island Coasts. The width of the lagoon-
coastal marsh terrain usually varies from 1 to 6
nautical miles. Except for tidal cliannels, the depth
of lagoons seldom exceeds 2 fm. and is generally |
less than 1 fm. The marshes are at sea level, be-
tween the high- and low-tide marks; and sediments
there are mud and organic plant debris. Tidal-
delta sands are aromid inlets. Barrier beaches are
clean sand often fonned into sand dunes by the
wind (see Lucke, 1934a, 1934b; and Fischer, 1961) .
Glacial jnoraines. — Running across the north-
ern part of the mapped area is a zone of low hills
separated from the southern New England sliore
by a series of bays and sounds. This region of old
glacial moraines forms numerous submerged fea-
tures as well as the backbones of Long Island,

U.S. FISH AND WILDLIFE SERVICE

Block Island, and the islands south of Massachu-
setts (Schafer and Hartshorn, 1965). Long Island
has two moraines: the Harbor Hill Moraine ex-
tends along the north shore to Orient Point and
then across Long Island Sound through Plum,
Great Gull, and Fishers Islands to Watch Hill
Point in Rhode Island and along the slioi*e (where
it is called the Charlestown Moraine) to Point
Judith; the Ronkonkoma Moraine runs through
central Long Island to Montauk Point. These two
moraines are considered to have formed during the
last advance of the late Wisconsin ice-sheet some
20,000 years ago (Flint, 1957; and Domier, 1964).
Tliey mei'ge to the west, south of Hempstead Har-
bor, and continue across Brooklyn to Staten Island
and New Jersey.

Wliere the Harbor Hill Moraine crosses Long
Island Sound there is a ridge of coarse rocky sedi-
ments (chart 0808N-5.3 of Stearns and Garrison,
1967). Between the high points on this ridge are
elongated depressions and channels, some as deep
as 55 fm., containing finer sediments. Some of
these depressions may be kettles formed by the
melting of buried blocks of ice (Elliott et al.,
1955), or they may have been cut by either ice-
scour or subglacial drainage streams (Dana, 1870,
1875, 1883, 1890; Loring and Nota, 1966, suggested
this origin for similar features in the Gulf of St.
Lawrence) . These pre-Holocene depressions would
have become fresh-water lakes shortly after being-
uncovered by the melting ice-sheet (Antevs, 1922,
1928; Lougee, 1953) ; evidence for these lakes, in
the form of fresh-water clay concretions, has been
found in one depression south of Fishers Island
(Frankel and Thomas, 1966). Some other depres-
sions may have been formed or at least modified,
by river erosion, during the period which followed
the retreat of the ice-sheet. All the depressions
probably have been scoured by tidal currents which
became effective in this area when the sea had
risen to 10 to 15 fm. below j^resent sea level.

The Ronkonkoma Moraine extends beyond Long
Island, from Montauk Point to Block Island, and
its crossing is marked by a broad ridge of coarse
rocky and bouldery sediments (charts 0808N-51
and -53). Near its center this band is breached by
a channel, which contains several 25- and 30-fm.
holes. This breach probably represents one of the
ancient channels for the rivers of Connecticut and

western Rhode Island. It was later eroded by tidal
currents when sea level rose to within 10 or 15 fm.
of its present level.

East of Point Judith, R.I., the Harbor Hill (or
Charlestown) Moraine appears to bend south-
ward around Narragansett Bay and to join with
the Buzzards Bay Moraine of western Cape Cod
by way of Browns Ledge and the Elizabeth Is-
lands (chart 0808N-51). This bend is marked by
a submerged ridge of coarse gravelly sediments.
East of Block Island the Ronkonkoma ^Moraine
also appears to bend to the south and to join with
moraines on the north shores of Martha's Vine-
yard and Nantucket Island by way of Nomans
Land, the Southwest Shoal, and Cox Ledge. The
bottom in this area is marked by a broad rocky
and gravelly ridge (Schafer, 1961; and Kaye,
1964) .

Between Block Island and Martha's Vineyard
this ridge is breached by a chamiel with depths as
great as 35 fm. The sea bottom between the two
moraines in this area contains an east-west chan-
nel with depths that approach 30 fm. to the north of
Block Island. This east-west channel continues
westward through Block Island Sound and east-
ward as far as the entrance to Vineyard Sound.
This channel probably represents an early Holo-
cene drainage system for much of southern New
England. Presumably, late Holocene drainage
from Connecticut broke tlirough the moraine east
of Montauk Point, while Rhode Island and Mas-
sachusetts drainage continued down the channel
east of Block Island. It appears that both these
systems entered the Block Channel across the shelf.
The channels have been modified by tidal scour and
tidal delta deposition wliich would have started
when the sea rose to about 25 fm. below present
sea level.

The moraines on Martha's Vineyard, Nantucket
Island, and Cape Cod cannot be traced to the east
with certainty (see chart 0708N-51). They prob-
ably merge with tlie lateral moraine of an ice-
sheet lobe that once extended soutliward through
the Great South Channel (see Zeigler, Tuttle,
Tasha, and Giese, 1964) . Between Martha's Vine-
yard and Nantucket Island is a double tidal delta
which appears to have been built in an old tribu-
tary of the Block Channel that once ran between
the Islands.

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLANTIC CONTINENTAL SHELF

53

Terrains Southwest of the Hudson Channel

Off the coasts of New Jersey, Delaware, and
Maryland, the bottom above about 50 fm. consists
of alternate ridges and longitudinal depi-essions,
whicli generally run northeast-southwest and are
interspaced by flat areas, escarpments, embay-
ments, and former channels. The sediments on
this part of the shelf are predominantly sands
with some coarser material. Muds are infrequent
above about 50 fm. and are not dominant shal-
lower than the shelf break.

The terrains in this area are similar to present
nearshore and modified subaerial alluvial terrains ;
this similarity is not surprising because the surf-
zone, the complex of lagoons and coastal marshes,
and the subaerial river regimes must have repeat-
edly migrated back and forth acro.ss the shelf.
Flint (1940) noted that north of the James River
the Pleistocene formations on the emerged coastal
plain are typical of compound alluvial deposits.
It seems that this is also true of the submerged
shelf, with the addition of numerous transgressive
marine features (see also MacClintock, 1943, and
Schlee, 1964) .

Delaware River channels. — From the mouth of
Delaware Bay a channel may be traced south-
eastward about 40 nautical miles (Lindenkohl,
1891; charts 0807N-56 and -57). Below 20 fm.
this channel is lost in a series of what appear to be
old lagoons and barrier beaches which continue
down to about 40 fm. To the northeast the chan-
nel is bounded by a scarp as much as 15 fm. high.
A well-defined ridge backing this scarp can be
traced 30 nautical miles soutlieastward from Cape
May, and its remnants extend for another 30 or 40
nautical miles.

Northeast of this ridge is a shallow embayment
that has a diffuse channel below 5 to 7 fm. (charts
0807N-55 and -56). Deeper than 20 fm. this
embayment flattens out and merges with what
appears to be a series of lagoons and barrier
beaches. Possibly this bay represents an older Dela-
ware River estuary which might be correlated
with a post-Sangamon channel in the Cape May
Formation on the Cape May Peninsula (Rich-
ards, 1962).

Great Egg Ilarhor Hirer rhannel. — Running
southeast from near Great Egg Harbor Inlet is
a smooth embayment that extends to a depth of
12 or 14 fm., where a bar has been built across its

54

mouth (chart 0807N-55). Beyond this bar the bay
narrows and a shallow channel continues south-
southeastward. Between 18 and 22 fm. a ridge,
about 20 nautical miles long, appears to have been
a large barrier beach. It encloses what was prob-
ably a former lagoon, now as much as 2 or 3 fm.
deeper than the surrounding bottom. Below this
feature, the channel is lost in a deeper series of
what seem to be lagoons and barrier beaches. The
northeast boundary of the embayment off Great
Egg Harbor Inlet is a low ridge extending south-
easterly from Brigantine Shoal ; it appears to be
composed of a series of submerged sand spits and
barrier beaches.

The old and new Delaware embayments and the
Great Egg Harbor embayment are each well
defined between about 10 and 20 fm. Below about
20 fm., however, the new Delawai-e embayment is
lost, and the old Delaware and Great Egg Harbor
embayments are combined, first into a large shal-
low depression (about 35 nautical miles long)
between 24 and 27 fm. and then into a single open
embayment between 27 and 29 fm. (charts 08O7N-
55 and -56). Below about 28 fm., this open embay-
ment narrows into a slender channel which con-
tinues southward to about 35 fm., where it is lost
in what may be a comjalex of fonner lagoons.

The Shelf northeast of Brigantine Shoal. —
Northeast of Brigantine Shoal the shelf is domi-
nated by several large northeastward trending
embayments, and by two north-south trending
channels, which are associated with a submerged
alluvial gravel deposit (Schlee, 1964; charts
0807N-54 and -55) . One of the north-south trend-
ing channels heads offshore near lat. 39°45' N. and
may be traced southward for about 30 nautical
miles, roughly along long. 73°50' W.

West of this channel is a very smooth and flat "1
plain, whose shallow limit is defined by the 10- or
11-fm. isobath. On the east it is bounded by a low-
scarp and backed by a north-south ridge with a
minimum depth of less than 9 fm. This ridge is
distinct for at least 35 nautical miles along the
l^ottom, and remnants of it extend even farther
both nortli and south.

East of this ridge is the second of the north -
south channels mentioned above. It originates near
lat. 39°50' N. and runs southward for about '-W
nautical miles between long. 73°28' and 73°33' ~\V.
This channel is defined by the 19- to 21-fm. iso-

U.S. FISH AND WILDLIFE SERVICE

baths and is extensively barred throughout its
length at those depths.

West of this second channel is another plain,
somewhat dissected by northeasterly trending de-
pressions; to the east is a broad flat-topped ridge
with minimum depths of between 17 and 18 fm.
Most of the channels on the east side of this ridge
trend northeastward toward the Hudson Channel.
North of lat. 39°50' N., all of the old shelf chan-
nels run eastward or northeastward toward the
Hudson Channel.

The gra\el deposits near these north-south chan-
nels seem to have added about 5 fm. to the shelf
surface off the coast of northern New Jersey. When
compared to the surface south of Long Island this
buildup is shown by a greater offshore extent of
the 20- to 30-fm. isobaths (compare charts 0807N-
54 and 0808N-54 and -55). According to Schlee
(1964), these deposits are at least 10,000 years old
and were probably deposited by the ancestral Hud-
son River.

The northernmost and largest of the northeast-
ward trending embay ments runs roughly along a
line between lat. 39°05' N., long. 74°04' W. and
lat. 39°24' N., long. 73°20' W. (chart 0807N-55).
It is well defined between about 20 and 25 fm. and
occurs immediately below the submerged gravel
deposit described by Schlee (1964) . It can be traced
for some 50 nautical miles across the shelf and ap-
parently connects with the 37- to 38-fm. depression
below Tiger Scarp (chart. 0807N-52). Southeast
of this largest embayment are four similar but
smaller embayments. All of these embayments are
bounded on their northwest sides by low scarps
and all lead into a north-northeast trending series
of apparent lagoons and chamiels below about
35 fm. To the south these embayments are defined
by the 24- to 26-fm. isobatjis, but they arc progres-
sively less well formed as the end of the Brigantine
Shoal Ridge is approached.

The Hudson Channel

The Hudson Cliannel is the best defined of the
old river valleys on the shelf. It was first discov-
ered during the 1842—14 surveys and originally
mapped as a series of discrete "mud holes." Dana
(1863) later suggested that these holes were pari
of a continuous valley that liad been eroded liy
the Hudson River. The survey of 1882 demon-
strated tlie continuity of the channel.

Tlie Hudson Cliannel extends some 85 nautical

miles across the shelf from off the entrance to New
York Harbor to the head of the Hudson Canyon
(charts 0807N-52 and -54, and 0808N-55). It is
very shallow at its upper end. but some 10 nautical
miles southeast of Sandy Hook it deepens
abruptly, runs about 15 nautical miles southward,
and then turns southeastward across the shelf. It
is divided into a series of basins which are floored
with mud and muddy sand. It becomes partially
lost in an elongated flood plain and delta below
about 40 fm., but several buried channels have been
traced through this area, the youngest of which
connects to the jaresent head of the Hudson Canyon
(Ewing, LePichon, and Ewing, 1963) .

According to Ewing et al. (1963), the present
Hudson Channel and Delta and the upper slope
portion of the Hudson Canyon have all been in
much the same position throughout the late
Pleistocene. Very likely, however, the present head
of the canyon is only one of the latest feeder chan-
nels for the lower canyon. Ewing et al. (1963)
showed some old buried discontinuities (possibly
erosion surfaces) which head northeast of the pves-
ent canyon. Robertson (1964) suggested that the
Georges Bank canyons were eroded during a
Pliocene emergence, filled during an upper Plio-
cene or very early Pleistocene submergence, and
then re-excavated during the Pleistocene. Some of
the canyons which are immediately northeast of
the Hudson Canyon, and which have their present
heads below 100 fm. may be of Pliocene age and
have not had their heads re-excavated because the
Hudson drainage moved out of the area.

Terrains Between the Hudson Channel and the
Block Channel

The shelf surface south of Long Island (charts
0808N-53, -54, and -55) has at least three types
of relict terrains. Between about 15 and 35 fm. it is
characterized by low ridges and shallow channels
and appears to be a stream-dissected alluvial plain
modified by minor features formed during the
Holocene transgression. It is not covered by exten-
sive late Pleistocene alluvial gravels like the shelf
southwest of tlie Hudson Channel.

The shelf surface above about 15 fm. is domi-
nated by Wisconsin glacial outwash and appears
as a sand plain in front of the old moraines on
Long Island. It has been much modified b}- early
Holocene stream erosion, the late Holocene marine
transgression, the modern surf -zone, and possibly

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLANiTIC CONTINENTAL SHELF

00

by present-day gtorm wave action (see discussions
of this region by Dana, 1875; Lindenkohl, 1885,
1891 ; Shepard and Cohee, 1936 ; Stetson, 1938b,
1949; Lougee, 1953; Elliott et al., 1955; Garrison
and McMaster, 1966; and Uchupi, 1968). Below
about 35 fm. the surface appears to be dominated
by deltaic and alliivial deposition rather than by
erosion.

As Garrison and McMaster (1966) pointed out,
two major directions of past drainage are apparent
on the present shelf surface south of Long Is-
land; one (north of about lat. 40°20' N.) is east-
ward into Block Channel, and the other east and
southeastward into a large embayment (well de-
fined between about 40 and 45 fm. on charts
0807N-52 and 0808N-54) near lat. 40°00' N. and
long. 72° 10-15' W.
The Block Channel

The Block Channel was discovered during the
same surveys of 1842-44 that found the Hudson
Channel. This broad and shallow channel extends
some 70 nautical miles across the shelf, from inside
Block Island Sound to its delta at the shelf break
(charts 0807N-51, and 0808N-51 and -52). Block
Channel has several minor tributaries entering
from the west and two major tributaries entering
from the east— one from Rhode Island Sound and
Buzzards Bay, and the other from the area south
of Nantucket Sound. The Channel and its Ehode
Island Sound tributary contain what are appar-
ently well-developed tidal deltas between about
23 and 26 fm.

Dana (1863) suggested that the Block Channel
had been eroded by the Connecticut River. Gar-
rison and McMaster (1966) considered it to have
been the main trunk for southern New England
drainage during late "Wisconsin and Holocene
times, and Krause (1966) suggested that its delta
was forming throughout the Pleistocene. These
authors noted that the delta's present form was
reached during the early Holocene when sea level
was about 45 fm. below the present one. This level
is similar to the depth of formation of about 43 f m.
proposed by Veatch and Smith (1939) for the
Hudson Delta.

Surficial sediments in the Block Channel consist
of about 16 inches (41 cm.) of fine fluvial and estu-
arine sands and silt, probably of Holocene age.
These overlie clean medium sands of Wisconsin
age and of fluvial origin. The upper 1 inch (2 cm.)

56

or so is sandy silt, with a very high water content ;
it is probably late Holocene or modern sediment
(McMaster and Garrison, 1966; Garrison and
McMaster, 1966).

Terrains Between the Block Channel and the
Great South Channel

The sea floor east of the Block Chaimel (exclu-
sive of Nantucket Shoals) is zoned much the
same as to the west, although it is very much
smoother, contains fewer stream channels and other
well-defined offshore features, and is partly covered
by considerably different sediments (charts
0807N-51, and 0808N-51 and -52).

Above about 20 fm. the bottom is rough and is
composed of Wisconsin glacial outwash and
morainal deposits modified by stream erosion, by
the late Holocene transgression, and by the
present surf-zone. Between about 20 and 35 f m. the
shelf is of very low relief and appears to be an
alluvial plain modified by a few transgressive
features.

The surficial sediments on this iilain are fine to
coarse sands, which Gan'ison and McMaster
(1966) considered to be pre-Holocene fluvial de-
posits later reworked by the Holocene transgres-
sion. To the east, around the margin of Nantucket
Shoals, these authors believed these fluvial sands to
be covered by fine sand derived from the Shoals
during the late Holocene or present.

The silty region south of Martha's Vineyard. —
Below about 30 to 35 fm. evidence of stream ero-
sion is sparse, the bottom is very smooth, and the
surface sediments change to sandy silt (chart
0808N-52). This region is unique because it is the
only extensive muddy deposit on the entire East
Coast Continental Shelf that is not associated with
a marked depression. It was first mentioned by
Pourtales (1870).

Lindenkohl (1885) considered this muddy area
to be a region of Tertiary outcrop that had not
been covered by Pleistocene deposits. Shepard and
Cohee (1936) thought that the silt was a modern
deposit derived from Georges Bank. Stetson
( 1938b) also thought that silt was now being added
to older sand deposits in the area, and Chamberlin
and Stearns (1963) have suggested a current eddy
to account for this deposition. Garrison and Mc-
Master (1966) noted that the northern edge of the
silt deposit is strongly intermixed with older al-
luvial sands and that the eastern edge appears to

U.S. FISH AND WILDLIFE SERVICE

be overlain by younger sand derived from Nan-
tucket Shoals. They believed that the silt accumu-
lated in a topographic depression during the Holo-
cene rise^ of sea level. Furthermore, they suggested
silt beds under Nantucket Shoals as the source and
placed the age as late Holocene (after tlie sea had
risen to about .3.5 fm. below present sea level) be-
cause the surface appears smooth and uneroded.

The smooth appearance in this area may be a
data artifact, resulting from a rather wide spacing
of survey tracklines. Just to the east of the Block
Delta is a small well-surveyed area (USCGS Hy-
drographic Survey No. 6659) that shows the bot-
tom finely dissected by many small channels and
covered with a few small mounds and depressions.
Although this sui^vey may indicate what the sur-
rounding region would look like if surveyed in
comparable detail, there is some doubt that it does."
The average standard deviation of the isobath posi-
tion error in the area of USCGS Hydrographic
Survey No. 6659 is 0.1.3 nautical mile and, because
the principal tracklines run parallel to the trend
of the small channels (i.e., up and down slope),
lengthwise line shifts of one or two times this
amount would account for much of the fine detail
shown. vSome of the crosslines run in this survey,
however, give evidence, of shallow channels, and it
seems probable that the true appearance of the
bottom lies somewhere between the two extremes
indicated.

Nantuc'kfif f^hoah. — For a distance of 30 to 50
nautical miles to the south and southeast of Nan-
tucket Island is a vast expanse of sand shoals and
a tangle of many smaller ridges and depressions
(charts 0708N-5i and -52). Collectively, this area
is called Nantucket Shoals and has been known
since the earliest explorations of the east coast (see
Kich, 1929). Two old maps showing Nantucket
Shoals, one made about 1656 and the other about
1730, are reproduced in Gottmann (1961).

From geologic mapping of Nantucket Island,
Martha's Vineyard, and Cape Cod, it appears that
Nantucket Shoals are relict glacial deposits laid
down when the sea was 25 fm. below its present
level. The large shoals abutting on the Great South
Channel contain a few patches of gravel and prob-
ably constitute a much modified glacial moraine
formed by a late Wisconsin ice-lobe in that chan-

- Personal communication from
logical Survey, Washington. D.C.

John S. Schlee, U.S. Geo-

nel. Farther to the west, Nantucket Shoals prob-
ably were derived by reworking outwash from the
west side of this South Channel moraine, or from
an interlobate outwash deposit formed between the
South Channel ice-lobe and another ice-lobe ex-
tending through Cape Cod Bay (Zeigler et al.,
1964, suggested that outer Ca^ie Cod is an inter-
lobate deposit formed between these two lobes),
or from end moraines of the Cape Cod Bay ice-
lobe. Whatever their exact source, these Shoals
have been much altered by early Holocene stream
erosion and by late Holocene and modem tidal cur-
I'ent and surf-zone action (Lindenkohl, 1883;
Curtis, 1913).

Old silt beds occur under the Shoals, and Living-
stone (1964) considered them to be of Sangamon
age. (Athearn (1957) came to the same conclusion
for a similar silt layer about 43 fm. below sea level
some 60 nautical miles south of Moriches Bay,
Long Island.) Groot and Groot (1964) found that
samples of the upper 5 feet (1.5 m.) of the silt
near Fishing Eip contained a mixture of Creta-
ceous, Tertiary, and Pleistocene pollen and spores,
as well as a marine shell about 11,500 years old.
It, thus, seems that the silt layer, at least near
Fishing Rip, has been covered by the Shoal sands
only in the late Holocene — probably by material
washed southwestward from the lateral moraine
of the South Channel ice-lobe. This type of win-
nowing has been invoked by Garrison and Mc-
Master (1966) to account for the band of fine sand
covering the silty area to the west of Nantucket
Shoals (see also Shaler, 1893). Uchupi (1968) sug-
gested, however, that some of this sand may have
come from the erosion of the outer arm of Cape
Cod.

The Great South Channel. — The existence of the
Great South Channel was inferred from local sur-
face currents by Captain John Smith as early as
1614 (Rich, 1929) . It sejiarates Georges Bank from
Nantucket Shoals and is a broad and flat but
rough-bottomed valley with a sill at about 40 fm.
(lat. 40°36' N. on chart 0708N-52). It is divided
into a number of sliallow basins by low sills. This
Channel was probalily occupied by a lobe of the
late-Wisconsin ice-sheet, from which outwash and
moraines contributed to Iwth Little Georges Shoal
to the ea.st and Nantucket Shoals to the west (see
Zeigler et al., 1964) . In pre-Pleistocene time Great
South Channel may ha^•e been a stream valley

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLAMTIC CONTINENTAL SHELF

57

(Johnson and Stolfus, 1924; Shepavd, Trefethen,
and Cohee, 1934; Emery and Uchupi, 1965; and
Uchupi, 1966a, 1966b).

Terraces and Shore Features
on the Outer Shelf

Below about 40 fm. tlie outer shelf is character-
ized by (1) an alternation of discontinuous scarps
and relatively flat terraces, some with superim-
posed linear ridges of coarse sands and gravels (es-
pecially well developed off New Jersey and Dela-
ware) and (2) by ancient river deltas (especially
south of New England) . Most authors describe the
scarps and terraces as old shoreline features, de-
veloped during lower Pleistocene sea levels (Tay-
lor, 1872; Newberry, 1878; Lindenkohl, 1891;
Shepard, 1932; Stetson, 1938b; Veatch and Smith,
1939; Dietz, 1952; and Emery, 1961).

OU shore lines. — Three sets of terraces with bars
and spits are observable throughout the area. The
deepest set is between 82 and 90 fm. and averages
about 85 fm. Remnants of this set may be seen be-
tween Veatch Canyon and Atlantis Canyon (86-
90 fm. on chart. 0708N-53), just to the east of the
head of Block Canyon (82-84 fm. on chart 0807N-
51), and to the northeast of Hudson Canyon (82-
86 fm. on chart 0807N-52). In addition, Ewing et
al. (1963) discovered an 80- to 90-fm. buried ero-
sion surface near the Hudson Canyon (their 165-
m. terrace) .

A shallower set, from 73 to 81 fm. and averag-
ing about 77 fm., may be seen between Veatch
Canyon and Atlantis Canyon (a double set at 78-
81 and 73-76 fm. on chart 0708N-53), and to the
northeast of Toms Canyon (73-78 fm. on chart
0807N-53). The 85- and 77-fm. sets of terraces
south of New England have been combined by
Garrison and McMaster (1966) into what they call
the 80-fm. terrace.

These terraces are backed by a discontinuous
scarp, whose foot is at an average depth of about
77 fm. ; this scarp is the NichoUs Shore of Veatch
and Smith (1939). It is well defined in the subsur-
face (Ewing et al., 1963) and, for the most part,
appears to be a constructional escarpment formed
by younger sediments deposited on an older sur-
face. A more poorly developed deeper scarp, with
its foot at about 86 fm., can be seen between Veatch
Canyon and Atlantis Canyon (chart 0708N-53),
and just to the west of Atlantis Canyon where it

merges with the higher Nicholls Shore (chart
0807N-51).

The next set of terraces is between 56 and 71
fm. and averages about 64 fm.; it may be seen
between Hydrographer Canyon and Veatch Can-
yon (59-62 fm. on chart 0708N-53), as well as to
the west of Atlantis Canyon (64-70 fm. on chart
0807N-51), and to the northeast of Hudson Can-
yon (59-62 and 62-70 fm. on chart 0807N-52),
Toms Canyon (64-71 fm. on charts 0807N-52 and
-53), Wilmington Canyon (56-59 and 63-65 fm.
on chart 0807N-56), and Baltimore Canyon (62-
66 fm. on chart 0807N-56). Referring to the re-
gion south of New England, Garrison and Mc-
Master (1966) called this set the 65-fm. terrace.
It is backed by a poorly developed scarp whose
foot is at an average depth of about 64 fm. Called
the Franklin Shore by Veatch and Smith (1939),
this scarp appears to be partly constructional and
partly destructional in origin. Ewing et al. (1963)
could not find a clear subsurface indication of the
Franklin Shore near the Hudson Canyon.

Although these three sets of terraces and scarps
were certainly formed when the sea v»'as at various
lower levels than at present, it is not easy to deter-
mine the exact levels. The difficulty was made
plain by Johnson (1910, 1932), Johnson and Win-
ter (1927), and Miller (1939) in discussions of the
problems involved in correlating old shorelines
now above sea level. These authors concluded that
at a given sea-level shoreline features can be de-
veloped at different elevations ajid that determina-
tion of former sea levels by physiographic meth-
ods alone is, consequently, very inaccurate.
Johnson (1932) has also pointed out that a dis-
tinction must be made between the elevations of
erosional and depositional features formed at the
same sea level. All of these conclusions are also
applicable to submerged features

Numerous estimates of former sea levels on the
outer shelf have been based on appraisals of the
eustatic lowering of sea level during the forma-
tion of the Pleistocene ice-sheets (e.g., Maclaren,
1842 ; Taylor, 1872 ; Shaler, 1875 ; Daly, 1925 ; Fair-
bridge, 1960; Curray, 1961; and Shepard, 1961).
Donn, Farrand, and Ewing (1962) give double es-
timates for this eustatic lowering which correspond
with two different estimates of the present thick-
ness of the Antarctic ice-cap. These, combined with
dates taken from Emiliani (1961, 1964, 1966) and

58

U.S. FISH AND WILDLIFE SERVICE

Broecker (1966), are: (1) a maximum Illinoian
lowering of about 75 or 88 fm. (some 110,000 years
ago), (2) a maximum early Wisconsin lowering
of about 63 or 74 fm. (some 53,000-60,000 years
ago), and (3) a maximum late Wisconsin lowering
of about 58 or 68 fm. (some 18,000-20,000 years
ago).

In addition to these three terraces, Garrison and
McMaster (1966) have noted the existence of an-
other terrace formed when sea level stood at about
45 fm. This level seems to have been the latest
episode in (1) large delta formation, especially
south of New England, and (2) extensive barrier
beach-lagoon formation off New Jersey and Dela-
ware. The 45-fm. terrace is well developed near
the Block Delta, where there is also evidence of
small lagoons to the east (chart 0808N-52) , and of
a large spit and a barrier beach-lagoon complex to
the west (charts 0807N-51 and 0808N-54). The
terrace is also well developed between the Block
Delta and the Hudson Canyon (chart 0807N-52)
and between Toms and Wilmington Canyons
where a large embayment and an extensive series
of barrier beaches and lagoons seem to have formed
(chart 0807N-53).

Delfa.s. — Old river deltas along the 45-fm. ter-
race are especially well developed northeast of the
Hudson Channel. The 45-fm. level was the most
recent ejjisode in a long history of large-scale del-
taic deposition on this part of the outer shelf. The
most typical and best preserved of the old deltas is
associated with Block Chamiel (Garrison and Mc-
Master, 1966). From seismic profiles Krause
(1966) has concluded that this delta probably-
existed throughout the Pleistocene. Where it bulges
out over the edge of the shelf and onto the upper
Continental Slope, Krause's profiles revealed a
large area of bottomset beds.

Between the Block and Hudson Deltas a small
delta is associated with the southeasterly drainage
pattern south of Long Island. Probably of late
Wisconsin or Holocene age, this delta appeare to
lie almost completely above the 64-fm. terrace
northeast of the Hudson Canyon (chart 0807N-
52).

The Hudson Channel disappears below about 40
fm. in what Veatch and Smith (1939) have called
the Hudson Apron, a large delta whose latest
stage of construction occurred when sea level stood
at about 43 fm. The large bar, or spit, just to the

northeast of the Hudson Canyon, may represent
the remains of an earlier delta built during or
shortly after the late Wisconsin maximum sea level
regression (which probably formed the 64-fm. sur-
face under this feature) . Similar large spits to the
northeast of both Wilmington and Baltimore Can-
yons (chart 0807N-56) may also be remnants of
early or late Wisconsin deltas — probably built in
this area by the Delaware River. Little evidence
exists of delta formation at the 45-fm. level east
of Block Chamiel.

Canyons and the. slope complex. — The Continen-
tal Slope of Eastern North America was discov-
ered in the early 19th century, but it was not
studied in detail until the 1870's, when the first
successful wire-sounding machines were intro-
duced. The Coast Survey steamer Blake surveyed
the slope during 1877-80 (Agassiz, 1888), and the
Fish Commission steamers FhJi Hawk and Alha-
fross did extensive deep-water biological dredging,
especially south of New England, during the
1880's.

Although the upper parts of canyons on the edge
of the Scotian Shelf and Grand Banks had long
l)cen known to connnercial fishermen (see Collins,
1885, and Johnson, 1885), no evidence of Middle
Atlantic canyons was obtained until the 1842 work
of the Coast Survey. After the soundings from the
1842 surveys were plotted, nautical charts carried
notations of a "145-fathom hole" near the head of
Hudson Canyon. Dana (1863) used an 1852 chart
to trace the Hudson and Block Channels across
the Shelf, but the new surveys of 1882 were re-
quired to show the immense size of the Hudson
Canyon and its extension to the bottom of the
Continental Slope (Lindenkohl, 1885). The upper
part of another canyon, later named the Atlantis
Canyon, was discovered by the Albatross in 1884
(Tanner, 1886) . After the discoveries of the 1880's
the canyons were much discussed (see Upham
1890a, 1890b, 1894: and Spencer, 1890, 1903, 1905a,
1905b) — usually in attempts to support theories
of a vast uplift of the North American continent
during the late Tertiary or early Pleistocene, which
was supposed to have caused the ice age — but little
new field work was done until the surveys by the
T'SCGS in the 193()"s (discussed by Shepard, 1931,
1933a, 19.33b, 1934, 1938; Daly, 1936; Shepard and
Beard, 1938 ; and Stetson, 1938a, 1938c) . This work
culminated in the report and cliai'ts of Veatch and

BATHYMETRIC MAPS AND GEOMORPHOLOGY OF MIDDLE ATLANfTIC CONTINENTAL SHELF

59

Smith (1939)— see also Smith (1939, 1940a, 1940b,
1941).

The origin of these canyons is still an open ques-
tion, but most recent authors Ijelieve that they were
formed by a combination of fluvial processes deliv-
ering sediment during lower stands of the sea and
submarine transport of the sediment by mass move-
ment and turbidity currents seaward of the shelf.
Review articles on the canyons as well as on the
Continental Slope and Rise have been made by
Johnson (1938-1939, 1939), Veatch and Smith
(1939), Stetson (1949), Deitz and Menard (1951),
Dietz (1952, 1963a), Kuenen (1953), Drake et al.
(1959), Heezen et al. (1959), Shepard (1963),
Guilcher (1963a, 1963b), Heezen (1963), Moore
and Curray (1963), Hoskins and Hersey (1965),
Emery (1966b), Krause (1966), and Heezen, Hol-
lister, and Ruddiman (1966) .

The surface sediments of the slope and canyons
consist of rock outcrops, deltaic deposits, and
slumping debris, all of which are more or less
covered by a veneer of late Pleistocene and present-
day muds and organic oozes.

Terraces and Shore Features
on the Inner Shelf

For the most part the inner shelf is made up of
alluvial plains that have been modified by glacial
outwash and by the Holocene transgi-ession. Much
of this has been discussed in preceding sections,
but some of the better defined features deserve fur-
ther mention. Although trausgressive featui'es oc-
cur on the inner shelf at almost every level between
the present shore and about 40 fm., they seem to
be concentrated in at least four major bands that
occur at about 6 to 15, 15 to 27, 28 to 33, and 33
to 40 fm.

The shallowest of these bands (6-15 fm.) has
been described by McMaster and Garrison (1967)
who noted evidence of a barrier spit and lagoon
south of Block Island at about 13 fm. (chart
0808N-51 ) . Similar spits can also be found at about
13 fm. southeast of Cape May (chart 0807N-56),
across the Great Egg Harbor River Channel and
east of Brigantiue Shoal (chart 0807N-55 ), south-
east of Montauk Point (chart 0808N-53), east of
Point Judith and south of Nomans Land (chart
0808N-51). Furthermore, Elliott ctal. (1955) have
noted a ridge, which crosses tlic Delaware Channel
at a depth of about 15 fm., and luive suggested that

this ridge may be the remains of a submerged
coastal terrace ( chart 0807N-57 ) .

The 6- to 15-fm. band is also well represented
by channel bars and small depressions off the coasts
of Delaware and New Jersey, by the barred terrace
below Cholera Bank south of western Long Island
(chart. 0808N-55), by the tidal delta between
Martha's Vineyard and Nantucket Island (chart
0808N-51), and by the higher parts of Nantucket
Shoals. Most of these features are probably of late
Holocene age.

The second band (15-27 fm.) is represented by :
many apparent channel bars, barrier beaches, and
lagoons oft' the coasts of Delaware and southern
New Jersey ; by spits and bars above Tiger Scarp
(chart 0807N-52) ; by Cox Ledge south of Nar-
ragansett Bay and the tidal deltas in the Block
Channel system (chart 0808N-51) ; and by a plat-
form witli numerous sand ridges south of the south-
eastern part of Nantucket Shoals (chart 0708N-
52). These features are probably of Holocene age,
with the possible exception of the platform south
of Nantucket Shoals. This platform may represent
the old silt beds under the Shoals and may be as
old as the Sangamon (Livingstone, 1964) ; how-
ever, its covering of sand ridges is probably Holo-
cene (Groot and Groot, 1964).

A Holocene age estimate for the features in this
band is supported by the discovery of fossil oysters,
Crassostrea rirginica, some with radiocarbon ages
of 7,300 to 10,300 years, at depths of 18 to 24 fm.
throughout the mapped area (Merrill et al., 1965:
Emery and Garrison, 1967). Living oysters of this
species are found almost entirely in shallow in-
shore waters. Old fresh-water peat deposits, with
radiocarbon ages of 8,600 to 11,000 years, have
also been found in this band on Nantucket Shoals
(Emery. Wigley, Bartlett, Rubin, and Barghoorn,
1967)."

The third band (28-33 fm.) is represented by
bars and lagoons oft' southern New Jersey and by
barred terraces south of Long Island and Massa-
chusetts. These features are also probably of Holo-
cene age. Fossil oysters, some with radiocarl)()n
ages of 9,800 to 10,800 years, have been found con-
centrated in this band throughout the area (Mer-
rill et al., 1965; Emery and Garrison, 1967). An
old peat deposit has been found at a depth of about
32 fm. on Georges Bank, just to the east of the
region discussed in the present report : this has a

60

U.S. FISH AND WILDLIFE SERVICE

radiocarbon age of about 11,000 years (Emery et
al., 1966, 1967).

The fourth band (33^0 fm.) is marked by
several terrace remnants, some with extensive bars
and lagoons. For example, the foot of Fortune
Scarp (northeast of the Hudson Delta) lies at
about 37 to 38 fm. and the foot of Tiger Scarp at
about 33 to 36 fm. (chart 0807N-52). Garrison
and McMaster (1966) also noted that a significant
percentage of what appear to be Holocene ridge
tops south of New England are at depths of 34 to
39 fm. and an old fresh-water peat deposit lias
been discovered at 36 fm. just south of the mapped
region (Emery et al., 1967). This peat has a radio-
carbon age of 13,500 years.

ACKNOWLEDGMENTS

J. Lockwood Chamberlin of the Bureau of
Commercial Fisheries encouraged me to write this
report. Charles B. Hitchcock, American Geo-
graphical Society, and Harris B. Stewart, Jr., and
Lome Taylor, both of ESSA (Environmental
Science Services Administration), provided in-
terest and support for publication of the maps.
John M. McAlinden and Charles E. Wittmann,
both of ESSA, contributed much to the final design
of the published maps. John A. Knauss, Robert
L. McMaster, and Louis E. Garrison, all of the
Narragansett Marine Laboratory, University of
Rhode Island, made Garrison's bathymeti-ic com-
pilations available. John S. Schlee, of the LT.S.
Geological Survey, and Anita J. Mondale reviewed
the manuscript. Janet A. Tippett made the
reliability computations.

LITERATURE CITED

Adams, K. T.

1942. Hydrographic manual. U.S. Coast Geod.
Surv.. Spec. Piibl. 14."? (rev. ed.). 940 pp.
Agassiz, Auexander.

1888. Three cruises of the U.S. Coast and Geodetic
Survey steamer "Blake" in the Gulf of Mexico, in
the Caribbean Sea, and along the Atlantic coast of
the United States, from 1877 to 1,880. Houghton
Mifflin Company, Boston, 2 vols., 314 -|- 220 pp.
Alexander, A. E.

1934. A petrographic and petrol ogic study of some
continental shelf sediments. J. Sediment. Petrol.
4 : 12-22.
Antevs, Ernst.

1922. The recession of the last ice sheet in Xew
England. Amer. Geogr. Soc, Res. Ser. 11, 120 pp.

1928. The last glaciation. Amer. Geogr. Soc., Res.
Ser. 17, 292 pp.
Atheaen, Wiixiam D.

1957. Comparison of clay from the continental shelf
off Long Island with the Gardiners Clay. J. Geol.
65 : 448-449.
Austen, Robert A. C.

1850. On the valley of the English Channel. Geol.
Soc. London, Quart. .1. 6 : 69-97.
Bigelow, Henry B.

1931. Oceanography : its scope, problems, and
economic importance. Houghton Mifflin Company,
Boston, 263 pp.
Broecker, Wallace S.

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east of Long Island, New York. Deep-Sea Res.
14: 635-639.

1968. Atlantic continental shelf and slope of the
United States : physiography. U.S. Geol. Surv.,
Prof. Pap. 529-C. .30 pp. [Including the bathymet-
ric map of Uchupi, 1965.]

Uchupi, Elazar, and K. O. Emery.

1967. Structure of continental margin off Atlantic
Coast of United States. Amer. Ass. Petrol. Geol.,
Bull. 51 : 223-234.
Upham, Warren.

1890a. The fiords and great lake basins of North
America considered as evidence of preglacial con-
tinental elevation and of depression during the
Glacial period. Geol. Soc. Amer., Bull. 1 : 563-
567.
lS90b. On the cause of the Glacial period. Amer.

Geol. 6 : 327-339.
1894. The fishing banks between Cajje Cod and New-
foundland. Amer. J. Sci. (ser. 3) 47: 123-129.
Vbatch, a. C, and P. A. Smith.

1939. Atlantic submarine valleys of the United
States and the Congo submarine valley. Geol. Soc.
Amer., Spec. Pap. 7, 101 pp.
Weatherburn, C. E.

1961. A first course in mathematical statistics.
Cambridge Univ. Press, Cambridge, 277 pp.

WiGLEY', Roland L.

1966. Rare fossils dredged off Atlantic Coast.
Commer. Fish. Rev. 28(11) : 28-32.
Wilson, J. Trzo.

1966. Did the Atlantic close and then reopen? Na-
ture (London) 211 ; 676-681.

YONGE, C. M.

1962. On the biology of the mesogastropod Tricbotro-
pis cancellata Hinds, a benthic indicator si)ecies.
Biol. Bull. (Woods Hole) 122 : 160-180.

Zeigler, John M., Shebwood D. Tuttle, Herman J.
Tasha, and Graham S. Giese.
1964. Pleistocene geology of outer Cape Cod, Massa-
chusetts. Geol. Soc. Amer., Bull. 75: 705-714.

66

U.S. FISH AND WILDLIFE SERVICE

U.S. GOVERNMENT PRINKNG OFFICE 1969 O — 334-130

FEEDING RATES OF STARFISH, ASTERIAS FORBESI (DESOR), AT CON-
TROLLED WATER TEMPERATURES AND DURING DIFFERENT SEASONS
OF THE YEAR

BY CLYDE L. MACKENZIE, JR., FISHERY BIOLOGIST
BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY
MILFORD, CONNECTICUT 05450

ABSTRACT

Starfish were held for 28 days in pans with running
sea water maintained at a series of constant tempera-
tures, with oysters as food. The average number of
oysters eaten per starfish during this period was 2.3 at
5° C, 3.0 at 10° C, 4.1 at 15° C, 5.0 at 20° C, 2.8 at
22.5° C, and 1.0 at 25° C. Starfish lost weight at 25° C.
To observe seasonal feeding rates, starfish and oysters
were held in trays suspended in Milford Harbor, Conn.
Starfish fed little from mid-January to the end of
March, but the rate of feeding then increased rapidly

to a maximum in late June and early July. After mid-
July, starfish fed at about one-third the rate of late
June. This second period of low feeding, which appeared
to be associated with both high temperatures and
spawning, lasted from July through September. From
late October through early December the rate of feeding
increased again to about two-thirds of the level in late
June and early July, before decreasing again to the
seasonal low in mid-January.

Information in the literature on feeding rates of
starfisli, Asferias forhesl (Desor), is limited, and
no one has reported studies of feeding rates at dif-
ferent si^ecific temperatures maintained within
ilosely controlled limits. In addition, no one has re-
ported quantitative studies that describe possible
changes in feeding rates during different seasons of
tlie year. Although Galtsoff and Loosanoff (1939)
stated that starfish in Ivong Island Sound feed
more actively during the summer than during tlie
winter, they did not determine specific rates.
Xeedler (1941) reported that Asterias vulgaris
( Verrill) in waters of Eastern Canada feed mostly
in the spring and fall and relatively little in tlie
winter. (In both Long Island Sound and Eastern
Canada, water temperatures fall to slightly below
0° C. in tiie winter.) According to Hancock (195.-),
1958), Axterias rubens L.. which inhabit English
waters, feed at a high rate throughout the winter.
-Vear P^ssex, England, where the studies were made,
water temperatures average 4° to 8° C. during the
winter. He reported that tlie only important sea-
sonal lull occurs just after the spawning season
in May and that feeding increases again sometime
between September and November. Because he

I'uhlishiul St'pteiiibtM- VW.K

KISllKHV lill.I.K'nX: VOL. OS. \(). 1

made no controlled laboratory stiulies of feeding
rates at a series of constant temperatures, he could
not determine whether the decline in feeding after
May was in response to high water temperatures,
which rose above 15'^ C, or to spawning. Thoi-son
(1955) found that tlie brittle star, Amphiur<t sp.,
does not feed for 1 month before spawning in late
summer; after spawning it lies quiescent on the
bottom, not feeding for about another month.

I have attempted to determine feeding rates of
starfish at a series of constant tem[)ei'atures and
during different seasons of the year. In tlie study
of seasonal feeding, I wanted e,specia]ly to obtain
a record of ijossible feeding during winter and to
determine whether feeding slows down in inidsuni-
luer after starfisli l)egin to spawn. Spawning of
starfisli in Long Island Sound begins in th(> middle
of June and continues intermittently through the
summer ((ialtsoff and I^oosanotf. WY.V.): I.,oosanuff.
10()1). During the eN|)erinients I also recorded the,
gains and losses in weight of starfish, f believed
that such a study would [)ro\ ide important data
Mil the biology of >tarHsh and useful in formatimi
foi' cDiiuiiei'cial li'rii" ers of shellfisli.

(iT

15.0
TEMPERATURE °C.

25.0

Figure 1. — Feeding rates of starfish on oysters at constant temperatures. (Points are based on combined data

of replicates at each temperature level — see table 1.)

FEEDING RATES AT CONSTANT
TEMPERATURES

METHODS

For the feeding experiments with starfish held
at constant temperatures, wooden frames, con-
structed to hold a bank of four enamel trays (C
cm. by 43 cm. by 50.5 cm.), were arranged on lab-
oratoi-y tables. Each bank was supj^lied witli a
separate, continuous flow of sea water. By mixing
cold and heated sea water in glass cylinders just
above the frames, we maintained the water in the
trays within ±1° C. of the temperature desired.

I belie\e the range of salinity of the water
(26.8%„-28.2%o), which corresponds with that of
the natural habitat of starfish near Milford, Conn.,
did not significantly influence the feeding rates
during the experiment.

At each temperature four or eight trays were
used, each containing 3 adult starfish and 40
oysters. The starfish weighed between 39 and 41
g. (starfish were drained individually for 30 sec-
onds before weigliing) and averaged &4 mm.
(range 53-75 mm.) from tip of two arms nearest
the madreporite to the madreporite. The heights

of the oysters averaged about 50 mm. (range 34--
80 mm.). Some oysters were in clusters, and others
were individuals. To ensure an ample food supply
for the starfish, shells of consumed oysters were
removed nearly every day and replaced by live
oysters.

A fresh group of starfisli was obtained in Jjoug
Island Sound off Milford for each repetition of a
28-day test at a series of temperatures. These
animals were placed in large containers of water
at the same temperatures as when they were col-
lected. As the water temperature gradually rose
indoors to the point desired, starfish were placed
in the experimental feeding trays maintained at
this temperature. Oysters, acclimated to the ex-
perimental temperature in the same way, were
placed in trays with the starfish 1 or 2 days latei-.
Only one starfish died in pans in whicli water tcin
peratures ranged from 5° to 22.5° C. At 25° C,
however, 14 of 72 starfish died during tlie ex-
periments and one additional starfish lost an arm.

RESULTS

Feeding rates are expressed as the number of
oysters consumed per starfish during the 28 days

68

U.S. FISH AND WILDLIFE SERVICE

of feediiifi. Only one test wiis made at .■)" C. (be-
I'luise ]<)\v temperatures could not l)e maintained
during late spring) ; three each at 10° ('., 15° C.
and 20° (\; one at 22.5° C; and four at 25° C.
Kcsults obtained during replicate tests at the same
temperature were similar (table 1).

The rate of feeding was strongly influenced by
tlietempei'ature of the water. At 5° C starfish con-
sumed an average of 2.3 oysters each during the
28-day period. The rate of feeding increased by
about 1 oyster for each 5° C. increase to 20° C. —
to ;5.0 oysters per starfish at 10° C, 4.1 at 15° (\.
and 5.0 at 20° C. ; it then decreased to 2.8 at 22.5° (\
and 1.0 at 25° C. (fig. 1). Thus, the optimum tem-
perature for feeding of starfish on oysters was
20° C.

Additional observations showed that frequently
two starfish and sometimes all three in a pan fed
simultaneously on the same oyster or grouji of
oysters in a cluster. Starfish did not always con-
sume all the tissues of oysters they killed; a small
amount often remained near the hinge of tlie oyster
after a starfish had left it.

Tahle 1. — Feeding rales of A. forbesi on oysters, height about
oO mm. (range 3^-80 mm.), at a series of controlled water
temperatures. Rates are given as the average number ofoysler.i
consumed per starfish in 28 days

Tempeiatuie

Starfish used

Oysters consumed

and test
number

Total

Per starfisli

5.0° C.

NiLinbeT

y umber

.Xumber

1

12

27

2.3

10.0° f.

1

12

35

2.!)

2

12

32

2.7

3

24

78

3.2

15.0° C.

1

12

57

4.7

2

12

47

3.9

3

24

:H

3. a

2(1.11° C.

1

12

Ii2

5.2

2

24

116

4.8

3

24

120

5.0

22.5° <;.

1

24

1)7

.2.8

25.0° C.

1

12

IK

1.5

2

12

13

1. I

3

24

2!)

1.2

4

24

13

.5

Jiesides obser\ing feeding rates (jf starfish, I
measured changes in their weight during 28-day
test periods. Average gains in weight were 4.4 g.
at 5° C, 7.1 g. at 10° C, 13 g. at 15° C, 13.7 g. at
20° v., and 5.8 g. at 22.5° C. At 25° C. starfish lost
an average of (5.5 g. ( fig. 2 ) .

The loss in weight by starfisli held at 25° C, e\ en

11 tliough they consumed food, shows that if starfish

were held at this temperature for an e.xtended

period of time, they would probably die. In figure

2 the line connecting the number of grams gained
or lost by starfish supplied with food crosses the
point where no weight is gained or lost at about
23.5° C It would seem, therefore, that starfisli from
Long Island Sound would probably die if they
were maintained for a long period at temjieratures
above 23.5 °C.

As controls in the weight studies, starfish were
held in three different situations without food.
Nine starfish held in a laboratory tray without
food for 28 days at 15° C. lost an average of 7.1 g.,
and 12 held at 25° C. lost an average of 8.6 g. (fig.
2). Twelve starfish held in a small plastic screen
cage in Milford Harbor from April 1 to 30, 1965,
when the temperature averaged 5.8° C. (range 2.7-
9.5° C.) , lost an average of 3.2 g.

FEEDING RATES DURING DIFFERENT
SEASONS

METHODS

To study feeding rates during different seasons,
trays, measuring 14 cm. by S3 cm. by 147 cm., were
suspended from the laboratory dock in Milford
Harbor. They were covered and lined on the inside
with plastic screening (mesh size 3 holes to the
cm.). Depths of water over the trays ranged from
0.75 m. at low tide to 2.5 m. at high tide. Each
tray held 20 adult starfish and 140 oysters. From
January 20, 19C4 to January 26, 1967, one tray was
examined once every 2 to 4 weeks. An examination
consisted of lifting the tray out of water, placing
the starfish in buckets of water, washing the tray
with a hose, counting the oysters consumed by star-
fish, replacing them with live oysters of the same
size, returning the .starfish to the tray, and then
lowering the tray to its normal position.

From May 17, 1966 to Januaiy 26, 1967, a period
of slightly more than 8 months, a second tray sim-
ilar to the first was examined in the same manner
on each date, except that after each examination
the starfish and oysters were transferred to a clean
replacement tray. Tliis procedure was followed to
ensure that stai-fish were not consuming large foul-
ing organi.sms, which might have set in tlie tray,
rather than the added oystei-s, thereby giAing a
false indication of tlieir i-ate of feeding.

RESULTS

Starfish in trays suspended in Milford Harbor
displayed the same pattern of feeding in each of
tlie 3 years of ol)ser\ations (fig. 3). 'I^lie rate of

Fi-;i:i)iN(; u.vrES of st.xkfisii

69

TEMPERATURE °C.

FiGUKE 2. — Averayo weight change of starfisli held at constant tcmiieratui-es for 2S days, with and without food.
(Points are based on combined data of replicates at each temperature.) Point (1) represents starfisli held
in a cage in Milford Ilarlior. April 1-30, when temperatures averaged 5.8° C. (range 2.7-9.5° C).

feeding was low from uiid-Jaimary until the end
of March. For example, in 1965 the 20 starfish con-
smned about 0.6 oyster per 7 days (0.12 oyster p&r
starfisli per 28 day.s) during this i^eriod of 2.5
months. From mid-AiJril to late Jmie and early
July the rate rose sharply, apparently as a result
of the rise in water temperature. At the time of
most intense feeding, in late June 1965, the 20 star-
fish ate about 20 oysters per 7 days (four oysters
per starfish per 28 days). In late July, August,
and September the rate of feeding decreased to
about a third of its level in late June and early
July. In late October, November, and early Decem-
Ijer the rate increased again to about two-thirds of
the rate in late June and early July. Beginning
in late December, feeding rates began to decline
but did not really become low in 1965 and 1966 un-
til mid-Januaiy. In 1967, however, l)ecau.se of un-
usually warm water, feeding had not declined to its
previous winter low by late January when observa-
tions were terminated.

As the experiment continued from 1961 tluoiigh
1966, the starfish grew larger. The new group of
oysters collected each spring was, however, of
about the same average size — 50 to 65 mm. (range
34-82 mm.) — as the original group fed to tlie star-
fish in 1964. Because the larger starfish consumed
more oysters (of a particular size) than the smaller
ones, feeding rates were higher in each successive
year.

The feeding in the .second tray, observed from
May 17. 1966 to January 26, 1967 (to e\aluato tlie
effect of possible consumption of fouling orga-
nisms on feeding rate), was essentially similar to
that in the first tra_v. Because the supply of oysters
was low, ]iowe\er, it was necessary to use smaller
oysters in tiiis tray after late August. Tiie starfish
in this second tray, consequently, showed a mudi
higlier consumption of oysters than did those in
the first trav which were feeding on larger oysters
(fig. 3).

70

U.S. FISH AND AVILDLIFM SIOKVICE

25|—

I'lcaiiE ;j. — Xumber of oysters consumed by 20 adult starfisli lield with 140 oysters in a tray from January 1964 to
January 1907 and (in a second tray) from May 1900 to January 1907. Both trays were suspendwl in Alilfnrd Harbor.
Temperatures are given in the upjier panel.

In 1964, 1965, and 1966, during the period of
little feeding from mid-January to the end of
March, water temperatures averaged 1° C. (range
-2.2° to 3.2° v.). Olxservations of starfish in trays
in Milford Harbor and of those dredged from the
bottom showed that they feed on oysters and other
food at temperatures at least as low as 0.2° C.
Temperatures increased to 7° to 9° C. by the end
of April, to 13.5° to 15° C. by the end of May,
and to 18.5° to 19.5° C. by the end of June (wlien
the rates of feeding were highest). By mid-to-late
July temperatures reached 22.5° C. and stayed
at or above that level until early or mid-Septem-
ber (during the jDcriod when rates of feeding were
about a third as intense as they were in the spring) .
In the 3 years temperatures averaged 13.5° to 15.3°
C. during October, 7.9° to 11.6° C. during Novem-
ber, and 3.6° to 5.8° C. during December, and dur-
ing this period of 3 months feeding rates were
about two-tliirds as intense as they were in late
June.

SUMMARY OF EFFECTS OF WATER
TEMPERATURES AND SEASONS ON
FEEDING RATE

A comparison of feeding rates of starfish at
constant temperatures with those in different sea-
sons shows that the rates in different seasons are
controlled primarily by seasonal temperatures.
Though laboratory studies were not conducted to
determine feeding rates at temjaeratures below 5°
C, low rates from mid-January to the end of
March are undoubtedly a result of temperatures
which average only 1° C. As temperatures rise in
tiie spring to nearly 20° C, the optimum tempera-
ture for feeding, by the end of June feeding in-
creases rapidly.

In summer the decline in feeding coincided with
high temperatures. For example, in 1964 tempera-
tures exceeded 22.5° C, the temperature at which
feeding probably begins to decline, on July 15,
about 2 weeks after a sharp declme in feeding had
already begun. In 1965 temperatures rose to above
22.5° C. for only a few days during July, coincid-

FEEDIXO R.VIES OF STARFISH

71

ing with tlie decline in feeding. In 1966 tempera-
ture's rose above 22.5° C. on July 7 shortly before
feeding declined. In 1964, because feeding began
to slow down before temperatures reached 22.5° C.
and continued low in late September and early
October after temperatures dropped well below
22.5° C, some other factor — probably the effects of
spawning which started in mid-June — seemed to
be partly responsible for the low feeding rate. In

1965, the possible effects of sjiawning were ob-
served thixjugh September because feeding was low-
even though temperatures were 16° to 21° C. In

1966, low feeding was recorded from mid-Septem-
ber through early October wlien temperatures
ranged from 16° to 22.5° C. The rate of feeding
increased again in late October and remained high
through most of November as temperatures
dropped to 15° C. and lower. Feeding rates
declined in late December when temperatures fell
to 2° to 4° C. and reached the winter low by mid-
January when the temperature fell to about 1° ('.

Asterias forhesi in Long Island Sound exhibits
a reduction in feeding in midsummer similar to
that reported by Needier (1941) for A. vulgaris
in Eastern Canada and by Hancock (1955, 1958)
for A. rubens in English waters. In contrast to
Amphiura sp., as described by Thor.son (1955), A.

forhesi apparently feeds actively right up to the
time it spawns.

ACKNOWLEDGM ENTS

Barry Baiardi, Eussell Clark, and Otis Lane
provided technical assistance, and Herman R. Glas
collected starfish.

LITERATURE CITED

Gai.tsoff, Paul S., and Victor L. Loosanofp.

1939. Natural history and method of controlling the
.starfish. Astcriax forhrfii (Dpsor). r?nll. T.S. Unr.
Fi.sh. 49 : 75-132.
Hancock, D. A.

19.5'). The feeding behaviour of starfish on Essex
oyster beds. .1. Mar. Biol. Ass. U.K. 34 : 313-331.
19.58. Notes on starfish on an Essex oyster bed. J.
Mar. Biol. Ass. U.K. 37: 565-589.
LoosANOFF, Victor L.

1961. Biology and methods of controlling the star-
fish, Asterias forbcsi (Desvor). U.S. Fis-h Wilrll.
Serv., Fish. Leafl. .520, 11 pp.
Needleb, a. W. H.

1941. Oyster farming in (^•lll^dil. Bull. Fish. lies.
Bd. Can. 60, 83 pp.

TriOliSON, GUNNAR.

19.55. Modern a.spects of marine level-botloiii animal
communities. .T. JInr. Res. 14 : 3S7-.S97.

72

U.S. FISH AM) Wir.DI.IFU SIOKVICK

U.S. GOVERNMENT PRINTING OFFICE : 1969 O— 3S7-743

FACTORS INFLUENCING THE ATTRACTION OF ATLANTIC HERRING,
CLUPEA HARENGUS HARENGUS, TO ARTIFICIAL LIGHTS

BY ALDEN P. STICKNEY, FISHERY BIOLOGIST

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY

W. BOOTHBAY HARBOR, MAINE 04575

ABSTRACT

Using artificial lights to attract flsh at nigijt is a com-
mon and often effective flsiiing technique. With Atlantic
herring the attraction is somewhat uncertain, however,
and does not always take place. This paper describes
experiments which showed that, in addition to the in-
herent variability of the fish themselves, certain exter-
nal conditions can modify the attraction to the light.
Attraction was greater at low than at high tempera-
tures, greater with underwater lights than with lights
above the surface, and greater when the fish were previ-
ously adapted to light than when they were adapted to
darkness. Very bright light (illumination 20-600 lux).

The use of artificial lights for attracting fish is
a common practice in fisheries throughout the
world. The methods have changed but little, how-
ever, the chief improvement being the substitution
of electric light sources for open flames or fuel-
burning lamps.

The attraction of Atlantic herring (Clupea
harenguH Mrengus) witli lights has been studied
experimentally and adapted to some extent for
commercial fishing. Lights have been used rou-
tinely on Norwegian purse seiners for many yeai's
to attract herring. According to Dragesund
(1958), herring are not always attracted to lights,
however, and even the fishermen do notagi-ee about
the behavior of herring in response to the lights
used on seiners. Dragesund studied the behavior of
fish schools from a research vessel and distin-
guished the following kinds of reaction to the
attracting light:

1. Fish descend and pack together.

2. Fish disperse.

3. Fish rise toward light, then shortly de-
scend.

4. Fish pack together, then rise toward the
light.

Blaxter and Parrish (1958) were able to attract
young lierring (5-25 cm.) to underwater lights at

Published September 1969.

especially above the surface, tended to repel the fish.
Light of intermediate intensity (illumination 1-30 lux)
was most effective.

The behavioral responses comprised an initial attrac-
tion resembling positive phototaxis, followed by ap-
parent disorientation, or confusion. The disorientation
may have been due to attempts by the fish to respond
with a dorsal light reaction, i.e. to assume postures
which would orient their dorsal surface toward the light
source even when such postures interfered with normal
swimming.

several levels of brightness and to bring them to
the surface by raising the lights. Tibbo (1965) re-
ported that herring in a large tank were attracted
to artificial lights of various intensities and colors,
although they were repelled at the highest inten-
sities. Gauthier (in press), collaborating with
fishermen on a commercial purse seiner, reported
catches of herring of 25 to 40 tons in trials with
underwater lights in the Gulf of St. Lawrence.

Lights were used traditionally along the At-
lantic Coast of North America for catching juve-
nile herring by "torching," a method probably
adopted from the Indians. A kerosene- or gasoline-
burning flare, or even a more primitive torch of
combustible material on a stick, was mounted on
the bow of a small boat. The procedure has been
described by Earll (1887) as follows. "The fisher-
men usually go to the shore late in the afternoon
and time their departure so as to reach the fishing
grounds shortly after sunset. As soon as it be-
comes sufficiently dark, the fire is lighted, one man
takes his jiosition in the stern to steer the boat and
another stations himself in the bow, armed with a
dip-net for securing the fish as they gather in lit-
tle bunches just in front of the light. The remain-
ing members of the crew row the boat rapidly
through the water, while the man in the bow is
busily engaged in throwing the fish into the boat

FISHERY BULLETIN: VOL. 68, NO. 1

73

by means of his dip-net. Great numbers of herring
are attracted by the light and it is not uncommon
for fifteen or twenty barrels to be taken in a few
hours."

The variability of the herring's response to light
is a characteristic feature and has been noted by
many investigators. Blaxter and Holliday (1963)
stated ". . . . Such i-eactions will vary widely de-
pending on the environment and the physiological
state and age of the fish as well as on the type of
stimulus itself." Other authors have demonstrated
how many factors, external and internal, can vary
the response of herring and other species to artifi-
cial lights. Kurc (in press) and others have pointed
out how the thermocline may prevent fish from
rising to a light, or may hold them in the surface
water so that they can be more readily attracted.
Strong ambient light (e.g. moonlight) may reduce
the effectiveness of the attracting light (Kurc, in
press; Strom, in press). Woodhead (19.56) showed
that starvation reversed the normal negative
phototaxis of tlie minnow Plioxlrms. Andrews
(1946) found that the attraction to light of the
white sucker {C atastomnis) decreased with increas-
ing temperature. Sudden changes in illumination
may cause the fish to disperse instead of attracting
them (Strom, in press; Gauthier, in press).

Although routine, uncritical use of lights to at-
tract fish may sometimes be successful, far greater
effectiveness might be a/chieved by a better imder-
standing of the underlying behavior of the fish
and its response to lights. Moreover, lights might
be of definite value in some circumstances where
they are not now used. In Maine the use of lights
for catching herring is generally illegal because
many fishei-men believe that the lights tend to dis-
pei-se the herring rather than attract thean (Scat-
tergood and Tibbo, 1959). This restriction appears
to be an instance where profitable use of lights has
been discouraged because the tmderlying beliavior
of the fish has been inadequately understood.

This paper is an attempt to explain some of the
biological and other factors that are conducive to
the attraction of herring by light.

METHODS

Tlie fish iLsed in the experiments were immature
Atlantic herring of age groups O (brit), I, and
II, which are processed as Maine sardines. They
were 75 to 200 mm. in total length and were taken

from conunei'cial catches near Boothbay Harbor,
Maine. The fish were held under the prevailing
seasonal conditions of salinity, temperature, and
dissolved oxygen in large tanks provided with iian-
nLng sea water and were fed daily a mixture of
ground trout food and canned cat food.

The experiments were conducted in a separate
tank. This tank was fiberglass, 5.5 m. long, 0.4 m.
deep, and 0.3 m. wide. An incandescent lamp sus-
pended in a glass cylinder at each end of the tank
provided the attracting illumination; by raising
or lowering the lamp bulb in the cylinder, the light
source could be located above or below the surface.
Sea water entered the left-hand end of the tank
and drained off at the right. A slight drift (less
than 4 cm. per minute) toward ih^ right resulted.
Tliis and other sources of left-right bias were c-om-
liensated by periodically alternating the location
of the light source between the right and left, ends
of the tank with a double thi-ow switch. For tem-
peratures above the seasonal sea-water tempera-
ture, the incoming water was lieated. An air Ixib-
bler near the point of entrance and another near
the center of the tank provided sufficient mixing
so that temperature differences within the tank
did not exceed 1° C. Cooling pipes, carrying a
chilled ethylene glycol-water mixture, located
along the walls of the tank provided uniform re-
frigeration when below-seasonal temj^eratures
were required.

Variations in dissolved oxygen were achieved
by recirculating the water through a tank of pure
oxygen under pressure (1.5-2.0 atmospheres) or
through a vacuum. These devices provided a range
of 50 percent to 250 percent oxygen saturation in
the experimental tank.

The intensity of the attracting lights was varied
by using light bulbs of different wattages or by
varying the supply voltage. The light gradient
for each intensity and source position (fig. 1) was
measured with a photovoltaic light meter* having
a waterproof housing for the sensitive element.
This element was held in a plane normal to the
directiion of the light rnys in the water. The meter
was factory-calibrated for a spectral response cor-
responding to that of the human eye. This response
is not identical to that given for herring (Blaxter,
1964), but is very similar: the difference was so
small that special calibration of the instrument
did not seem warranted.

74

U.S. FISH AND WILDLIFE SERVICE

1000.0

1.0

NTENSr

B= BELOW SURFACE
A= ABOVE SURFACE

25 50 75 100 125 150

CENTIMETERS FROM SOURCE

Figure 1. — Light gradients at the three light intensities
used in the experiments.

The fish were taken at random from a storage
tank and transferred to the experimental tank,
where they were allowed to accommodate for
periods of 30 minutes to 15 hours before each
trial. Except where light or dark adaptation was
at issue in the experiment, the period preceding-
each trial was at room illumination. I found no
significant difference in the responses of indi-
vidual herring allowed a half-hour or full-hour
period of accommodation to the tank. Once the
fish recover from tlie initial disturbance after
transfer, it is not likely that any further time for
accommodation is necessary. This factor should
not affect the results of the experiments, because
for any given experiment the accommodation
periods of all fish were the same. Accommodation
periods were progressively reduced throughout
the series to save time.

No attempt was made to acclimatize the fish
to arbitrarily selected temperatures because facili-

ties for this purpose were not available. The fish
were transferred from water at seasonal temper-
atures to the experimental tank. Because temper-
ature acclimatization exerts a definite influence on
the subsequent reactions of fish to temperature, it
could conceivably affect their response to light at
different temperatures. For that reason I have
specified the acclimatization (= seasonal) temper-
ature for the fish used in each experiment
(table 1). It will be noticed, however, that several
combinations of acclimatization and experimental
temperatures produced no qualitative difference
in the results of experiments where the effect of
temperature was being tested.

T.

\BLE 1.-

-Summary

of pretrial
herring

experience

of experimental

Experiment

Accommo-

Acclimati-

Experi-

number

dation

zation

mental

period

temperature

temperature

Hours

"C.

" C.

Month

1..

15

5

6, 12. 16

December

2..

15

3

6

February

a..

1-2

10-13

15-17

October

4..

H-2

10-13

15-17

October

5..

H-2

10

15-17

October

6..

6

5

6, 12, 16

December

7..

6

10-14

5-6, 15-17

July

8..

3

13-16

8-10, 15-17

July-August

«..

6

2-3

4-6

Marcli

10.

6

10-14

16.5-17

June

11.

6

10-14

6-9

July

12.

6

13-16

16-17. 5

August-September

U

1

13

15-17

October

14.

3

3

5

January

l.'i.

6

13-16

15-17. 5

August-September

16.

1

14-16

15.5-17

September

An experiment consisted of several trials in
which the variables of interest were given pre-
determined values; each trial could be given a
different set of conditions or could replicate
another trial. For experimental variables that
could be changed quickly (e.g. light location or
intensity), several trials were completed in a
single day. For conditions that required a longer
time to establish (e.g. temperature or gas content) ,
only one trial could be completed in a day, and
an experiment might last several weeks. In pro-
tracted experiments of this sort, when only two
treatments were involved, the trials were alter-
nated; when several were involved in the same
experiment, the trials were ordered randomly.

Two routine procedures were used. When fish
were tested singly (experiments 1 to 4), the
attracting light w^as turned on at the right end of
the tank for 5 minutes, and the amount of time
spent by the fish in the illuminated half of the

FACTORS INFLUENCING ATTRACTTION OF ATLANTIC HERRING TO ARTIFICIAL LIGHTS

75

tank recorded. Then the illumination was switched
to the left end of the tank and the time spent in
that half by the fish was recorded. The illuminated
half of the tank was reversed end for end every
5 minutes over 30-minute periods. The score by
which the attraction to light was measured was the
cumulative amount of time spent by the fish in
the illuminated half of the tank.

The second routine procedure was used when-
ever a group of fish were tested (experiments 5 to
16). Ten randomly selected herring were placed
in the tank, the attracting light on the right was
turned on, and the number of fish present in the
illuminated half was counted each minute for
5 minutes. The illumination was then switched to
the left side, and the fish present in the illuminated
half of the tank were again counted each minute
for 5 minutes. The lights were, thus, alternated
from end to end at 5-minut6 intervals until 30
counts had been made. The sum of the 30 counts
was the score for groups of fish. A variant of this
procedure was used in two experiments (13 and
16). Each trial lasted only 1 minute, and counts
were made at 15, 30, 45, and 60 seconds. The light
position remained the same throughout the period
of one trial, but equal numbers of trials were made
with the left side illuminated and with the right
side illuminated.

In no experiment were the same fish used in
successive trials; after being used once, every
fish was returned to a separate holding tank and
was not used again for at least 2 weeks.

Comparisons of scores between only two con-
ditions were analyzed statistically with a "t"-test ;
comparisons among several kinds and levels of
treatment were analyzed with a fixed-model
analysis of variance.

GENERAL BEHAVIOR

After the fish had become accustomed to the ex-
perimental tank their behavior stabilized into one
of three general patterns : (1) swimming regularly
back and forth fr<Mn one end of the tank to the
other (in a loose school, if in a group), (2) re-
maining at one end of the tank, or (3) milling
about randomly throughout the tank. After the
room was darkened and the attracting light was
turned on, whatever behavior pattern had been
adopted by that particular fish or group of fish

continued; this behavior tended to obscure the re-
sponse of the herring to the attracting light. Al-
though a brief fluri-y of activity near the lamp
frequently occurred at the begining of each trial,
the degree of attraction was not obvious by casual
observation ; it oould be demonstrated only by re-
fjeated counts over an extended period. The fish
siiowed no tendency to gather in any locality of
optimum light intensity.

The exact behavioral mechanisms involved in
tlie attraction of fish to artificial lights are not
known, although several theories have been pro-
posed, ranging from a straightforward positive
phototaxis to a conditioned response where light
is associated with food. One of the more interesting
theories is that of Verheijen (1959 and in press).
He suggested that an artificial light creates an un-
natural light field which leads to a disoriented be-
havior of the fish, because "such simplified visual
environments" may not "deliver adequate in-
formation to all integration levels involved in the
jjerformance of the fish's natural behavior." The
net effect is one of trapping fish rather than merely
attracting them.

Close observation of herring in some of my own
experiments yielded clues about their behavior in
an unnatural light field which may amplify some-
what the ideas of Verheijen. The typical behavior
of a single herring consisted of the following
events :

(1) Starting from the dark half of the tank,
the fish swims slowly at first, then with
increasing speed directly toward the light.

(2) Upon reaching the light, sometimes strik-
ing it squarely with its snout, the fish
turns more or less broadside to it and pro-
ceeds to circle it, or swim to and fro in
short courses which lie generally along
the circumference of a circle around it.

(3) This behavior is frequently interrupted
by movements which give the impression
of confusion or disorientation. Close ob-
servation indicates that these movements
are, in fact, attempts by the fish to orient
its dorsal surface toward the light source.
When the light is under water, these at-
tempts lead the fish to assume momen-
tarily vertical postures or horizontal pos-
tures on its side with its back toward the
light.

76

U.S. FISH AND WILDLIFE SBRVIOB

(4) In retreating from the light, the fish
swims in a zigzag course, the legs of which
become progressive!}' more nearly perpen-
dicular to the direction of the light, and
the fish eventually returns to it ; or the legs
become progressively more oblique and
the fish escapes into the darkened zone.

(5) After a short stay in the dark zone, the
fish repeats the entire procedure.

Many of these actions appear to be manifesta-
tions of the "dorsal light reaction" (Frankel and
Gunn, 1961) in which a fish orients itself in a posi-
tion so that its dorsal surface is more or less per-
pendicular to the direction of the light rays.
Woodhead and Woodhead (1955) have described
such a phenomenon in herring larvae. Under nat-
ural lighting, where the predominant direction of
the light is downward, the herring can orient to the
rays in its nonnal swimming {wsture, descending
when tlie light is too strong, and rising wheii it
decreases. Wlien a single light source is close to
the surface or beneath it, phototaxis can take place
with no departure from the normal swiiruning
post/ure, but dorsal orientation to the light (except
when the fish is direx:.tly beneath it) requii-es pos-
tures that interfere vnth normal swimming —
hence, the apparent disorientation and difficulty in
escaping the influence, of the light.

VARIATION IN SUSCEPTIBILITY TO
LIGHT ATTRACTION

Whatever may be the effect of external condi-
tions in modifying the response of herring to light,
individual differences among the fish lead to wide
variation in this response even under identical ex-
ternal conditions. This variability is ~ illustrated
by five experiments.

FREQUENCY DISTRIBUTION OF THE RESPONSE
TO LIGHT OF INDIVIDUAL FISH

Individual fish vary in behavior as well as physi-
cal characteristics. If this variation were reason-
ably close to a nonnal distribution, the statistical
treatment used in this study would be more likely
to be valid than if the variation was not normally
distributed. The following experiment was made
to examine the variation among individaial fish.

Exiaeriment 1. Ninety herring, selected at ran-
dom, were obsei-ved individually to determine the
degree to which they were attracted to an imder-

water light of medium intensity ; 30 were observed
at 6° C, 30 at 12° C, and 30 at 16° C. Scoring was
based on the amount of time spent in the illumi-
nated half of the tank. The mean scores of 16.2,
17.2, and 17.8 at 6°, 12°, and 16° C, respectively,
were not significantly different (F=0.92, P>0.1).
The three frequency distributions each showed a
reasonable tendency toward normality (fig. 2).
Wlien all the scores were combined, this tendency
was more pronoimced (fig. 2, dashed line).

CHANGES IN SUSCEPTIBILITY TO LIGHT
ATTRACTION

If herring differ from individual to individual
in their susceptibility to light attraction, do indi-
viduals vary in themselves over a period of time?

Experiment 2. To answer this question, 25 her-
ring were fin clipped to identify individuals and
tested and scored as in the preceding exj^eriment.

6-89 9-119 12-149 15-179 18-209 21-239 24-269

MINUTES IN LIGHT ZONE

Figure 2. — Frequency distribution of scores (experiment
1) based on the time in minutes out of a ix>ss4ble 30
minute.s spent by individual herring in the Illuminated
half of a tank. Solid lines, distribution of scores at each
of thrtK' temperatures; dashed line, distribution of all
scores, regardless of temperature.

FAOTORS INFLUENCING ATTRACTION OP ATLANTTIC HERRING WO ARfTIFICIAL UGHTS

77

They were then transferred to another tank and
left undisturbed for 1 week. After this interval
they were again scored as befoi-e. (Two of these
fish died in the interval, so that data from only
23 were complete.)

If the degre« of response is a fixed characteristic,
the response should be the same on the second oc-
casion as on the first, or if a change has occurred, it
should affect all the fish more or less similarly, so
that a high degree of correlation should be found
between the scores in the first test and the scores
in the second. Actually, some fish increased their
scores and some decreased them (table 2) ; some
changed from a positive response (more than half
the time spent in the lighted zone) to a negative
one. The correlation coefficient of R = 0.55 was vei-y
weak, although it was barely significant. This
result can be interpreted to mean that although
individuals tend to maintain a certain inherent re-
sponse characteristic, this characteristic may vary
substantially with time.

Table 2. — Scores (number of miinulps spent in iHuminated
half of tank) for indwidual herring in two 30-mmute
tests, 1 week apart (experiment 2)

First score (by rank)

Score 1
week later

Minutes Minutes

25.27 16.18

24.17 ..__ ia06

23.18. 16.45

21.90 19.32

21.02 19.35

20.67 20.58

20.03 14.15

19.03.. 18.08

18.98 10.70

18.62 15.43

18.13 14.53

18.08..... 14.80

17.77. 19.37

17.73 18.05

15.82..... 16.78

15.60 17.98

14.82 20.85

14.17. 8.46

14.08 13.88

13.05 9 97

12.48..... ::::::: 7.35

12.12... 13.20

12.08 11.03

EFFECT OF CONDITION ON SUSCEPTIBILITY TO
LIGHT ATTRACTION

There may be many possible reasons for the
variability in response among individual fish.
Three reasons which readily suggest themselves
are differences in sex, physical condition, and age. I
did not attempt to determine the effect of sex ex-
perimentally because of the need for economy in
use of specimens; determination of sex requires
killing the fish. Evidence that strong sex differ-
ences occur, however, does not show in the fre-

78

quency distribution of responses. If males and
females differed greatly in response, one would
expect some indication of bimodality to the
distribution.

Experiment 3. To determine the effect of condi-
tion, 32 herring were tested individually at 15 to
17° C, and the time spent in the illuminated zone
was recorded for each 30-minute trial. The
medium-brilliance, subsurface illumination was
reversed end for end every 5 minutes according to
the routine procedure. Half of the herring were in
excellent physical condition and half were starved
and emaciated. The mean scores of 18.1 for the fish
in good condition and 18.9 for those in poor condi-
tion were not significantly different (F = 0.22^.

EFFECT OF AGE ON SUSCEPTIBILITY TO LIGHT
ATTRACTION

Two experiments were done to determine
whether any differences in attraction to light could
be attributed to the age of the herring; the first
of these dealt with individual fish, the second with
groups of fish.

Experiment 4. Nineteen herring in age group O
and an equal number in age group I were tested
individually according to the same procedure used
in experiment 3. The mean scores of 20.4 for the
0-group fish and 19.5 for the I-gi'oup fish were
not significantly different (t = 0.59).

Experiment 5. Herring of age group O and age
group I were tested in groups of 10 individuals
according to the second routine procedure de-
scribed under "Methods." The scores were based
on the number of fish counted each minute for 30
minutes in the illuminated half of the tank, which
was reversed end for end every 5 minutes. The
mean scores for 10 trials with each age group were
120 for the O-group and 132 for the I-group fish ;
the difference was not significant (F<1.0).

EFFECTS OF EXTERNAL VARIABLES ON
THE ATTRACTION OF HERRING TO
LIGHT

EFFECT OF TEMPERATURE

The experiments in the preceding section dealt
primarily with variables inherent in the fish them-
selves. In this and following sections the experi-
ments deal chiefly with external variables.
Evidence from experiment 1 indicated that tem-
perature had little effect on the attraction to light
of individual fish. The experiments in the present

U.S. FISH AND WILDLIFE SERVICE

.J

section involve groups of fish and, as will be seen,
temperature does exert a definite effect on herring
in groups.

Experiment 6 (cf. experiment 1). Ninety her-
ring, selected at random, were tested in groups of
10 individuals at three temperatures: 6°, 12°, and
16° C. Three trials were made at each temperature.
The scores of 205, 129, and 121 at the three tem-
peratures, respectively, were significantly different
(F=6.19, P <0.05).

Experiment 7. The purpose and methods of this
experiment were similar to those in experiment 6,
except that only two temperature levels were pro-
vided and these on alternate days. In the previous
experiment, trials at low temiDerature were made
first, followed by trials at the two higher
temperatures.

Five trials were made ait. temperatures of 5 to
6° C. and five at 15 to 17° C. The fish were taken
from storage at 10 to 14° C. and held 6 hours at
the experimental temperature before each trial.
The mean scores were 201 at low temperature and
129 at high temperature (table 3). If the scores
are treated simply as two sets of five observations,
the difference in means is of marginal significance
(t=2.04, P = 0.075) ; if the scores are treated as
five sets of paired observations, however, t=10.1
and the differences are highly significant. Because
the low-temperature score for each trial was con-
sistently higher than the immediately following
high-temperature score, the analysis as paired ob-
servations seems reasonable, and the hypothesis
that lower temperature increases the attraction to
light is confirmed.

Table 3. — Compariaon of scores ' for light attraction of
herring at low and high temperatures {ex-periment 7)

Temp. Score Temp. Score

"C.

°C.

6.2

180

16.4

120

6.7

234

16.6

155

6.6

198

15.2

139

5.5

179

16.2

115

6.7

214

16.2

119

Means .5.6

201

15.9

129

'Score = sum of numbers of herring counted in the illuminated half of
the tank at 30 1-minute intervals. Ten herring were used in each test; maxi-
mum possible score =300.

EFFECTS OF TEMPERATURE, LIGHT INTENSITY,
AND LIGHT POSITION

Experiment 8. The responses of groups of 10
herring were observed at two temperature levels
(8-10° and 15-17° C), at three levels of light

intensity (fig. 1), and with the attracting light
either above or below the surface. Each combina-
tion of conditions was replicated once. The fish
were taken from storage at 13 to 16° C. and held
3 hours at the experimental temperature before
each trial. Table 4 shows the scores. The differ-
ences in response were highly significant between
high and low temperature (F = 69.2) and between
above- and below-surface lights (F = 48.7). There
was also a significant interaction between light
position and intensity, such that the bright light
above the surface had the poorest attraction and
the bright and medium lights below the surface
had the greatest. The difference in response due
to position of the light was significantly greater at
low temperature. In general, below-surface lights
were more effective at low temperature than at
hieh.

ATTENUATION OF

LIGHT
TIME

ATTRACTION WITH

Experiment 9. The degree to which light will
hold the herring in its vicinity is a significant
component of the total attraction to light. This
experiment was intended to determine whether
this holding effect would decrease with time, and,
if so, whether such decrease was affected by light
intensity or position.

Table 4. — Comparison of scores ' for light attraction of
herring in relation to light location, light intensity, and
temperature {experiment 8)

High temperature

Low temperature

(16-17

'C.)

(8-10=

C.)

Light intensity

Mean

Light

Light

Light

Light

score

above

below

above

below

surface

surface

surface

surface

High

136

264

122

166

146

100

254

159

139

Medium..

192

230

169

179

167

163

229

150

180

Low..

186

212

149

172

159

180

217

161

164

Mean score

169

232

148

167

' Score = sum of numbers of heiTing counted in the illuminated halt of the
tank at 30 1-minute intervals. Ten herring were used in each test; maximum
possible score =300.

The experiment comprised 24 trials. Each trial
consisted of three phases: the first, a 30-minute
series of counts on a group of 10 fish, the same as
the routine procedure used in other experiments;
the second, an 18-hour interval with the attracting
light left on; and the third, another 30-minute
series of coimts like the first. The 24 trials repre-

FACrrORS INFLUENCING ATTRACmON OF ATLANiTIC HERRING rTO AR/TIPICIAL LIGHTS

79

379-242 O - 70 -

sented three levels of light intensity (high,
medium, and low) and two light positions (above
and below the surface). Each combination of
lighting characteristics was replicated four
times — two with the light on the left during the
18-hour interim and two with the light on the
right. Table 5 gives the scores of the trials, before
and after the 18-hour interim. The number of fish
in the lighted zone was reduced significantly after
18 hours (F = 13.4, P<0.01). This reduction was
significantly greater when the lights were above
the surface (F= 11.83, P<0.01) than when the
lights were below, but the differences in re-
duction associated with light intensity were not
significant.

T,\BLE 5. — Comparison of scores for light attraction before
and after an 18-hour interval of constant stimulus, in
relation to light location and intensity (experiment 9)

Before interval

After interval

Light intensity

Light
above
surface

Light
below
surface

Mean

Light
above
surface

Light
below
surface

Mean

High 109

144

109
158

Medium

Low

Mean 143

138
132
133

149

134

94
80
57
126

130
125
114
147

127

209

164

80

230

133

177

138

101

149

119

188

76

186

103

172

87

167

143

136

161

97

90

117

224

139

136

90

163

133

136

143

147

127

138

114

' Score = sum of numbers of herring counted in the illuminated half of the
tank at 30 1-minute intervals. Ten herring were used in each test; maximum
possible score = 300.

EFFECT OF OXYGEN CONCENTRATION

The possible imix)rtance of oxygen concentra-
tion to the light i-esponse was suggested partly by
observations that the habitat of juvenile heiTing
was frequently supersaturated with oxygen in sum-
mer (Colton, Marak, Nickerson, and Stoddard,
1968; Stickney, 1968) and partly by a comment of
Kalle ( 1965) that the vertical migration of herring
(usually considered a resix)nse to light) might be
due to depletion of oxygen in dense schools near
the bottom.

Experiment 10. Groups of 10 herring were tested
on alternate days in water normally saturated or
highly supersaturated with oxygen before each
trial. The temperature of the experiment was 15.5
to 17° C. ; the mean oxygen levels were 8.1 p.p.m.

(98 percent saturation) and 17.2 p.p.m. (212 per-
cent saturation). The herring were taken from
storage at 11 to 14° C, 110 to 125 percent 0, satura-
tion. Each trial consisted of the routine exposure
to an attracting light; scoi-es were based on the
number of fish counted each minute for 30 minutes
in the lighted end of the tank. The mean score for
six trials in normal water was 122; that for six
trials in suiiereaturated water was 164. The dif-
ference had a "t" value of 2.04 (P<0.1) ; treated
as paired data, the differences between each pair
of trial scores had a "t" value of 4.28 (P<0.01).
The experiment seemed to indicate that supersatu-
ration had a significant effect on the attraction of
the herring to light. Subsequent experiments (11
to 13) did not cori-oborate these results, however.

Experiment 11. Herring were taken from hold-
ing tanks at 10 to 14° C. and 105 to 130 percent
saturation of oxygen and held 6 hours under the
experimental conditions before each trial. Nor-
mally saturated and supersaturated water averag-
ing 9.6 p.p.m. (93 percent saturation) and 19.7
p.p.m. (185 percent saturation) of oxygen, respec-
tively, at 6 to 9° C. were, provided on alternate
days. In five triaJs at each oxygen level, mean
scores were 198 in the normal water, 205 in the
supersaturated water. The difference is not sig-
nificant (t=0.43).

Exjjeriment 12. This experiment was actually a
part, of experiment 15 and included the additional
variable of light-dark adaptation. The three levels
of oxygen concentration were low (mean = 5.3
p.p.m., 63 percent saturation), saturated (mean
= 7.9 p.p.m., 93 percent saturation), and super-
saturated (mean = 21.8 p.p.m., 240 percent satura-
tion). Herring which had been adapted 6 hours to
light or darkness before each trial were tested at
each level of oxygen, making six combinations of
experimental variables, each combination repli-
cated five times. The herring were taken from stor-
age at 12 to 17° C. and 100 to 124 percent
saturation of oxygen and exposed 6 hours to the
experimental conditions before each trial. The
mean scores for ten trials at each level of oxygen
were 125, 138, and 123. The difference among them
was not significant (F=0.7).

Experiment 13. The effects of light or dark
adaptation were most pronounced during the first
minute of exposure to the attracting light. Because
this critical time period may not have been ade-

80

U.S. FISH AND WILDLIFE SERVICE

quately monitored in the other experiments with
oxygen concentration, observations were made on
groups of 10 fish 15, 30, 45, and 60 seconds after
the attracting light was turned on. The location
of the light was alternated between right and left
with each trial. Four trials were made each day;
normally siiturated and supersaturated water were
used on alternate days. The sequence was repeated
twice, making eight trials at each oxygen level, all
at a mean temperature of 15.5 to 17.0° C, and mean
oxygen concentrations of 7.3 p.p.m., 88 percent
saturation and 16.8 p.p.m., 200 percent saturation.
The mean scores of 31 and 29 were not significantly
different.

The weight of evidence indicates that neither
oxygen concentration nor percentage saturation
has any effect on the attraction of herring to light.

EFFECT OF PREVIOUS ADAPTATION

Experiment 14. Preliminary observations showed
a tendency for herring to be le&s strongly attracted
to light if they had been kept in darkness before-
hand. Therefore, for most of the experiments the
herring liad I)een held in full room illumination
so that their response would be as strong as pos-
sible. Nevertheless, some specific tests seemed de-
sirable to confirm the preliminary observations.

Sixteen trials, two each day, were made with
groups of 10 herring at a temperature of 5° C.
Each group was exposed to a medium-intensity,
underwater light after a 3-hour period of adapta-
tion to light or darkness just before each trial.
These adaptation periods were alternated with re-
spect to time of day, forenoon or afternoon.

Because the fish had necessarily to be held at all
times other than tlie 3-hour adaptation period at
some lighting condition or another, the possibility
existed that whatever this lighting was would also
influence the subsequent behavior of the fish.
Therefore, half of the trials were preceded with
exposure to total darkness the night before and
half with full illumination. The 10 trials were ar-
ranged as follows: eight in the morning and eight
in the afternoon; four of each of these eight were
preceded with a 3-hour period of darkness, and
four with a 3-hour period of light ; two of each of
these four followed an overnight period of dark-
ness and two an overnight period of light. An
analysis of vaiiance showed significant variation
only witli respect to the 3-hour pretrial light- or

dark-adaptation period (F = 5.8, P = 0.05). The
effects of overnight lighting and time of day were
of doubtful significance (F = 3.4, P = 0.1, and
F = 2.6, P>0.1, respectively) . The scores are shown
in table 6. Pretrial adaptation to darkness reduced
the effectiveness of light attraction.

Table 6. — Comparison of scores ' for light attraction of
herring in relation to prior tight experience and time of
day (experiment 14)

Time of day

Overnight
darlraess

Overnight
light

Darlc2

Light !

Dark 2

Light 1

103

90

127

205

105

163

132

134

100

168

146

193

155

162

136

170

AM

PM..

Mean score 114 143

• Score =suni of numbers of herring comited in the illuminated half of the
tank at 30 1-minute intervals. Ten herring were used in each test; maximum
possible score =300.

2 Light condition for 3 hours preceding trials.

Experiment 15. This experiment was done later
in the year than experiment 14 at the higher tem-
perature range of 15 to 17.5° C. No allowance was
made for any previous light experience of the fish
prior to a 6-hour light or dark period of adapta-
tion before each trial. The experiment also in-
cluded the additional variable of oxygen concen-
tration and was actually a part of experiment 12.
The mean score for 15 trials preceded by a 6-liour
dark period was 122; that for 15 trials preceded
by a 6-hour light period was 136. The difference
between them was not significant (F = 1.48, P>
0.2). Apparently, previous adaptation to light or
dark makes little difference in the response of her-
ring to light at high temperature.

Experiment 16. The pretrial adaptation of her-
ring to light produced the strongest positive re-
sjwnse when the trials were made at low tempera-
ture. The most marked attraction in experiment
14 occurred during the first minute of the trial :
the scores during the first minute differed by 57
percent; the total scores differed by only 25 per-
cent. This fact suggests that light or dark adapta-
tion affects the initial attraction to light more than
it affects the tendency for the light to liold the fish.

Although the total scores at high temperature in
experiment 15 did not differ significantly between
light- and dark-adapted herring, tlie first minute
scores were somewhat (though not significantly)
higher for light-adapted herring. Experiment 16

FACfTORS INFLUENCING ATTRACTION OF ATLANTIC HERRING TO ARTIFICIAL LIGHTS

81

demonstrated that the first minute scores
for light-adapted herring were, in fact, sig-
nificantly higher even at high temperature than
those for dark-adapted herring. Four trials at 15
to 17.5° C. were made each day for 4 days; each
trial was preceded by a 1-hour period of light or
darkness. Counts of the fish were made at 15, 30,
45, and 60 seconds after the attracting light was
turned on. The end of the tank illuminated, left
or right, was alternated with each trial. The mean
score for the fish adapted to light for 1 hour was
significantly higher (F=32.7, P<0.01) than the
mean score for the dark-adapted fish (table 7). A
significant bias for one side of the tank also was
apparent in this experiment. Such a bias some-
times occurred for unknown reasons and made left-
right alternation of the illuminated side of the
tank a necessary part of the procedure in all
experiments.

This experiment showed that previous adapta-
tion to light increases the initial attraction of the
herring to light regardless of temperature; on the
other hand, the holding effect of the light was
weakened at high temperature regardless of the
prior adaptation.

Table 7. — Comparison of scores^ for light attraction of
herring during first minute of exposure, in relation to
prior light experience (experiment 16)

Herring

Location of light

Light Dark
adapted adapted

Left 31 36

37 33

29 25
34 21

Right 23 5

30 6
30 10
33 7

Meanscore. 31 ig

' Score = sum of numbers of herring counted in the illuminated hall of the
tank at four 15-second intervals. Ten herring were used in each test; maii-
mum possible score = 40.

ANALYSIS OF BEHAVIOR IN RESPONSE
TO LIGHT

The attraction of herring to artificial lights is a
composite behavior pattern made uji of two gen-
eral categories of responses: those that draw the
fish toward the light and those that hold the fish
under the light's influence. The initial attraction

82

seems to be a (usually) positive telotaxis, defined
by Frankel and Gunn (1961) as direct attainment
of orientation, without deviations, to a source of
stimulus as if it were a goal. This response is
stronger in some individuals than in otliei-s and in
a few may even be negative (away from the light) .

The holding power of the light, on the other
hand, is determined by several, often dissimilar, re-
sponses of the fish. One of these is the dorsal light
reaction discussed earlier; it holds the fish near
the light by interfering with nonnal swimming
movements which would lead to escape. Another
is photokinesis, where- general activity and swim-
ming speed increase with increasing light inten-
sity ; this response works in opposition to the dor-
sal light reaction, tending to cause dispersal.
Adaptation and fatigue probably accompany con-
tinued exjDosure to the light and may weaken both
of the other reactions. Finally, there is the startling
or shock effect of sudden changes in light inten-
sity, which may repel the fish, as if by fright.

The response of fish to light is determined by
the way in which conditions influence these be-
havioral components. Some of these reactions can
be summarized as follows: Temperature affects
primarily the degree to which the fish are held un-
der the influence of the light, probably through
its effect on their activity ; higher temperature in-
creases general activity, which in tuni tends to
cause dispersal. The position of the light above or
below the surface also affects the holding power of
the light. Herring are accustomed naturally to
light rays directed downward from the surface,
and light from a source below the surface is likely
to produce orientation which interferes with
normal swimming and escape from the lighted
zone. Previous adaptation affects primarily the
initial attraction to the light, which is stronger in
light-adapted fish than in dark-adapted fish.

An attempt to measure the startle effect of light
indicated that whenever the attraction or holding
power of the light was strong, the startle effect was
less pronounced than when the attracting or hold-
ing power was weak. The startle effect was meas-
ured by the ratio of tlie number of fish in either
side of the tank before the light was turned on to
the number present immediately afterwards. A
correlation of —0.957 was found between these
ratios and the scores for 10 experiments selected

U.S. FISH AMD WILDLIFE SERVICE

to include those circumstances favorable to light
attraction and those unfavorable.

The difference in resjDonse to light shown by
individual fish and by fish in groups under other-
wise similar conditions may be another significant
aspect of behavior. The data from experiment 1,
in which the responses of 90 individual herring to
light were tested at three different temperatures,
and from experiment 6, in which the responses of
90 herring were tested in groups of 10 at the same
three temperatures are an example. If the fish
tested individually are combined arbitrarily into
three gi-oups of 10 for each temperature, and the
mean score for each group is expressed as a percent-
age of the maximum possible score, measures of
variance among the groups can be calculated. Simi-
larly, the variance among the scores, expressed as a
percentage of the maximum possible score, can be
calculated for the actual groups of 10 fish observed
in experiment 6. A comparison shows that the
variance among the scores of the actual groups of
10 fish is significantly greater than the variance
among the scores of the arbitrarily created groups
of fish tested individually. In fact, the variance
among the scores of the actual groups is not sig-
nificantly different from the variance among the
scores of individuals. These facts imply that the
collective response of 10 herring in a group is not
simply an average of their uidividual responses.
Instead, the collective response seems to reflect the
individual responses of only one or two fish in the
group.

To explain the apparent lack of thermal in-
fluence on fisl^ individually in contrast to the
significant thennal influence on groups, I suggest
the following hypothesis. Most herring are only
feebly influenced by temperature in their response
to light. The preponderance of fish in this category
causes the average response to appear uninfluenced
by temperature when each fish responds as an indi-
vidual, even though a few individuals may be
strongly influenced. When the fish are in groups,
however, the weakly influenced majority respond
not so much to the stimulus itself as to the strongly
influenced minority, whose behavior dominates
the group. I believe that in this interaction lies
II the significance of the school in fish behavior:
i| the interaction provides to the group a sensitivity
'I and an ability not possessed by individuals to
react in an unequivocal manner to a situation.

FAOTORS INFLUENCING ATTRACTION OF ATLANTTIC HERRING TO AR(TIFICIAL LIGHTS

RESPONSES OF HERRING TO LIGHT
AND THEIR APPLICATION IN THE
FISHERY

Without doubt attraction to artificial lights at
night is a significant behavioral response of
herring, and it is potentially useful in the herring
fishery. The question is: Under what conditions
is this response brought out most strongly and
what tactics in using lights can be most effectively
employed ?

Most of the evidence indicates that a sub-
merged light is more effective than one above the
surface. One reason is that the entire output of
the underwater light is used, whereas a large por-
tion of the light from above the water is reflected
from the surface. Tlie submerged light is also
more uniform : the rays do not flicker from the
effect of a ruffled surface. Moreover, the sub-
merged light has an improved attracting effect
which is independent of its gi-eater efficiency. A
submerged light which produced only 1/10 to
1/1,000 the underwater illumination of a light
above an unruffled surface proved to be the more
effective in laboratory experiments. Because of
refraction, the rays from a light above the surface
project sharply downward, even at some distance
from the light source. It may be that the direction
of the rays in relation to the position of the fish
are important, and that rays from above the sur-
face approaching the vertical tend to repel
herring. The light from the sun, sky, or a bright
moon would be of this nature; all of these light
sources tend to keep the herring from the surface
and may be the cause of the characteristic diurnal
vertical migrations of herring.

E\ddence from my experiments and also from
other studies shows that the brightest lights are
not necessarily the most effective for attracting
herring. Although a brighter light will have a
greater range and can be seen by fish at a greater
distance, the illumination within a certain radius
may exceed the optimum and tend to repel the
fish even if they are attracted up to that radius.
To obtain maximum range while still attracting
nearby fish, certain manipulations of the light
have been used effectively. The simplest method
is to dim the light gradually (Gauthier, in press;
Kurc, in press; Strom, in press). Another scheme
was described by Sasaki (1959) : A series of lights
of optimum brilliance extend some distance from

83

the fishing operation. The outermost light is
turned on for a time until a substantial number
of fish are attracted. This light is then extin-
guished, and another somewhat closer to the fish-
ing operation is illuminated. Each light in the
series is lighted and extinguished in sequence,
attracting in turn the fish gathered about the pre-
ceding one.

Besides the properties of the lig'ht itself, cei-tain
factors of the environment govern the effectiveness
of the light, especially in relation to the time of
day or time of year it is used. Kawamoto (1959)
showed that in some species of fish the light-seek-
ing tendency was stronger in the daytime than at
night. Tamura ( 1959) , discussing this phenomenon
and certain physiological changes in the eye of the
fish when adapted from light to darkness, sug-
gested "this may be one of the fundamental reasons
why fishing with the use of light is usually more
effective before than aft-er midnight." The results
of my own experiments with herring show a
greater attraction to light of light-adapted fish,
especially the initial attraction. All of these ob-
servations suggest that fishing with a lig'ht would
be most effective shortly after dusk.

I can find no reference to the effect of tempera-
ture on the response of herring to light except as
it relates to their passage through the thermocline;
there are records, however, indicating that temper-
ature does affect the response to light of other spe-
cies of fish. Andrews (1946) showed that the posi-
tive phototaxis of suckers {Catastorrvus) was
weakened at high temi>erature ; Grubisic (1962)
stated that the attraction of sardines {Sardina
pilchardvs) to light was weaker in the sununer-
time than at other seasons and that this weakness
was "more e\adent when the summers are more
than normally hot."

Because the attraction of herring to light seems
also to be weakened at high temperature, success
in fishing for them with artificial lights might well
depend in part on the season of the year and the
temperature characteristics of particular localities.
Moreover, temperature seems not only to affect di-
rectly the attraction to light, but also to modify
the effects of light position and previous adapta-
tion to light or darkness.

My purpose in the experiments involving tem-
perature was limited to finding out whether tem-
perature had any effect at all. Obviously, it did, but

the critical values of both experimental and adap-
tation temperatures need yet to be defined. It is
possible that the temperatm'e preferendum de-
scribed elsewhere (Stickney, in press) represents
the critical point above which tlie light i-esponse
weakens.

The use of lights in the herring fishery of the
Canadian and United States Atlantic Coast has
been in disfavor for some time and is even illegal
in many places. Even wliere it is still legal, it is a
method of little importance probably because fish-
ermen believe that lights frighten the herring away
(Scattergood and Tiblxi, 1959). Fishing at night
is earned on with as little light showing as pos-
sible. Because above-water lights, excessively
bright lights, and lights suddenly flashed on or
moved about do apparently frighten herring, the
caution used in showing lights is probably justi-
fied. On the other hand, practical experience and
biological evidence indicate that lights properly
used under some circumstances can attract herring
effectively. It would seem that artificial lights used
in accordance with what is known about herring
behavior would provide an extremely useful
method for controlling the lierring schools so that
they would be in locations most conducive to set-
ting purse seines or stop seines around them.

LITERATURE CITED

Andrews, C. W.

1946, Effect of heat on the light behaviour of fish.
Proc. Trans. Roy. Soc. Can., Ser. 3, 40 : 27-31.
Blaxteb, J. H. S.

1964. Spectral sensitivity of the herring, Clupea
harengus L. J. ESp. Biol. 41 : 155-162.
Blaster, J. H. S., and F. G. T. Holliday.

1963. The behaviour and physiology of herring and
other clupeids. In F. S. Russell (editor). Advances
in marine biology, vol. 1, pp. 261-393. Academic
Press, London and New York.
Blaster, J. H. S., and B. B. Parrish.

19.58. The effect of artificial lights on fish and ma-
rine organisms at sea. Mar. Res. Scot. 2 : 1-25.
CoLTON, John B., Robert R. Mabak, Samuel R. Nickeb-
soN, and Ruth R. Stoddard.

1968. Physical, chemical, and biological obser^'ations
on the Continental Shelf, Nova Scotia to Long Is-
land, 1964-66. U.S. Fish Wildl. Serv., Data Rep.
23, V + 190 pp. on 3 microfiches.
Draoesund, Olav.

1958. Reactions of fish to artificial light, with special
reference to large herring and spring herring in
Norway. J. Cons. 23 : 213-227.

84

U.S. FISH AND WILDLIFE SERVICE

EABIlL, R. EtoWAKD.

1887. The herring fishery and the sardine industry.
In G. Brown Goode (editor), The fisheries and
fishery industries of the United States, vol. I,
sect. V, pp. 417-524.
Frankel, Gottfried S., and Donald L. Gunn.

1961. The orientation of animals. Dover Publica-
tions, Inc., New York, 376 pp.

Gauthier, M.

(In press) Peche avec lampes immerg^es pratiquSe
dans le Golfe Saint-Laurent. Proceedings of the
Conference ou Fish Behaviour in Relation to Fish-
ing Techniques and Tactics, FAO Fisheries Rep. 62.

GrubiSic, Fabjan.

1962. Observations on sardine behavior under artifi-
cial light. Special Publication, Oceanography and
Fisheries Institute — SPLIT, pp. 3-15. ( Translated
and published for U.S. Department of the Interior
and the National Science Foundation, Washington,
D.C. by the NOLIT Publishing House, Belgrade,
Yugoslavia, 1967.)

Kalle, K.

1965. Possible effects of oxygen lack on shoaling
fish. Int. Comm. Northwest Atl. Fish., Spec. Publ.
6: 645-646.
Kawamoto, Nobu Yuki.

1959. The significance of the quality of light for the
attraction of fish. In H. Kristjonsson (editor).
Modern fishing gear of the world, pp. 553-555.
Fishing News (Books) Ltd., London.

KtTRC, G.

(In press) L'application k la peche des reactions
phototropiques des poissons. Proceedings of the
Conference on Fish Behaviour in Relation to Fishing
Techniques and Tactics, FAO Fisheries Rep. 62.
Sasaki, Tadayoshi.

1959. The use of light attraction for traps and set
nets. In H. Kristjonsson (editor), Modern fishing
gear of the world, pp. 556-558. Pishing News
(Books) Ltd., London.
ScATTERGOOD, LESLIE W., and S. N. TiBBO.

1959. The herring fishery of the Northwest Atlantic.
Bull. Fish. Res. Bd. Can. 121, 42 pp.

Sticknet, a. p.

(In press) Orientation of juvenile Atlantic herring

{Clupea harengus harengua L. ) to temperature and

salinity. Proceedings of the Conference on Fish

Behaviour in Relation to Fishing Techniques and

Tactics, FAO Fisheries Rep. 62.

Stickney, Axden p.

1968. Supersaturation of atmospheric gases in the
coastal waters of the Gulf of Maine. U.S. Fish
Wildl. Serv., Fish. Bull. 67:117-123.
Strom, P.

(In press) Philippine purse seining with light at-
traction. Proceedings of the Conference on Fish
Behaviour in Relation to Fishing Techniques and
Tactics, FAO Fisheries Rep. 62.
Tamura, Tamotsu.

1959. Fundamental stu<\ies on the visual sense in
fish. In H. Kristjonsson (editor) , Modern fishing
gear of the world, pp. 543-547. Fishing News
(Books) Ltd., London.
TiBBO, S. N.

1965. Effect of light on movements of herring in the
Bay of Fundy. Int. Comm. Northwest Atl. Ksh.,
Spec. Publ. 6 : 579-582.
Verheijen, F. J.

1959. Attraction of fish by the use of light. In H.
Kristjonsson (editor). Modem fishing gear of the
world, pp. 548-549. Fishing News (Books) Ltd.,
London.
(In press) Some aspects of the reactivity of fish to
visual stimuli in the natural and in a controlled
environment. Proceedings of the Conference on
Fish Behaviour in Relation to Pishing Techniques
and Tactics, FAO Fisheries Rep. 62.
Woodhead, p. M. J.

1956. The behaviour of minnows (Phoxinus phox-
inus L. ) in a gradient. J. Exp. Biol. 33 : 257-270.
Woodhead, P. M. J., and A. D. Woodhead.

1955. Reactions of herring larvae to light : a mech-
anism of vertical migration. Nature 176 : 349-350.

FAOTORS INFLUENCING ATTRACTION OF ATLANTIC HERRING [TO AR/TIFICIAL LIGHTS 85

U.S. GOVERNMENT PRINTING OFFICE : 1969 0— 357-104

VARIATIONS IN MARINE ZOOPLANKTON FROM A SINGLE LOCALITY IN

HAWAIIAN WATERS

BY RICHARD S. SHOMURA AND EUGENE L. NAKAMURA, FISHERY BIOLOGISTS

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY
HONOLULU, HAWAII 95812

ABSTRACT

Data on marine zooplankton and hydrography were
obtained off Oahu, Hawaii, at monthly intervals from
June 1957 through December 1958.

Samples collected at 3-hour intervals for 48 hours
in June 1957 were examined for diel variation. Volumes
of zooplankton exhibited the expected sinusoidal vari-
ation during the first 24 hours, but not during the
second. High volumes during the second morning
were attributed to the presence of an unidentified
diatom that retarded drainage of moisture during de-
termination of volumes of zooplankton. Variations in
abundance were sinusoidal for Ostracoda, Euphausi-
acea, Pteropoda, and fish larvae. Similar variations in
surface temperature and depth from the surface to
the top of the thermocline were attributed to solar

heating and internal waves, respectively.

The 19 monthly samples showed correlations between
volumes of zooplankton and salinities and between
volumes of zooplankton and depth to the top of the
thermocline. The 19 months were divided into nine
successive periods, each with a temperature-salinity
curve differing from that of the preceding and follow-
ing periods. Volumes of zooplankton and the abundance
of Siphonophora, Chaetognatha, Euphausiacea, deca-
pod Crustacea, and Pteropoda increased when portions
of the temperature-salinity curves greater than 35.0 %„
increased during the nine periods; and, conversely, the
volumes of zooplankton and the abundance of these
groups of zooplankters decreased as the amount of
water with salinity greater than 35.0 %o decreased.

Once every month from June 1957 through
December 1958, members of the Bureau of Com-
mercial Fisherie.s Biological Laboratory, Honolu-
lu, collected hydrographic and meteorological
data from a station located at lat. 21° 10.3' N., long.
158° 19.0' W. for the Island Observatory Project
of the International Geophysical Year Oceano-
graphic Program (Scripps Institution of Ocean-
ography, 1965). This position, i-ef erred to as the
IGY station, is about 32 km. southwest of Barbers
Point, Oahu, where the depth of the water is about
3,000 m.

Samples of zooplankton were also collected at
the IGY station for studies of variations in the
standing crop and composition of marine zoo-
plankton in relation to enviromnental factors at
a single locality in Hawaiian waters. The results
showed that volumes of zooplankton were high in
waters of high surface and subsurface salinities.

METHODS

The samples of zooplankton were collected with
a net having a mouth diameter of 1 m. ; a flow-

Published September 1969.

FISHERY BULLETIN: VOL. 68, NO. 1

meter was mounted in the center of the opening.
The body of the net was constructed of synthetic
fiber of 0.656 mm. aperture width ; the rear section,
including the cod end, was made of synthetic fiber
of 0.308 mm. aperture width. Detailed descriptions
of tlie construction of the net and the method of
making the tow have been presented by King and
Demond(1953).

The nets were towed obliquely from the surface
to a depth of 60 m. and back in one-half hour. In
June 1957, such hauls were made at 3-hour in-
tervals over a 48-hour period to measure diel
variations. In the succeeding months, four half-
hour hauls were made each time the station was
occupied : two successive daylight hauls starting
at about 1600 l.s.t. (local standard time) and two
successive night hauls between 2100 and 0300 l.s.t.

The methods of processing and determining the
volumes of the samples of zooplankton have been
described by King and Hida ( 1954, 1957a) . Counts
of various groups of plankters were made on the
night samples.

For the counts, an aliquot of a sample was
first placed in a counting cell (a 15 by 20 by 1.5-cm.

87

plastic dish) which had 300 subdivisions ruled
into its bottom. The organisms in 40 randomly
selected squares were identified and counted
under a dissecting microscope. The estimated
number of a group of organisms in 1,000 m.'
of water was calculated by the following formula
(modified from King and Demond, 1953) :

PA

where E = number of organisms per 1,000 m.' of
water
C = counted number of organisms
A=area of counting cell (300 cm.^)
f=fraction of total sample in the counting

cell
a=area of square (1 cm.^)
n=number of squares counted (40)
W= cubic meters of water strained by net

Usually, on each visit to the IGY station, two
hydrographic casts were made, one during the
highest tide and the other during the lowest tide.
Ordinarily, each cast was from to 500 m. depth
and consisted of 12 Nansen bottles, but on some
occasions the casts were deeper. Temperature
and salinity data were obtained with each cast,
and with a few exceptions, oxygen and inorganic
phosphate were also measured. Additional temper-
ature data were obtained with bucket thermom-
eters and bathythermographs.

Salinity determinations were made by a modi-
fication of the Knudsen method ("Van Landing-
ham, 1957) ; inorganic phosphate determinations
were made with a Beckman ^ spectrophotometer.

Temperature, salinity, phosphate, and oxygen
values used in the study were averaged as follows :

Surface value: average of measurements ob-
tained at water surface during high tide and low
tide.

to 60 m. value: average of measurements at
depths of 0, 10, 20, 30, 40, 50, and 60 m. during
high tide and low tide.

200 to 300 m. value: average of values at 15-
unit increments between the 400 and 300 thenno-
Bteric anomaly surfaces on a temperature-salinity
plot. These two anomaly surfaces represented ap-
proximately 200 and 300 m., respectively.

' Trade names referred to in this publication do not imply
endorsement of commercial products.

Vertical temperature distribution: isotherms
were contoured on the basis of the average tem-
peratures at the following depths : 0, 9.2, 15.2, 30.5,
45.8, 61.0, 76.2, 91.5, 100.6, 122.0, 149.4, 152.5, 183.0,
199.8, 213.5, 244.0, and 274.5 m. Readings were
limited to a maximum of five bathythermograms
per month.

DIEL VARIATIONS

In central Pacific waters, diel variation in vol-
umes of zooplankton and in abundance of certain
zooplankton has been shown to vary as the curve
of the sine function (King and Hida, 1954;
Legand, 1958; Nakamura, 1967) ; the peak equated
to midnight. The volumes and abundance of zoo-
plankters determined from samples obtained at 3-
hour intervals from June 21 to 23, 1957, were
examined for similar variations. Temperatures and
depths fo the top of the thennocline for this
period were also examined for diel variations.

VOLUMES OF ZOOPLANKTON

The volumes of zooplankton obtained for the 48-
hour series ranged from a low of 13 cc./l,000 m.^
of water strained to a high of 40 cc./l,000 m.'', with
a mean of 26 cc./l,000 m.^ (fig. 1). The volumes of
the samples obtained during the night were greater
than those of the samples collected by daylight;
the night to day ratio was 1.3 : 1. The greater abun-
dance of zooplankton in darkness has been attrib-
uted by investigators to some combination of an
upward migration by the zooplankters and an
increased avoidance of the net by some organisms
in daylight (King and Hida, 1954, 1957a; Flem-
inger and Clutter, 1965 : Brinton, 1967).

The volumes from the 48-hour series appeared
to conform approximately to a sinusoid for the first
24-hour period but not for the second. The volumes
remained high through the second morning. An
unusually large amount of an undetermined species
of diatom was present in samples 11, 12, 15, and
16. The greater resistance of these samples to mois-
ture drainage than of those without diatoms re-
sulted in a greater determination of wet volume.
This fact may have explained the unusually high
volumes in samples 12, 15, and 16. On the other
hand, the volume of sample 11 did not appear to
be unusual even though it too contained diatoms.

88

U.S. FISH AND WILDLIFE SERVICE

45

40

SAMPLE NUMBER
7 8 9 10

16

~r-

z
o
o
o

I

i

m

i

I i i

J

MEAN VOLUME

III

I

I II I J J

%

^

II

1

^

i

^

I I

i

i

-T"" .^^., .^ _p ,^^ y^ .^ .^ ^^ _^

2100 0000 0300 . 0600 0900 1200 1500 1800 2100 0000 0300 0600 0900 1200
LOCAL STANDARD TIME

Figure 1. — Variations in volumes of zooplankton over a 48-hour period, June 21-23, 1907, at the IGY station.
Sunrise during this perioid was at 0503 and simset at 18r46 hours.

1500 1800

COMPOSITION OF ZOOPLANKTON

Abundance of groups of plankters expressed as
average numbers per 1,000 m.' of water strained
and as a\'erage jjercentages of total niimlters of
plankters is summarized in table 1. By far the most
numerous organisms in the samples were copepods,
which on the average constituted about 60 percent
of all organisms present. Chaetognatha and Halo-
sphaera viridis,- almost equal in average abun-
dance, were the second and third most common
organisms in the samples. Numerically, each aver-
aged less than 10 percent of the copepods.

Distinct diel variations, with gi^ater numbers
during darkness, were exhibited by Ostracoda,
Euphausiacea, Pteropoda, and fish larva© (fig. 2).
Amphipoda exhibited such a die! variation only
during the second half of the series (fig. 2). In
addition to the aforementioned groups, Annelida

(Polychaeta) and calanoid Copepoda have been
shown previously to exhibit distinct diel variations
in Hawaiian waters (Nakamura, 1967). In this
study, these two groups did not show the character-
istic peaks of abundance during darkness. Perliaps
if specific or generic identifications had been made

^This phytoplnnkter was present in every sample and was
included in all counts.

Table 1. — Average abundance and average percentage
composition of various plankters for 16 samples of the
48-hour series

Plankters Average Average
abundance composition

No.llflOOm? Percent

Halosphaera^ .- 1,654 5.6

Foraminifera 776 2.6

Radiolaria -.. 572 1.9

Siphonophora - 1,088 3.7

Chaetognatha 1,626 6.6

Annelida -- 132 .4

Calanoid Copepoda 17,788 69.8

Noncalanoid Copepoda.- _ 1,024 3.4

Ostracoda 866 2.9

Euphausiacea -- 664 2.2

Amphipoda 1,189 4.0

Decapod Crustacea 1,076 3.6

Pteropoda 290 1.0

Heteropoda - 147 .5

Gastropod larvae 64 .2

Pelecypoda ..- 60 .2

Thaliacea - 61 .2

Appendicularla .-- 422 1.4

Fishlarvae 129 .4

Fish eggs 36 .2

others - 82 .3

' Haloaphaera viridit, a pbytoplankter, numerous in all samples.

diel fluctuations would have been revealed, for
Nakamura (1967) found that the following genera
of calanoid copepods were concentrated in the
upper waters during darkness: PJewrom-am.ma,
Neocalunus, Candacia, Undimula, and Eiwhaeta.
In the present study abmidance of Heteropoda
reached a peak during daylight as well as at night.

VARIATIONS IN MARINE ZOOPLANKTON IN HAWAIIAN WATERS

89

SAMPLE NUMBER
4 5 6 7 8 9 10 II

12 13 14 15 16

3,000
2,500
2,000

1,500

1.000

500

400
300
200
100

OSTRACODA

800
600
400
200

f,V,"^

A PTEROPODA /\ y. -

V — /!

HETEROPODA

0000 0600 1200 1800 0000
LOCAL STANDARD TIME

0600 1200

Figure 2. — Variation in the abundance of various groups
of zooplanliters during June 21-23, 1957, at the IGY
station.

TEMPERATURE

The diel variation in surface temperature (fig.
3) was attributed to solar heating during the day
and cooling at night. A subsurface thermal dis-
turbance was evident between 0400 and 1200 hours,
June 22. It was probably caused by advection;
however, unusual changes in the voliunes of

90

zoop'ankton did not occur during the thermal
disturbance.

DEPTH FROM SURFACE TO TOP OF
THERMOCLINE

The sinusoidal variation in the depth from the
surface to the top of the thermocline (fig. 3)
showed fluctuations probably caused by internal
waves. The variations in depth to the top of the
thermocline, however, did not appear to influence
the abundance or composition of the zooplankton
during the 4-8-hour period. The depths for the
hauls of zooplankton in this series ranged from 52
to 65 m. The depth from the surface to the top of
the thennocline ranged from 23 to 61 m. Sample 8
was the only one collected entirely within the iso-
thermal layer above the thennocline. The volume
of sample 8 was not unusual. Chaetognatha had
their least abundance and Pelecypoda their great-
est abundance in this sample.

CORRELATIONS BETWEEN ZOOPLANK-
TON AND PHYSICAL AND CHEMICAL
FACTORS

King and Hida (1954, 1957b), in their studies
of the distribution and abundance of zooplankton
in Hawaiian waters, were imable to show a con-
sistent relation between the standing crop and
temperature, surface phosphate, dissolved oxygen,
and depth from the surface to the top of the ther-
mocline. Analyses of their data from seven cruises
gave one statistically significant correlation
(P<0.05) Ijetween zooplankton and temperature
(at 10-m. depth) and one significant correlation
(P <0.01) between zooplankton and surface phos-
phate. King and Hida's samples were taken from
a large area around the Hawaiian Islands.

Consistently high or low standing crops regard-
less of changes in the environment (McGary 1955 ;
Seckel, 1955) have been found in certain areas in
Hawaiian waters. For example. King and Hida
(1954, 1957b) foimd consistently low volumes of
zooplankton from immediately east of the island
of Hawaii.

The results of the correlation analyses for the
present study, where sampling was confined to one
locality, are summarized in table 2. Volumes of
zooplankton were examined in relation to the phys-
ical and chemical data for tiie surface, to 60 m.
(range in depth of the hauls for zooplankton),

U.S. FISH AND WILDLIFE SERVICE

p 270

^26

Ijj

I- 250

UJ

§ 240

o:

3 ?^o

TOP OF
THERMOCLINE

I , , I

2100 0000 0300 0600 0900 1200 1500

LOCAL STANDARD TIME

2100 0000 0300 0600 0900

FiGtTBE 3. — Vertical distribution of temperature during June 21-23, 1957, at the IGY station.

Table 2. — Summary of correlations between volumes of
zooplankion and certain physical and chemical environ-
mental factors

First variate
(Xi)

Second variate (Xi)

Degrees
of free-
dom

Correla-
tion
coefficient
(r)

Surface salinity

(7oo).

Zooplankton
volume (cc./l,000
m.»).

Night hauls -
Day hauls. .

, 16
16

0.397
••.655

Surface oxygen
(ml.A).

Zooplankton
volume (cc./l,000
m.s).

Night hauls-
Day hauls. -

14
14

-.029
.228

Surface inorganic
phosphate
O-g.at.A).

Zooplankton
volume (cc./l,000
m.').

Night hauls.
Day hauls. -

13
13

-.132
-.227

0-60 m. salinity

(°/oo).

Zooplankton
volume (cc./l,000
m.!).

Night hauls.
Day hauls . .

16
16

.464
••.706

0-60 m.
temperature
P C).

Zooplankton
volume (cc./l,000
m.J).

Night hauls.
Day hauls. -

16
16

.025
-.236

200-300 m.

salinity ("/„„).

Zooplankton
volume (cc./l,000
m.3).

Night hauls -
Day hauls. -

16
16

•.507
.455

Depth to top of
thermocline
(m.).

Zooplankton
volume (cc./l,000
m.3).

Night hauls.
Day hauls- -

16
16

•-.524
•-.544

•Significant at 5- percent level.
••Significant at 1-percent level.

and about 200 to 300 m., and also the depth from
the surface to the top of the thermocline. Changes
in volumes of zooplankton and in physical and
chemical factors of the environment during the 19
months are illustrated in figures 4, 5, and 6. Sur-
face values are given in table 3.

Except for June 1957 and October 1958, the
volumes of zooplankton obtained <at night were
greater than those collected by day (fig. 4). The
ratio of night to day volumes ranged from 0.9 : 1
to 3.3 : 1 and averaged 1.8 : 1.

Volumes of zooplankton sho"wed close correla-
tions with salinities and depths of the isothermal
layer but not with other environmental factors.
Positive correlations were significant at either the
5 percent or 1 percent probabilities between vol-
umes of zooplankton for day hauls and salinities
at the surface and at to 60 m., and for night hauls
and salinities at 200 to 300 m. (table 2). Correla-
tions between volumes of zooplankton for night
hauls and salinities at to 60 m. and for day hauls
and salinities at 200 to 300 m. were very close

VARIAJTIONS IN MARINE ZOOPLANK/TON IN HAWAIIAN WATERS

91

z

O 75
O

o

^ 50

T 1 1 1 1 1 1 r

"1 r

J L

J I I I L

1 1 1 r

NIGHT HAULS

DAY HAULS

I RANGE OF VOLUME

JUNE JULY AUG. SEPT OCT NOV. DEC JAN FEB. MAR APR. MAY JUNE JULY AUG. SEPT OCT NOV DEC.

A . )

Y
1957

r
1958

Figure 4. — Monthly variations in volumes of zooplankton collected by night and by day at the IGY station

from June 1957 to December 1958.

FiGUKE 5. — Monthly vertical distribution of temperature at the IGY station from June 1957 to December 1958.
92 U.S. FISH AND WILDLIFE SERVICE

(

28.0

d 26

22
35 30

35.20

J 1 \ I I \ 1 1

J \ I I I I I

T r I I — I — I — I — I — I — I — I — I — r

J L

J I \ L

J J A S N D J FMAMJ JASONO

r 1 '

1957 1958

Figure 6. — Monthly variation In temperature and salinity
at the IGY station from June 1957 to December 1958.
A. Mean to 60 m. temperatures. B. Mean to 60 m.
salinities (solid line) and mean 200 to 300 m. salinities
(dashed line).

to sijniificance at the 5 percent probability (for
P = 0.05 and d.f. = 16, r = 0.468). Negative cor-
relations were significant between volumes of zoo-
plankton for both night and day haids and depths
from the surface to the top of the tliennocline.
Neither temperature, oxygen, nor inorganic i:)hos-
phate was correlated with volumes of zooplankton.
We believe the significant relations between zoo-
plankton and salinity and between zooplankton
and the thickness of the isothermal layer resulted
from tlie advection of dift'erent types of water into
the Hawaiian area. The biomass of zooplankton
was higher in waters of high salinity.

ZOOPLANKTON AND TEMPERATURE-
SALINITY CURVES

Seckel (1962) indicated that the Hawaiian Is-
lands are located near the northern boundary of
the transition zone between two major types of

Table 3. — Monthly values of surface salinity, inorganic
phosphate, and oxygen during low and high tides at the
IGY station

Month

Salinity °/o,

Low High
tide tide

Oxygen ml.A

Phosphate
(ig.at./l

Low High Low High
tide tide tide tide

1957

June - 34.97

July 34.87

August. 34.96

September 35. 07

October 35.19

Novem'^er 35.12

December 34.72

19S8

January 34.81

February 35.03

March 34.94

April 35.10

May 34.80

June 34.90

July 34.81

August 34.91

September 34.86

October 34.94

November 34.96

December 34.94

34.97 0.22 0.20 4.29 4.32

34.88 .29 .24 4.47 4.46
34.96 .20 .22 4.79 4.78

35.12 .13 .16 4.46

35.16 .10 .16 4.63 4.61

35.12 .11 .16 4.78 4.64

34.81 3.65 4.58 4.66

34.85 .12 .13 4.79 4.69

35.05 .22 .20 4.85 4.84

34.96 .64 1.60 4.60 4.66

35.07

34.77 .06 .62 4.65 4.62

34.82 4.08 4.18

34.80 .49 .70 4.77 4.80

34.89 .39 .22 4.43 4.65

34.87 4.65 4.64

34.96 .21 .23 4.40

34.94 .11 .10

35.05 36 4.64

surface water: (1) the high-salinity (surface
values >35.0%o) North Pacific Central "Water, and
(2) the low-salinity (surface values <34.2%o)
North Pacific Equatorial Water. These water
types corresponded approximately with the sub-
surface water masses as defined by Sverdrup,
Johnson, and Fleming (1942). Se«kel (1962) clas-
sified the Califoniia Current Extension, which
forms the core of the transition zone, as a third
type. He showed that the boundaries of these water
types shifted seasonally and affected the type of
water to be found near Oahu.

Our data were analyzed from the standpoint of
advection of different types of water as indicated
by changes in the temperature and salinity during
the 19 months of observation. The data were di-
vided into the following nine chronological periods
(fig. 7) on the basis of the similarity in the tem-
perature-salinity (T-S) curves for successive
months : June to July 1957, August 1957, Septem-
ber to November 1957, December 1957 to March
1958, April 1958, May 1958, June to July 1958,
August to November 1958, and December 1958.
Each period had temperature and salinity char-
acteristics that were different from the preceding
and succeeding periods. The average monthly
(0-60 m.) temperatures, the average monthly
salinities (0-60 m. and 200-300 m.), and the
average depth from the surface to the top of the
thermocline for the nine periods are illustrated
in figure 8.

VARIATIONS IN MARINE ZOOPLANKTON IN HAWAIIAN WATERS

93

-HK3H TIDE LOW TIDE

ZO

\i

-

1

JUNE-JULY
1957 /

\

1

-

-

AUG.

\

/ /

/

/

25

-

_

DEC-MAR.
1957-1958

rN

s.

\

f'

-

-

APR.

)

11

)

I

-

-

\
MAY

/I

'

1

t —

AUG.- NOV.

/

!

/

3500
SALINITY (•/..)

-

-

DEC.
1958

1

//

[/

1'

270
260

NINE-PERIOD MEAN

1

1
*

I

1

1

-

•

24

-

* -

230

^

-

??n

A

35 30
35 20
35 10
35.00
34.90
34.80

34 70

35 20

35,10

35 00

34 90
Or

10-

20-

30-

40
50
60
70
80-
90
100-

*

D

Figure 7. — Monthly temperature-salinity relation at
highest high tide and lowest low tide at the IGY station
by periods.

JUNE AUG. SEPT DEC APR. MAY JUNE AUG DEC.

JULY nAv mAr JULY NOV.

1957 1957-1958 1958

Figure 8. — Physical and chemical characteristics of the
nine periods. A. Average to 60 m. temperatures. B.
Average to 60 m. salinities. C. Average 200 to 300 m.
salinities. D. Average depth from the surface to top
of thermocline.

94

U.S. FISH AND WILDLIFE SERVICE

Table 4.- — Average abundance (No. /1, 000 m.') of various plankters from samples taken at night al the IGY station

Plankters

Period and (in parentheses) number of samples

June,
July 1957

(2)

Aug. 1967
(1)

Sept., Dec. 1957,
Oct., Jan.,

Nov. 1957 Feb.,
Mar. 1958
(3) (4)

Apr. 1958

(1)

Aug.,

June, Sept.,

July 1958 Oct.,

Nov. 1958
(2) (4)

CD

Eight-
period
mean

(8)

Halosphaera' ---- ---- 6,392

Foraminifera - 660

Kadiolaria - 204

Siphonophora.. --- 2, 196

Chaetognatha 1,346

Annelida, .-- 184

Calanoid Copcpoda 12,762

Non-calanoid Copepoda... 1,369

Ostracoda - 1,974

Euphausiacea 1,338

Amphipoda 958

Decapod Crustacea - 2,120

Pteropoda._ 486

Heteropoda 247

Gastropod larvae - - 60

Pelecypoda 60

Thaliacea 11

Appendicularia - 135

Fish larvae -- 234

Fish eggs - - 96

' Halosphaera viridit, a phytoplankter.

1,771

651

394

3,643

2,834

157

38, 733

2,362

2,659

2,440

905

3,976

946

79

197

167

167

236

79

3,047

283

158

6,943

2,955

238

32,069

2,301

2,633

4,541

626

4,460

1,361

394

174

74

202

851

269

31

3,569

286

156

3,055

1,259

188

18,704

1,192

3,616

1,673

401

1,842

546

38

33

177 .
464
720
292
90

6,284
1,308

366
4,185
4,813

366

30, 395

4,028

6,069

3,139

942

3,768

1,360

62

105

1,308
3,191

1,582

94

38

6,137

2,420

357

20, 078

1,796

607

1,662

869

3,060

446

68

138

44

668

216

692

25

2,400
274
142

3,723

2,346

128

13, 489

1,898
650

1,893
648

3,331

1,049
118
136
132
146
256
171
21

6,102

569

298

4,358

3,128

410

24, 916

2,905

1,937

1,788

521

5,028

1,378

298

223

372

1,639

112

3,618

502

220

4,142

2,638

254

23,893

2,230

2,480

2,309

709

3,448

946

124

141

88

416

896

282

96

The physical, chemical, and biologioal character-
istics of each of the nine periods are discussed be-
low. For the discussion the averages for each
period are considered liigh or low relative to the
overall average for the nine jjeriods. A night sam-
ple of zooplankton was not taken in May 1958;
thus, the counts of zooplankton for night collec-
tions are divided into eight rather than nine
periods (table 4).

JUNE TO JULY 1957

This period was characterized by relatively high
temperatures, low salinities, and a shallow isother-
mal layer. The average to 60 m. temperature was
25.6° C. The to 60 m. and 200 to 300 m. average
salinities were 34.92%o and 35.00%o, respectively,
compared to the nine-period means of 34.97%o and
35.08%o. The average depth to the top of the ther-
mocline was 51.4 m. (fig. 8).

The average volume of zooplankton for day
hauls equaled tlie nine-iieriod mean of 20 cc./
1,000 m.^ (fig. 9) ; the average night volume of 25
cc./l,000 m.^ was lower, however, than the eight-
period mean of 37 cc./l,000 m.^ Most of the counts
of groups of organisms were low (table 4) ; Halo-
sphaera, Foraminifera, Amphipoda, and Heter-
opoda were exceptions. The abundance of calanoid
Copepoda, which numerically make up about 59
percent of the total standing crop of zooplankton,
was very low during this period.

AUGUST 1957

August 1957 appeared to be a transition period
(fig. 7). The to 60 m. salinity increased from
34.92%o to 34.98%o, and the 200 to 300 m. salinity
increased slightly from 35.00%o to 35.02%o. The
to 60 m. temperature (26.0° C.) also increased.
The depth of the isothermal layer (49.1 m.) de-
creased from the previous period.

The volume of zooplankton for the day hauls
(18 cc./l,000 m.^) for this period was slightly less
than the average for June to July 1957 ; however,
the night volume (44 cc./l,000 m.^) showed a sub-
stantial increase. Kadiolaria and calanoid Copep-
oda were more abundant in August 1957 than in
any other period.

SEPTEMBER TO NOVEMBER 1957

Temperature and depth of the isothermal layer
for this period were lower; salinities were higher
than in the previous period. The average to 60
m. temperature was 25.9° C. The depth to the top
of the thermocline was 47.4 m. The to 60 and 200
to 300 m. salinities were 35.14%o and 35.11%o,
respectively.

The average volumes and counts of zooplankton
were high. Volumes for day (25 ce./l,000 m.^) and
night (56 cc./l,000 m.') samples were both higher
than the corresponding averages (20 cc./l,000 m.^
and 37 cc./l,000 m.^) for all periods. Euphausiacea
and Heteropoda were more abundant in this period
than in ai>y other.

VARIATIONiS IN MARINE ZOOPLANKfTON IN HAWAIIAN WATERS

95

379-242 O - 70

^aNKSHT
E3DAY

EIGHT -PERIOD
NIGHT AVERAGE

NINE -PERIOD
DAY AVERAGE

^

i

m

SEPT-NOV DEC-MAR

1957-1958

JUNE -JULY AUG -NOV DEC

1958

FiGUBE 9.— Average valuines of zooplankton during niue periods at the IGT station.

DECEMBER 1957 TO MARCH 1958

MontMy changes of the measured properties
from July to November 1957 were gradual; the
change from November to December 1957, how-
ever, was abrupt. The to 60 m. temperature
dropped from an average of 25.9° C. in November
1957 to 24.6° C. in December 1957 (fig. 6A) and
remained low, averaging 24.1° C. for December

1957 to March 1958 (fig. 8A). The monthly to 60
m. salinity likewise changed considerably, drop-
ping from 35.12%o in November to 34.82%o in De-
cember (fig. 6B). The December 1957 to March

1958 average was 34.92%o (fig. 8B).

The 200 to 300 m. salinity (35.10%o) changed
slightly (fig. 8C), but the depth to the top of the
thermocline showed a considerable deepening from
an average of 47.4 m. during September to No-
vember 1957 to 84.6 m. (fig. 8D) for this period.

The volumes of zooplankton declined markedly
from the preceding period. The night volume
dropped from an average of 56 cc./l,000 m.^ in
September to November 1957 to 28 c^'./l,000 m.^
The day volumes of zooplankton declined from 25
cc./l,000 m.^" to 17 cc./l,000 m.^ (fig. 9). Except
for Halosphaera, Ostracoda, Pelecypoda, and
Thaliacea the abundance of plankters was rela-
tively low during this period.

APRIL 1958

Maximum and minimum values were recorded
for the physical and chemical properties during

April 1958 (figs. 6 and 8). The to 60 m. temper-
ature (22.8° C.) was the lowest recorded during
the 19 months. The to 60 m. salinity (35.14%o)
equaled the September to November 1957 average,
the highest average for the nine periods. The 200
to 300 m. salinity (35.18%o) was also the highest
for the nine periods. The isothermal layer during
this period was the shallowest (22.6 m.) of the nine
periods.

The zooplankton showed marked differences
from the preceding {period. The day and night vol-
umes of 30 cc./l,000 m.^ and 50 cc./l,000 m.^ for
April were much higher than those for December
1957 to March 1958. With the exception of Pele-
cypoda, all of the organisms were more numerous
than in the preceding period.

MAY 1958

In May the physical and chemical characteristics
of the water differed markedly from those of April
1958. The to 60 m. temperature increased from
the low of 22.8° C. in April to 24.6° C. in May.
The most important change, however, was in the
to 60 m. salinity, which decreased from 35.14%.
in April, the highest for the nine periods, to
34.78%o in May, the lowest for the nine periods.
The 200 to 300 m. salinity decreased slightly from
35.18%o in April to 35.13%o in May. These dif-
ferences suggest that the major change from April
t-o May was in the upper watei-s. The depth to the
top of the thermocline (62.8 m.) was slightly
greater than the nine-period mean (59.4 ni.).

96

U.S. FISH AND WILDLIFE ,SERVIOB

The average volume of zooplankton for the day
hauls was 15 cc./l,000 in.'', lower than that for any
previous period.

JUNE TO JULY 1958

Except for a continued rise in temperature and
a shallower isothermal layer, the changes during
this period were not very great. The average to
60 m. temperature was 25.5° C. The a\-erage to
60 m. salinity increased to 34.86%o. The average
200 to 300 m. salinity declined further to 35.10%o.
The average depth to the top of the thermocline
was 49.8 m.

The night volumes of zooplankton for June to
July averaged 41 cc./l,000 in.^ as compared to the
eight-period average of 37 cc./l,000 m.^, and the
average day volume of 20 cc./l,000 m.^ was the
same as the nine-period day average. Siphono-
phora, Annelida, Amphipoda, Tlialiacea, and fish
larvae were relatively abundant in this period.

AUGUST TO NOVEMBER 1958

Changes in temperature, salinity, and depth of
isothermal layer continued. Tlie to 60 m. tem-
perature reached its 1958 peak in this period with
an average of 26.3° C. The average to 60 m.
salinity (34.02%o) increased over the pre^-eding
period (34.86%o). The average 200 to 300 m.
salinity continued to decline to 35.00%o. This
period and June to July 1957 had the lowest 200
to 300 m. salinities for the nine periods. The depth
to the top of the thermocline deepened to an
average of 74.0 m.

The low abundance of zooplankton was similar
to the lows of June to July 1957, December 1957 to
Marcli 1958, and r>eceml>er 1958. Only tlie averages
for Pteropoda and Pelecypoda were above the
eight-period average.

DECEMBER 1958

This period was characterized by a marked de-
crease in temperature, rising salinities, and a pro-
gressively deepening isothermal layer. As in 1957,
the to 60 m. temperature underwent a large drop
between November and December. For 1958 the
decline was from 25.9° C. in November to 24.1° C.
in December (fig. 6A). The to 60 m. salinity of
35.07%o continued to increase from 34.82%o in July
(fig. 6B). The 200 to 300 m. salinity (35.06%o) in-
creased from the previous period. The depth to
the top of the thermocline was 93.3 ra.

The volume of zooplankton for December 1958
was again lower than the nine-period average.
Except for seven groups {Halosphaera. Forami-
nifera, Ostracoda, Amphipoda, Heteropoda,
Thaliacea, and fish larvae) , however, the plankton
during December 1958 was more abundant than
in June to July 1957, December 1957 to March
1958, and August to November 1958.

COMPARISON BETWEEN PERIODS

A noticeable feature in the 19 months' observa-
tions was the dissimilarity of the hydrographic
features for the same months of the 2 years. The
200 to 300 m. salinities for June to July were sub-
stantially lower in 1957 than in 1958, whereas the
to 60 m. and 200 to 300 m. salinities for August
to November were liigher in 1957 than in 1958. The
depth to the top of the thermocline was shallower
in the fall of 1957 than in the fall of 1958. Tlie
to 60 m. temperatures reflected the seasonal fluctu-
ations of high temperatures in summer and fall
and low temperatures in winter and spring and
so did not vary greatly between years for the same
months.

Zooplankton was more abundant during the fall
of 1957 than in the fall of 1958 (figs. 4 and 9).
Previous studies of th& distribution of zooplankton
in Hawaii have indicated a lack of consistent sea-
sonal change. In 1950 and 1951, volumes were
significantly liigher during early summer and
midsummer than in late summer and fall (King
and Hida, 1954). But in 1956, the standing crop
of zooplankton was greatest in January, April,
and September (Nakamura, 1967).

June to July 1957 and August to November 1958
were alike. Both had .similar T-S curves (fig. 7),
hence their temperature and salinity character-
istics were similar (fig. 8). Both of these periods
had low volumes of zooplankton (fig. 9). The day
volume of zooplankton for June to July 1957 was
equal to the nine-period mean while that for Au-
gust to November 1958 was low.

December 1957 to March 1958 and May 1958
were also alike. Both had similar T-S curves (fig.
7). Both had low day volumes of zooplankton. A
night volume was not available for May 1958.

The two jieriods (Septemlx>r to November 1957
and April 1958) that had high night and day
volumes of zooplankton (fig. 9) also had high

VARIATIONS IN MARINE ZOOPIiANK/TON IN HAWAIIAN WATERS

97

to 60 m. and 200 to 300 m. salinities (fig. 8), but
their temperatures were quite dissimilar (fig 8).

VARIATIONS OF ZOOPLANKTON AND
SALINITY

Of great interest were the coincident variations
in the night volumes of zooplankton with varia-
tions in the portions of the T-S curves with salini-
ties >35.0%o. As shown in figures 7 and 9, increases
or decreases in night volumes of zooplankton ap-
peared with corresponding changes in the salinity.
The T-S curves indicated a progressive invasion
of high-salinity wat«r in the upper surface layers
from June to July 1957 to September to November
1957. The night volumes of zooplankton increased
correspondingly during these same periods. In
December 1957 to March 1958, less saline waters
returned to the uppermost layer of the ocean and
the volume of zooplankton dropped below that of
the preceding period. Then in April 1958 high-
salinity water again invaded the area, and the
volume of zooplankton increased. During May
1958 the salinity maximum was about the same as
in the previous period, but the surface water was
less saline. A night volume of zooplankton was not
available for this period. During the next two
periods, June to July 1958 and August to Novem-
ber 1958, the occurrence of high-salinity waters
decreased progressively. Corresponding decreases
also were evident in the night volumes of zooplank-
ton. Water of higher salinity returned again in the
uppermost layer during December 1958 coincident
with an increase in the night volume of zooplank-
ton.

Thus, waters of high salinity appeared to sustain
a greater biomass of zooplankton. The abundance
of several groups of zooplankton fluctuated coinci-
dentally with the night volumes and with salinity.
These groups were Siphonophora, Chaetog-
natha, Euphausiacea, decapod Crustacea, and Pte-
ropoda (fig. 10). Because of the correlation of the
abundance of these zooplankters with water type,
the possibility of finding endemic species appeared
favorable. Sherman (1963) found certain species
of calanoid Copepoda (Pontellidae) associated
with, and thus useful as indicators of, waters of
high salinity (North Pacific Central Water) in
the Hawaiian area. These groups of zooplankton

98

9flOO

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

5,000

4,000

3,000

2,000

1,000

50,000

40,000

2 30,000

o
o

Q. 20.000

o 10,000

UJ

2

3 6.000

§

5,000

4,000

3.000

2,000

1,000

7,000

-EIGHT-PERIOD MEAN

m

^

m

m

"^

I
i

2a

va

i

■I

m

rti

i

6,000-
5,000
4,000
3,000
2,000
1,000

'777/

3,000

Siphonophora

1

i

Chaetognotho

I

Calanoid Copepoda

m

1

Euphousioceo

■I

Decapod Crustacea

P

i
I

2,000

1,000

-

T\

m ,

Pll

Pteropoda

r^

JUNE AUG SEPT DEC Al
JULY NOV MAR

1957 1957-1958

MAY JUNE Ay6. DEC.
JU.Y NOV

1958

Figure 10. — Average abundance of six groups of zoo-
plankton at night during eight periods at the IGY
station.

U.S. FISH AND WILDLIFE SERVICE

may include other species possibly useful as
indicators.

SUMMARY

1. Data on zooplankton and hydrography were
obtained at lat. 21° 10.3' N., long. 158° 19.0' W.
from June 1957 to December 1958. The station was
visited once a month, and samples were taken once
at highest tide and once at lowest tide. In June
1957, the station was occupied for 48 hours to
obtain samples for studies of diel variation.

2. Volume of zooplaniiton from the 4:8-hour
series conformed to the characteristic sinusoidal
variation for the first, day, but not for the second.
A diatom that prevented drainage of moisture dur-
ing determination of the volumes probably caused
the high volumes during the morning of the second
day. Variations in abundance were distinctly sinu-
soidal for Ostracoda, Euphausiac«a, Pteropoda,
and fish larvae. Variations in surface temperature
were attributed to heating during the day and cool-
ing during the night. Variations in the depth to
the top of the thermocline were attributed to inter-
nal waves.

3. Correlations were significant and positive be-
tween day volumes of zooplankton and salinities
at the surface and at to 60 ni., and for night vol-
umes of zooplankton and salinities at 200 to 300
m. Positive correlations for night volumes of zoo-
plankton and salinities at to 60 m. and for day
volumes and salinities at 200 to 300 m. were vei"y
close to the 5-percent probability. Correlations
were significant and negative between both day
and night volumes of zooplankton and depths to
the top of the thermocline.

4. The 19 months were divided into nine periods,
each period having a temperature-salinity curve
different from the preceding and the following
periods.

5. Salinities and depths to the top of the thermo-
cline were dissimilar for the same months in 1957
and 1958. Night volumes of zooplankton were high-
est in the fall of 1957.

6. Variations in the night volumes of zooplank-
ton coincided with variations in salinities > S5.0%c.
As the salinity increased, zooplankton increased;
as salinity decreased, zooplankton decreased. The
abundance of Siphonophora, Chaetognatha, Eu-
phausiacea, decapod Crustacea, and Pteropoda

fluctuated coincidentally with the night volumes
of zooplankton and with salinity.

ACKNOWLEDGMENT

Paul E. Smith, William H. Lenarz, and George
D. Grice reviewed our manuscript.

LITERATURE CITED

Beinton, Edwabd.

1967. Vertical migration and avoidance cai)ability of
euphausiids in the California Current. Limnol.
Oeeanogr. 12: 451^83.
Flemingeb, Abraham, and Robert I. Clutter.

1965. Avoidance of towed nets by zooplankton. Lim-
nol. Oeeanogr. 10 : 96-lOi.
King, Joseph E., and Joan Demond.

1953. Zooplankton abundance in the central Pacific.
[U.S.] Fish Wild]. Serv., Pish. BuU. 54: 111-144.

King, Joseph E., and Thomas S. Hida.

1954. Variations in zooplankton abundance in
Hawaiian waters, 1950-52. [U.S.] Fish Wildl.
Serv., Spec. Sci. Rep. Fish. 118, vi -f 66 pp.

1957a. Zooplankton abundance in the central Pacific.

Part II. U.S. Fish Wildl. Serv., Fish. Bull. 57 : 365-

395.
1957b. Zooplankton abundance in Hawaiian waters,

1953-54. U.S. Fish Wildl. Serv., Spec. Sci. Rep.

Fish. 221, iv + 23 pp.
Legand, Michel.

19.58. Etude .sommaire des variations quantitatives

diurnes du zooplancton autour de la Nouvelle-Cale-

donie. Rapp. Sci. Inst. Franc. Oc6an. (6), 42 pp.
McGart, James W.

1955. Mid-Pacific oceanography, Part VI, Hawaiian
ofiPshore waters, December 1949-November 1951.
[U.S.] Fish Wildl. Serv., Spec. Sci. Rep. Fish. 152,
iii -1- 138 pp.

Nakamura, Eugene L.

1967. Abundance and distribution of zooplankton in
Hawaiian waters, 1955-56. U.S. Fish Wildl. Serv.,
Spec. Sci. Rep. Fish. 544, vi -f- 37 pp.
ScRipps Institution of Oceanography of the Univebsity
OF Galifoknia.
1965. Oceanic observations of the Pacific: 1957.
Berkeley and Los Angeles, University of California
Press, 707 pp.
Seckel, Gunter R.

1955. Mid-Pacific oceanography, Part VII, Hawaiian
offshore waters, September 1952-August 1953.
[U.S.] Fish Wildl. Serv., Spec. Sci. Rep. Fish. 164,
vi 4- 250 pp.

1962. Atlas of the oceanographic climate of the
Hawaiian Islands region. U.S. Fish Wildl. Serv.,
Fish. Bull. 61 : 371^27.

SHEatMAN, Kenneth.

1963. Pontellid copepod distribution in relation to

VARIATIONS IN MARINE ZOOPLANKfTON IN HAWAIIAN WATERS

99

surface water types in the central North Pacific. general biology. Prentice-Hall, Inc., New York.

Ldmnol. Oceanogr. 8 : 214-227. 1,087 pp.

SvEBDBup, H. U., Martin W. Johnson, and Richabd H. Van Landinqham, John W.
Fleming. 1957. A modification of the Knudsen method for

1942. The oceans; their physics, chemistry, and salinity determination. J. Cons. 22: 174-179.

100 U.S. FISH AND WILDLIFE SERVICE

U.S. GOVERNMENT PRINTING OmCE: 1969 O— 357-IOS

ADDITIONAL REFERENCES ON THE BIOLOGY OF SHRIMP, FAMILY

PENAEIDAE '

BY DONALD M. ALLEN AND T. J. COSTELLO, FISHERY BIOLOGISTS
BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL FIELD STATION

MIAMI, FLA. 33149

About one thousand references to shrimp are given.
References include those on biology and fishing gear.

ABSTRACT

Citations are listed alphabetically by author.

The Bureau of Commercial Fisheries Biologi-
cal Laboratoiy, Galveston, Tex., is studying the
commercial shrimp of the family Penaeidae that
inhabit the Gulf of Mexico. As background for
this research. Chin and Allen (1959) iniblished
literature references on shrimp biology. We now
present about one thousand additional references
to supplement that list. Most references contained
in our report were published from 1958 through
1966, although we have included a few that were
previously' overlooked.

Many unpublished reports and theses concern-
ing Penaeidae came to our attention while we
were compiling the published citations. These un-
published reports are presented to indicate addi-
tional sources of pertinent information. Published
and unpublished references are listed separately.

We have followed generally the procedure used
by Chin and Allen (1959). Keferences are listed
alphabetically by the author's surname. Only
references concerning shrimp of the family
Penaeidae are listed, and the subject is limited
primarily to shrimp biology. References concern-
ing fishing methods and gear, however, are
included because they are useful to fishery biolo-
gists. We made no special effort to obtain ref-
erences to paleontological studies, the shrimp
processing industry, or shrimp statistics, although
the list contains some citations in those fields. "

Additional exclusions from the lists of citations
should be noted. We have not included literature

' Contribution No. 260 from the Bureau of Commercial Fisheries Biological
Lalioratory. Galveston. Tei. 77552.
Published November 1969.

FISHERY BULLETIN: VOL. 68, NO. 1

published after 1966. Some articles that concern
Penaeidae were not available to us for checking
the accuracy of citation and have not been in-
cluded. No attempt was made to include all brief
notes on shrimp research and shrimp fisheries
that appeared in CFR (Commercial Fisheries
Review). These notes are cited in the CFR yearly
index. Pertinent lead articles appearing in CFR,
however, are included. Many Florida State Board
of Conservation Special Mimeographed Reports
contained pertinent but limited information on
shrimp and were excluded. We often excluded
popularized articles derived from more basic re-
ix)rts already cited in our list, abstracts that were
followed by complete reports, and unpublished
papers that were superseded by published ver-
sions. Some duplication of information, however,
was unavoidable.

PUBLISHED REFERENCES

Aaron, Richard L.

1904. Studies of rh.vthmic variations in the jihotic
motivation and irfiototactic drive of the pinli shrimp,
Penaeus diiorarum Burlcenroad, using low intensity
light. M.S. thesis, Univ. Miami, Coral Gables, Fla.,
85 pp.

.\aron'. Richard L., and Warren J. AVisby.

1964. Effects of light and moon phase on the be-
havior of pink shrimp. Proc. Gulf Carib. Fish.
Inst., leth Annu. Sess., pp. 121-130.

Aguilar I.. Fedkrico.

1963. Notas sobre las investigaciones del camar6n
en el noroeste y los resultados practices obtenidos.
Inst Nac. Invest. Biol.-Pesq. (Max.), Trab. Divulg.
6(.57),4pp.

101

Aldbich, David V.

1963. Physiology and behavior program. In Biologi-
cal Laboratory, Galveston, Tex., fishery research
for the year ending June 30, 1962, pp. 55-56. U.S.
Fish Wildl. Serv., Circ. 161.

1963. Tolerances to environmental factors. In
Biological Laboratory, Galveston, Tex., fishery
research for the year ending June 30, 1962, pp. 57-
60. U.S. Fish Wildl. Serv., Circ. 161.

1964. Physiology and behavior program. In Biologi-
cal Laboratory, Galveston. Te.x., fishery research
for the year ending June 30, 1963, p. 60. U.S. Fish
Wildl. Serv., Circ. 183.

1964. Behavior and tolerances. In Biological
Laboratory, Galveston, Tex,, fishery research for
the year ending June 30, 1963, pp. 61-64. U.S.
Fish Wildl. Serv., Circ. 183.

19^1. Incidence and potential significance of Pro-
christianella penaei, a cestode parasite of commer-
cial shrimp in Galveston Bay. In Biological
Laboratory, Galveston, Tex., fishery research for
the year ending June 30, 1963, pp. 68-70. U.S.
Fish Wildl. Serv., Circ. 183.

1965. Experimental biology program. In Biological
Laboratory, Galveston, Tex., fishery research for
the year ending June 30, 1964, p. 76. U.S. Fish
Wildl. Serv., Circ. 230.

1965. Observations on the ecology and life cycle of
Prochristianella penaei Kruse (Cestoda: Trypa-
norhyncha ) . J. Parasitol. 51 : 370-376.

1965. Shrimp parasitology. In Biological Labora-
tory, Galveston, Tex., fishery research for the year
ending June 30, 1964, pp. 82-83. U.S. Fish Wildl.
Serv., Circ. 230.

1966. Experimental biology program. In Annual
report of the Bureau of Commercial Fisheries
Biological Laboratory, Galveston, Texas, fiscal year
1965, p. 39. U.S. Fish Wildl. Serv., Circ. 246.

1966. Behavior and ecological parasitology. In
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year 1965, pp. 39-41. U.S. Fish Wildl. Serv..
Circ. 246.
Allen, Donald M.

1963. A device for measuring live shrimp. In Bio-
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1963. Shrimp farming. U.S. Fish Wildl. Serv., Fish.
Leafl. 551, 8 pp.
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1962. Grading large numbers of live shrimp for
marking experiments. Progr. Fish-Cult. 24 : 46-48.

1963. The use of Atkins-type tags on shrimp. In
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1966. Releases and recoveries of marked pink shrimp,
Penaeus duorarum Burkenroad, in south Florida
waters, 1958-64. U.S. Fish Wildl. Serv., Data Rep.
11, ii -I- 77 pp. on 2 microfiches.

Allen, George.

1964. Succulent shrimp. Ala. Con.serv. 34(1) : 17-
19.

Allen, J. A.

1966. The rhythms and population dynamics of dec-
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Allsopp, W. H. L.

1960. Onvervi'agt brackishwater fish culture station
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Bull. 3, 53 pp.
Anderson, William W.

19.58. Recognizing important shrimp of the South.
U.S. Fish Wildl. Serv., Fish. Leafl. 366 (Revised),
7 pp.

1958. The shrimp and the shrimp industry of tlie
southern United States. U.S. Fish Wildl. Serv.,
Fish. Leafl. 472 (Revised) , 9 pp.

1962. Recognizing important shrimps of the South.
U.S. Fish Wildl. Serv., Fish. Leafl. 536 (Revised),
5 pp.

1966. The shrimp and the shrimp fishery of the south-
em United States. U.S. Fish Wildl. Serv., Fish.
Leafl. 589 (Revised). 8 pp.
Anderson, William W., and Jack W. Gehbinqek.

1965. Biological-statistical census of the species en-
tering fisheries in the Cape Canaveral area. U.S.
Fish Wildl. Serv., Spec. Sci. Rep. Fish. 514, 79 pp.

Anderson, William W., and Milton J. Lindner.

1965. Clave provisional para camarones de la familia
Penaeidae, con referenda especial a las especies
Americanas. Inst. Nac. Invest. Biol.-Pesq. (,Mex.),
Trab. Divulg. 9(90), 51 pp.
Anderson, William W., and G. Robert Lunz.

19(>5. Southern shrimp — a valuable resourc-e. Atl.
States Mar. Fish. Conmn. Leafl. 4, 6 pp.
Angelescu, Victor, and Enrique E. Bosohi.

1959. Estudio biol6gieo pesquero del langostino de
Mar del Plata en conexion con la ojieracion nivel
medio. Argent. Seer. Mar. Serv. Hidrogr. Nav.
Publico H. 1017, 135 pp.

Anonymous.

1957. Raising of shrimp. Oommer. Fish. Rev. 19
(1):33.

1958. Controlled culture of shrimp seen on horizon
on a commercial scale. Frosted Food Field 26
(6) : 1, 9, 10.

19.58. Progress report on prawn research. Fish.
Newslett (Aust.) 17(1): 9.

1959. Double rig shrimping in the Gulf of Mexico.
Nat. Fish. 40(5) : 13-14.

1959. Miami biologists play tag with shrimp.
Trucking 11(2) : 5-7.

1959. Shrimp fisheries research. La. Conserv. 11
(5-6) : 14-15.

1959. Want legal length for prawns. Fish. News-
lett. (Aust.) 18(8) :5.

1959. Challenge finds new deep water prawn. Fish.
Newslett. (Aust.) 18(9): 5.

1960. Two new prawns. Fish, Newslett. (Aust.)
19(2) : 5.

102

U.S. FISH AND WILDLIFE SERVICE

Anonymous — Continued

1960. Now you can grade your shrimp at sea. Fish

Boat 5(12) : 51.
1960. Tagged shrimp swims 100 miles. La. Conserv.

13(10) : 19-20.
1960. New species of shrimjp found in deep water by

exploratory vessel. Ommer. Fish. Rev. 22(1) :

61-62.

1960. Firm plans to raise shrimp in ponds. Oommer.
Fish. Rev. 22(5) : 53-54.

1961. Dr. Fujinaga's shrimp cultivation. Pac. Fish.
59(12) :38.

1962. Getting prawns with mid-water trawl. Fish.
Newslett. (Aust.) 21(6) : 19.

1962. Report on farming of prawns. Fish. Newslett.

(Aust.) 21(7) : 21.
1962. Prawn farming shows promise. World Fish.

11(4) : 59-60.

1962. The Versaggi story is the saga of the shrimping
indu.stry. Fish Boat including Seafood Merch.
7(10). 20 pp.

1963. Breeding prawns in Japan. World Fish. 12
(5) :56.

1963. Marine biology : cultured prawns. Time SI

(13) : 43-45.
1963. Midwater trawling in East China Sea. Can.

Fish. 50(9) :23.
1963. Prawn ponds yield proteins for Singajxjre.

New Sci. 17(331) : 619.
1963. Shrimp: pinks reared from eggs to juvenile

stages. Commer. Fish. Rev. 25 ( 1 ) : 49-50.
1963. Artificial cultivation of pink shrimp from egg

to adult. Commer. Fish. Rev. 25(8) : 49-50.

1963. Small mesh net surveys in New Guinea. Fi.sh.
Newslett. (Aust.) 22(12) : 22-23.

1964. U.S. "know how" is building greatest shrimp
fishery in the we.stern hemisphere — 75,000 square
miles. Fish Boat including Seafood Merch. 9(3) :
73-75, 79. 100. 130, 131, 132.

1965. El "cultivo" de camarones. (Tlie cultivation
of shrimp. ) Mar Pesca 2 : 22-24.

19(>.5. INOS chairman describes probe into promising
shrimp and prawn stocks. S. Afr. Shipping News
Fish. Ind. Rev. 20(6) : 81-83.

1965. New electronic shrimping system from U.S.A.
Aust. Fish. Newslett. 24(2) : 24-25.

1965. Gulf prawn stocks — next step to test commer-
cial value. Aust. Fish. Newslett. 24(5) : 5, 7.

1965. Plotting prawn trawls. Aust. Fish. Newslett.
24(8) : 24-2.5.

1965. Now about those small shrimp. Fish Boat in-
cluding Seafood Merch. 10(4) : 12, 13. 14, 34, 35.

1965. Program for Gulf would study shrimp landings
fluctuations. Fish. Gaz. 82(6) : 50. 51. 73.

1965. Electronic trawl ready for marketing. Fish.
Gaz. 82(6) : 54,76,77.

196.5. Research aids the Australian crayfish and
prawn industry. Fish. News Int. 4 : 485.

19(>5. 1. U.S. firms plan African fishing ventures.
2. Extended survey to be made of shrimp resources.
Commer. Fish. Rev. 27(4) : 78-79.

1966. Ross go after Gulf shrimp. Simrad Ek;ho 15,

p. 5.
1966. There's no rest for the weary shrimp. Fish.
Gaz. 83(3) : 14-15, 51-52.
Abnold. Edgar L., Ray S. Wheeled, and Kenneth N.
Baxter.

1960. Observations on fishes and other biota of East
Lagoon, Galve.ston Island. U.S. Fish Wildl. Serv.,
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Audouin. J.

1965. Repartition bathym^trique des crevettes sur
les cotes algeriennes entre les lies Zaffarines et les
lies Habibas. Oomm. Int. Explor. Sci. Mer
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Avila, Quinto, and Harold Loesch.

1965. Identification de los camarones (Penaeidae)
juveniles de los e.steros del Ecuador. Bol. Cient.
T6c. (Guayaquil), 1(3) :24pp.

Bainbridge. Richard.

1961. Migrations, /n T. H. Waterman (editor). The
physiology of Crustacea 2 : 431—163. Academic
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Ball. Gordon H.

1959. Some gregarines from crustaceans taken near
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19.59. Decapoda. 8. Systematik. Geschiehte des
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und Heidelberg.
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1965. Size distribution and growth of Mctapenaeus
dobsoni Miers and their effect on the trawler catches
off Kerala. Mar. Biol. Ass. India, [Abstract 47.]
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Bas, C.

1965. Estudios de la gamba rosado o carabinero
(Aristeus antennatus). Publ. T^. Junta Bstud.
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Bates, Don H.

1957. Royal red shrimp. Sea Front. 3 : 9-13.
Baughman, Jack.

1965. Delicious royal red shrimp still wait accept-
ance. Nat. Fish, combined with Maine Coast Fish.
46(8) :37, 42.

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1963. Abundance of juvenile shrimp. In Biological

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Wildl. Serv., Clrc. 161.
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future shrimping success. Proc. Gulf Carib. Fish.

In.st., 15th Annu. Sess.. pp. 79-87.

1966. Abundance of postlarval and juvenile shrimp.
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1963. The proper zoological name of the North
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1956. Proposal to abolish prawn legal length. Fish.
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1963. Brown shrimp mortality studies. In Biologi-
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1904. Mark-recapture experiments with brown and
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116

U.S. FISH AND WILDLIFE SERVICE

Klima, Euward F. — Continued

1965. Evaluation of biological stains, inks, and
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Fish Wildl. Serv., Spec. Sci. Rep. Fish. 511, 8 pp.

1966. Shrimp behavior studies. In Annual report
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Ki.iMA, Edward F., and Joseph A. Benigno.

1965. Mark-recapture experiments. In Biological
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Klima. Edward F., and Kenneth W. Osborn.

1964. Brown and white shrimp mortality studies.
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]9.")9. A rontriliution to tlie biology of the spotted

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K.NAKi:, Boms O., James F. Mi'rdock, and James 1*.

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1958. Double-rig .shrinii) trawling in the Gulf of
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1966. Mark-recapture experiments, lii Annual re-
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Knowles, Sir Francis.

1955. Crustacean colour change and neurcsecretion.
Endeavour 14(54) : 95-104.
Koczy. V. F., M. O. RiNKEL, and S. J. Niskin.

1960. The current iwtterns on the Tortugas shrinip
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Ko.nosu, S., T. Akiyama, and T. Mori.

1958. Muscle extracts of aquatic animaJs. 2. Amino
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KosKi. Charles H.

1963. The Colorado River-Matagorda Bay study. In
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Krishnakumaran, A.

J957. Structure and chemical nature of the cuticle
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1964. Hypersaline bays as an environment of young
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1959. Parasites of the commercial shrimps, Pcnacus
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1963. Infection of commercial shrimps with spores
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Kruse, Paul J., Jr.

1966. Offshore gear research photoinstrumeutation,
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KUBO, ITSUO.

1961. Shrimps of southern parts of Osumi Penin-
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1960. On new records of five species of Penaeinae
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19.");^. A preliminary survey of tlie liottom fauna and
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1961. Utilization of maerocrustaceans for food by
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1965. Developing the Costa Rican fish industry.
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1964. New records of decapod Crustacea from the
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1960. Sporadic mass shoreward migrations of de-
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1

118

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LoEscH, Harold, and Quinto Avila — Continued

1966. Observaeiones sobre la presencia de camaroues
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1966. Estudios sobre las iioblaciones de camaron
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1958. An ecological survey of the West African ma-
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1965. Shrimp potential of the eastern Gulf of Guinea.
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1965. Mariculture — its recent development and its
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1960. A useful method for collecting Crustacea.
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1963. Problems of sea farming aren't all technical.
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1945. Where all those big shrimp come from.
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1962. Pho.sphorus content of some fishes and shrimp
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1957. La gamba y los crustaceos comestibles de la
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1966. Seasonal variation in the size of larvae of the
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1961. Report to the government of Brazil on devel-
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1960. A first appraisal of the landing and mechanism
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1960. Design and mass production of shrimp trawl-
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1965. Dispersion and growth of young brown shrimp.
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1965. Biological and taxonomic notes on the blue
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1962. Catalogue des crustac^s d^capodes brach-
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1962. La crevette "bresilienne" (Penaeus dunrarum
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1958. Shrimp re.search by the U.S. Fish and Wild-
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1963. Realism in the management of estuaries. Ala.
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1961. Les peches maritimes en Haiti. FAO Ex-
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1966. An investigation of the palatability of marine
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1963. Fisheries progress in Colombia. Proc. Gulf
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1962. Shrimp research in Louisiana. La. Conserv.
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1966. Studies of the brown shrimp, Penaeus aztecus,
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1966. Diurnal rhythm in vertical migration of
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1964. The shrimp Trachypencus similis in Tampa
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1954. Los camarones de mar Cubanos. Asesoria
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1965. Consideraciones sobre el estudio del langostino
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1961. The androgenic organ in some Indian Crustacea
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1961. The detection of spoilage In shrimp by ultra-
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1963. Storage materials utilized by starved Pcnaeus
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1965. Crustaceans. University of Michigan Press,
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1962. Farming the water pond fisheries of the Far
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1966. The effect of temperature uix)n the growth of
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1965. Effect of injected biological stains on oxygen
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ZiLBERBERQ EjCHEL, FRIDA.

1965. Notes on crustacean decapods. [Abstract]
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AXDRicH, D. v., and Z. P. 2terN-Ei,DiN.

1963. Laboratory results relating to shrimp culture.
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Allen, Donald M.

1958. Ecology of shrimp. In Annual report of the
Gulf fishery investigations for the year ending
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Galveston, Tex.

Berrt, Richard J.

1964. Forecasting shrimp abundance and fishing
success. Paper presented at Amer. Pish. Soc. 94th
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file Bur. Commer. Fish. Biol. Lab., Galveston, Tex.]

Bradley, Edward.

1965. Population studies of fin-fish on artificial shell
reefs in Corpus Christi Bay and the Upp«r Laguna
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1964, pp. 331-338.

Breuer, Joseph.

1959. Life history studies of the important sports
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1958-1959, 2 pp.

1961. An ecological survey of the South Bay area,
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1961. Life history studies of the important sports and
commercial fish of the Lower Laguna Madre. Tex.
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1960, 5 pp.

1961. A survey of the waters of Willacy County
which are affected or influenced by the Port Mans-
field Pass, jetties, or channel. Tex. Game Fish
Comm., Mar. Fish. Div. Proj. Rep. 1959-1960, 3 pp.

1962. Life history studies of the important com-
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Div. Proj. Rep. 1960-1961, 3 pp.

1964. Coordination of coastwide fln-fish investiga-
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Bboad, Carter.

1950. Pink doubloons in Key West waters! Univ.
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BuLLis, Harvey R., Jr.

1962. A current appraisal of the deepwater fishery
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Butler, Philip A.

1963. Effects of i)esticides on commercial fisheries.
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Caillouet, Chari^s W., Jr., David M. Soileau, Ronald
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1966. Some factors affecting catch of postlarval
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Cain, Stanley A.

1965. Some thoughts on the importiince of research
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Chapa Saldana, Hector.

1965. Plan de obras a desarroUar en la zona de
operacidn de la Coop. Gral. Ldzaro Cdrdenas, S.C.L.,
de E.scuinapa, Sinaloa, encaminadas al incremento
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Childress, U. R.

1961. Survey of shrimp populations and migrations
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1963. Populations of juvenile shrimp in the San An-
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1964. A study of populations of juvenile .shrimp in
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1965. A study of juvenile shrimp in the San Antonio
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Chin, Edward.

1958. The bait shrimp fishery of Galveston Bay. In
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CoMPTON, Henry.

1961. Survey of the commercial shrimp and associ-
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1962. A study of the bay populations of juvenile
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1962. Survey of the commercial shrimp and associ-
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1965. A study of tlie post-larval penaeid shrimp
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1965. Biological survey of the commercial shrimp
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130

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Mexleo. Tex. Parks Wildl. Coastal Fish. Proj.

Rep. 1904, pp. 145-157.
1966. A survey of shrimp populations in the inshore

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1962. Migration study on brown shrimp in Bay area
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1963. Biological survey of the commercial shrimp
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1963. A study of the post-larval jjenaeid shrimp
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1961. A study of the post-larval penaeld .shrimp en-
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1964. Biological survey of the commercial shrimp
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Costeli.o, T. J., Jr.

1958. Shrimp marking. In Annual report of the
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Galveston, Tex.

Day, Donald S.

1959. Inventory of invertebrate forms present with
annotations on the commercial si>ecies of shrimp.
Tex. Game Fi.sh Comm., Mar. Fish. Div. Proj. Rep.
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1959. Study of the diet of the brown shrimp. Tex.
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1961. Inventory of vertebrate forms present and rel-
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De Freitas, A. J. O.

1963. Nota preliminar sobre o camarao de Baia de
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1966. A maturity key for Penaeus duorarum Burken-
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1963. Monthly abundance and distribution of penaeid
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EwALD, Joseph J.

1963. Raising of pink shrimp from egg to adult. Gulf
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1964. Primer Informe anual al Fondo Nacional de
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1965. Programa de marcaje de camarones para el
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FUJINAGA, M.

1962. Culture of kuruma-shrimp (Penaeus japoni-
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59, 2 pp.
FuTCH, Charles R., and Dale S. Beaumakiage.

1965. A report on the bait shrimp fishery of Lee
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FBCML 65-1, 22 pp.
Goodwin, Charles B.

1961. Studies on the larval life history of the white
shrimp, Penaeus setiferus ( Linn. ) . Tex. Game Fish
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GuNTER, Gordon.

1961. The field program (shrimp). Tex. Game Fish
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1961. Shrimp landings and production of the State
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Hawley, William C, Jr.

1962. Shrimp investigation (Upper Laguna Madre).
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1963. Populations of juvenile shrimp in the Upper
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1964. Populations of juvenile shrimp in the Upper
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1964. Population studies of the sjKirts and commercial
fin-fish and forage species of the Upper Laguna
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1963, pp. 371-386.

1965. A study of the juvenile shrimp populations of
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Higman, James B., and Robert Ellis.

1955. Investigation of .sport and commercial fishing
activities in Old Tampa Bay north of Gandy Bridge.
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HOESE, HiNTON D.

1959. Hydrographic studies related to Rollover Pass

and possible effects on the fauna. Tex. Game Fish

Comm., Mar. Fish. Div. Proj. Rep. 1958-1959, 3 pp.
Idyll, Clarence P.

1950. Report on exploratory fishing for shrimp on the

Florida west coast. Mar. Lab., Univ. Miami, Rep.

to Fla. State Bd. Conserv. 9, 6 pp.
1950. Latest developments in the new Key West

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1958. Program of research on the Tortiigas shrimp

fisliery. Mar. Lab., Univ. Miami, Miami, 11 pp.

ML 6015.
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Galveston, Tex.

1964. A summary of information on the pink shrimp,
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1963. Progress reiK>rt on a study of the juvenile
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Idyll, Clarence P., E. S. Iversen, R. M. Ingle, and W. W.
Anderson.

1957. Summary of available biological information

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Idyll. Clarence P., Albert C. Jones, and D. Dimitriou.

1982. Production and distribution of pink shrimp
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Idyll, Clarence P., A. C. Jones, and E. S. Iversen.

1960. The eflec-tiveness of the Tortugas shrimp regu-
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Ingle, Robert M., Lyle St. Amant, William J. Demoran,
.losHa-H H. KuTKUHN, Terrance R. Leary, and Jack C.
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1962. Present research on .shrimp in the Gulf of
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Iversen, E. S.

1965. Tortugas shrimp and rainfall. Gulf States
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Johnson, Roy' B.

1964. A study of the juvenile shrimp populations of
the Lower Laguna Madre. Tex. Parks Wildl.
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1964. Evaluation of the effects on fin-fish popula-
tions of opening the Port Mansfield channel in the
Lower Laguna Madre. Tex. Parks Wildl. Coastal
Fish. Proj. Rep. 1963, pp. 403-411.

1965. A study of the juvenile shrimp populations of
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Jones, Albert C.

1983. Does temperature affect the abundance, of pink
shrimp larvae? Gulf States Mar, Fish. Comm.
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Jones, Albert C, D. Dimitriou, and J. Ewald.

1963. Abundance and distribution of pink shrimp lar-
vae. Mar. Lab.. Univ. Miami, Annu. Rep. July
1962-June 1963 to U.S. Fish Wildl. Serv., 5 pp.

Jones, Albert C, Dolores E. Dimitriou, Jay Ewald, and
John H. Tweedy.

1963. Distribution of pink shrimp larvae (Penaeux
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132

shelf. Gulf of Mexico. Mar. Lab., Univ. Miami,

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Jones, Albert C, C. P. Idyll, and S. Dobkin.

1961. The larvae of the Tortugas pink shrimp. Atl.

States Mar. Fi.sh. Couim. [Minutes], Apjjend. SA-2,

pp. 1-6.
Joyce, Eiiwin A.

1983. Penaeid shrimp studies of Florida's northeast

coast. [Extract.] Gulf States Mar. Fish. Comm.

Meet. March 21-22 [Minutes], pp. 5-6.
King, B. D. III.

1964. Population studies of the sports and commer-
cial fin-fish and forage species of the Matagorda Bay

system. Tex, Parks Wildl. Coa>tal Fish. Proj. Rep.

1963, pp. 311-322.
Klima, Edward P.

1966. Report — technical and feasibility study

.shrimp .survey — Gabon. [U.S,] Bur, Commer.

Fi.sh,, Branch Tech. Assistance, Washington, D.C,

23 pp.
KuTKUHN, Joseph H.

1963. Federal research on commercial shrimps in the
Gulf of Mexico — 1962. Gulf States Mar. Fish.
Comm. Meet. March 21-22 [Minutes], 4 pp.

1964. Shrimp size in relation to resource con.serva-
tion. Bur. Commer. Fish. Biol. Lab., Galveston,
Tex., 14 pp.

Leary, Terrance R.

1961. White shrimp migration in area M-6, part 2
(Copano and Aransas Bays). Tex. Game Fish
Comm., Mar. Fish. Div. Proj, Rep. 1959-1960, 7 pp.

Leary', Terrance R.. and Henry Compton.

1961. A study of the bay populations of juvenile shrimp,

Petmeus aztccim and Pcnacu.s sciifcnis. Tex. Game

Fish Comm., Mar. Fish. Div. Proj. Rep. 1959-1960,

32 pp.
Lindner, Milton J.

19.59. Estimation of natural mortality of white

shrimp, Penaeus aetifcrus, and some implications.

Address : Shrimp As.s. Amer., Mexico City. 14 pp.

[On file Bur. Commer. Fish. Biol. Lab., Galveston,

Tex.]

LONOHURST, A. R.

1981. Report on the fisheries of Nigeria. Fed. Fish.

Serv,, Min, Econ. Develop., Lagos, 42 pp.
Martinez, Rudy.

1981, Shrimp investigation (Upper Laguna Madre).

Tex. Game Fish Oomm., Mar. Fish. Div. Proj. Rep.

1959-1960, 4 pp.

1962. Survey of commercial shrimp populations in
Corpus Christi, Nueces and Oso Bays. Tex. Game

Fish Comm., Mar. Fish. Div. Proj, Rep. 1960-1961,
5 pp.

1983. Populations of juvenile shrimp in the Corpus
Christi Bay complex. Tex. Game Fish Comm.,
Coastal Fi.sh. Proj. Rep. 1961-1962, 6 pp.

1964. A study of populations of juvenile shrimp in
the Cori>us Christi Bay complex. Tex. Parks
Wildl. Coastal Fish. Proj. Rep 1963, pp. 105-110.

19(54, Population studies of the .sports and commer-
cial fin-fish and forage .species of the Corpus Christi

U.S. FISH AND WILDLIFE SERVICE

Martinez, Rudy — Continued

Bay system. Tex. Parks Wikil.. Coastal Fish. Proj.
Rep. 1963, pp. 355-370.
1965. A study of iiopulations of juvenile shrimp in
the Corpus Christi Bay complex. Tex. Parks
Wildl., Coastal Fish. I'roj. Rep. 1964, pp. 107-116.

MOFFETT, A. W.

1964. A study of the Texas Bay populations of ju-
venile shrimp, Pcnacus aztecus, Pcnacns setiferus,
and Pcnacus duoranim. Tex. Parks Wildl., Coast-
al Fish. Proj. Rep. 1963, pp. 1-49.

1964. A study of the juvenile .shrimp populations
of the Galveston Bay system. Tex. Parks Wildl.,
Coastal Fish. Proj. Rep. 1963. pp. .51-67.

1965. A study of the Texas Bay populations of ju-
venile shrimp. Pcnacus aztecus, Pcnacus sctifcrus,
and Pcnacus dnorariim. Tex. Parks Wildl., Coast-

. al Fish. Proj. Rep. 1964, pp. 1^5.

1965. A study of the juvenile shrimp iwpulatious of
the Galveston Bay system. Tex. Parks Wildl.,
Coastal Fish. Proj. Rep. 1964, pp. 47-70.

1966. A study of the Texas shrimp populations.
Tex. Parks Wildl., Coa.«tal Fish. Proj. Rep. 1965.
pp. 1-30.

More, Bill.

1964. Population studies of the sports and com-
meroial fin-fish and forage species of the Galves-
ton Bay .system. Tex. Parks Wildl., Coastal Fish.
Proj. Rep. 1963, pp. 281-309.

MUNRO, GEORdE .1.

1965. A study of the juvenile shrimp populations
of the Matagorda Bay system. Tex. Parks W'ildl.,
Coastal Fish. Proj. Rep. 1964, pp. 71-SS.

196.5. A study on the effects of the closure of Brown
Cedar Cut. Tex. Parks Wildl., Coastal Fish. Pioj.
Rep. 1964, pp. 42.5-434.
MuNRO, J. L., A. C. .Tones, and D. Dimitriou.

1965. Abundance and distribution of the larvae of
the pink shrimp (Pcnacus duo-rarum) on the Tortu-
gas Shelf of Florida. In.st. Mar. Sci., Vniv. Miami,
Final Rep. to U.S. Bur. Commer. Fish., .52 pp.
Murray, F. A.

1964. A study of i)opulations of juvenile shrimp in
the Matagorda Bay area. Tex. Parks Wildl.,
Coastal Fish. Proj. Rep. 1963, pp. 69-78.
Murray, F. A., and A. W. Moffett.

1963. Populations of juvenile shrimp in the Mata-
gorda Bay complex. Tex. Game Fish. Comm.,
Coastal Fish. Proj. Rep. 1961-1962, 7 pp.
OSBORN, Kenneth W.

1963. Populations of juvenile shrimp in the Lower
Laguna Madre. Tex. Game Fish Comm., Coastal

Fish. Proj. Rep. 1961-1962, 7 pp.
Pakrasi, B. B., p. R. Das, and S. C. Thakurta.

1964. Culture of brackish-water fishes in impoiind-
ments in West Bengal. India. Iiidn-Pac. P'ish.
Counc, 11th Sess. Occas. Pap. 66/8, Doc. IPFC/C/64
Tech. 19, 13 pp.

Pullen, Edward J.

1961. A checklist of invertebrate animals; abun-
dance and distribution with regards to hydrographic
co:iditions (I'pper Galveston Bay). Tex. Game

Fish Comm., Mar. Fish. Div. Proj. Rep. 1959-1960,
14 pp.

1963. A study of the Bay and Gulf populations of
shrimp : Penacus aztecus, Pcnacus sctifcrus, and
Penaeus duorarum. Tex. Game Fish Comm.,
Coastal Fish. Proj. Rep. 1961-1962, 53 pp.

1963. A study of the juvenile shrimp populations,
Pcnacus aztecus and Penaeus sctifcrus, of Galves-
ton Bay. Tex. Game Fish Comm., Coastal Fish.
Proj. Rep. 19(>l-lt»62, 23 pp.

1963. Migration study on brown shrimp. Penaeus
aztecus (Ives), in the Lower Laguna Madre. Tex.
Game Fish Comm., Coastal Fish. Proj. Rep. 1961-
1962, 8 pp.

Raitt, D. F. S., and D. R. Niven.

1965. Preliminary report on the prawn resources of
the Nigerian continental shelf. Int. Counc. Explor.
Sea, Atl. Comm. (Attention Shellfish Comm.), 8 pp.

1966. Exploratory prawn trawling in the waters off
the Niger delta. UNESCO, FAO and OAU ( Results
of ICITA and GTS) [Abstract 17.] Symp. on
Oceanogr. and Fish. Resour. of the Trop. Atl., Abid-
jan, Oct. 20-28.

Renfro, William C.

1959. Checklist of the fishes and commercial shrimp

of area M-2. Tex. Game Fish Comm., Mar. Fish.

Div. Proj. Rep. 1958-1959, 30 pp.
RiNGO, Robert D.

1964. Distribution and abundance of postlarval and
early juvenile stages of the brown shrimp (Pcnacus
aztecus Ives) in Galveston Bay. Paper given at
meeting of S. Div. Amer. Fish. Soe., Oct. 18-21, 14
pp. [On file Bur. Commer. Fish. Biol. Lab., Galves-
ton, Tex.]

St. Amant, Lyle S.

1966. Review : the shrimp fishery nf the Gulf of
Mexico (GSMFC informational bulletin No. 3 ma-
terial). Gulf States Mar. Fish. Comm. Meet.,
Biloxi, Miss. Mar. 17-18 [Minutes], pp. 24-25.

St. Amant, Lyle S., Robert M. Ingle, and G. Robert

LUNZ.

1963. Commercial shrimp or fi.sh culture - panel.
Gulf States Mar. Fish. Comm. Meet. Oct. 17-18
[Minutes]. 4 pp.
Schultz, Ronnee L.

1962. A survey of commercially important shrimp in
the Aransas-Copano Bay area. Tex. Game Fish
Comm., Mar. Fish. Div. Proj. Rep. 1960-1961, 5 pp.

1962. Survey of the invertebrate species present in
Aransas and Copano Bays. Tex. Game Fish
Comm., Mar. Fish. Div. Proj. Rep. 1960-1961, 12 pp.

1962. A survey of the invertebrate species present in
Mesquite Bay and Cedar Bayou Pass. Tex. Game
Fish Comm., Mar. Fish. Div. Proj. Rep. 1960-1961,
16 pp.

1962. Vegetation found in association with shrimp
(Aransas and Copano Bays). Tex. Game Fi.sh
Comm., Mar. Fish. Div. Proj. Rep. 1960-1961. 2 pp.

1963. A study of populations of juvenile shrimp in
the Aransas Bay complex. Tex. Game Fish Comm.,
Coastal Fish. Proj. Rep. 1961-1962, 10 pp.

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ScHULTZ, RoNNEE L. — Continued

1963. Population studies of the sports and com-
mercial fin-fish and forage species of the Aransas
Bay system. Tex. Game Fish Comm., Coastal Fish.
Proj. Rep. 1961-1962, 24 pp.

1964. A study of populations of juvenile shrimp in
the Aransas Bay complex. Tex. Parks Wildl.,
Coastal Fish. Proj. Rep. 1963, pp. 91-104.

1964. Population studies of the sports and com-
mercial fin-fish and forage species of the Aransas
Bay system. Tex. Parks Wlldl., Coastal Fish. Proj.
Rep. 1963, 335-354.

1965. A study of the juvenile shrimp populations of
the Aransas Bay system. Tex. Parks Wildl., Coast-
al Fish. Proj. Rep. 1964, pp. 97-105.

Shahe3;n, a. H.

1965. Shrimp fishery in Lake Menzalah. Cons. G§n.
Peches MMiter., 8th Sess., Doc. Tech. 36, 26 pp.

SHIDLiai, JON K.

1961. Preliminary survey of invertebrate species
(Galveston Bay). Tex. Game Fish Comm., Mar.
Fish. Div. Proj. Rep. 1959-1960, 15 pp.
1961. Interim shrimp study (Galveston Bay). Tex.
Game Fish Comm., Mar. F1.sh. Div. Proj. Rep. 1959-
1960, 19 pp.
SoiLEAU, David M.

1965. Diurnal fluctuations in abundance of postlarval

penaeid shrimp near Cheniere la Croix, Marsh

Island, Louisiana. Paper presented at Annu. Meet.

S. Div., Amer. Fish. Soc, Tulsa, Okla., Oct., 7 pp.

Stevens, James R.

1961. Study of the commercial shrimp of area M-1
(Sabine Lake). Tex. Game Fish Comm., Mar. Fish.
Div. Proj. Rep. 1959-1960, 5 pp.

Tabb, Dubbin C.

1958. Report on the bait shrimp fishery of Biscayne
Bay, Miami, Florida. Mar. Lab., Univ. Miami, Rep.
to Fla. State Bd. Conserv., 12 pp., ML 6030.

1963. A summary of existing information on the
fresh-water brackish-water and marine ecology of
the Florida Everglades region in relation to fresh-
water needs of Everglades National Park. Mar.
Lab., Univ. Miami, Rep. to Supt. Everglades Nat.
Park, 152 pp., ML 63609.

1965. Estuaries and fisheries. Gulf States Mar. Fish.
Comm. Meet. Oct. 6-8 [Minutes], 3 pp.
Tabb, Durbin C, and David L. Dubbow.

1962. Biological data on pink shrimp, Penaeus

duorarum, of north Florida Bay and adjacent estu-
aries in Monroe County, Florida, September 1957-
March 1962. Mar. Lab., Univ. Miami, Rep. to Fla.
State Bd. Conserv., 89 pp., ML 62239.
Thomas, D.

1966. Prawn fishing in Nigerian waters. UNESCO,
FAO and OAU (Results of ICITA and GTS) [Ab-
stract 24.] Symp. on Oceanogr. and Fish. Resour.
of the Trop. Atl., Abidjan, Oct. 20-28.

1966. Some observations on the catch composition
when fishing with different types of trawls off
Lagos. UNESCO, FAO and OAU (Results of
ICITA and GTS) [Abstract 25.] Symp. on Oceanogr.
and Fish. Resour. of the Trop. Atl., Abidjan, Oct.
20-28.
Thompson, John R.

1964. Shrimp explorations in the southwestern Carib-
bean. (Comments and film.) Gulf States Mar. Fish.
Comm. Meet, Oct. 15-16 [Minutes], 3 pp.
Thompson, Seton H.

1962. Expanded shrimp research program. Gulf
States Mar. Fish. Comm. Meet. Oct. 18-19
[Minutes], 4 pp.
[U.S.] Bureau of Commercial Fisheries.

1964. Tortugas pink shrimp stocks and the Ever-
glades estuaries. U.S. Fish Wildl. Serv., Bur.
Commer. Fish. Reg. Off., Region 2, St. Petersburg,
Fla., 45 pp.

United States Embassy, Mexico.

1959. Information of the shrimp industry of
Honduras. 3 pp.
United States Embassy, San Salvador.

1965. Shrimp industry 1964 — El Salvador. 4 pp.
Wathne, Fred, and John K. Holt.

1964. Electrical shrimp trawl development — A status
report. May 18, 1964. [U.S.] Bur. Commer. Fish.,
Gear Res. Sta., Panama City, Fla., 6 pp.
Williams, Austin B.

19&1. A postlarval shrimp survey in North Carolina.
N.C. Dep. Conserv. Develop., Div. Commer. Fish.,
Spec. Scl. Rep. 3, 5 pp.
Wyatt, Bruce.

1959. Movements of the white shrimp, Penaeus
sctiferus, from Copano Bay. Tex. Game Fish
Comm., Mar. Fish. Div. Proj. Rep. 1958-1959,
13 pp.

134

U.S. FISH AND WILDLIFE SERVICE

U.S. GOVERNMENT PRINTING OFFICE : 1969 0—356-411

FOOD, GROWTH, MIGRATION, REPRODUCTION, AND ABUNDANCE OF
PINFISH, LAGODON RHOMBOIDES, AND ATLANTIC CROAKER, MICRO-
POGON UNDULATUS, NEAR PENSACOLA, FLORIDA, 1963-65

By DAVID J. HANSEN, FISHERY BIOLOGIST

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL FIELD STATION

GULF BREEZE, FLORIDA 32561

ABSTRACT

The abundance, growth, age composition, food, mi-
gration, and reproduction of the two species were
studied at two locations for each species from August
1963 to December 1965. The materials comprised 22
fish collections at each station, taken in about 500
hours of trawling.

The stomach contents of 3,577 piniish and 2,520
Atlantic croakers indicated that pinfish are omnivorous
and croakers carnivorous. Principal foods were vegeta-
tion, crustaceans, and polychaetes for pinfish and
annelids, fish, and arthropods for croakers. Types of
food in pinfish stomachs were similar at all sizes and
seasons, but the relative amount of each type differed
by season and size of fish. Foods in croaker stomachs
differed at the two stations but were similar from year
to year. The average food volume in the stomachs varied
with time of year, location, and fish size. Volumes of

food in stomachs of both species decreased when the
fish moved from the estuary.

Length-frequency distributions can be used to
estimate age in both species. Pinfish, and possibly
croakers, form annuli on their scales. Growth of pinfish
and Atlantic croaker varied from year to year.

Some fish of both species had developing gonads in
the fall of their first year of life and may spawn. Both
species migrate offshore in the fall to spawn. The fry
and some adults return to the estuary in the winter
and spring.

Abundance of pinfish and Atlantic croakers was
highest in late spring and early summer. Pinfish at
both stations and croakers at one station were less
abundant in 1964 than in 1963 or 1965. Yearly differences
in abundance of croakers were not large at the other
location.

Pinfish, Lagodon rhomboides, and Atlantic
croaker, Mlcropogon undulafus, are -two of the
most abundant species of fish in the Pensacola area
and other estuaries in tlie Southeastern States. The
life history of pinfish from areas other than Pensa-
cohi has been investigated by Reid (1954), Kilby
(1955), Caldwell (1957), and others; and that for
Atlantic croaker has been studied by Pearson
(1928), Hildebrand and Cable (1930), Wallace
(1940), Gunter (1945), Haven (1957 and 1959),
and others. The purposes of the present study were
to investigate the life histories of these species in
the Pensacola Estuary and to contribute to the gen-
eral knowledge of the biology of these fishes.

Published November 1969.

FISHERY BULLETIN: VOL. 68, NO. 1

DESCRIPTION OF THE STUDY AREA

The "Pensacola Estuary" (so termed for con-
venience) has an area of about 370 km.^ ; it encom-
passes three bays (two of which are shown in fig.
1 ) and a sound. The estuary supports commercially
liarvested stocks of fisli and sliellfish.

Two stations in the lower estuary were selected
for study of pinfish. The sandy bottom at both
supports a dense growth of grasses — predomi-
nantly turtle-grass, Thalassia testudinum, and sea-
grass, Ruppia inaritima. Station I is on the north
side of Santa Rosa Sound across from Sabine
Island, site of the Bureau of Commercial Fisheries
Biological Field Station, Gulf Breeze, Fla. ; station
II is on the south side of Pensacola Bay. Average
depth at mean low water is 3.0 m. at station I and

135

i

87° 20" W.

30° 35- N.

30° 30"

30° 25"

30° 20'

SANTA ROSA ISLAND—"

GULF OF MEXICO

-I L

Figure 1. — Location of sampling stations in the Pensacola Estuary for pinflsh (I and II) and Atlantic croaker

(III and IV).

136

U.S. FISH AND WILDLIFE SERVICE

2.5 m. at station II. Salinities at both stations
ranged from 4 to 31 p.p.t. and averaged 23 p.p.t.
at station I and 24 p.p.t. at station II. Water tem-
peratures were similar at both stations, ranging
from 9° to 30° C. and avei^aging 23° C.

Two locations in the upper estuary were selected
for study of Atlantic croakers — station III, off the
eastern shore of Escambia Bay, near Trout Bayou,
and station IV, oft' the western shore of the bay.
The bottom at both is predominantly mud; at-
tached vegetation is lacking, but station III has
isolated oyster reefs. Average depth at mean low
water is 2.5 m. at station III and 2.0 m. at station
IV. Salinities ranged from to 29 p.p.t., average 15
p.p.t., at station III and from to 27 p.p.t., average
12 p.p.t., at station IV.

MATERIALS AND METHODS

Collections were made with a 5-m. otter trawl of
12-mm. bar mesh. This trawl is the standard "try
net" used by commercial shrimj^rs in Pensacola
Bay to find commercial quantities of shrimp. The
trawl was pulled behind the ll-in. research vessel
Dolphin at about 2.5 knots.

All stations were visited 22 times from August
1963 to December 1965; usually 10 trawl hauls (30
minutes) were made at each Atlantic croaker sta-
tion and 30 hauls (15 minutes) at each pinfish
station. Trawling usually began in the middle of
the montli and lasted 7 days (not necessarily con-
secutive). The number and duration of hauls were
selected to give a reliable estimate of fish abun-
dance. In periods when fish were not abundant the
number of trawl samples was reduced to less than
half that during periods of abundance.

Treatment of both species after capture was simi-
lar. On the boat they were counted, measured to the
nearest millimeter of standard length, and when-
ever possible 50 fisli from each 25-mm. size group
were preserved in a mixture of 4 jDercent formalde-
liyde and sea water of 16 p.p.t. salinity. Fish were
slit open to presence innards (including stomach
and gonads). At the laboratory, preserved fish
were measured for length and weight (to the near-
est millimeter and 0.01 gram) and stomachs and
scale samples were removed.

Confidence intervals were computed for the num-
ber of fisli cauglit per trawl-haul and on the
average length of the fish. Mention of significant
differences indicates that confidence intervals, 95
percent confidence coefficient, do not overlap.

Stomach contents of fish captured at the same
time were combined by length of the fish — 14 to 75
mm. or >75 mm. — and stored in 70 pei'cent
ethanol. After identifying and sorting the contents,
I blotted them dry and determined their liquid
displacement.

Discussion of tlie volume of stomach contents
includes all of the contents but discussion of the
composition excludes unidentifiable material;
which represented 8.8 percent of the 205.8 ml. of
food from 3,577 pinfish stomachs and 25.2 percent
of the 58.4 ml. of food from 2,520 Atlantic croaker
stomachs. The unidentifiable component of the
stomach contents included small particles of
inorganic and organic detritus and food digested
beyond recognition. Reid (1954) also found large
amounts of unidentifiable material in croaker
stomachs.

Ages were determined from length- frequency
distributions and by examination of scales. The
scales were predominantly from fish at the size
range where length-frequency distributions indi-
cated a change in age. The scales were taken from
the area above the lateral line behind the opercu-
lum, stored between sheets of paper, and examined
under a monocular microscope. The distances from
focus of the scale to the annulus and to the margin
of the scale were measured to the neare.st 0.1 mm.
witli an ocular micrometer.

Tlie spawning season extends throughout the
winter (about November to March for pinfisli and
November to February for croakers) . In assigning
ages to these fish, I used January 1 of the year
following the winter of hatching as the first
birthday.

I used two methods to study the growth. First,
I used tlie differences in average lengths between
consecutive trawling periods to compute the aver-
age daily increases in length. Second, I used
measurements of scales from yearling pinfish io
compute growth increments; increases in length
after annulus formation were determined for eaeh
sampling date and used to derive daily growth for
each season.

To discover movements before spawning, I
clipped fins of 26,980 pinfish and 5,269 Atlantic
croakers. Fish from different localities were
marked differently by removal of either one or
both pelvic fins. After the marking, the fish were
kept in a tank of circulating water on the boat

LIFE HISTORIES OF PINFISH AND ATLANTIC CROAKER

137

until the next trawl-haul was completed, and only
fish that seemed healthy were released. The area of
release was not fished again for at least 15 minutes.
Fish movement could be noted if fish fin-clipped at
one station were recaptured at any of the other
three stations or at other locations sampled spo-
radically. I also marked 284 pinfish by attaching
an Atkins tag in front of the dorsal fin with
nickel wire.

I estimated numbers of eggs in ovaries by meas-
iiring the volume of eggs in both ovaries (after
most ovarian tissue had been removed) and divid-
ing that value by the average volume of an egg
as estimated from measurement of 25 eggs.

PINFISH

Pinfish are one of the dominant animals in the
fauna of vegetated areas in the lower Pensacola
Estuary. Therefore, I investigated the seasonal
and annual change in the food, growth, migration,
reproduction, and abundance at two locations from
August 1963 to December 1965.

FOOD

Pinfish were omnivorous feeders on the grass
flats where stations I and II were located. Gunter
(1945) and Reid (1954) on the Gulf of Mexico
Coast and Linton (1904) on the east coast of the
United States found a large variety of food orga-
nisms in pinfish stomachs. I identified 10 phyla of
animals and a wide variety of vegetation (includ-
ing diatoms, filamentous algae, and vascular
plants). The type of food varied witk season and
fish size (table 1), but not by station.

Vegetation contributed 40.6 percent of the total
volume of identifiable items (including sand) in
the stomachs. It was the dominant food in the sum-
mer and fall ; the amount usually increased in late
spring or early summer and decreased in the late
fall. Diatoms were most imi^ortant in fish less than
76 mm. long, and filamentous algae and vascular
plants in larger fish.

Crustaceans, polychaetes, and chordates were
dominant in pinfish stomachs in the winter and
spring. Small pinfish usually contained a higher
total number and volume of small crustaceans than
large pinfish. The crustaceans were mainly amphi-
pods, copepods, crabs, cyprids, isopods, mysids,
and shrimp. Chordates — amphioxus and (second-
arily) fish — were most abundant in large fish.
Other animals eaten in smaller amounts were
brachiopods, bryozoans, chaetognaths, echino-
derms, moUusks, and nemerteans.

The mean volume of food in pinfish stomachs
was highest during the summer and early fall
(table 2) . The increase in the volume usually began
in May or June for both size groups of fish and
came with increase in ingestion of vegetation. The
volume decreased in the fall as fish became more
carnivorous. In the fall most fish over 90 mm. long
leave the estuary. Amounts of food in the stomachs i
decrease during the spawning season, as is common
in many si^ecies of fish.

The mean volume of food in pinfish stomachs
was generally low and nearly constant from late
fall until late spring, except for a short-term in-
crease in February, when large numbers of caprel-
lid amphipods and polychaetes were found in
stomaclis of small fish.

Table 1. — Percentage of lolal volume contributed by differ en
items in pinfish stomachs collected in the lower Pensacola
Estuary at stations I and II in different seasons, 1963-66

Fish length class, season, and number of stomachs

1

Items in

<76

mm.

76-173

mm.

stomachs

All

Spring Sum-

Fall

Win-

Spring
(l84)

Sum-

Fall

Win-

(3677)

(537)

mer

(570)

ter

mer

(675)

ter

(887)

(122)

(683)

(19)

Pet-

Per-

Per-

Per-

Per-

Per-

Per-

Per-

Pet-

ant

cent

cent

cent

cent

cent

cent

cent

cent

Crustaceans -

68.3

2.8

21.7

44.8

8.7

4.6

5.6

24.9

26.9

Polychaetes

. 17.3

1.0

2.9

43.4

8.0

4.0

4.0

19.4

9.9

Chordates. -

3.1

1.6

1.1

10.8

12.6

2.0

2.9

31.3

6.6

Vegetation--

4.6

87.2

66.6

.9

21.9

66.4

66.6

23.1

40.6

Sand. -

12.9

6.7

6.6

.0

44.4

18.9

29.6

.2

13.8

other'

3.8

.8

1.2

. 1

15

4.1

1.4

1.1

2 2

1 Numbers of stomachs from both stations are shown in parentheses.

2 Other items include brachiopods, bryozoans, chaetognaths, echlnoderms,
moUusks, and nemerteans.

Table 2. — Average volume of stomach contents of small
and large pinfish collected in the lower Pensacola Estuary
at stations I and II in the months of sampling, 1963-65

Fish length class

Month

<76 ram.

76-173 mm.

Stomachs Stomachs

Examined Average Examined Average
contents contents

January

February...

March

April

May

June

July

August

September- -

October

November..

No.

Ml.

No.

Ml.

32

0,01

1

O07

SO

.05

18

.08

6

.01

2

.08

341

.01

111

.07

190

.01

71

.11

326

.02

174

.11

296

.03

214

.12

265

.06

295

.14

183

.03

239

.07

228

.04

289

.08

169

.01

47

.03

138

U.S. FISH AND WILDLIFE SERVICE

AGE AND GROWTH

Pinfish were aged by using length- frequency
data and by examination of scales. Length fre-
quencies have been used to age pinfish (Caldwell,
1957) but scales have not. Pinfish from the two
stations were of similar lengths ; therefore, length-
frequency data for the stations were pooled (fig.
2). The bimodal length- frequency distribution in-
dicates at least 2 year-classes of jDinfish.

Average length of pinfish at annulus formation,
as determined by scale measurements, was similar
to the average length of fish measured in early
spring. Most of the annuli formed in April of both
196J: and 1&65. The percentage of yearling fish that
showed an annulus in different months in 1964 and
1965 (data combined) were as follows (number of

fish in parentheses) : January — 12 percent (57) ;
February — 13 percent (85) ; March — percent
(2); and early May — 100 percent (42). Back-
calculation of fish lengths showed that the 1963
and 1964 year classes formed a year-mark at aver-
age lengths of 61 and 78 mm., respectively. Fish
from tliese year classes were at this size as yearlings
in March or April. The average length of fish
entering their tliird year of life was 127 mm. (15
fish) at the time of annulus formation.

The average size of pinfish varied during the
different years (table 3). Yearly differences in
average size result from a number of factors such
as differences in hatching time and growth rate.
Standard lengths of fish caught by trawling and
seining during the study were 13 to 152 mm.; fish

>-
o

z

UJ

3

o

UJ
DC
li.

o

IT

30
10

30

10
30
10

40
20

I 30

UJ

O 10
o

UJ

u- 10

^20

)^ 10
oc

UJ

Q. 20

10

20
10

30 50 70 90 110
STANDARD LENGTH (MM.)

■i I

FEBRUARY

I96S

N=33

MARCH 1965

MAY (EARLY) 1965
N=2A52

MAY (LATE) 1965
N = 3|972

SEPTEMBER 1965
N = 1,723

OCTOBER 1965
N = l/»20

DECEMBER (EARLY) 1965
N=262

10 30 ' 50 70 90
STANDARD LENGTH (MM.)

150

Figure 2.-

-Length-freqnency distribution of pinfish caught in the lower Pensacola Estuary at stations I and II,

1963-65.

LIFE HISTORIES OF PINFISH AND ATLANTIC CROAKER

139

Table 3. — Standard lengths of pinfish of age-groups 0, I, and II in the lower Pensacola Estuary at stations I and II, 1963-65

Date

Age-group

Age-group I

Age-group II

Fish

Length

Fish

Length

Fish

Leng
Average

h

Average

Range

Average

Range

Range

Num\
1,316

er Mm.
60
67

14 .

22 .
39

57
68
76
80
77
72

30 .

""""28""

42
48
64
59
64
68
71
20

Mm.

44-102
47-107

'"'21-60"
42- 79
62-93
50- 94
60-101
59-109
53-110

"""i9^'32'
26- 69
28-78
33-94
35-105
42-109
45-110
49-116
14- 22

Numbe
56
67

38

336

771

65

62

84

25

33

2

82
63
21
00

49

17

37

264

r Mm.
118
117

47
56
82
100
109
116
112

81
78
96
102
112
118
120
123
121
60

Mm.

105-145
107-145

43-83
43- 79
61-1)3
81-130
91-140
96-133
102-128

"69^ '97"
77- 79
76-116
77-111
97-130
113-125
110-137
113-139
112-146
47- 92

Number

.

1

2
2

fl

1

2

2
1

Mm.

128';.';

132
136

134';;;

137
136
136
141 ...

Mm.

2,642

1

1

1.008

1, 567

129-136

829

136-137

438

362

270
132

1

6

2, 369

3,917

136-138

3,098

131-143

2, 623

136-136

2,414

1,706

1,383

8

ms

August 30-September 6

October 29-November 1

1964

January 10-15

FelHuary 28-March3.-.

May 12-14.

June29-July 1.

August 3-5.

August 31-September 2.

September 28-30

October 30-Novemt)er 3

November 23-25 -

1965

January 12..

March3

March 29

May 6-12..

June 1-3 -

June 25-29-

August 2-4 . -

August 30-September 1

September 22-24

October 26-27

December 6-8

caught at the sampling stations were 14 to l-tfi mm.
long.^

Pinfisli growth rates computed from changes in
lengths between consecutive trawling periods
varied with age group and season. Daily increase
in length averaged 0.19 mm. for 0-group pinfish
and 0.12 mm. for yearlings. Growth of both age
groups slowed as the seasons progressed from
spring to winter. Daily increase in length of
0-group pinfish averaged 0.32 mm. in the spring,
0.23 mm. in summer, and 0.01 mm. in fall; yearling
pinfish averaged 0.32 mm. in the spring, 0.21 mm.
in summer, —0.04 mm. in fall, and —0.02 mm. in
winter. Caldwell (1957) also observed maximum
growth in the spring and negligible gro\\-th in the
fall and winter.

Annual growth rate of yearling pinfish, esti-
mated from increase in length after annulus for-
mation, was closely similar to that based on
increase in measured lengths, but seasonal growth
rates determined by the two methods ditfered.
Annual increase in length computed from scale
measurements a\'eraged 0.14 mm. per day, and
seasonal increases averaged 0.12 mm. per day in
tlie spring, 0.14 mm. in the summer, 0.20 mm. in
the fall, and O.09 mm. in the winter.

1 standard length = 0..S5 forit length or 0.7S total length on the
basis of measurements of 100 fish, 44 to 101 mm. long.

MIGRATION AND REPRODUCTION

Limited data on estuarine movements of pinfish
were obtained from recaptures of fin-clipped or
tagged fish. Of 2(1,980 pinfish fin-clipped. 234
(0.87 percent) were recaptured at the area of orig-
inal capture during the trawling period in which
they were released and only 47 (0.17 percent) were
recovered 1 month or more after marking. There
could be several reasons for the low recapture
rates. The proportion of the population marked
was small, the marking mortality was high, or
unmarked fish from other areas were moving in.
Of the 47 fish recovered 1 month or more after
marking, 39 were caught at tlie station of release,
and eight had moved either from station I to
station II or from station II to station I (five did
.so in tiie 3 principal months of the spawning mi-
gration — August, September, and October). Of
284 pinfish tagged in April 19(i4, two were recap-
tured — one in July about 125 m. from wliere it was |
tagged and the other in Octol^er about 3 km. closer]
tothe mouth of the bay.

On the basis of results of trawling and seining,!
I believe that most pinfish remain over the grass |
flats where they live in the spring until tliey
migrate out of the estuary in late summer and I
fall. Most appear to move very little in the summer, !
but a few may wander over the grass flats. Fish j

140

U.S. FISH AND WILDLIB'E SPmVICE

may congregate in response to abundance or
scarcity of food during this time but schools are
not formed.

At the start of the spawning migration into the
Gulf of Mexico, however, the pinfish school in
large numbers. These schools seem to consist of
fish of the same age. Large numbei"s of pinfish cap-
tured in Chesaioeake Bay in October, as noted by
Hildebrand and Schroeder (1927), probably were
schools of seaward migrants. Aggregations of pin-
fish have also been seen in the Gulf of Mexico
(Springer, 1957). In the late winter and spring,
I have observed schools of pinfish in Santa Rosa
Sound, Fla., that were probably returning from
the Gulf of Mexico. Most of these fish were in their
second year of life. Few fish live to reenter the
estuary in their third year.

The stage of gonad development before migra-
tion varied. In most years, maturation of gonads
l)robably takes place during the migration or
while the fish are at or near the offshore spawning
site. In October 19ti5, when most fish over 80 mm.
were mature enough to permit determination of
sex, the gonads ranged from the late stage 1 to the
late .stage 3 of Homans and Vl-adykov (1954) —
gonads growing in size; yellow, opaque eggs
microscopic to visible, and testes pinkish to flesh-
colored or wliite and slightly distended. None liad
gonads that would produce milt or eggs wlien

pressed (stage 4 or 5) . Because the examination of
scales showed that most fish under about 110 mm.
were in their first year of life, it is likely that some
0-group fish and all yearling pinfish spawn.

Eight pinfish 111 to 152 mm. long had ovaries
with eggs that were mature enough for counting;
eggs in smaller fish were too small to count accu-
rately. Tlie diameters of eggs were 0.09 to 0.66 mm.
(average 0.38) and the estimated numbers of eggs
were 7,700 to 39,200 (average 21,600). Caldwell
(1957) examined a pinfish 157 mm. long which
had an estimated 90,000 eggs that averaged about
0.5 mm. in diameter.

ABUNDANCE AT THE SAMPLING STATIONS

Pinfish are present in moderate numbers in the
deejier parts of Pensacola Bay in the summer;
they are most abundant in the southern part of the
estuary in extensive flats covered witli turtle grass.
Reid (1954) and Kilby (1955) also observed that
l)infish were most numerous in vegetation along
the Gulf Coast of Florida. Pinfisli are distributed
unevenly on the flats, as they tend to aggregate in
response to tlie environment — concentrations of
food especially attract them.

Despite the wide confidence limits on the average
number of fish caught, sea.sonal trends are clearly
evident ( table 4) . Because the periods of maximum
and minimum al»undanc<>, and monthly changes in

Tablk 4. — Pinfish caught per 15-minuie trawl-haul in the lower Pensacola Estuary, 1963-66 '

Date

Station I

Station II

Averages

both
stations

Average Confidence

interval 96 percent

Range

Average Confidence

interval 96 percent

Range

August 30- September 6

196S

Number
312

Number
183-441
35- 96

0- 3

1- 7
11-28
11-114

4- 18

9- 19
6- 14
3- 10
1- 7

0- 2 "

0- 4
32-84
82-157
98-186
61-138
26- 62
15-29
13-26

3- 12

Number
5-791
0-263

0- 23
0- 40
0- 97
1-621
0- 77
0- 45
0- 40
0- 33
0- 43

' "^ 2

0- 6
0-208
0-299
4-409
3-326
1-123

1- 83
0- 71
0- 61

Nu mber
66
59

JO
8

40
110

19
4
3
3
1

-•0
6
=
29
80
231
144

30
2

Number
21-112
48- 70

= 0-

0- 16
26- 54
65-156
10- 28

3- 5

1- 4
1- 4
0- 1

0- 1
0- 18

0- 1
12- 47
49-112

177-286
75-212
52-132
45- 92
18- 41

1- 2

Number
6-219
9-146

0- 1
0-111
2-136
1-412
0- 96
0- 10
0- 20
0- 9
4

0- 1

1- 23
0- 1
0-214
0-326
3-541
0-776
0-469
0-21'i
0-137
0- 6

Number
214

October 29-November 1..

January 10-16

February 28-March 3

''1964"

66

1

"4

62

1
6

May 12-14 _ . .

19

30

June 29-July 1

. . .. . 63

86

11

14

10

- 6

4

15

August 31-Septenber 2. _
September -28-30- -

9
6

4

November 23-25

9

ms

JO

March 3 .

1

3

March 29-

1

1

May 6-12

58

44

June 1-3

120

100

June 25-29

142

186

August 2-4

99

122

August 30-September 1

40

66

September 22-24 - -

22

45

October 25-27.

19

25

8

6

' 30 trawl-hauls wore made at each station on each visit, with the following exceptions {number of hauls in parentheses): Aug. 30-Sept. 6, 1963— station I (16),
station 11 (10); Jan. 12, Mar. 3, and Mar. 29, 1966— each station (6).
' Less than 0.6.

LIFE HISTORIES OF PINFISH AND ATLANTIC CROAKER

141

abundance, were similar from year to year, I as-
sume that average catch gives a reasonably good
estimate of general abundance.

Pinfish young (0-group) and older migrants re-
turning to the estuary began to arrive on the grass
flats at both stations in late November and early
December. Trawling did not capture young fish
in numbers indicative of their actual abundance
but seining caught large numbers of them near
both stations. The migiation continued until the
population had reached a maximum by late June.
The month that young first appear seems to depend
on conditions offshore, because salinity and tem-
perature changes in the estuary show no relation to
the time of migration. Progressively fewer fish
were captured after June because of natural
mortality and emigration.

Pinfish abundance changed from year to year.
If catch in August (a month fished in each of 3
years) is used as an indicator of yearly changes in
abundance, pinfish were significantly less plentiful
in 1964 than in 1963 or 1965. Pinfish were most
numerous at station I in 1963 and at station II in
196.5. Tlie number of fish caught in the winters of
1963-64 and 1964-65 did not differ from November
to February at station I and November through
April at station II.

The numbers of fish caught at the two stations
at each sampling time were similar, differing sig-
nificantly only in August and September of each
of the 3 years. This period marks the start of mi-
gration out of the estuary ; significant changes in
abundance might, therefore, be expected if the fish
left one station earlier than the other.

ATLANTIC CROAKER

Atlantic croakers are one of the dominant fish
in the upper Pensacola Estuary. Therefore, I in-
A'estigated seasonal and annual change in the food,
growth, migration, reproduction, and abundance
at two locations from August 1963 to December
1965.

FOOD

Atlantic croakers are carnivorous (table 5) . The
animal food in the present collections included
five phyla and numerous species. Vegetation and
sediments in some stomachs were probably taken
incidentally while fish were capturing animal
food.

142

Table 5. — Percentage of total volume contributed by different
items in Atlantic croaker stomachs collected in the tipper
Pensacola Estuary at stations III and IV in different
seasons, 1963-66

Fish length class, season, and number of stomachs

1

Items ill
stomachs

<76mm.

76-173 mm.

111

Spring

Sum

Fall Win-Spring

Sum- Fall

Win-lengths

mer

ter

mer

ter 1

2,520)

(488)

(222)

(63) (2S0)

(317)

(981) (162)

(7)

Per-

Per-

Per- Per-

Per-

Per- Per-

Per-

Per-

ceiU

cent

cent cent

cent

cent cent

cent

cent

Arthropods-.

. 35.8

3.2

4. 1 20. 6

26. 5

28. 7.

8.1

14.3

MoUusks

. 2.3

3.3

.0 .1

8.4

9.2 1.7

.0

Annelids

. 43.4

74.2

92.6 51.6

26.4

40.0 66.9

89.5

61.5

Nemerteans-

.6

1.4

.0 .0

.1

.2 .3

.0

.3

Fish

. 19.9

11.9

. 9 27. 1

35.1

17.0 17.3

.»

15.9

Vegetation . .

. 1.5

1.5

.0 .2

1.8

4.3 4.2

1,3

2.0

Sediments. -.

. 6.5

4.5

2.4 .4

1.7

1.3 2.6

1.1

I Numbers of stomachs from both stations are shown in parentheses.

Annelids were the major food except in large
fish in the spring, when fish were dominant. Pear-
son ( 1928) , who collected along the Gulf Coast, and
Roelofs (1954), on the Atlantic Coast, found that
annelids were dominant and that the other foods
listed in table 5 were present in the stomachs of
young croakers.

Fish were most common in Atlantic croakers
over 75 mm. long. At station III, fish were most
plentiful in stomaclis in the spring and summer.
At station IV, fish were most abundant in the
winter in croakers less than 76 mm. long and in
tlie spring in croakers over 75 mm.

Arthropods, chiefly crustaceans, were most plen-
tiful in small fish in the winter and spring and in
large fish in the spring and summer. The most
important crustaceans were copepods, amphipods,
isopods, mysids, shrimp, and crabs; larger forms
were most common in stomachs of large fish. In-
sects — mainly tendipedids. dytiscids, and anisop-
terans — made up 67 percent of the arthropods in
stomachs collected at station IV after heavy runoff
in the spring.

Mollusks and nemerteans were minor constitu-
ents ill the stomachs of Atlantic croakers. Mollusks
were most plentiful in stomachs of large fish in the
spring and summer.

The volume of food in croaker stomachs wixs
greatest in the winter and spring; average for
768 fish under 76 mm. long was 0.0-2 ml. and for
3-24 fish over 75 mm. long, 0.04 ml. Food volumes
decreased in the summer and fall ; for 285 fish less
than 76 mm. long the average volume was 0.01 ml.
in both summer and fall, and for fish longer than

U.S. FISH AND WILDLIFE SERVICK

75 mm., the average was 0.03 ml. in the summer
(981 fish) and 0.01 ml. in the fall (162 fish).

AGE AND GROWTH

I determined the age of Atlantic croakers by
lusing lengtli- frequency data. Fish from the two
stations were of similar lengths, except for some
segregation by size according to salinity (see next
paragraph). Length-frequency data for the sta-
tions were, therefore, pooled (fig. 3). The data
hidicated that only 18 of 19,107 croakers (less than
).l percent) were in their second year of life.

Scales may be suitable for age determination of
Atlantic croakers from the study area, but this
nethod was miacceptable for Lake Pontchartrain
isli (Suttkus, 1955). In the Pensacola Estuary,
) of 201 Atlantic croakers had what may have
)een an annulus on their scales. The age of fish

30
20
10

30
20
10

30
20
10

20

>-

10

z

UJ

20

D

o

10

UJ

K

U.

20

H

10

Z

bJ

o

20

UJ

10

0.

30

10

40

20

AUGUST 1963

OCTOBER 1963
N = 49

FEBRUARY 1964
N=50

MAY (EARLY) 1964
N=^35

JUNE 1964
N = I^IO

JULY 1964
N = 89l

- AUGUST 1964
N = 847

SEPTEMBER 1964
N = I29

NOVEMBER 1964
N = II4

JANUARY (EARLY) 1965
N = 223

"T I I I — I — I — I — I — I — I — r~
70 90 110 130 150 170

10 30 50

STANDARD LENGTH (MM.)

as indicated by scales conformed to that indicated
by length-frequency data.

Changes in the size distribution of Atlantic
croakers within this estuary occur when the larger
fish move to areas of higher salinity. A faster
growth rate in more saline waters would accen-
tuate this size difference. In June 1964, 620 croak-
ers averaged 70 mm. at station IV, and 1,290 aver-
aged 76 mm. long at station III ; in collections 8 and
12 miles below station III, 283 fish averaged about
9-1: mm. Length differences were still apparent in
July. Average lengths were 90 mm. at station IV
(149 fish), 91 mm. at station III (742 fish), and
98 mm. 12 miles below station III (155 fish).

The average size of Atlantic croakers varied dur-
ing the different years (table 6) as a result of dif-
ferences in hatching time and growth rate. In 1965,
fish arrived in the estuary earlier than in 1964;

20
10

30
20
10

30
20

10

20

§20

S 10

tr.

^"20
I- 10

z

UJ
"20

UJ 10
Q.

30
20
10

40
20

60
40
20

JANUARY (LATE) 1965
N=279

FEBRUARY 1965
N = I57

MARCH 1965
N = I23

MAY (EARLY) 1965
N = 2,269

MAY (LATE) 1965
N = 2^I2

JUNE 1965
N = 3P0I

AUGUST 1965
- N=767

SEPTEMBER 1965
N = 2I

J.

T-i — r

10 30

A

DECEMBER 1965
N = I3

T — I — I — I — I — I — I — I — I — I — I — r—
50 70 90 no 130 150 170

STANDARD LENGTH (MM.)

iQURE 3. — Length-frequency distribution of Atlantic croakers caught in the upper Pensacola Estuar.v at stations III and

IV. 1963-65.

JFE HISTORIES OF PINKISH AND ATLANTIC CROAKER

143

379-242 O - 70 - 10.

Table 6. — Standard lengths of Atlantic croakers of age-groups and I in the upper Pensacola Estuary at stations III and IV,

1963-66

Age-group

Age-group I

Date

Length

Length

Fish Average Range

Average Range

I96S Number

August 22-29-..- --- 1,291

October 21-24 -- 49

1964

January 6-14 - - - 2

February 24-27-..- - ----'-■ ---- 60

May 6-11.. - 2,336

June 22-26 - - - -• 1,909

July 27-30. --- -- 891

August 24-27 ..: --1--- ...-. -. 847

September 21-24 -- 129

October 26-29. .'--- -

December 8-10 - Ill

January5-7 220

January 26-28 - 274

February 23-March 2 - ._-,-. 157

March 22-31 - - -. 122

May 3-7 --Lj--.:. -- 2,269

May 25-28 - 2,211

June 21-24. - .- - -.■.---- 2,999

July 26-30- - 2,422

August 24-27 - - - 767

September 20-21 --- --- 21

December 1-2--- - 13

Mm.

107
117

32
38
65
76
91
94
102

Mm.

91-162

24- 40
20- 66
36-117
45-128
61-131
70-140
86-125

35

41
46

64
61
67
68
74
99
111
118
47

24- 50

17- 60
15- 64
21- 74
30- 79
34-113
34-123
51-136
68-151
93-155
106-129
38- 63

Number Mm. Mm.

--.- --.

.

1 166

- -.-

-

3 106 94-118

3 93 91- 96

5 102 94-118

-.

1 112

1 132 .-

2 163 163-173
2 164 161-168

-

-

therefore, they were larger in the winter, and from
January through August grew at a faster rate
(0.30 mm. per day in 1964, 0.36 mm. per day in
1965) so that in August they averaged 17 mm.
longer than in 1964. Growth was greatest in the
spring in 1964 and in the summer in 1965, and
maximum growth was in July in both years (0.60
mm. per day).

MIGRATION AND REPRODUCTION

Migrations of Atlantic croakers are extensive.
In December and January the young begin to
enter the estuary from spawning grounds in the
Gulf of Mexico and move to areas of low salinity.
Haven (1957) noted that these fish move up the
estuary in the salt-water "wedge" near the bot-
tom. Two days of trawling (February 10-11, 1964)
at all depths near the mouth of the Pensacola
Estuary, however, caught no young croakers.

Atlantic croakers of age-group O appeared ear-
lier and were more abundant at station IV in the
years when estuarine water temperatures were
relatively high in November and December. The
average temperatures in November-December
were : 1963—14.0° G., 1965—16.4° C., and 1964—
19.2° C. In the winter of 1963-64 the first young-of-
the-year croakers were caught in early January.
In the winter of 1964-65 and 1965-66 they ap-
peared in late November and early December (in

the greater numbers in the winter of 1964-65).
Young fish appeared first and in greatest abun-
dance in areas of low salinity (station IV). They
moved to areas of higher salinity as they grew
and appeared in the lower estuary (stations I and
II) in late spring. Fish cauglit at stations I and II
were never as small as fish captured in the upper
estuary near the beginning of the fry migrations.

Of 5,269 fin-clipped Atlantic croakers only 6
(0.1 percent) were recaptured, and only 2 of tliese
liad l)een marked at least 1 month before recap-
ture. None liad left the area of marking.

The migration of Atlantic croakers out of the
estuary begins in late summer and ends before No-
vember. All fish probably leave the estuary; no
croakers have been captured after the period of
gulfward migration until the newly hatched fish
enter the estuary.

Pearson (1928), Suttkus (1955), and Roith-
mayr (1965) foimd that, along the Gulf Coast,
Atlantic croakers spawn at the end of their second
year of life. In the Pensacola Estuary, most croak-
ers had developing gonads in the fall of their first
year of life. Most females and males examined had
well-developed gonads (stage 2 or 3 of Homans
and Vladykov, 1954). Although it is possible that
the developing eggs are retained, these croakers
may spawn in their first year of life.

Ovaries of 18 croakers, 101 to 145 mm. long,

144

U.S. FISH AND WILDLIFE SERVICE

caught in the fall of 1963, near the end of their
first year of life, had an average of 41,200 eggs.
The diameter of eggs was 0.02 to 0.72 inm. and
averaged 0.34 mm. Hildebrand and Cable (1930)
indicated that a mature egg probably has a diam-
eter less than 1 mm. The eggs in the large yellow
ovaries had fat globules.

ABUNDANCE AT THE SAMPLING STATIONS

Atlantic croakers are most abundant in low-
salinity areas in tlie Pensacola Estuary. Young
(O-groujj) enter the estuaiy in the winter and
spring and move out in the fall. Fish in the estuary
are rarely moi-e than 10 months old.

Montlily changes in abundance (table 7) are
caused primarily by migrations and, to a lesser
extent, by natural mortality. In the winter young
croakers move rapidly from the Gulf to the upper
estuary; catches were largest at the station of
lowest salinity. The number of fish increases to a
maximum in May or June. Yearly differences in
abundance were small at station III but croakers
were most numerous at station IV in 1965.

SUMMARY

Life histories of pinfish and Atlantic croaker in
tile Pensacola Estuary were studied from August
1963 to December 1965. Their food, growth, age

composition, migrations, reproduction, and abun-
dance were studied from fish collected at intervals
of about 1 month for 21/^ years. Each species was
sampled 22 times at each of two stations.

Feeding, migrations, and other aspects of the
biology of pinfish from the Pensacola Estuary
change seasonally. They spawn in the Gulf of
Mexico in winter. Young and adults enter the
estuary in the winter and spring where they con-
gregate on grass flats and feed primarily on ani-
mals — crustaceans, polychaetes, and cliordates —
and attain maximum abundance in June. From
June until the fall migration pinfish apparently
move only short, distances over the grass flats and
are primarily herbivores. The amount of food in
tlie stomachs is at its highest level at this time.
The gonads of all fish except the smaller ones in
their first year of life begin to develop in the fall ;
ovaries contain about 22,000 developing eggs. The
maturing pinfish school and leave the estuary in
the fall. Food of the remaining fish includes fewer
plants, and the amount of food in their stomachs
decreases. Usually pinfish fonn the first annulus
on their scales in April of their second year of life.

The life histoi-y of Atlantic croakers from this
area is similar to that of pinfisli. Croakers spawn
in the Gulf of Mexico in the late fall and winter,

Table 7. — Atlantic croakers caught per 30-minute trawl-haul in the upper Pensacola Estuary at stations III and TV, 1963-66'-

Date

Station III

Station XV

Average

Confidence
Interval
95%

Range

Confidence
Average Interval

95%

ms

August 22-29

October 21-24

1964

January 6-14

February 24-27 _

May 5-11

June 22-25

July 27-30-

August 24-27

September 21-24

October 26-29

December 8-10

1B66

January 5-7. -

January 26-28

February 23-Maich 2

March 22-31

May 3-7--

May 25-28

June 21-24-.. _

July26-30- -

August 24-27.

September 20-21

December 1-2

Number

107

3

6

85

102

221

93

27

4

Number

63-150

2- 6

0- 5

0- 1

0- 4

3- 8

43-127

80-124

145-297

17-170

18- 36

0- 8

Number
25-229
0- 8

'0 20-0 0-1

280 218-342 202-463

228 81-375 11-527

74 54- 94 27-110

48 21- 74 1-134

11 3- 18 1- 26

-- ----

0- 3

0- 1

1- 3

2- 14
3-172

67-172
67-436

1-378
10- 47

0- 8

Number

22

2

20

5

9

62
13
41

2

.
11

22

28

16

6

174

496

332

149

50

.

3

Number
18- 27

20-

0- 10
7- 12

37- 87

9- 21

28- 64

1- 4

1- 22

8- 36
6- 50

0- 33

1- 12
128-220
349-642
284-380

87-212
35- 65

0- 10

Range

Number

11- 34

1- 2

0- 1
0- 16
5- 16

19-100
5- 26

13- 74
0- 7

0- 38

3- 66

0- 77

0- 83

0- 26

89-320

136-801

239-408

76-363

17- 86

0- 13

Average

both

stations

Number
64

20

2
144
146
44
44

17

20

12

6

130

298

276

121

38

2

2

' 10 trawl-hauls were made at each station per month with the following exceptions (number of hauls in parentheses): Station ni, 1964— Dec. 8-10 (3); 1966—
Jan. 6 (3), Jan. 28 (4), Mar. 2 (3), Sept. 21 (5), and Dec. 2 (2); Station IV, 1965— Sept. 20 (5), and Dec. 1-2 (6).
2 Less than 0.6.

LIFE HISTORIES OF PINFISH AND ATLANTIC CROAKER

145

and the young move rapidly to the upper estuary ;
adults rarely reenter the estuary. The young arrive
earlier and are more abundant in the winter of
years of liigh water temperatures in November and
December but maximum abundance, reached in
May or June, seems to be unrelated to water tem-
peratures. The volume of food in the stomachs
of croakers is greatest during the first few months
after their arrival in the upper estuary. While in
the estuary they feed primarily on animals; poly-
chaetes are the dominant food of all sizes of fish.
Mollusks, large crustaceans, and fish are eaten in
greater amounts as croakers become larger. As
croakers grow, the larger individuals move down
the estuary causing a stratification by size along
the salinity gradient. Migration to the Gulf and
gonadal development begin in the late summer
and fall. Ovaries of fish in their first year of life
contain about 40,000 eggs.

ACKNOWLEDGMENTS

Hughey L. Jones, Nelson R. Cooley, and Philip
A. Butler of this laboratory assisted me.

LITERATURE CITED

Caldwexl, David K.

1957. The biology and systematics of the pinfish,
Lagodon rhomboides (Linnaeus). Bull. Florida
State Mus. 2(6) : 1-173.
GuNTER, Gordon.

1945. Studies on marine fishes of Texas. Publ. Inst.
Mar. Sei., Univ. of Tex. 1 : 1-190.
Haven, Dexter S.

1957. Distribution, growth, and availability of Ju-
venile croaker, Micropogon nndulatus, in Virginia.
Ecology 38 : 88-97.
1959. Migration of the croaker, Micropogon undula-
tus. Copeia 1959 : 25-30.

HiLDEBRAND, SAMUEL F.. and LOUELLA E. CABLE.

1930. Development and life history of fourteen tele-
ostean fishes at Beaufort, North Carolina. U.S.
Bur. Fish. Bull. 46 : 383-188.

HiLDEBRAND, SAMUEL F., and WILLIAM C. SCHROEDER.

1927. Fishes of Chesapeake Bay. U.S. Bur. Fish.
Bull. 43 : 1-366.

HoMANS, R. E. S., and V. D. Vladykov.

1954. Relation between feeding and the sexual cycle
of haddock. J. Fish. Res. Bd. Can. 11 : 535-542.

KiLBY, John D.

1955. The fishes of two Gulf coa.stal marsh areas of
Florida. Tulane Stud. Zool. 2(8) : 175-247.

Linton, Edwin.

1904. Parasites of fishes of Beaufort, North Carolina.
U.S. Bur. Fish. Bull. 24 : 321-428.
Pearson, John C.

1928. Natural history and conservation of redfish and
other commercial sciaenids on the Texas coast.
U.S. Bur. Fish. Bull. 44 : 129-214.

Reid, George K.

1954. An ecological study of the Gulf of Mexico

fishes in the vicinity of Cedar Key, Florida. Bull.

Mar. Sci. Gulf Carib. 4 : 1-94.
RoEiOFS, Eugene W.

1954. Food studies of young sciaenid fishes, Micro-
pogon and Leiostomus, from North Carolina. Co-
peia 1954 : 151-153.

RoiTHMAYR, Charles M.

1965. Review of industrial bottomfish fishery in
Northern Gulf of Mexico, 1959-62. Commer. Fish.
Rev. 27(1) : 1-6.
Springer, Stewart.

1957. Some observations on the behavior of schools of
fishes in the Gulf of Mexico and adjacent waters.
Ecology 38 : 166-171.
SuTTKus, Royal D.

1955. Seasonal movements and growth of the Atlantic
croaker (Micropogon undulatus) along the east
Louisiana coast. Proc. Gulf Carib. Fish. Inst.
Seventh Annu. Sess., pp. 151-158.

Wallace, David H.

1940. Sexual development of the croaker, Micropogon
undulatus, and distribution of early stages in Chesa-
peake Bay. Trans. Amer. Fish. Soc. 69: 475-^82.

146

U.S. FISH AND WILDLIFE SERVICE

U.S. GOVERNMENT PRINTING OFFICE : 1969 0—361-679

CONDITIONS RELATED TO UPWELLING WHICH DETERMINE
DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA'^

BY MAURICE BLACKBURN, RESEARCH BIOLOGIST

INSTITUTE OF MARINE RESOURCES, SCRIPPS INSTITUTION OF OCEANOGRAPHY
UNIVERSITY OF CALIFORNIA, SAN DIEGO, CALIF. 92037

ABSTRACT

Six oceanographic cruises were made oif the west
coast of southern Baja California in June through
November, 1959-66, and some of the results were com-
pared with contemporaneous fishery data on the
distribution of yellowfin tuna, Thunnus albacares,
and skipjack tuna, Euthynnus pelamis. The object
was to test the hypothesis that the tunas generally
do not aggregate in waters cooler than 20° C. even
when suitable food is abundant, but do aggregate in
warmer waters provided that suitable food is abundant.
The measure of abundance of suitable food was the
concentration of the pelagic red crab Pleuroncodes
planipes, a herbivore which is the principal component
of the tunas' diet in the Baja California region.

The results supported the hypothesis very well except
on the cruise made in June. Then the coastal upwelling
was still strong and some tuna entered waters as cold
as 17° C, but no colder, where red crabs were abundant.
Areas with temperatures 20° C. or over were very lim-
ited, and food was generally scarce in them, although
it was plentiful in the extensive areas of upwelled water
under 17° C. On each of the other five cruises, which
covered the period of decay and disappearance of up-
welling, extensive areas contained abundant food at
temperatures at and over 20° C. Tunas aggregated in
or very near those areas, and nowhere else in the cruise
region. Red crabs were most abundant in places where
their food, phytoplankton (measured as surface chloro-
phyll a), was most plentiful, and in the upwelling
season these places were areas of cool upwelled water.

The tunas aggregated at first around the edges of the
cool areas, which were rich in chlorophyll a and red
crabs. Later, when surface temperatures in the cores
of the cool areas rose past 20° C, the tunas aggregated
there as well. Eventually, after all upwelling had ceased,
the distribution of surface chlorophyll a, red crabs, and
tunas became rather uniform off the Baja California
coast.

These relations are considered to support the follow-
ing general statement of tuna ecology, for which there
was some prior justification: temperatures set limits
of total range, sometimes differently for different
species, and food supply determines distribution
within the range limits.

Tuna avoid the Cape San Lucas front when it con-
tains water below 20° C, but otherwise the front may
have no effect upon them. There is no evidence of aggre-
gation of tuna prey in the front.

As a result of the association of red crabs with phyto-
plankton (surface chlorophyll a) tuna generally occur
in the parts of the Baja California region where surface
chlorophyll a concentrations are relatively high,
provided that surface temperatures are not below 20° C.
If the region could be thoroughly and frequently
monitored for surface temperature and surface chloro-
phyll a during a tuna season, areas of probable tuna ag-
gregation could be specified. It may eventually be prac-
ticable to do the monitoring from ships, aircraft, or
satellites. It would not suffice to monitor surface
temperature only.

Most species of tunas liave a wide range in the
world's oceans. Their distribution appears to de-
pend mainly uix)n two oceanic properties: teniper-

' Contribution from the Scripps Institution of Oceanography, University
of California, San Diego, Calif. 92037.

2 This work was part of the research of the .STOR (Scripps Tuna Ocean-
ography Research) Program. It was supported by the Bureau of Commercial
Fisheries under Contracts 14-19-008-9354, 14-17-0007-139, 14-17-0007-221,
14-17-0007-306, 14-17-0007-)58, and 14-17-0007-742. Part of the cost of cruise
TO-65-1 was provided by the National Science Foundation through a grant
in support of the ship operations of the Scripps Institution of Oceanography.

Published November 1»69.

FISHERY BULLETIN: VOL. 68, NO. 1

ature, which sets limits of total range for each
species; and standing stock of animals that tuna
will eat, which determines distribution within the
range limits. This opinion is reasonable, widely
held, and supported by a large amount of infonna-
tion (Blackburn, 1965).

Much of the evidence for the hypothesis, how-
ever, is indirect. Because tunas are difficult sub-
jects for experiments, tuna ecologj' depends upon

147

comparisons between occurrences of tuna and dis-
tributions of properties as observed in the ocean.
Many of these comparisons have been based on
noneontemporaneous data. Distributions of tuna
prey have been inferred from other property dis-
tributions more often than they have been ob-
served. Different kinds of data on tuna occurrence,
some of better quality than others, have been used.
Tlie tendency has existed to compare tuna data
with environmental data on broad scales of space
and time, a procedure which is more suitable for
generating hypotheses than for testing them.

The hyixjthesis must survive tests of detailed
close comparison between tuna and environment
on narrow scales of space and time if it is to be
accepted, but very few suitable tests have been
made. The need for a good test became particularly
evident about 5 years ago, when plans were being
made for a series of oceanographic surveys of the
eastern tropical Pacific Ocean (the EASTROPAC
Expedition, 1967-68). One of the purposes of the
expedition was to identify areas, outside the limits
of existing fisheries, in which skipjack tuna,
Euthynmus ■peJ<i'mts, might be abundant. It was
necessary to know whether that purpose would be
served by measuring standing stock of tuna prey
routinely on the expedition.

The STOR (Scripps Tuna Oceanography Re-
search) Program made a series of cruises off the
west coast of southern Baja California to test the
hypothesis. This paper gives the results of the test.
The area off southern Baja California was se-
lected for the following reasons:

1. It is the area closest to the Scripps Institu-
tion of Oceanography in which both yellowfin
tuna, Thunnus alhacar'es, and skipjack tuna occur
regularly in abundance. These are the principal
species taken in American tima fisheries in the
eastern tropical Pa^^ific. The most detailed pre-
vious study of tuna ecology in the eastern tropical
Pacific dealt particularly with yellowfin tiuia
(Blackburn, 1962, 1963), but the need is now press-
ing for work on skipjack tuna as well.

2. Yellowfin and skipjack tuna move seasonally
from the tropics into the area west of Baja Cali-
fornia and then back to the tropics. This shift has
been shown by tagging experiments (Schaefer,
Cliatwin, and Broadhead, 1961 ; Fink, unpub-
lished). The northern range limits of both species
are generally in the area or south of it (fig. 1).
Property distributions in the area should, there-

fore, show which properties correspond with range
limits and which do not.

3. The food chain of yellowfin and skipjack
tuna is shorter and simpler in the Baja California
area than elsewhere in the eastern Pacific in ways
that were expected to facilitate the study. In the
other areas both tuna species consume a great vari-
ety of fishes, crustaceans, and cephalopods, most
of whicli are presumably carnivores (Alverson,
1963). Off the west coast of Baja California, liow-
ever, both tuna species feed mainly on the gala-
theid crab Pleuroncodes planipes (Alverson,
1963), which is a facultative herbivore and some-
times the dominant herbivore in the area (Long-
hurst, Lorenzen, and Thomas, 1967). P. planipes,
frequently called red crab, is commonly pelagic,
easy to collect in nets from a research sliip, and
conspicuous (easy to sort) in net catches. It is the
principal species of the micronekton — about 80
percent of the total, by volume — in the area west
of southern Baja California (Blackburn, 1968).
Boyd (1967) recently published a good illustra-
tion.

CalCOFI (California Cooperative Oceanic
Fisheries Investigations) has provided much
oceanographic information about waters west of
Baja California, through a program of seasonally
repetitive cruises that began in 1949. lATTC
(Inter- American Tropical Tuna Commission) has
been recording commercial catches of yellowfin
and skipjack tunas in the same area and elsewhere
since the beginning of 1951. Tlie lATTC tuna
data were suitable for the )>roposed stiuly, but the
CalCOFI oceanographic data were not very suit-
able because they had been obtained for other pur-
poses. The CalCOFI cruises generally coA-ered
only about half the area that yellowfin and skip-
jack occupy off Baja California (see example in
fig. 7) ; they frequently missed the period when the
tunas were most widespread in the area ; and they
seldom provided any information on phytoplank-
ton or on animals eaten by tuna. It was necessary,
therefore, to make special cruises for tuna ecology
studies. Five such cruises, together with one Cal-
COFI cruise that was equipped to serve the same
purpose, were made. They covered most of the
period of the year (in different years) when tropi-
cal tunas occur off Baja California.

The hypothesis to be tested was that yellowfin
and skipjack tunas generally do not occur in wa-
ters of surface temperature below 20° C, even

148

U.S. FISH AND WILDLIFE SERVICE

Figure 1. — Changes in latitudinal position of the 21° C s«rface isotherm and of the northern limits of commercially
caught yellowfin and skipjack tunas off the coast of Baja California and California, 1951-65.

when suitable food is abundant in those waters, but
do occur in waters of surface temperature at and
above 20° C, provided suitable food is abundant.
"Suitable food" was defined as pelagic red crab,
and "abundant" was defined as a concentration at
or above 40 ml. displacement volume per 1,000 m.^
of water. The specified temperature, prey species,
and concentration of prey are explained below.

The cruises were intended also to identify
environmental properties that determine the dis-
tribution of the red crab, which is important in
the diet of other commercial fishes as well as
yellowfin and skipjack tunas (Boyd, 1967). Noth-
ing was known about these properties except that
temperature was not one of them (Longhurst,
1967) . I thought that the properties would include
standing stock of phytoplankton or of zooplank-
ton, depending upon whetlier the red crab was
predominantly herbivorous or carnivorous in the
area studied; in the outcome it proved, as ex-
pected, to be predominantly lierbivorous (Long-
hurst et al., 1967). Further, the cruises were

intended to investigate possible relations between
the tuna-connected properties — temperature, prey,
food of the prey — and physical features of the
environment such as upwellings and fronts. The
results of those studies are included in this paper.
The range-limiting temperature was specified in
the hypothesis as 20° C. for both species of tuna,
but some deviation from it was expected. Range-
limiting temperatures for yellowfin and skipjack
have been discussed by Uda (1957), Blackburn
and associates (1962), Laevastu and Rosa (1963),
Broadhead and Barrett (1964), Blackburn (1965),
and others. It is evident from these papers that
successful commercial fishing, which requires a
fairly high concentration of the fish, seldom occurs
at temperatures below 20° C. for yellowfin tuna
or below 19° C. for skipjack tuna. Both species
can occur in waters as cool as 15° C. in some parts
of the world, however. In the eastern Pacific the
limiting temperature appears to be nearl}- always
close to 20° C. for commercial concentrations of
both species. Blackburn and associates (1962)

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

149

found that the northern range limits of the species
agreed in position with tlie 21° C. (70° F.) surface
isotherm at almost any time. Broadhead and
Barrett (1964) showed a similar agreement of
both northern and southern range limits with the
20° C. (68° F.) surface isotherm.

Figure 1 shows the kind of data that Blackburn
and associates (1962) presented for the period
1951-59, together with similar data for 1960-65.
It gives the approximate latitudinal position, in
each montli of 1951-65, of the northern limit of
commercially caught yellowHn tuna, the northern
limit of commercially caught skipjack tuna, and
the 21° C. surface isotherm. The latitudes shown
are those along the entire west coast of Baja
California and the southern part of the coast of
California. Tuna range limits are based on
lATTC catch data that are grouped by 1° squares.
They have been graphed at the midpoint of the
1° range of latitude at which the most northern
commercial catch (regardless of its amount) was
made during the montli. Temperatures for 1951-59
are from the series of monthly temperature charts
published by Eber, Saur, and Sette (1968), except
for August 1952 when CalCOFI cruise data
showed a more northward penetration of the
21° C. isotherm. Temperatures for 1960-65 are
from monthly temperature charts published by
the BCF (Bureau of Commercial Fisheries) Bio-
logical Laboratory, San Diego, Calif. Because the
BCF temperature data were contoured in inter-
vals of 5° F., including 70° F. (21° C), it was
more convenient to compare tuna limits with
21° C. than with 20° C.

As mentioned jji-eviously, figure 1 illustrates
the seasonal movement of yellowfin and skipjack
tunas along the west coast of Baja California
(and in some yeai"s, California) . It is not a spawn-
ing migration for either species (Orange, 1961;
Klawe, 1963). The timas appear west of the south-
em tip of Baja California (lat. 23° N.) in late
spring or early summer, extend their ranges north-
ward during the summer, contract their ranges
southward during the autumn and early winter,
and leave the area (except in 1958) during the
late winter and early spring. The 21° C. surface
isotherm changes position in the same way. The
positions of the isotherm and the range limits
vary from year to year in the same month, but
they generally agree closely with one another in

any particular month. It is because of this agree-
ment that I think temperature determines the
range limits. Figure 1 shows a few disagreements
which could have resulted from temperature data
or tuna data that were unrepresentative of con-
ditions within a month. The two kinds of data
were not collected together. All temperature data
ajjply to the sea surface or the upper 10 m., where
yellowfin and skipjack tunas are generally seen
and caught.

The range of skipjack tuna appears to be limited
also by a high temperature, about 28° C, and the
same temperature or a higher one may possibly
limit the range of yellowfin tuna (Blackburn,
1965, and references there). Such temperatures
seldom occur in extensive areas off western Baja
California, however.

Nothing indicates that temperature plays any
direct part in determining the patchy distribution
of the tunas within their range limits (Blackburn,
1965). According to the hypothesis being tested,
food supply is responsible for this aspect of the
distribution. The principal food organism of trop-
ical tunas off western Baja California is red crab,
as mentioned above. Alverson (1963) sorted stom-
ach contents of 567 yellowfin and 151 .skipjack
tunas taken off the west coast of Baja California
and the coast of California. The comj^osition
of the stomach contents of yellowfin tuna by vol-
ume was 78 percent red crab, 10 percent northern
anchovy, Engraidis mordax^ and 12 percent other
animals (euphausiids absent). The composition of
the skipjack tuna stomach contents was 37 percent
red crab, 28 percent northern anchovy, 19 percent
euphausiids, and 16 percent other animals. North-
ern anchovies are much more abundant off Cali-
fornia and northern Baja California than off
southern Baja California, however (Baxter, 1967;
Ahlstrom, 1967) ; in the latter area red crabs are,
therefore, probably a larger component of the
tunas' diets than Alvereon showed. Northern an-
chovies were very seldom taken on the cruises de-
scribed in this paper, jjrobably because they were
not common in the area. Euphausiids were taken
on these cruises, but it was decided not to attempt
to study their distribution in relation to that of
the tunas, for the following reasons. Euphausiids
are more difficult to sort and measure \olumetri-
cally than red crabs are; they are not routinely
catchable or observable by some of the methods

150

U.S. FISH AND WILDLIFE SERVICE

Table 1. — Concentrations of Pleuroncodes planipes, adults and juveniles {not larvae), in ml. /IC^m.^ of water strained, on

cruise TO-64-1

ILetters under kind of observation signify: M, micronekton tiaul; Z, zooplankton liaul; S, seen in tlie water. Where concentrations were measured or estimated by
more than one metiiod, the highest concentration, corresponding to the first letter, is listed]

Station No.

Kind of

Concen-

Station No.

Kind of

Concen-

Station No.

Kind of

Concen-

observation

tration

observation

tration

observation

tration

Ml.llO>m.'

MI.IIO^.'

Afl./;0»m.»

a

.... M

32

•24

Z

7

S3-.

Z

866

4

.... Z

69

26

Z

62

64...

Z

310

6...

.... Z

34

27...

z

7

m...

Z

35

.... z

7

28

z

18

66...

z

2,364

9...

.... s

>40

29

M

7

.S7...

z

1,092

in

.... M,Z

>40

30...

z

26

68...

z

1,446

11

.... Z

17

34

Z,M

68

69-..

z

614

1?

. ... Z

123

.3,1 .

Z

6

60...

z

225

15

.... Z

7

36

Z

176

61...

.... z

108

Ifi

.... M,Z

72

48

M

46

62...

z

492

17

.... Z

386

49...

Z

5

63...

.... z

284

IS

.... Z

316

,W .

Z

43

64...

.... z

1,142

in

.... Z

13

Bl

z

6

66...

z

80

23—

.... M,Z

36

62...

z

198

66...

.... z

3,437

that were use.ful with red crabs (high-speed net
catches, and observations at the sea surface) ; and
yellowfin tuna do not eat them. In any event, north-
ern anchovies and some euphausiids are faculta-
tively herbivorous like red crabs and miglit be
expected to have a similar distribution.

I decided to distinguish between concentrations
of red crabs that were greater or less than 40
ml./l,000 m.', as mentioned above. Concentrations
above zero ranged from 0.1 to 5,238 ml./l,000 m.'
(tables 1-6), with median 36 ml./l,000 m.^ It is
implicit in the hypothesis being tested that tunas,
which are highly mobile, encounter and aggregate
around the highest concentrations of food in any
area which they enter. It was, therefore, desirable,
on the one hand, to use some value at least as high
as the median to distinguish high concentrations
from low. On the other liand, the frequencies at
successive intei"vals of concentration declined
sharply above the median, to the extent that chart-
ing would have be«n difficult if a value appreciably
over 100 ml./l,000 m.^ had been used. Trial made
it evident that the projiei-ty charts presented later,
and the conclusions of tlie study, were much the
same at a value of 40 (just above the median) and
at 100 ml./l,000 m.^ Therefore, the former value,
wliich made more data available for drawing iso-
grams of abundance of red crabs on the charts, was
chosen.

MATERIAL AND METHODS

The following sections give information about
the cruises and stations from which data were ob-
tained; the methods used for measuring surface
temperature, surface chlorophyll a, and concentra-

tion of red crabs ; and the kinds and sources of con-
temporaneous data on tunas.

CRUISES AND STATIONS

The oceanographic data for this study were ob-
tained in six cruises — one made in 1959, which gen-
erated the hypothesis mentioned above, and five
made in 1964-66. The area of study was restricted
to south of lat. 28° N., where the tunas (fig. 1) and
red crabs (Longhurst, 1967) occur each year ; these
species appear farther north in some years, but not
in all. Figure 2 identifies localities and topograpliic
features to which I refer in this paper. The princi-
pal banks (underwater elevations of the bottom)
within and beyond the 100-fathom (183-m.) line,
and the small islands known as Alijos Rocks, are
shown. Tuna fishermen consider that these fea-
tures rej^resent good fishing areas, a matter which
is discussed later.

The tracks and station positions for the six
cruises are shown in figures 3, 5, 7, 9, 11, and 13,
which appear in later sections of this report. They
were based on tlie CalCOFI basic station plan
(since 1950) , and most of the stations can be iden-
tified easily with CalCOFI station positions
(Anonymous, 1963), although they have not been
numbered in the CalCOFI way. Two of the cruises
were devoted entirely to occupying a series of Cal-
COFI stations (figs. 7 and 9) . On each of the other
four cruises (figs. 3, 5, 11, and 13) a series of Cal-
COFI stations was occupied first (part 1 of the
cruise, terminating in the southern part of the
area) and the ship then returned northward by a
different route, occupying special stations in areas
of particular interest (part 2 of the cruise). The

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

151

POINT

SAN
EUGENIO

116" W.

115° 114° 113° 112° 111° 110'

FiGUKE 2. — Localities and topograpliic feaitures referred to in the paper.

I

figures identify the stations that were occupied
close to local noon and midnight so as to indicate
approximately which portions of the track were
covered in daylight and which in darkness.

Although many physical, chemical, and biolog-
ical properties were measured at several deptlis at
most stations, this paper is concerned only with
data on surface temperature, standing stock of
phytoplankton, pelagic crabs, and tunas, for rea-
sons given earlier. The stock of phytoplankton was
measured as concentration of chlorophyll a, and in
this paper I discuss only surface concentrations.

which were measured much more often than con-
centrations at other levels.

SURFACE TEMPERATURE

The term "surface temperature" is used for con-
venience, for the temperature data in this paper
are not precisely from the sea surface. Mainly they
are from 10 m. below the surface, where tempera-
ture was measured at almost every station witli a
reversing thermometer. Temperatures read from
bucket thermometers, bathythermographs, and
thermographs that recorded sea-water injection

152

U.S. FISH AND WILDLIFE SERVICE

temperatures aboard vessels were used in cliart-
ing isotherms between station positions. The data
for cruises TO-59-2 (considered as part of Cal-
COFI cruise 5908), 6608, TO-64-1, and TO-64-2
have been publislied (Scripps Institution of Ocean-
ography, 1961, 1968, 1969). The data for cruises
TO-65-1 and TO-66-1 are available from the
Scrijjps Institution of Oceanography.

SURFACE CHLOROPHYLL A

On cruise TO-59-2, concentrations of chloro-
phyll a were determined by spectrophotometric
measurement of optical density of acetone extracts
by use of the equations of Kichards with Thompson
(1952). These data have been published (Black-
burn, Griffiths, Holmes, and Thomas, 1962). On
cruises TO-64-1 and TO-64-2, concentrations were
determined by mesisuring the fluorescence of ace-
tone extrax-ts ( Holm-Hansen, Lorenzen, Holmes,
and Strickland, 1965; Lorenzen, 1966). The data
have been published (Scripps Institution of
Oceanography, 1969). On the other three cruises,
determinations were made by measuring the fluo-
rescence of acetone extracts or in vivo suspensions
(Lorenzen, 1966) or both. The data for these
cruises are available at tlie Scripps Institution of
Oceanography. All available surface measure-
ments were used in this study, irrespective of the
time of day or night at which the material was
collected. Concentrations are given in mg./m.'

PELAGIC RED CRABS

The jielagic red crab was collected or observed
and its concentration in the water estimated in sev-
eral ways. Tables 1-6 list stations and localities be-
tween stations where red crabs were collected or
observed on the six cruises and give the estimated
concentrations in milliliters (displacement vol-
ume) /1,000 m.^ These data refer to adults and
juveniles (iM)stlarvae), but not larvae.

One method of collection (M in tables 1-6) was
the standard micronekton net haul, which was
made usually once eacli niglit. Tlie net wa.s the 1.5-
m. (5-foot) net described by Blackburn (1968);
it was hauled obliquely at a ship speed of 5 knots
(9.3 km./hour). On cruises TO-59-2, TO-65-1,
and TO-66-1, the hauls were made to a deptli of
about 90 m. with 350 m. of wire. On cniises TO-
64-1 and TO-64-2 they were made to about 140 m.
with 500 m. of wire. Wire was paid out at speeds of

20 to 30 m./minute and retrieved at speeds of 10 to
15 m./minute. This method was not used on cruise
6608; other methods, mentioned below, were em-
ployed on that cruise. The volume of water strained
on each haul was estimated from the distance
traversed in meters, the mouth area of the net in
square meters, and an empirical filtration coeffi-
cient, 0.76 (Blackburn, 1968). Crab volumes were
measured directly.

Another method (Z in tables 1-6) was the stand-
ard zooplankton net haul with the CalCOFI 1-m.
net, which was usually made at each station. These
hauls were made obliquely to a depth of about 140
m. at a ship speed of less than 2 knots (3.7 km./
hour). Thrailkill (1956) described the net and
hauling procedure. A flowmeter measured the
volume of water strained on each haul. Volumes of
red crabs were measured directly for cruises TO-
64-1, TO-64-2, and TO-65-1. For the other three
cruises the volumes were estimated from counts of
crabs, using an empirical average volume of 3.0
ml. per crab, or 1.0 ml. per crab if they were re-
corded as small. Some crabs probably avoided these
slowly moving nets, even at night. At 46 night
stations both standard micronekton hauls ajid
standard zooplankton hauls were made and red
crabs collected. Volumes per 1,000 m.= were equal
in the two hauls at 3 stations, gi-e<ater in the micro-
nekton hauls at 31 stations (including 18 when the
zooplankton haul was negative) , and greater in the
zooplankton haul at 12 stations (including one
with a negative micronekton haul) .

A third method (H in tables 1-6) was the high-
speed micronekton net haul described by Black-
burn (1968). This net is hauled horizontally at
about 10 m. below the surface at the ordinary
cruising speed of the ship. Such hauls were made,
usually at night, on all cruises except TO-64-1.
Their duration was from 2 to 3 hours on cruise
TO-59-2, from i/o to II/2 hours on cruise TO-64-2,
and 1 hour on other cruises. The volume of water
strained was estimated from the distance traversed,
the mouth areu of the net, and an empirical filtra-
tion coefficient, 0.94 (Blackburn, 1968). Crab
volumes were measured directly. I showed earlier
(Blackburn, 1968) and found again in this study
tliat volumes per 1,000 m.^ from these hauls aver-
age much smaller than those from standard micro-
nekton hauls made at about the same time and
place; the ratio, high-speed net volume/standard

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

153

micronekton net volume, is of the order 1 : 10. The
reasons are unknown; possibly red crabs are
scarcer in the upper 10 m. than at greater depths,
or they may tend to avoid a fast-moving ship. The
concentrations shown for this method in tables 1-6
have all been multiplied by 10 to make them
broadly comparable with those from the other
hauls.

The remaining sources of information about red
crabs were sightings of aggregations at the sea
surface and occurrences in the stomachs of pred-
ators that were captured from the ship. The con-
centration for each sighting was obviously over 40
ml./l,000 m.^ and is listed accordingly (see S in
tables 1-6). On four occasions the stomachs of
predators contained crabs. The predators were yel-
lowfin tuna, dolphin, Coryphaena hippums, and
an unidentified turtle. Three of these occurrences
were represented by only one predator individual ;
it was not then safe to assume that red crabs oc-
curred at a concentration over 40 ml./l,000 m.^ In
the other occurrence, three predator individuals
(yellowfin tuna) containing red crabs were cap-
tured and many others seen ; here it was reasonable
to assume that a high concentration of red crabs
was available (see P in table 5) .

For stations at which two or more estimates of
concentration were available, the highest one was
listed in tables 1-6. In chai-t.ing the isogram of 40
ml./l,000 m.^ concentration for each cruise, I used
the data of tables 1-6, together with the zero con-
centrations recorded for the remaining stations.
In view of the opinion of Boyd (1967) and Long-
hurst (1967) that red crabs make diurnal vertical
migrations, I occasionally ignored estimates of low
or zero concentrations based upon daytime catches
or observations when other evidence suggested the
probability of high concentrations in the area — for
instance when surface chlorophyll a was high, and
high concentrations of crabs were encountered dur-
ing one or both of the adjacent nights. An addi-
tional justification for this procedure is that most
of the daytime information was obtained from
zooplankton hauls, wliich frequently yield low es-
timates of concentration as shown above. On the
other hand, if a series of night observations all
yielded low estimates of concentration I concluded
definitely that red crabs were not abundant in tlie
area examined, whatever the other circumstances
were ; I sometimes ignored an occasional low con-

154

centration in a series of high ones obtained during
the same night.

Stations 60-66 of cruise TO-64-1 were occupied
very close to each other, in an area of about 5
nautical miles (9 km.) radius, during a period
of about 3 days. The odd-numbered stations were
occupied about noon, the even-numbered stations
about midnight. Table 1 shows the crab concen-
trations measured in zooplankton hauls at these
stations which were all much higher than 40
ml./l,000 m.^ Concentrations were lower at noon
than at midnight, as expected. Concentrations in
consecutive hauls diflFered by a factor of about
three in both tlie noon and midnight series. I have
found similar differences for other kinds of orga-
nisms in noon and midnight series of micronekton
hauls tliat were closely adjacent in space and time
(Blackburn, 1968). Concentrations of red crabs
estimated from single net hauls might, therefore,
differ by a factor up to three from concentrations
actually present in the water. I tried to allow for
this possibility in charting the isogram of 40
ml./l,000 m.^ for each cruise.

TUNAS

Data on the recorded occurrence of yellowfin
and skipjack tunas were obtained from lATTC,
which has such data in various forms, one of which
gives average catch per unit of fishing effort by
species, by fishing method (live-bait and purse-
seine), location by 1° .squares, and by months.
Such information had been very useful in pre\'ious
work on tuna ecology in the Gulf of Tehuan tepee
(Blackburn, 1963) but was rather unsatisfactory
for this study. The isograms of temperature,
chlorophyll a, and red crabs intersected the paral-
lels and meridians in a way that was frequently
very complicated (e.g., fig. 6), and it was evident
that their position did not always remain un-
changed for the whole of the calendar month in
which they were observed.

I used lATTC data on tuna occurrences that
liad definite dates and positions. Figures 4, 6, 8,
10, 12, and 14 (see later sections) show these oc-
currences separately for each species and for mixed
catches of the two species. They refer eitlier to the
whole period when the ship was in the area of the
charts or to some part of that period, as explained
later for cacli cruise. The original data were avail-
able from baitboats and jjurse seiners separately,
but the distributions of tuna from these two

U.S. FISH AND WILDLIFE SERVICE

sources were generally similar and are not dis-
tinguished in this paper. Data were available on
the amounts of tuna captured at each of the
charted positions, but they are not given here be-
cause size of catch is not necessarily a measure of
abundance. Catch per unit of fishing effort can
be considered as a measure of abundance, but it
would be difRcidt to establish the amount of elfort
expended at each of the individual points shown
on the charts. For this study, any commercial catch
of tuna indicates an aggregation of the fish, and
the main interest lies in the general distribution
of the aggregations.

In areas where no occurrences are shown, there
was either no significant fishing effort (hence
tuna distribution unknown) or no fish, at the
period of the cruise. Data showing absence of fish
are few; they refer to combinations of 1° squares
and months in which at least 5 boat-days of fishing
effort yielded no catches. These examples of un-
productive effort are mentioned later for the
individual cruises.

A few catches and observations of yellowfin and
skipjack tunas made from the oceanographic ves-
sels have been included in the charts.

RESULTS OF INDIVIDUAL CRUISES

In the following sections, six cruises are dis-
cussed in the order that best represents the typical
seasonal change during the period of the year when
yellowfin and skipjack tunas occur west of Baja
California. The distributions of surface tempera-
ture, surface chlorophyll (7, red crabs, and tunas
are described and explained for each cruise, with
special reference to their relations with the sea-
sonal cycle of coastal upwelling.

CRUISE TO-64-1

This cruise showed environmental conditions
that are probably typical of the beginning of a
yellowfin and skipjack tuna season off western
Baja California (see fig. 1). Figure 3 shows the
track and station positions, omitting individual
positions of two clustei's of stations that were
occupied for special purposes. Figure 4 gives the
essential features of the distributions of the prop-
erties previously discussed ; this and similar figures
show only selected isograms of surface tempera-
ture and surface chlorophyll a. The isotherms in
figure 4 refer only to the temperature distribution

on part 1 of the cruise, June 9-15, 1964. At the few
stations that were re-occupied on part 2 of the
cruise, temperatures averaged about 2° C. higher
than on part 1. Figure 4 includes only those tuna
occurrences that were recorded for the period
June 9-15. The charted distributions of chloro-
phyll a and red crabs are based on all available
data fi'om the entire cruise, as they are also for
the other cruises. The red crab data are given in
table 1.

Along the Baja California coast below Point
San Eugenio the coastal upwelling typically be-
gins about April, is strong from April through
June, and ceases about August (Keid, Roden, and
Wyllie, 1958; Wyllie, 1961; Lynn, 1967).
CalCOFI stations 123.37 and 143.26, which are the
same as stations 2 and 18 in figure 3, are con-
sidered to be the centers of the two principal
coastal upwelling areas (Lynn, 1967). These
areas, one along the coast south of Point San
Eugenio and the other south of Cape San Lazaro,
are indicated by the 15^ C. surface isotherm in
figure 4. In the northern area, surface tempera-
tures below 13° C. were recorded off San Pablo
Point. The 16°, 17°, and 18° C. isotherms lie gen-
erally parallel to the coast, rather than in the wavy
configurations described later for certain offshore
isotherms on subsequent cruises. This parallel
orientation apjjears to be normal in June
(Anonymous, 1963).

Off Cape San Lucas a well-defined tempera-
ture front existed at the sea surface, oriented in
much the same way as in May 1960 and April 1961
(Griffitlis, 1963, 1965). Surface water below 17°
C, in part below 16° C, lay in a narrow band just
west of Cape San Lucas ; it was probably upwelled
farther north, where temperatures were similar.
Eastward from this cold area along the south
coast of the peninsula, surface temperatures rose
to above 25° C. The 17° to 21° C. isotherms trended
more or less to the southeast from Cape San Lucas,
whereas the 22° to 25° C. isotherms trended paral-
lel to the south coast of Baja California. The
front, therefore, was very strong close to Cape San
Lucas but split about 15 nautical miles (28 km.)
offshore into two weaker parts. Some 60 miles (110
km.) southwest of Cape San Lucas, a tongue of
water over 19° C, mostly over 20° C. (the two
isotherms are close together), protruded north-

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

155

CRUISE TO -64-1
JUNE 1964

JUNE 9

JUNE 26

®

lis"

FRONT •.
36 -.STATIONS'-.
- 37-46 .:

JUNE 15

PART 1 (JUNE 9-15)
PART 2 (JUNE 15-26)
NOON STATIONS
MIDNIGHT STATIONS
OTHER STATIONS

W" IM- 113' 112" 111"

Figure 3. — Track and station positions for cruise TO-64-1.

28"

N.

27"*

26*

25°

24'

23"

22*

110°

109°

ward into the cruise area. Such a warm tongue ap-
pears frequently at this time of year; for example,
it occurred in June 1951 and June 1957 (Anony-
mous, 1963) and is shown in several of the BCF
June temperature charts.

The standing stock of surface chlorophyll a was
highest in the cold coastal water (upwelling or
recently upwelled water), as exjjected. The 1.0
mg./m.^ isogi-am follows the coast and includes the
principal upwelling areas, where some concentra-
tions exceeded 6.0. Concentrations below 0.1
mg./m.^ were confined to the offshore region in

the extreme south of the area (stations 31-34), and
none of these values was below 0.06.

The area of red crab concentration over 40
ml./l,000 m.'' was large and broadly similar to that
of chlorophyll a concentration over 1.0 mg./m.'
Thus, the red crab and its food supply had the
same distribution. A separate small area of high
concentration lay near Cape San Lucas, and an-
other one farther offshore.

The tuna occurrences were in two groups in the
southern part of the area — one (yellowfin tuna
onl}') east of the front along the south coast of

156

U.S. FISH AND WILDLIFE SERVICE

CRUISE TO -64-1
JUNE 1964

CAPE

SAN

LUCAS,

\ir

YELLOWFIN TUNA

A SKIPJACK TUNA

• BOTH TUNA SPP.

SURFACE TEMPERATURE, °C.

null REOCRAB, >40ML./10^M.^

SURFACE CHLOROPHYLL, > 1 .0 MG./M.^

Figure 4. — Distributions of surface temperature, surface chlorophyll a, and red crabs for cruise TO-6-1-1

and locations of contemporaneous tuna catches.

2r

N.

27»

26*

25*

\2f

2f

Baja California, and the other (both species) in
and northwestward of the warm offshore tongue.
Neither of tliese groups of tuna was in tlie area
of highest concentration of food, although the
second group reached the edge of it. In the front
area virtually no red crabs were caught in three
standard night micronekton hauls, and concen-
trations of all animals in these hauls (i.e., all poten-
tial tuna prey) ranged only from 9 to 16
ml./l,000 m.^ In the other tuna area concentra-
tions of red crabs were 7 and 46 ml./l,00(J m.^ at

stations 29 and 48, and concentrations of all other
micronekton were 14 and 10 ml./l,000 m.^ Some of
the tuna aggregations in each of these areas were
only about 25 nautical miles (46 km.) from a much
richer food supply (over 100 ml./l,000 m.' of red
crabs — e.g., at station 52), but the fish would have
had to encounter temperatures below 17° C to
reacli it. Figure 4 shows that the tunas will tolerate
17° C. and suggests that lower temperatures are
not acceptable.

A reasonable interpretation of figure 4 is that

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

157

both tuna species prefer some temperature at or
over 20° C, will move into adjacent water as cool
as 17° C. if food is more plentiful there, and will
not enter water below 17° C. even if food is ex-
tremely abundant. If so, tuna will not round Cape
San Lucas from the east as long as water under
17° C, and perhaps under 20° C, remains there ;
data from Griffiths (1963) indicated that 20° C.
was the limiting temperature in May 1960. Under
those circumstances their entry into the area west
of Baja California will be by the offshore tongue
of warm water, as suggested by figure 4. Tlie area
enclosed by the offshore 20° C. isotherm in figure
4 was well occupied by both species in the second
half of June and the first half of July, although
there were still no records of tuna caught between
that area and the coast (between long. 110° and
in° ^V.). Tuna were not recorded in the latter
area until the second half of July, when they
suddenly became widespread; these fish were all
yellowfin tuna, and probably the same aggrega-
tions as shown to the east of the front in figure 4.
Probably the 20° C. isotherm moved northward
from Cape San Lucas about mid-July and per-
mitted the yellowfin tuna to round Cape San
Lucas; this isotherm was located at about lat. 25°
N. during the last 10 days of July (Scripps In-
stitution of Oceanography, 1966). Thus, tuna
appear to follow two pathways from the tropics
into the area west of Baja California at the begin-
ning of a tuna season, both determined by the
distribution of surface temperature. One is from
the east around Cape San Lucas, and the other
is from the south. The former is mainly for yellow-
fin tuna, and the latter is for both species; skipjack
tuna are much less common than yellowfin tuna to
the east of the meridian of Cape San Lucas in most
years (Joseph and Calkins, 1969).

Cruise TO-64— 1 was the only one of tliis series
in which tuna occurred at temperatures substan-
tially lower than 20° C. They probably can tolerate
temperatures down to 17° C. to obtain a larger
food supply, as indicated above. Lee (1952) found
that cod will enter waters over 2° colder than those
in which they usually occur if food is jjlentiful.
On cruise TO-64-1 only one small area had more
than 40 ml./l,000 m.^ of red crabs in water at
20° C. or over (station 34, with 68 ml./l,000 m.^*).
On all tlie later cruises, such areas were extensive

and the concentrations of red crabs in them were
generally over 100 ml./l,000 m.^

Several tuna boats were fishing off the south
coast of Baja California at the time the front was
surveyed, and their operations were watched to see
if their fishing success bore any relation to the
position of the front. The only obvious relation
was that they worked mainly to the east or north
of the front and occasionally on its warm edge.
They were probably avoiding water under about
20° C, and the front itself, as distinct from the
limiting isothenns located in it, seemed to have
no effect.

Various authors have suggested that tunas may
aggregate in fronts in response to aggregations
of prey organisms. Griffiths (1963, 1965) found
that some kinds of zooplankton were more
aljundant in the middle of the Cape San Lucas
front than on either side of it, but, on the other
hand, micronekton (potential tuna forage) was
most abundant on the warm side. On cruise TO-
64— 1 micronekton hauls were again made on both
sides of the front and in the middle, all on the
same night ; the highest concentration was on the
warm side, as in Griffiths' series, but all three con-
centrations were similar (16.3 ml./l,000 m.' warm
side; 9.1, middle; 11.8, cold side).

All the foregoing observations were made in the
part of the front that is oriented parallel to the
south coast of Baja California. Another series
of seven micronekton hauls, made across the
stronger part of the front near Cape San Lucas on
cruise TO-64-1, showed highest concentrations
in the upwelled water on the cold side. The
evidence, therefore, does not support the idea of
a concentration of tuna forage in the Cape San
Lucas front. This front may have no special at-
traction for tunas and is probably avoided by
them when unsuitably cold water occurs in it.

CRUISE TO-64-2

The results of this cruise, whicli was made in
August of a rather cold year (see fig. 1), are
probably typical of conditions in the early part
of the tuna season, including July, when the fish
rapidly expand their range nortliward. Figures 5
and 6 show ci'uise coverage and property distribu-
tions. The isotherms in figure 6 refer to the tem-
perature distribution on part 1 of the cruise, Au-
gust 5-16, 1964. At the few stations that were re-

158

U.S. FISH AND WILDLIFE SEEVICB

IIB-'W.

115° 114" 113° 112° 111°

Figure 5. — Track and station positions for eruise TO-&4-2.

occupied on part 2 of the cruise, temperatures were
about the same as on part 1 except on August 21
and 22, when tliey were about 2° C. higher. Figure
6 includes only those tuna occurrences that were
recorded for the period August 5-20. The red crab
data are given in table 2.

Detailed surface temperature charts for the area
in July and August show in most yeare a different
configuration of isotherms fi-om that found in
Jime (Anonymous, 1963). Instead of lying more
or less parallel to the coast, the isotherms become
wavy ; tongues of relatively cool water extend away

from the coast, separated from each other by
tongues of relatively warm water extending to-
ward the coast. Figure 6 shows this situation very
well ; cold tongues njn offshore from the two prin-
cipal upwelling areas identified on cruise TO-64— 1,
and the northern area gives rise to at least two
tongvies. This distribution is i)robabl3' caused by
the eddies that characteristically a^jpear about
July and August (Wyllie, 1966). In figure 6 and
later figures, the isotherms selected for charting
always included those which showed the tongues,
if present, in most detail. Temperatures under 20°

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

159

IIS^W.

Figure 6. — Distributions of surface temperature, surface chlorophyll a, and red crabs for cruise TO-64-2 and

locations of contemporaneous tuna catches.

occurred almost all along the coast on cruise TO-
64-2 ; minima, at stations 1, 8, and 31, were between
15° and 16° C, and maxima, at stations 53 and
54, were between 26° and 27° C.

Concentrations of surface chlorophyll a ranged
from 6.4 to 0.01 mg./m.^ Their generally much
lower values than on cruise TO-64-1 reflect some
decay in the upwelling regime. Only station 32
had a concentration above 1.0 mg./m.^ The isogram
of 0.2 mg./m.^ in figure 6 follows rather closely
the edge of the cool water, except in the extreme

northwestern part of the area covered. It pro-
trudes farther offshore between lat. 23° and 24°
N. than the corresponding protrusion of the iso-
therms. The 0.1 mg./m.' isogram (not shown)
follows it closely in most areas.

The position of the isogram showing 40 ml./
1,000 m.^ of red crabs is close to the 21° C. isotherm
and the 0.2 isogram of chlorophyll a, except in the
northwestern part of the area (fig. 6). In general,
relatively high standing stocks of red crabs and

160

U.S. FISH AND WILDLIFE SERVICE

Table 2. — Concentrations of Pleuroncodes planipes, adults and juveniles {not larvae), in mlJlOhn} of water strained, on

cruise TO-eJf-2

[Letters under kind of observation signify: M, micronekton haul; Z

zooplankton haul;

H, high-speed net haul between stations;

S,

seen in the water. Where

concentrations

were measured

or estimated by more than one method

the highest concentration, corresponding to the first letter,

U listed]

Station No.

Kind of

Concen-

Station No.

Kind of

Concen-

Station No.

Kind of

Concen-

observation

tration

observation

tration

observation

tration

Ml.lKfim.i

Ml.llff>m.>

MlMOm*

4-5

... H

620

30-31..

. H

143

68-59.

. H

16S

7

... Z,M

63

32

. Z

631

60

.. S

>40

7-8

... H

>40

34

. Z

4

63

.. /,

103

12

... Z,M

24

36

- Z

13

64

.. z

17

12-13...

... H

18

40

. Z

11

65

.. z

33

12-13...

... H

879

44

- Z

9

69

.. z

M

13

... S

>40

45

. S

>40

70

. z

9

16

... M

1

46

. M,Z

365

73

.. z

9

16-17...

... H

190

50

. Z

4

74

.. z

7

17-18...

... H

333

61

. Z

48

76

.. z

13

17-18...

... H

18

61-52..

. H

3

76

.. z

89

23

... M

7

52

. M,Z

37

77

.. z

197

23-24...

... H

268

52-63.

. H

35

78....

_

.. z

26

23-24...

... H

>40

55

. Z

6

79

.. z

sez

24

... Z

11

56

. M

1

80

.. z

232

24-25...

... H

314

66-67..

. H

83

81

.. z

101

27

... Z

4

67

. Z

13

(').—

.. M

>«

29

... M

1

58

- Z,M

6

> Series of night surface hauls with the large micronekton net near Uncle Sam Bank.

chlorophyll a occurred together in the upwelling
or in recently upwelled water.

The occurrences of tuna (both species) were on
the edges of the area of high concentration of red
crabs where surface temperatures were all between
22° and 18° C. No tuna were recorded in the large
inshore areas where red crabs were equally or more
abundant and temperatures were lower; the fish
probably avoided these areas. One 1° square,
bounded by lat. 26° and 27° N. and long. 114° and
115° W., had a significant amount of fishing effort
(six boat-days) tliat yielded no tuna in the month
of the cruise. According to figure 6, almost all of
this area was either colder than 20° C. or had less
than 40 ml./l,000 m.' of red crabs; it is not sur-
prising then that tuna were not found. Elsewhere,
in areas where no occurrences are shown in figure
6, the distribution of yellowfin and skipjack tunas
at the time of the cruise is not known. Tunas could
ha\-e occurred along other parts of the edge of the
cool, food-rich, water.

Figure 6 shows an isolated occurrence of abim-
dant red crabs far offshore, where surface chloro-
phyll a was below 0.1 mg./m.' and tuna distribu-
tion unknown. Such offshore distributions, which
Boyd (1967) and Longhurst (1967) have reported
previously, may represent individuals that the
California Current has carried out of tlie coastal
region.

CRUISE 6608

This OalCOFI cruise, made in August 1966,
covered only part of the area of interest. The

results represent conditions at a slightly later
stage in the year tlian those for cruise TO-64-2.
The CalCOFI stations have been given serial num-
bers as shown in figure 7. Figures 7 and 8 show
cruise coverage and distributions of properties.
The red crab data are given in table 3.

The surface isotherms (fig. 8), especially 23° C,
show the same tonguelike distributions as before.
Cool tongues ran offshore from areas which lie
south of Point San Eugenio and Abreojos Point;
here a small inshore belt of upwelling or upwelled
water under 20° C. occurred. Warmer water lay on
both sides of these tongues. Surface temperatures
for the whole area were between 17° and 26° C. —
very close to the range (16°-25° C.) in an average
August (Anonymous, 1963).

Concentrations of surface chlorophyll a ranged
from 2.0 to 0.03 mg./m.^, but those over 1.0 mg./
m.^ were confined to a small inshore area between
Point San Eugenio and San Pablo Point. It was
not possible to draw an isogram for 0.1 mg./m.^
with confidence, because observations were not
made in some parts of the area. In general, con-
centrations below 0.1 mg./m.^ were in water over
23° C, outside the main cool tongue shown in
figure 8, but some of them were in the small (east-
em) cool tongue as well. All concentrations above
0.2 were in the cooler water, as expected. They
are charted in figure 8 to show two areas, which
may, however, have been joined, because observa-
tions were not made between them.

The sampling of red crabs on this cruise was

DISTEIBUTION OP TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

161

AUG. 20

CRUISE 6608
AUGUST 1966

(S) NOON SfATIONS

# MIDNIGHT STATIONS

• OTHER STATIONS

28"
N.

127"

26'

25°

24"

^23"

22"

116"W. 115" 114" 113" 112° 111"

Figure 7. — Track and station positions for cruise 6608.

110°

109"

more restricted than on most of the other cruises
because no standard micronekton hauls were made.
Figure 8 shows four areas with concentrations
over 40 nil./l,000 m.^ The northern area was in
water whicli was cool and rich in chlorophyll a
(over 0.2 mg./m.^ ) ; the eastern area was partly
in and partly adjacent to the same kind of water;
the southwestern area was in and adjacent to a
tongue of cool water, with chlorophyll a concen-
trations about 0.1 mg./m.^; and the remaining
small area was in warmer water where no chloro-
phyll data were obtained.

The data on tuna occurrence for the period of
the cruise, August 20-26 (fig. 8) show a single
record in the northern part of the area, located,
like those on cruise TO-6+-2, on the edge of an
area that was rich in food but rather cold. The
other records show a distribution of tuna right
across one of the tongues of cool water, where tem-
l^eratures were nevertheless high enough (over
20° C.) to permit the tuna to exploit the high con-
centration of red crabs; the tuna were located
partly in and partly on the edge of this concen-
tration of food. A significant amount of fishing

16i

U.S. FISH AND WILDLIFE SERVICE

CRUISE 6608
AUGUST 1966

▲

Mini

YELIOWFIN TUNA

SKIPJACK TUNA

BOTH TUNA SPP.

SURFACE TEMPERATURE, °C.

REDCRAB, >40ML./10'M.^

SURFACE CHLOROPHYLL, > 0.2 MG./M.^

IIB-W.

28°
N.

27"

26°

25°

24°

23°

22°

Figure 8. — Distributions of surface temiierature, surface clilorophyll a, and red crabs for cruise 6C08 and

locations of contemporaneous tuna catches.

effort (nine boat-days) in one 1° square, bounded
by lat. 26° and 27° N. and long. 114° and 115° W.,
took no tuna in tlic month of the cruise. According
to figure 8, nearly all of this area was either colder
than 20° C. (the northeastern corner) or had less
than 40 ml./l,000 m.^ of red crabs at the time of
the cruise. It would not, therefore, be expected
to contain many tuna. Elsewhere the distribution
of tunas at the time of the cruise is not known.
Fishing effort was not significant in the area of
high concentration of red crabs in the southwest-

ern part of the cruise area, where temperature and
food were suitable for tunas.

CRUISE TO-59-2

This cruise, made August 16-29, 1959, was in
a warm year (see fig. 1), and the results represent
conditions at a later stage in the year than those
for the previous cruise. The cruise started farther
south than the others in this series; the area im-
mediately to the north was covered at the same
period by CalCOFI cruise 5908 which yielded

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

163

Table 3. — Concentrations of Pleuroncodes planipes, adults and juveniles (not larvae), in ml./lO 'm.' of water strained, on

cruise 6608

(Letters under kind of observation signify: Z, zooplankton haul; H,

high-s

seed net haul between stations; S,

seen in the water. Where concentrations

were meas-

ured or estimated by more than one

method, the highest concentration, corresponding to the first letter,

is UstedJ

Station No.

Kind of

Concen-

Station No

Kind of

Concen-

Station No

Kind of

Concen-

observation

tration

observation

tration

observation

tration

Ml.lKfim.'

Ml.limm.'

Ml.llCfim'

1

Z

>40

23....

- Z

25

36

Z

113

1-2....

H

>40

23-24.

H

1,069

38

Z

6

2

Z

12

24....

Z

7

41-42..

H

17

5-6....

H

392

24-25.

H

334

43

Z

56

6

Z

13

25....

S,Z

>40

43-t4..

H

426

7

Z

6

30-..

Z

28

44

S,Z

>40

14-15..

H

1,353

31....

S,Z

>40

45

z

67

15

Z

13

31-32.

H

818

45-46..

H

468

16

Z

215

32....

- Z

20

46

Z

24

20

Z

7

32-33.

.- H

12

(■)....

H

5

21

Z

45

33-34.

H

27

(1).-.-

H

735

21-22..

H

701

34....

Z

14

(')----

H

1,762

22-23-

H

1,044

35-36.

- H

58

(').-..

H

14

' After station 47, on northbound track between lat. 26°30' N. and 27°50' N., at night.

temperature data (Scripps Institution of Ocean-
ography, 1961), but no data on chlorophyll or red
crabs. Cruise coverage and property distributions
are shown in figures 9 and 10. Data on red crabs
are given in table 4.

Surface temperatures were between 18° and
30° C. but the areas under 20° C. and over 28° C.
were extremely restricted (fig. 10). The cold
inshore region between Point San Eugenio and
San Pablo Point probably represents upwelling
at a very late stage. A large tongue or tongues
of relatively cool water (less than 25° C.) ran
offshore from the coastal upwelling area as shown
for previous cruises. No such signs of relatively
cool water were off Magdalena Bay, where ui:)well-
ing probably ceases earlier than it does farther
north.

Observations on surface chlorophyll a were
fewer on this cruise than on the others. Concentra-
tions were much lower than before — from 0.11 to
0.02 mg./m.^, which is consistent with the indica-
tions of a further weakening of upwelling. Con-
centrations were at or above 0.1 mg./m.^ only at
stations 20, 30, 37, 38, 41, and 42. The isogram of
0.05 mg./m.^ follows the 25° C. isotherm fairly
well (fig. 10), so the oflFshore tongue of relatively
cool water generally had a higher concentration
of chlorophyll than the surrounding warmer
water.

The area in which concentrations of red crabs
exceeded 40 ml./l,000 m.^ was broadly congruent
with the area of cool water and the area of highest
surface chlorophyll. The isograms of these three
properties tend to be displaced a little from each

other, but otherwise they agree in considerable
detail. There was an isolated patch of red-crab-
rich water off Magdalena Bay; it was not cool,
and chlorophyll was not sampled in this particular
area.

About half of the tuna catches that were made
at the time of the cruise were north of Abreojos
Point, where data on chlorophyll and red crabs
are lacking; temperatures were mostly over 20° C.
Tlie catches to the south of Abreojos Point all were
from water over 20° C. and show the kind of asso-
ciation with chlorophyll and red crabs that was
mentioned for cruise 6608. The tuna were not only
on the edges of the biologically rich areas but in
the cores of these areas as well. The areas of
abundant forage, which on cruise TO-64-2 were
too cold for tunas except at the edges, were warm
enough for the fish to penetrate on this cruise. As
before, tuna distribution was not determined
(insignificant amount of fishing) in certain large
areas, including some in which temperature and
food conditions appeared highly suitable.

CRUISE TO-65-1

This cruise (figs. 11 and 12), which was in Sep-
tember 1965, represents a still later stage in the
year, when the distribution of surface temperature
gives no indication of any coastal upwelling. The
lowest temperatures, between 20° and 21° C, were
offshore and probably indicate California Current
water. The highest temperatures were slightly
over 28° C. Temperatures on part 2 of the cruise
were about the same as on part 1. On CalCOFI
cruise 6509, which extended into the northern part
of the area near the end of cruise TO-65-1, sur-

164

U.S. FISH AND WILDLIFE SERVICE

CRUISE TO-59-2
AUGUST 1959

AUG. 29

®

NOON STATIONS
MIDNIGHT STATIONS
OTHER STATIONS

28*
N.

27"

26"

25"

24"

23"

22"

121°

116°W. 115" 114" 113" 112° 111°

FiouEE 9. — Track and station positions for cruise TO-59-2.

110'

109°

face temperatures were about 1.5° C. lower in a
few inshore localities, and elsewhere about the
same as on TO-65-1 (Scripps Institution of
Oceanography, 1967). Even these lower tempera-
tures were over 20° C. and would not be expected
to affect tuna distributions ; therefore, all tuna oc-
currences for the whole period, September 8-25,
1965, have been given in figure 12. Data on red
crab concentrations are given in table 5.

Surface chlorophyll a concentrations were all
below 1.0 and ranged down to 0.02 mg./m.^, al-

though they were generally higher than on cruise
TO-59-2. The 0.2 mg./m.^ isogram encloses the
area of highest concentration, which is tonguelike
and originates on the coast south of Point San
Eugenio, as on previous cruises. It probably rep-
resents the biological result of a tongue of up-
welled water which can no longer be distinguished
from the surrounding water by its temperature.
All stations inshore of this tongue and tlie follow-
ing stations offshore had over 0.1 mg./ni.^: 4—6,
12, 13, 17, 23, 26-29, 32, and 36.

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

165

A ▲

• .A*^ \ N^ — ~;P0INT SAN EUGENIO"-

▲ •*

LSAN PABLO POINT

CRUISE TO-59-2
AUGUST 1959

iililll

YELLOWFIN TUNA

SKIPJACK TUNA

BOTH TUNA SPP.

SURFACE TEMPERATURE, °C.

RED CRAB, >40ML./I0'M.^

SURFACE CHLOROPHYLL, > 0.05 MG./M.'

28"
N.

27"

26°

25"

24"

23°

22"

Figure 10. — Dl.stril)utions of surface tenii>erature, surface chlorophyll a, and red crabs for crui.se TO-59-2

and locations of contemporaneous tuna catches.

The area where red crabs were over 40 ml./l,000
m.^ shows the same close but not exact correspond-
ence with the chloropliyll-rich area that was
found on previous cruises, and all the tuna catches
were made in or very close to this area. The high-
est concentrations of carnivores (tuna) , herbivores
(red crabs), and plants (chlorophyll a) all were
in the same restricted area. Because all tempera-
tures were suitable for tunas, the tunas occuri-ed,
as before, not only around but through the food-
rich areas.

CRUISE TO-66-1

The cruise period in the area of interest was
November 4-21, 1966. The cruise (figs. 13 and 14)
included stations with numbers below 15 and above
70, which were occupied on behalf of another in-
vestigator and were all north of lat. 28° N.

As I expected, conditions were much more uni-
form throughout the area on this cniise than on
any of the others, because coastal upwelling had
ceased. The only inshore pocket of cool water.

166

U.S. FISH AND WILDLIFE SERVICE

Table 4. — Concentrations of Pleuroncodes planipes, adults and juveniles (not larvae), in ml.jlO^m} of water strained, on

cruise TO-59-2

[Letters under kind of observation signify: M, micronekton haul; Z, zooplankton haul; H, high-speed net haul between stations; S. seen in the water. Where
concentrations were measured or estimated by more than one method, the highest concentration, corresponding to the first letter, is listed]

station No. Kind of

Concen-

observation

tration

m.llCPm.^

1

S

>40

2

Z.M

>40

5-6 -.

H

o

6-7. -

H

4

7

Z

>40

8

M

176

8-9

H

35

9-10„_.

H

3

11-12—

H

1

13

M

42

13-U

.- H

26

15

Z

6

16-16

11

2

17-18 --

H

225

18

Z

>40

18-19

H

24

19-20

H

43

19-20

H

213

Station No. Kind n(

Concen-

Station No. Kind of

Concen-

observation

tration

observation

tration

Ml. 110' m.^

Ml./lO'

m.'

20

S.Z

>40

30...

Z

«

21

M

64

38

M,Z

•M

21-22

H

36

38-39

H

2

22-23... .-

H

20

40-41

H

9S

26

Z

158

41^2

H

S

26-27

H

IS

42

M

132

26-27

H

16

42^3

.— H

S

27-28

H

8

43-44..

H

8

28-29

H

6

46-47....

H

6

30-31

H

8

46^7...

H

27

30-31

H

1,158

62....

M

108

31....

Z

7

53

Z

128

32

Z,M

229

63-54

H

495

32-33

H

158

54

Z

9

33

Z

58

55...

z

8

34

z

9

57

z

15

35

z

13

57-58

H

2

35-36

H

59

58

M,Z

20

which might have indicated upwelling, was a very
small one off Point Tosco (21°-22° C). Tempera-
tures for the whole area were between 18° and 26°
C. on part 1 of the cruise; on part 2, temperatures
at reoccupied stations were only slightly (less than
1° C.) lower.

The range of chlorophyll a. concentrations was
about the same as on cruise TO-65-1, but their
distribution was more uniform. Concentrations
were ov-er 0.1 mg./m.^ in most of the area as shown
in figure 14. Concentrations were over 0.2 mg./m.^
at all stations north of lat. 26° 20' N., and there
only. Similarly, concentrations of red crabs were
40 ml./l,000 m.^ or higher in most parts of the
cruise area (see table 6 for data). Finally, the
recorded catches of tuna (all tliose for the period
November 4-21) were scattered through the large
area of suitable temperatures and abundant red
crabs.

There was no opportunity to make a similar
cruise closer to tlie end of the .season for yellowfin
and skipjack tunas off western Baja California, say
in December or January. Such a cruise would
probably have shown that the area available for the
tunas had contracted because of the southward
movement of isotherms, and a rather featureless
distribution of the tunas — similar to that on cruise
TO-66-1, associated with relatively uniform dis-
tributions of red crabs and chlorojihyll a — in the
area of suitable temperature.

OCEANIC PROPERTIES AND THE
DISTRIBUTION OF TUNAS

Tlie results of cruises TO-64^1, TO-64-2, 6608,
and TO-59-2 all show the expected close agreement
in detail between areas of relatively cool water
that are attributable to upwelling and areas of
relatively high surface chlorophyll a. The poor
agreement between isograms of temperature and
chlorophyll a in the northwestern portion of the
cruise area shown in figure 6 is not necessarily an
exception to the preceding statement, because the
cool water may not represent upwelling there. The
results of cruise TO-65-1 show a region of rela-
tively high surface chlorophyll a in a locality and
with a shape, which suggest an origin in upwelled
water. No signs of upwelling appeared on cruise
TO-66-1. The distributions of surface isotherms in
space and time are consistent with previous in-
formation al)out upwelling off southern Baja Cali-
fornia. Temperatures rise and chlorophyll a
concentrations fall in the upwelling areas as the
upwelling bei-omes weaker.

The results of all the cruises show rather close
agreement in detail between the areas of relatively
high surface chlorophyll a and the areas in wliich
the concentration of red crabs is more than 40
ml./l,000 m\ The concentration of chlorophyll a
whicli shows this agreement varies; on most of the
cruises it was 0.2 or 0.1 mg./m\, but it was higher
on cruise TO-64^1 and lower on cruise TO-59-2.
The only complete lack of agreement appears in

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

167

CRUISE TO -65-1
SEPTEMBER 1965

®

116'W.

PART 1 (SEPT. 8-20)
PART 2 (SEPT. 20-25)
NOON STATIONS
MIDNIGHT STATIONS
OTHER STATIONS

HP 114° 113° 112' 111*

Figure 11. — Track and station positions for cruise TO-65-1.

27°

26"

25°

24°

23°

22°

110°

the northwestern part of the cruise area shown in
figure 6. Elsewhere in all the charts, agreement is
fair to good. The area boundaries for the two
proi>erties seldom coincide, but they tend to lie
close together and to have the same shape. Where
the isograms of chlorophyll a follow those of tem-
perature, all three properties — temperature,
chlorophyll a, and red crabs — have a closely similar
distribution (e.g., fig. 10).

The occurrence of red crab maxima with chlo-
rophyll a maxima is not surprising because red
crabs feed on phytoplankton, but the circum-

stances whereby they maintain aggregations in
chlorophyll-rich areas are not altogether clear. On
the one hand, the distribution data of Boyd ( 1967)
and Longhurst (1967) indicate that the red crab
can be swept away from the coast by the California
Current during its pelagic phase. On the other
hand, substantial numbers of this species occur in
the benthos along the Continental Shelf and Slope
(Boyd, 1967) , and these individuals probably help
to maintain pelagic concentrations in coastal areas
by generating larvae and by ascending into the
upper waters from time to time. Larvae are most

168

U.S. PISH AND WILDLIFE SERVICE

CRUISE TO-65-1
SEPTEMBER 1965

<21

lllllll

YELLOWFIN TUNA

SKIPJACK TUNA

BOTH TUNA SPP.

SURFACE TEMPERATURE, °C.

RED CRAB, > 40 Ml./lO^M.^

SURFACE CHLOROPHYLL, > 0.2 MG./M.'

IIB-W.

28"
N.

2T

26-

25°

24"

23"

22"

riGUBE 12. — Distributions of surface temjierature, surface chlorophyll a, and red crabs for cruise TO-65-1

and locations of contemporaneous tuna catches.

numerous in inshore waters off the west coast of
southern Baja California before and during the
upwelling season, and benthic adults probably pro-
duce many of them (Longhurst, 1968a) . The main-
tenance of pelagic aggregations is probably served
also by the formation of inshore eddies after June
(Wyllie, 1966). I assume that these processes, to-
gether with the animal's own appreciable mobility,
maintain high concentrations in inshore areas
where food (phytoplankton) is abimdant; when
food is scarce inshore red crabs presumably sink.

disperse, or die.

The presence of red crab concentrations in cool
water on some of the cruises results from the
relation between chlorophyll a and upwelling, and
is, therefore, not apparent on cruises TO-65-1 and
TO-66-1. Longhurst (1967) showed that red crabs
are practically eurythermal between about 9° and
28° C.

The data on tuna occurrence are all consistent
with the hypothesized association with surface
temperature (about 20° C. or more) and food sup-

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

169

Table h.—Concenlralions of Pleuroncodes planipes, adults and juveniles {not larvae), in ml./Wm? of water strained, on

cruise TO-BS-l

(Lettersunder kind of observation signify: M, micronekton haul; Z, zooplankton liaul; H, liigli-spced net haul between stations; S, seen in the water; P, found in
predator stomachs. Where concentrations were measured or estimated by more than one method, the highest concentration, corresponding to the first letter,
is listed)

Station No. Kind of

Concen-

Station No. Kind of

Concen-

Station No. Kind of

Concen-

observation

tration

observation

tration

observation

tration

m./mm.'

m.ltCflm?

Afl.//0'm.'

2 .

Z

64

21-22

H

9

64

Z,M

3

3 -.

M

1

22-23

H

15

(1)

P

>40

6

Z

32

26

M

22

60

Z

7

M

1

29

S,Z

>40

61

Z

55

7-8

8 -

H

Z

500
6

z

21

62

z

3

37

Z,M

12

63....

z

32

10. -

11

S,Z

Z

>40
4

64

z

39

z

5

66

z

10

11-12

12

H

M,Z

5
3

40

41

M,Z

Z

4

z

4

P) .--

M

>40

12-13

H

5

42

z

6

(').. —

H

12-13

H

20

44

z

2

(?)

H

15-16

H

5

4.'i

M

<1

m -

H

16

M,Z

5

49

z

18

(»)

H

16-17

H

342

49-50

H

16

(») -

H

18

Z

9

50

M,Z

24

(')--.

H

20-21

H

18

51

Z

2

(?)

H

1 stomach contents of 3 yellowfln tuna (Thunnus albacares) at Thetis Bank.

2 Series of night surface hauls with the large micronekton net near Uncle Sam Bank.

3 After station 67, on northbound track between lat. 25°50' N. and 26°40' N., at night.

ply (40 ml./l,000 m.=' or more of red crabs), for
all cruises except TO-64-1. On that cruise tlie
tunas showed a tolerance of temperatures down to
17° C, but no lower in the presence of a larger
food supply than that available to them at or over
20° C. Only one small area of abundant food (over
40 ml./l,000 m.^) and no area in which it was
highly abundant (over 100 ml./l,000 m.^) had
temperatures at and over 20° C; food was highly
abundant only at temperatures below 17° C. This
difficulty (for the tunas) did not arise on any of
the other cruises. On cruise TO-64-2 the edges of
the areas of abundant food were warm enough
for the tunas, which were found there and nowhere
else. On cruises TO-59-2, TO-65-1, and TO-66-1
all parts of the f ood-ricli areas were warm enough
for tunas, which were, accordingly, widespread in
them; they might have been found in still other
places in the food-ricli areas if the fishermen had
searched there. On cruise 6608 the situation was
partly like cruise TO-64^2 and partly like the
other cruises. Except on cruise TO-64^1, no tuna
were ever found more than 20 nautical miles (37
km.) from the charted boundaries of the food-rich

areas.

From these results I may conclude that yellow-
fin and skipjack tunas aggregate in the areas of
most abundant food where surface temperatures
are about 20° ( ±1°) C. or over in waters west of
Baja California, except at the beginning of their

seasonal entry into those waters wlien they may
occur at temperatures down to 17° C. Temperature
determines range limits (penetration northward
and toward the coast) , and food supply determines
distribution within the range limits. Because the
principal food in this area is the red crab which
occurs in areas rich in phytoplankton, tunas gen-
erally aggregate in or near the areas of highest
surface chlorophyll a, provided that temperatures
are suitable.

Because the distributions of temperature, cliloro-
phyll a, and red crabs are all partly controlled by
the seasonal coastal upwelling, at least through
September, the same is true of the distribution of
the tunas. Concentrations of tuna prey are much
higher off western Baja California than anywhere
else in the eastern tropical Pacific, where they are
generally less than 10 ml./l,000 m.^' (Blackburn,
1968). These high values are a consequence of the
upwelling and of the unusually short tuna food
chain. Tlie upwelling, however, furnislies an envi-
ronment that tends to be too cold for yellowfin and
skipjack tunas in spite of its biological richness,
and this physical feature is decisive. The tunas do
not enter the area and exploit the rich food supply
until temi>eratures begin to rise. They then aggre-
gate around the edges of the large tongues or
patches of food and gradually penetrate into the
cores of those areas as they become warm. Later
the distribution of both the food and the tunas

170

U.S. FISH AND WILDLIFE SERVICE

(NOV. 21) 70^

28"
N.

27"

CRUISE TO -66-1
NOVEMBER 1966

PART 1 (NOV. 4 - 18)
PART 2 (NOV. 18-21)
NOON STATIONS
MIDNIGHT STATIONS
OTHER STATIONS

68 (NOV. 18)

116°W

115° 114° 113° 112° 111°

FiQUEE 13. — Track and station position.s for crui.se TO-66-1.

110"

26°

1 25°

24°

23°

22°

109°

becomes rather uniform in areas of suitable tem-
perature, and finally the physical environment
again becomes unsuitable with the start of winter
cooling. The supply of pelagic red crabs remains
fairly high throughout the year (Longhuret, 1967;
Blackburn, 1968; and this paper).

The foregoing interpretation of the tuna dis-
tribution data might be criticized on two grounds.
One is that nearly all the tuna catches shown in
the charts were within 100 nautical miles (185
km.) of the coast, although suitable environmental
conditions occurred much farther offshore on some

of the cruises (see figs. 8 and 10), as well as in the
inshore areas where the catches were made. Charts
of lATTC data from the commercial fishery for
many years, compiled by Joseph and Calkins
( 1969) , show clearly that most of the fishing effort
in the Baja California area is expended and most
of the catch of both species taken within about
100 nautical miles of the coast. This situation is
understandable because the tuna are associated
with upwelling, which is a coastal process, and
fishermen generally do not operate farther off-
shore than is necessary to make good catches. On

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

171

CRUISE TO-66-1
NOVEMBER 1966

YELLOWFIN TUNA

SKIPJACK TUNA

BOTH TUNA SPP.
— SURFACE TEMPERATURE, °C.

I I I RED CRAB, > 40 ML./lO^M.'

SURFACE CHLOROPHYLL, >0.1 MG./M.^

116° W. "

Figure 14. — Distributions of surface temperature, surface clilorophyll o, and red crabs for cruise

and locations of contemporaneous catches.

28°
N.

27°

26°

25°

124°

r

22°

109°
TO-66-1

the otlier hand, the lATTC charts show that yel-
lowfin and skipjack tunas are sometimes sought
and f aptured offshore, for instance at Alijos Rocks,
about 150 nautical miles (278 km.) from the coast
(fig. 2) , and even about 1° of longitude to the west
of that locality. Nothing suggests that these off-
shore tuna are not aggregated in food-rich areas
of suitable temperature in the same way as the
inshore tuna. Furthermore, one definite record of
an offshore commercial tuna catch appears to be
associated with a tongue of food-rich water (fig.

10). This catch was at Alijos Rocks on cruise
TO-59-2. The only other cruise in the present
series which yielded information about properties
at Alijos Rocks was TO-65-1 (see fig. 11, station
14). On that occasion, no tongue of biologically
rich water reached the Rocks area, concentrations
of chlorophyll a and red crabs were low, no tuna
were seen or caught while the scientific party was
fishing at the Rocks, and no commercial catches
were recorded tliere during the cruise period.
The other possible objection to the model of

172

U.S. FISH AND WILDLIFE SERVICE

Table 6. — Concentrations of Pleuroncodes planipes, adults and juveniles {not larvae), in mLjK^m} oj water strained^ on

cruise TO-66-1

fLetters under kind of observation signify: M, micronekton haul; Z. zooplankton haul; H, high-speed net haul between stations; S, seen in the water. Where

concentrations were measured or estimated by more than one method, the highest concentration, corresponding to the first letter, is listed]

Station

Vo. Kind of

Concen-

Station No. Kind of

Concen-

Station No. Kind of

Concen-

observation

tration

observation

tration

observation

tration

Ml.llO>m.'

Ml/mm. 3

Afl./;0>m.'

15

S

>40

33-34

H

6,238

60

S.Z

>40

16...

M

<1

34

S,Z,M

>40

62-63

H

43

17

Z

6

34-35

H

720

63

S, Z,M

>40

ISA

Z

12

35

Z

7

53-54

H

26

20

S,Z

>«

36

Z

36

53-64

H

87

20-21

H

23

37

Z

7

56

Z

>40

21..

S,Z,M

>40

38-39

H

20

67....

M

<1

21-22

H

2

39

Z

41

59

Z

7

23-24...

S

>40

39-40

H

13

60

S

>40

24

z

7

40

M.Z

67

61...

Z

57

24-25

H

20

41

Z

7

62

Z

50

25

M,Z

>40

42....

Z

7

63

Z

7

25-26

H

53

43

S,Z

>40

65

S

>40

26

Z

27

43-44.

H

73

68

Z

>40

27

Z

18

44

Z,M

19

(') -

H

233

29

Z

26

46

S,Z

>40

(')

H

70

29-30.. .-

H

37

46

Z

13

(')

H

150

30

S,Z,M

>40

47

Z,S

>40

(■).... -.-.

H

82

30-31

H

H

704

792

48..

48-49

M,Z

H

144

87

69

S.Z

>40

30-31

W .-

H

>40

33

S.Z

>40

49.

Z

205

33-34

H

>40

49-50

H

260

' After station 68, on northbound track between lat. 23"'40' N. and 25°30' N., at night.
' Immediately after station 69, on northbound track, at night.

tuna distribution offered in this paper is that many
people who are acquainted with the Baja Cali-
fornia fisheiy consider that yellowfin and skip-
jack tunas are distributed in relation to the banks
shown in figure 2 and that abundance is higher
at the banks than elsewhere, except when tempera-
tures are low. No publications clearly demonsti-ate
this relation as far as Baja California is con-
cerned, and no studies off Baja California or else-
where show conclusively the nature of any "bank
effect" which might be attractive to tunas. In
fact, only one such study has be€n attempted
and the results were inconclusive (Bennett and
Schaefer, 1960, at Shimada Bank in the eastern
tropical Pacific). Nevertheless, belief in some kind
of favorable bank effect upon tunas is so wide-
spread that it must be considered here.

The tuna catches charted in figures 4, 6, 8, 10,
12, and l-t may be compared with the bank posi-
tions in figure 2. Many of the catches were made
at or veiT near banks; they can be classified into
two gi-oups. All of those for the periods of cruises
TO-64-2, 6608, TO-59-2, and TO-65-1 were in
or close to tongues or patches of upwelled water,
which either enveloped or touched the banks. None
of the catches in the periods of cruises TO-64— 1
and TO-66-1 were associated with upwelled water.
On TO-64-1 no such water was warm enough for
the tunas to enter, and on TO-66-1 there was none

at all. The charts show also that many catches
were in areas of upwelled water which were not
close to banks, except on cruises TO-64— 1 and
TO-66-1.

When upwelled water of coastal origin extends
over banks, it provides a ready explanation not
only for the catches of tmia on banks (and at
Alijos Rocks, as noted above) but also for the
catches made between the banks. The unspe<;ified
bank effect may exist independently of the upwell-
ing effect, but it is not required to explain the
tuna distributions. If a bank effect exists, it is
probably small in relation to the upwelling effect,
and the banks are probably more suitable for tuna
when upwelled water reaches them (providing it
is not too cold) than when it does not. An observa-
tion from Uncle Sam Bank, which is very fre-
quently visited by fishermen during the tuna
season, is pertinent. Surface temperature charts
for CalCOFI cruises 6007-8 (July 26 to Aug. 13,
1960, in the area of interest) and 6008 (Aug. 20-22,
1960) both show tongues of cool water (but over
20° C.) protruding offshore from the northern
upwelling area. On the earlier cruise the tongue
lay considerably west of Uncle Sam Bank, but on
the later cruise it had changed its position and
enveloped the bank (Scripps Institution of Ocean-
ography, 1962a, 1962b). No tuna catches were re-
corded near the bank during the first cruise period.

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BA.IA CALIFORNIA

173

but some were recorded there during the second
period.

On the other hand, tuna aggregations upon
banks which are not affected by upwelled water
might be primarily attributable to a bank effect.
Further work is needed to establish the reality of
the bank effect and to explain it if it does exist.
Obviously, this research should be attenii^ted in
a situation where upwelling is not likely to inter-
fere with the bank environment, such as one of
the offshore southern banks toward the end of the
tuna season. In the meantime, it is reasonable to
assume that some feature of banks makes them
slightly more attractive to tunas than other areas
when temperatures are suitable, and that this fea-
ture affects tuna distributions in situations where
upwelled water does not interfere. Off Baja Cali-
fornia these situations are probably most common
in the southern j^art of the area, where upwelled
water does not seem to reach far offshore; at the
begimiing of a tuna season when tuna are unable
to enter upwelled water; and after all upwelling
has ceased.

Fishermen often make an additional observation
that tunas aggregate near boundaries between blue
and green water. Some of the results of this study,
especially for cruise TO-64-2, are consistent with
that opinion. Blue water would frequently have
suitable temperature but not much food; green
water may contain suitable food but be too cold.
Tuna would be expected to aggregate at the bound-
arj- under those circumstances.

The relation of tuna to the Cape San Lucas front
was discussed under cruise T0-6ni— 1. Evidence is
lacking that this particular front has any effect
upon tunas independent of the tuna-limiting tem-
peratures that may occur in it. Low temperature
tends to be limiting, whether located in the front
or not, and no other feature of the front seems
to have any effect upon the tunas.

If the area west of Baja California could be
thoroughly and frequently monitored for surface
temperature and surface chlorophyll a during a
tuna season, it would be possible to specify areas in
which aggregations of yellowfin and skipjack tunas
would be expected — including offshore areas which
fishermen might not otherwise visit — and those in
which tuna would not be expected. This work could
perhaps be done from ships, which already yield
much data on surface temperature and could be

equipped to yield data on surface clilorophyll a
(Lorenzen, 1966). The chlorophyll equipment
would be costly, however (about $2,000 per ship),
and require careful maintenance aboard ship.
Overflying aircraft or satellites offer another possi-
bility. They would probably yield much more use-
ful data than ships except in cloudy situations.
Methods of measuring surface temperature from
sensors above the ocean already exist, and measure-
ment of surface chlorophyll is said to be feasible
(Duntley, 1965). Obviously, the chlorophyll in-
formation could assist in mapping distributions
of other useful organisms besides tiuia — for exam-
ple, the red crab itself, a possible human resource
(Longhurst, 1968b), and other herbivores. Tem-
perature data alone would be insufficient to specify
distributions of tuna or red crab.

ACKNOWLEDGMENTS

Many people assisted in the work reported in this
paper. The Inter- American Tropical Tuna Com-
mission supplied data on tuna catches, and the fol-
lowing persons commented on the first draft : G.
Flittner, J. Joseph, "W. Klawe, A. Longhurst, C.
Onuige, E. Owen, "W. Thomas, F. Williams, and B.
Zeitzschel.

LITERATURE CITED

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AxvEKSON, Franklin G.

1963. The food of yellowfin and skipjack tunas in
the eastern tropical Pacific Ocean. Inter-Amer.
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Spanish.]
Anonymous.

1963. CalCOFI Atlas No. 1: CalCOFI atlas of IO-
meter temi)eratures and salinities, 1949 through
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B.\xTER. John L.

1967. Summary of biological information on the
northern auchovy EngrauHs mordai Girard. Calif.
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1960. Studies of physical, chemical, and biological
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Islands during the "Island Current Survey" of
1957. Inter-Amer. Trop. Tuna C-omm., Bull. 4 : 217-
317. [English and Spanish.]

174

U.S. FISH AND WILDLIFE SERVICE

Blackburn, Maurice.

1962. An oceanographic study of the Gulf of Te-
■huantepec. U.S. Fish Wildl. Serv., Spec. Sci. Rep.
Fish. 404, iv + 28 pp.

1963. Distribution and abundance of tuna related to
wind and ocean conditions in the Gulf of Tehuante-
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1965. Oceanography and the ecology of tunas.

Oceanogr. Mar. Biol. Ann. Rev. 3: 299-322.
1968. Micronekton of the eastern tropical PacLflc
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and relations to tuna. U.S. Fish Wildl. Serv., Fish.
Bull. 6T : 71-115.
Blackrurn, Maurice, and Associates.

1962. Tuna oceanography in the eastern tropical Pa-
cific. U.S. Fish Wildl. Serv., Spec. Sci. Rep. Fish.
400. iv + 48 pp.
Blackburn, Maurice, Raymond C. Griffiths, Robert W.
Holmes, and William H. Thomas.

1962. Physical, chemical, and biological observations
in the eastern tropical Pacific Ocean : three cruises
to the Gulf of Tehuantepec. 1958-59. U.S. Fish
Wildl. Serv., Spec. Sci. Rep. Fish. 420, iii + 170 pp.

Boyd, Carl M.

1967. The benthic and pelagic habitats of tJie red
crab, Pleuroncodes planipes. Pac. Sci. 21 : 3!>i— 103.

Beoadhead, Gordon C, and Izadore Barrett.

1964. Some factors affecting the distribution and ap-
parent abundance of yellowfin and skipjack tuna
in the Eastern Pacific Ocean. Inter-Amer. Trop.
Tuna Comm., Bull. 8: 417-473. [English and
Spanish.]

Duntley, Seibert Q.

1965. Oceanography from manned satellites by means
of visible light. In "Oceanography from space," pp.
39-45. Woods Hole Oceanogr. Inst., Ref. 60-IO.

Ebeb, L. E., J. F. T. S.\ur, and O. E. Sette.

1968. Monthly mean charts : sea surface tempera-
ture. North Pacific Ocean, 1949-62. U.S. Fish
Wildl. Serv., Circ. 258, vi + 168 pp.

Griffiths, Raymond C.

1963. Studies of oceanic fronts in the mouth of the
Gulf of California, an area of tuna migrations.
FAO Fish. Rep. 6 : 1583-1605.

1965. A study of ocean fronts off Gape San Luca.s,
Lower California. U.S. Fish Wildl. Serv., Spec.
Sci. Rep. Fish. 499, vi + .54 pp.
Holm-Hansen, Osmund, Carl J. Lorenzen, Robert W.
Holmes, and John D. Strickland.

1965. Fluorometric determination of chlorophyll. J.
Cons. 30 : 3-15.
Joseph, Jambs, and Thomas P. Calkins.

1969. Population dynamics of the .skipjack tuna (Kat-
sutconus pelamis) of the Eastern Pacific Ocean.
Inter-Amer. Trop. Tuna Comm., Bull. 13: 1-273.
[English and Spanish.]

Klawe, Witold L.

1963. Observations on the sjiawning of four species
of tuna (Xcothunnus macroptcrus, Katsuwonus
pelamis, AuTis thazard and Euthynnus lincatus) in

the Eastern Pacific Ocean, based on the distribu-
tion of their larvae and juveniles. Inter-Amer.
Trop. Tuna Comm., Bull. 6: 447-540. [English and
Spanish.]
Laevastu, Taivo, and Horacio Rosa.

1963. Distribution and relative abundance of tunas
in relation to their environment. FAO Fish. Rep.
6 : 1835-1851.
Lee, Arthur J.

1952. The influence of hydrography on the Bear Is-
land cod fishery. Cons. Pemia. Int. Explor. Mer,
Rapp. Proc.-Verb. Reunion 131 : 74-102.
LoNGHUBST, Alan R.

1967. The pelagic phase of Pleuroncodes planipes
Stimpson (Crustacea, Galatheidae) in the Califor-
nia Current. Calif. Coop. Oceanic Fish. Invest Rep.
11: 142-154.
1968a. Distribution of the larvae of Pleuroncodes
planipes in the California Current. Limnol.
Oceanogr. 13 : 143-155.
1968b. The biology of ma.ss occurrences of galatheid
crustaceans and their utilization as a fisheries re-
source. FAO Fish. R«p. 57 : 95-110.
LoNGHURST, Alan R., Carl J. Lorenzen, and William
H. Thomas.

1967. The role of pelagic crabs in the grazing of
phytoplankton off Baja California. Ecology 48 :
190-200.
Lorenzen, Carl J.

1966. A method for the continuous measurement of
in vivo chlorophyll concentration. Deep-Sea Res.
13 : 223-227.

Lynn, Ronald J.

1967. Seasonal variation of temperature and .salinity
at 10 meters in the California Current. Calif. Cocrp.
Oceanic Fish. Invest. Rep. 11 : 1,57-186.

Orange, Craig J.

1961. Spawning of yellowfin and skipjack tuna in the

eastern tropical Pacific, as inferred from studies of

gonad development. Inter-Amer. Trop. Tuna

Comm., Bull. 5: 457-526. [English and Spanish.]

Reid, Joseph L., Gunnar I. Roden, and John G. Wyllie.

1958. Studies of the California Current system.

Calif. Coop. Oceanic Fish. Invest. Rep. 6 : 27-56.

Richards, B^bancis A., with Thomas G. Thompson.

1952. The estimation and characterization of plank-
ton populations by pigment analysis. II. A spectro-
photometric method for the estimation of plankton
pigments. J. Mar. Re.s. 11 : 156-172.
ScHAEFEat, MiLXEas B., Bruce M. Chatwin, and Gordon
C. Bboadheiad.

1961. Tagging and recovery of tropical tunas, 1955-
1959. Inter-Amer. Trop. Tuna Comm., Bull. 5 : 341-
455.
SoRiPPs Institution of Ocelanookaphy, University of
California.

1961. Physical and chemical data : CalCOFI cruises
5908 and 5909. Its Ref. Rep. 61-19, 101 pp.

DISTRIBUTION OF TROPICAL TUNAS OFF WESTERN BAJA CALIFORNIA

175

1962a. Physical and chemical data : CalCOFI cniise

6007-8. Its Ref . Rep. 62-9, 58 pp.
1962b. Physical and chemical data : CalCOFI cruises

6008, 6009, and 6009-10. Its Ref. Rep. 62-10, 90 pp.

1966. Physical and chemical data : CalCOFI cruises
6404 and 6407. Its Ref. Rep. 66-20, 130 pp.

1967. Physical and chemical data : CalCOFI cruises
6507 and 6509. Its Ref. Rep. 67-17, 138 pp.

1968. Physical and chemical data : CalCOFI cruises
6607, 6608, and 6609. Its Ref. Rep. 68-21, 94 pp.

1969. Physical, chemical and biological data : cruise
TO-64-1, June 1964, and cruise TO-64-2, August
1964. Its Ref. Rep. 69^, 57 pp.

Thrailkill, James R.

1956. Relative areal zooplankton abundance off the
Pacific coast. [U.S.] Fish Wildl. Serv., Spec. Sci.
Rep. Fish. 188, i + 85 pp.

Uda, Michitaka.

1957. A consideration on the long years trend of the
fisheries fluctuation in relation to sea conditions.
Bull. Jap. Soc. Sci. Fish. 23 : 368-372.

Wyllie, John G.

1961. The water masses of Sebastian Vizcaino Bay.

Calif. Coop. Oceanic Fish. Invest. Rep. 8: 83-93.
1966. CalCOFI Atlas No. 4 : Geostrophic flow of the

California Current at the surface and at 200 meters.

State of California, Marine Research Committee,

xiii + 288 pp.

176

U.S. FISH AND WILDLIFE SERVICE

U.S. GOVERNMENT PRINTING OFFICE : 1969 O— 362-6S5

YOUNG OF THE ATLANTIC SAILFISH, ISTIOPHORUS PLATYPTERUS'

BY JACK W. GEHRINGER, FISHERY BIOLOGIST

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY

BRUNSWICK, GA. 31520

ABSTRACT

One hundred fifty-four Atlantic sailfish, 26.1 to 216
mm. in standard length, were dip netted on cruises of
the Bureau of Commercial Fisheries charter vessel
Silver Bay off the south Atlantic Coast of the United
States in 1960 and 1962. This group of specimens (larger
than any previously available collection of sailfish of
similar size) was examined to determine changes during
development. Thirty-four eastern Atlantic specimens
13.8 to 238 mm. in standard length that were dip netted
in 1968 on a cruise of the Bureau's vessel Undaunted

in the Gulf of Guinea were compared with the specimens
from the western Atlantic.

Five western Atlantic specimens are illustrated. Loss
of larval characteristics and development of fins and
fin rays and pigmentation are discussed. Correlations
of numbers of fin rays and statistics describing rela-
tionships of measurements of selected body parts for
western Atlantic specimens are presented. Principal
differences between eastern and western Atlantic
specimens are the slightly longer pectoral fin, snout,
and head in eastern Atlantic specimens.

Collections of the young stages of Istiophoridae
that include a sufficient number of larvae and
juveniles for detailed studies of developmental
stages are rare. The literature on young Atlantic
sailfish, Istiophonis platypteru-s (Sliaw and Nod-
der),- is jjrimarily on small larvae and has infor-
mation on only 21 specimens longer than 25 mm.
SL (standard length) — (Voss, 1953, 4 specimens
29.5-208 mm.; Gehringer, 1957, Ifi specimens
27.4-101 mm.; and de Sylva, 1963, 1 specimen,
167 mm.).

This paper is based primarily on a collection of
154 sailfish from the western Atlantic Ocean, 26.1
to 216 nun. SL. They were collected At dip net and
nightligiit stations on cruises of the BCF (Bureau
of Commercial Fisheries) charter vessel Silver
Hay off the southeastern coast of the United States
in June and July 1960 and September and October
1962. Subsequent to my examination of the west-
ern Atlantic specimens and preparation of a draft
of a manuscript describing them, I examined 34
specimens, 13.8 to 238 mm. SL (all but 1 over
25 mm. SL), collected by dip net at nightlight
stations on a cruise of the BCF vessel Vndmmted

' Contribution No. 95 from the Burea\i of Commercial Fisheries
Biological Laboratory, Brunswick. Ga. 31520.

-In using the name Istiophonis platyptcrua (Shaw and
Nodder), I follow Morrow and Harbo (1969).

Published .Tanuar.v 1970.

FISHERY BULLBTIN: VOL. 68, NO. 2

in the Gulf of Guinea, ofi' the west coast of Africa,
in April 1968.

For western Atlantic specimens I include
detailed line drawings of a developmental series,
statistics showing the relationships of measure-
ments of selected body parts, and discussions of
dorsal and anal fin rays and changes during their
development. I compare eastern and western
Atlantic specimens of similar size and include in
my discussion of western Atlantic material those
variations I found in eastern Atlantic material.

METHODS AND DATA
MEASUREMENTS

Measurements were made with dial calipers
calibrated in 0.1 -mm. units and are recorded to the
nearest 0.1 mm. if less than 100 mm. or to the near-
est millimeter if 100 nnn. or greater.

DEFINITIONS OF TERMS

I consider all specimens in this study to be
juveniles, by definition of the juvenile stage as
sexually immature specimens whose numbers of
fin rays are within the ranges for the adult.

Measurements

Standard length, head length, snout length,
pectoral and pelvic fin lengths, eye diameter, and

177

pterotic and main preopercular spine lengths are
as defined by Gehringer (1957). Trvnik length is
the distance between the posteriormost margin of
the orbit and anterior point of emergence of the
upper keel on the caudal peduncle on specimens
85 mm. SL or longer (de Sylva, 1957). On speci-
mens smaller than about 85 mm. SL, which lack
keels, the posterior point for this measurement is
the insertion of the leading edge of the finfold of
the dorsal lobe of the caudal fin. This point is
directly above the anterior edge of the caudal keel
on larger specimens. Body length is the distance
between the tip of the mandible and the tips of
the midcaudal fin rays (Rivas, 1956). Body depth
is a vertical measurement at the insertion of the
first pelvic fin i-ay. Pelvic fin to anal fin is the dis-
tance between the insertion of the first pelvic fin
ray and the insertion of the first anal fin ray.

Fin Rays

The dorsal and anal fins are single fins in the
larval and juvenile stages, but in the adult the
terminal six or seven rays of both fins are sepa-
rated from anterior portions of these fins to form
second dorsal and anal fins. The fins are not
divided in the largest specimens in this study, 216
to 238 mm. SL, although the anal fin is nearly
divided. Even on my smallest western Atlantic
specimen (26.1 mm. SL), the shape and size of
the terminal six or seven rays distinguish them
from the few, less robust, more widely spaced rays
immediately ahead of them (which are overgrown
with tissue in the adult). I recorded ray counts
separately for the anterior and po.sterior j^ortions
of both dorsal and anal fins. The terminal ray in
the dorsal and anal fins though divided to its base,
is recorded as one ray.

STUDY MATERIAL

Western Atlantic specimens are from Silver Bay
cruises, all taken by dip net at the surface, under
a nightlight: Sta. 2139: 29°55' N., 80°38' W.
(about 35 nautical miles E. of St. Augustine,
Fla.) ; 2045-2245 hours, June 12, 1960; 33 m., sur-
face temperature 25.6° C; 3 specimens, 81.9 to
155 mm. SL. Sta. 2172: 35°00' N., 75°19' W.
(about 20 nautical miles SE. of Cape Hatteras,
N.C.) ; 2200-0250 hours, July 18-19, 1960; 146 to
366 m., surface temperature 27.3° C. ; 10 sj^eci-
mens, 67.1 to 216 mm. SL. Sta. 2201: 34°34' N.,
75°40' W. (about 50 nautical miles E. of Cape

Lookout, N.C.) ; 0030-0400 hours, July 24, 1960;
146 to 165 m., surface temperature 28.9° C; 135
specimens, 26.1 to 167 mm. SL. Sta. 2268:
32°36' N., 78°30' W. (about 70 nautical miles E. of
Charleston, S.C.) ; 0115-0300 hours, July 29, 1960;
190 to 198 m., surface temperature 28.9° C. ; 4 speci-
mens, 37.1 to 91.1 mm. SL. Sta. 4326:28°32' N.,
80°03' W. (about 25 nautical miles E. of Cape
Kennedy, Fla.) ; 2310-0115 hours, September 3^,
1962; 70 m., surface temperature 27.8° C. ; 1 speci-
men, 137 mm. SL. Sta. 4403: 28°56' N., 80°25' W.
(about 30 nautical miles N. of Cape Kennedy,
Fla.) ; 2345-0145 hours, October 4-5, 1962; 24 m.,
surface temperature 28.9° C. ; 1 specimen, 169 mm.
SL.

Eastern Atlantic specimens are from Undaunted
Cruise 6801, all taken by dip net at the surface,
under a nightlight : Sta. 126 : 00°11' S., 08°39' E. ;
2000-2400 hours, April 16, 1968 ; 1,080 m., surface
temperature 28.8° C. ; 1 specimen, 104 mm. SL. Sta.
132: 00°38' N., 07°21' E.; 1900-2400 hours, April
17, 1968; 2,664 m., surface temperature 29.6° C; 3
specimens, 29.9 to 49.8 mm. SL. Sta. 138 : 01°20'
N., 07°55' E.; 2030-0230 hours, April 19-20, 1968;
2,400 m., surface temperature 28.6° C. ; 13 speci-
mens, 13.8 to 147 mm. SL. Sta. 152: 02°25' N.,
06°29' E.; 2200-0200 hours, April 23-24, 1968;
1,520 m., surface temperature 28.9° C; 1 specimen,
47.9 mm. SL. Sta. 158 : 04°52' N., 05°34' E. ; 0000-
0215 hours, April 25, 1968 ; 240 m., surface temper-
ature 28.8° C. ; 16 specimens, 29.5 to 238 mm. SL.

All study material is cataloged in the fish col-
lections of BCF Tropical Atlantic Biological Lab-
oratory, Miami, Fla.

DEVELOPMENT AND GROWTH

My discussion of changes during development
and growth concerns loss of larval characteristics,
pigmentations, fin rays, and relations of measure-
ments of various body parts.

LOSS OF LARVAL CHARACTERISTICS

Within the size range represented here, head
spines are lost, scales undergo changes, caudal
keels develop, and changes occur in the doi"sal,
anal, and ])el\ic fins.

Head Spines

In an earlier paper on the Atlantic sailfish
(Gehringer, 1957). I reported pterotic and pre-
opercular spines on a 101-mm. SL specimen. Voss

178

U.S. FISH AND WILDLIFE SERVICE

(1953) stated that these spines were not present
on a 208-mm. SL specimen. In the present large
series of western and eastern Atlantic sailfish, pte-
rotic spines are present only as traces on some fish
as short as 100 mm. SL, are present on all fish up
to 150 mm. SL, and are absent on specimens longer
than 150 mm. SL. Preopercular spines are present
on all specimens but the largest, 216 to 238 mm.
SL — they are probably lost at about this size.

Scales

Scale spines are first discernible on the dorsolat-
eral surface of the body on sailfish about 30 mm.
SL. Specimens about 50 mm. SL have spines on the
cheeks and most of the body, except for the area
on the side covered by the depressed pectoral fin
and on the back along the anterior portion of the
dorsal fin. Scales on the largest specimens, 216 to
238 mm. SL, are cycloid and differ from the illus-
tration and description of scales on a 101-mm. fish
(Gehringer, 1957) as follows : shape more elliptical
than round, spine relatively shorter and weaker,
and concentric ridges greater in number. On all
specimens longer than 30 mm. SL the spine tips
protrude through the skin and give a feeling of
roughness.

Development of Caudal Keels

Two keels on each side, extending from the base
of the caudal fin onto the caudal peduncle, develop
at about 84 to 92 mm. SL. The smallest sailfish
with keels is 83.8 mm. SL, and the largest without
keels is 91.4 mm. SL. The upper keel apparently
develops first as it is the only one present on the
few fish 85 to 90 mm. SL with but one keel.

Development of Dorsal and Anal Fins

As discussed under definitions of terms, the last
six or seven rays of both dorsal and anal fins form
distinct second fins in the adult. The dorsal and
the anal fins on all specimens in the present series
are single and continuous. On larger specimens the
few anal rays immediately forward of tiie terminal
six or seven rays are small and weak; these rays
are weak and overgrown with skin in the adult.
Dorsal rays in this relative position are not so
weak, but are less robust than those immediately
ahead or behind which do not become overgrown
with skin. On most specimens over SO mm. SL,
the distal portion of the anal ray immediately
ahead of the terminal six or seven ravs is de-

pressed, overgrown with tissue, and nearly adnate
to the base of the succeeding ray.

Pelvic Fin

The first and second rays of the pelvic fin, which
in the adult are fused into one robust bony ray,
are nearly fused on the largest specimens, 216 to
238 mm. SL — the first ray appears as a short, tri-
angular-shaped segment of the leading edge of
the second ray. The third ray is separate and dis-
tinct at all sizes.

PIGMENTATION

Pigmentation of Atlantic sailfish larvae, juve-
niles, and adults has been described by several
authors, including Voss (1953), Gehringer (1957),
Robins and de Sylva (1963) , and de Sylva (1963) .
My comments here on pigmentation of fins and
body bars supplement these accounts for .speci-
mens 26 to 238 mm. SL and apply to both eastern
and western Atlantic specimens.

Fins

The pectoral fins are clear except for a few
melanophores at the bases of the first few rays
on the largest specimens.

The pelvic fins are lemon-yellow with a few
melanophores on the membrane between the sec-
ond and third rays on sailfish over 155 mm. SL.

Pigment on the anterior portion of the dorsal
fin is uniformly dusky to dark except for two to
several large, dark spots scattered in a nonuniform
pattern over the fin (figs. 1-5). On some fish the
first few dorsal rays are less densely pigmented
than the rest of the fin. Pigment extends posteri-
orly on the fin to the 34th to 40th ray — the last few
rays of the anterior portion have no pigment. The
posterior portion (terminal six or seven rays) of
the fin is clear except for pigment on the bases of
the fin rays and fin membrane on specimens longer
than about 135 mm. SL.

The anal fin is clear on all specimens.

The smallest sailfish with jiigment on the caudal
fin is 44.2 mm. SL; the largest without pigment on
the caudal fin is 51.7 mm. SL. A group of a few
melanophores is present on the lower lobe of the
caudal fin of a series of fish 44.2 to 60.0 mm. SL,
and a similar group of melanophores is also on the
upper lobe of a series of specimens 50.0 to 64.0 mm.
SL. The melanophores are coalesced into blotches
on several fish 53.2 to 67.0 mm. SL, and, though

YOUNG OF ATLANTIC SAILFISH

179

^*^<

Figure 1. — Juvenile saillish, 37.1 mm. standard length, Silver Bay Sta. 2268.

Figure 2. — Juvenile sallflsh, 55.1 mm. standard length, Silver Bay Sta. 2268.

larger and covering more of the fin lobes, the
blotches are distinct on a series of specimens 101 to
119 mm. SL. On a 190-mm. SL sailfish, pigment
spreading posteriorly from the base of the fin joins
that spreading anteriorly on the lobes and covers
the fin except for the distal half of the middle se\-en
caudal rays and ray membrane, which remain clear.
On the largest specimens, 216 to 238 mm. SL, the
clear area of the middle part of the caudal fin is

reduced to the distal third of the middle six caudal
rays and ray membrane, the lobes of the caudal fin
ai-e dusky, and the tissue covering the bases of the
rays is densely pigmented.

Body Bars

Pigment on the sides of the body is concentrated
in five to seven bars on fish of about 30 mm. SL.
Bars are not discernible on smaller specimens. Sail-

180

U.S. FISH AND WILDLIFE SERVICE

FlQUBE 3. — Juvenile sallflsh, 98.9 mm. standard length, Silver Bay Sta. 2201.

FiGUKE 4. — Juvenile sailfisli, 155 mm. standard length, Silver Bay Sta. 2139.

fish about 100 mm. SL have 7 to 12 bars, and tlie
few specimens between 150 and "200 mm. SL have
12 to 14 bars. The largest western Atlantic speci-
men, 216 mm. SL, has 22 bars. Throughout the
size range examined here the bars are distinct on
some fish but indistinct on others and arranged in
pairs on some specimens but not on others.

FIN RAYS

The numbei-s of fin rays for western and eastern
Atlantic specimens with undamaged fins are

witliin the adult complements. I prepared tables
of mimbers of fin rays for western Atlantic speci-
mens only. The fins of a number of eastern Atlantic
specimens were damaged, and too few counts are
available to make usefid tables. The nuniljers of
fin rays for eastern Atlantic specimens are within
the ranges for western Atlantic specimens, except
for a few differences which are mentioned in the
discussions.

The total number of dorsal fin rays ranges from
■47 to 56 (mean, 51.6) for 142 western Atlantic

YOUNG OF ATLANTIC SAILFISH

181

FiGDBE 5. — Juvenile sailfish, 216 mm. standard length, Silver Bay Sta. 2172.

specimens ■■' (one eastern Atlantic specimen has
57), and the total number of anal fin rays ranges
from 21 to 25 (mean, 23.6) for 143 fish (one eastern
Atlantic si>ecimen has 20). Table 1 shows the total
numbers of dorsal and anal fin rays for 139 west-
ern Atlantic sailfish.

Table 2 shows the numbers of rays in the
anterior and posterior portions of the dorsal fin
for 142 western sailfish. The range for the anterior
portion is 43 to 50 (mean, 45.0) for 46 specimens
(32.4 percent) with six rays in the posterior por-
tion (51 for one eastern Atlantic specimen), and
40 to 49 (mean, 45.0) for 96 specimens (67.6 per-
cent) with seven rays in the posterior portion. Tlie

■■' The numbers o( fish shown in tables 1 to 4 are not the same.
Of the 154 western Atlantic specimens, 139 had complete (un-
damaged) dorsal and anal fins, the rest had a complete dorsal
or anal fin. or complete anterior or posterior portions of these
fins. To take advantage of the greatest number of specimens for
correlations. I used all sailfish with counts for desired fins or
portions of fins. The same fish were not always involved.

mean of total number of rays in the dorsal fin is
51.0 for western Atlantic siiecimens with six rays
in tlie posterior portion and 52.0 for those with
seven rays in the posterior portion.

Table 3 shows the numbers of rays in the
anterior and posterior portions of the anal fin for
143 western Atlantic sailfisli. The range for the
anterior portion is 15 to 19 (moan. 17.3) for 66
specimens (46.2 percent) witli six rays in the pos-
terior ])ortion (14 for one eastern Atlantic speci-
men), and 14 to IS (mean, 16.8) for 77 si)ecimens
(53.8 percent) with seven rays in the posterior
l)oi-tion. The mean of total numl)er of rays in the
anal tin is 23.3 for western Atlantic specimens with
six rays in the posterior portion and 23.8 for those
with seven rays in the posterior portion.

Table 4 shows the numbers of fin rays in the
posterior portions of the dorsal and anal fins for
the western Atlantic sailfish. Nearly half (46.8
])ercent) of 141 specimens have seven rays in this

Table 1. — Number and (in parentheses) percentage of sailfish with different combinations of dorsal and anal fin

rays, in a series of 139 specimens from the western Atlantic

Anal fin rays

Dorsal fin rays

47 48 49 50

Number Number Number Number Number

21 1

22 4 3

(2.9) (2.2)

23 17 9

(0.7) (5.0) (6.5)

24 1 , 3 7

(0.7) (2.2) (5.0)

25 2 1

(1. 4) (0. 7)

51

52 53 54 55 56

Number Number Number Number Number

1 -

(0.7)

1

(0.7)

10 8 3 1

(7.2) (5.8) (2.2) (0.7)

11 9 8 2 1
(7.9) (6.5) (5.8) (1.4) (0.7)

5 5 6 1

(3.6) (3.6) (4.3) (0.7)

Number

4
(2.9)

(6.6)

14

(10. 1)

1
(0.7)

182

U.S. FISH AND WILDLIFE SERVICE

Table 2. — Number and (in parentheses) percentage of sailfish with different combinations of fin rays in the anterior
and posterior portions of the dorsal fin, in a series of 142 specimens from the uestern Atlantic

Posterior portion
fin rays

Anterior portion fin

rays

40

41

42

43

44

45

46

47

48

49

60

Number
6

Number

Number

Number

Number

10
(7.0)

11
(7.7)

Number

9

(6.3)

18

(12.7)

Number

11

(7.7)

19
(13.4)

Number

10

(7.0)

21

(14.8)

Number

(1^4)

15

(10.6)

Number

3

(2.1)

3
(2. 1)

Number

Number
1

7

1
(0.7)

•>

5
(3.6)

(0.7)

(0.7)

Table 3. — Number and (in parentheses) percentage of
sailfish with different combinations of fin rays in the
anterior and posterior portions of the anal fin, in a
series of 143 specimens from the western Atlantic

Posterior

portion fin

rays

Anterior portion fin rays

16

17

Number Number Number Number Number Number

1 11 27 23 4

(0.7) (7.7) (18.9) (16.1) (2.8)

1 4 20 33 19

(0.7) (2.8) (14.0) (23.1) (13.-3)

portion of both tins, 24.8 percent have six rays in
each, 20.f) percent hnve seven dorsal and six anal
rays, and the rest (7.8 percent) have six dorsal
and seven anal rays. Twenty (about 75 percent)
of 27 eastern Atlantic specimens have six rays in
both tins.

The numbei- of pectoral tin rays ranges from 17
to 20; 10 (6.9 percent) of 145 western Atlantic
specimens have 17, 126 (86.9 percent) have 18, 8
(5.5 percent) have 19, and 1 (0.7 percent) has 20.
Fifteen of 28 eastern Atlantic specimens have 17
rays, 12 have 18, and 1 lias 19.

All specimens iiave nine npi^er and eight lower
principal caudal rays. Counts were 11 or 12 upper
and lower secondary caudal rays for several speci-
mens (40-216 mm. SL) which were cleared and
stained or X-raved.

T.VBLE 4. — Number and (in parentheses) percentage of
sailfish with different combinations of fin rays in
the posterior portions of the dorsal and anal fins, in a
series of I4I specimens from the uestern Atlantic

Dorsal fin

rays

6

7

Number
6

7

Number

35

(24.8)

11

(7.8)

Number

29
(20.6)

66
(46.8)

Fin-ray counts given by Robins and de Sylva
(1963) for adult Istiopliorus pl<it,ypterus are:
dorsal spines, 40 to 49; second dorsal rays, 6 to 8
(1 of 59 fish had 8 rays) ; anal spines, 12 to 17;
second anal rays, 6 to 8 (1 of 59 fish had 8 rays),
pectoral rays, 18 to 21. The difference between
their range of 40 to 49 dorsal spines and my range
of 43 to 50 rays in the anterior portion of the
dorsal fin and their range of 12 to 17 anal spines
and my range of 14 to 19 rays in the anterior por-
tion of the anal tin may reflect degeneration of
several rays immediately ahead of the second
dorsal and anal fins and tlieir overgrowth by skin
in the adult. A comparison of the percentages of
my fish with six and seven rays in the posterior por-
tions of the dorsal and anal fins with the informa-
tion given by Robins and de Sylva is interesting.
Roughly, one-third of their and my (western At-
lantic) fish (32.2 percent and 32.4 percent, respec-
tively) had six second dorsal fin rays and two-
thirds (66.1 percent and 67.6 percent, respectively)
had seven second dorsal fin rays (they recorded one
fish with eight second dorsal rays, I had none).
They recorded these same percentages of sailfish
for numbers of second anal rays; 32.2 percent with
six, 66.1 percent witli seven, and one with eight
rays. My counts are different; they show 46.2 per-
cent with six rays, 53.8 percent with seven, and
none with 8 in the posterior portion of the anal fin.

REGRESSIONS OF BODY PARTS
ON TRUNK LENGTH

Comparisons of the changes in various body
parts of fishes during development have been
variously based on standard, fork, or total length.
The snout and caudal rays are .so frequcntlj-
damaged in the billfishes that measurements in-
volving one or both of these parts may be inaccu-
rate. Body length, recommended by Rivas (1956)
as the preferred ba.se length for billfishes, is the
distance between the tip of the mandible and the

YOUNG OF ATLANTIC SAILFISH

183

tips of the middle caudal fin rays. This measure-
ment involves fin rays that are fragile and fre-
quently damaged on small specimens. The base
length that I selected for my comparisons is the
trunk length, defined by de Sylva (1957) as the
distance between the posterior margin of the orbit
and the anterior insertion of the caudal keels. This
length involves neither the snout nor the caudal
rays.*

* See definition for trunk lengtli in section on methods and data
for determination of posterior point for this measurement of
sailfish without caudal Iteels.

Initially, individual measurements of selected
body parts of the western Atlantic sailfish were
plotted against trunk length on arithmetic paper
(figs. 6-l;2). The distribution of tlie data suggested
that the relatively fewer specimens with trunk
length greater tJian (iO mm. should l>e treated sepa-
rately. Two regression lines were calculated — one
for those with trunk length less than 62 mm. and
one for longer specimens. The regression equation
is Y=a + bX (table 5). Inspection of the graphs
with tlie calculated regression lines added suggests
tliat tlie location of point of inflection varies some-

100 -

80

t.

60 -

<

40 -

20

1 —

, , , ,

1 1

1

1

' '

1

1 ' '

' 1

1 1

' 1

I

O

T

-

-

-

».

-

'

y^

-

-

•

-

-

.y

-

y^

-

-

O

e

-

—

y^

•

—

-

X '

-

-

•.

-^t'

-

-

y^

-

_

e

-

c
• J*

/

-

-

o

■^'''

-

—

o

r^_

v^

—

-

.•

-

-

OOO.

■^

-

—

.r

—

•

-

-

1

. 1 1 1

1 1

1

1

1 1 1

1 1

1

1 1

. 1

1 1

1 1

1

1

20

40 60 80

TRUNK LENGTH (MM.)

100

120

Figure 6. — Relation of head length to trunk length in sailfish. Small dots represent western Atlantic sijecimens ; open
circles, eastern Atlantic specimens. Regression lines represent western Atlantic data only.

184

U.S. FISH ANB WILDLIFE SERVICE

80

60

o

z

^, 40

3

o

Z

10

20

I I r^

I I I

1 I r^

~T 1 I I I 1 r-

I I t I r I I

±

_L

20

40 60 80

TRUNK LENGTH {f^/A.

100

120

Figure 7. — Relation of snout length to trunk length in sailfish. Small dots represent western Atlantic specimens ; open
circles, eastern Atlantic specimens. Regression lines represent western Atlantic data only.

~i 1 1 1 1 1 r

T 1 r

8 -

t
t

5 4
<

o

>-
tu

-J I L.

J ] I I L

-J 1 I I I I u

20

40 60 80

TRUNK LENGTH (f^//^.)

100

120

riouRE 8. — Relation of eye diameter to teimk length in sailtisli from the western Atlantic.
YOUNG OF ATLANTIC SAILFISH

185

15

I—

o
O

10

1 1 1 1 1 1 1 1 1 r-

T 1 1 1 r-

-I 1 1 1 1 r

_L

_L

20

40 60 80

TRUNK LENGTH (MM.)

100

120

Figure 9. — Relation of bcxly depth to tnink length in sailfish from the western Atlantic.

Table .5. — Slatisties describing regressions of body parts on trunk length, or body length, for sailfish from the

western Atlantic

Ix, mean ot values of X; y, mean of values of Y; N, number of specimens; b, slope of regression line; a, Y-intercept of regression line; Sy.x, standard deviation

from regression (standard error of estimate)]

Independent variable X and specimen size '

Dependent variable Y

Sy.x

Trunk length:

Small _ Head length..

Large _ do

Small Snout length

Large do.__

Small Eye diameter

Large ..do

Small Body depth

Large do

Small Pectoral fin length.

Large do

Small Pelvic fin length...

Large do

Small Pelvic fin-anal fin..

Large ...do

Body length:

Small Trunk length

Large do

37.92

35.87

130

0.942

0.142

1.610

86.04

78. 32

24

.694

18. 592

3.263

37. 'J2

26.37

130

.782

-3. 279

1.517

gfi.04

60. 94

24

.538

14. 619

3.2«l

37.65

3.30

121

.045

1.6'26

.111

86.66

5.19

23

.029

2.677

.273

37.92

6.20

130

.W,!

2.067

.273

86.04

11.92

24

.r27

. 997

.367

37.92

5.82

127

. 109

1.678

.372

83.85

9. 99

18

.078

3. 421

.444

37.26

15.04

124

.405

-.042

.937

83.85

33.40

18

.348

4.237

1.499

37.92

18.64

130

.486

.227

.510

86.04

41.32

24

.477

.282

.923

52. 87

37.58

124

.786

-3. 961

.981

14.38

85.79

22

.796

-6.204

1.377

> Small, 16.0-61.5 imn. trunk length; large, 64.5-126 mm. trunk length.

186

U.S. FISH AISTD WILDLIFE SERVICE

1 —

— 1 1

1

T

1 1

1 1 1 1 1 1

' ' 1

1 1

' 1

1 1

1 oi

T

.

o,---'

^^•

?

e

^""^

5

10

»" >-

,„<<

I

' .p^^^t

(-

^-^''^

o

-

•

^^^^

-

z

* ^'^

LU

_

*' >^*^^

_

_l

• s*^^r^"" .

z

-

<r 'y^ •'

.

• * i>*^*

u.

o

.

—J

<

6^

. • ' '

o:

5

—

J •

'^'

^

O

%■

^

*•• •

1-

_j^

•

U

'

^

^

*

"

LU

7^

•

Q.

1

J 1

1

1

1 1

1 1 1 1 1 1

1 1 1

1 1

1 1 1

1 ,

I

20

40 60 80

TRUNK LENGTH (MM.)

100

120

Figure 10. — Relation of pectoral fin length to trunk length in sailfish. Small dots represent western Atlantic specimens;
open circles, eastern Atlantic specimens. Regression lines represent western Atlantic specimens only.

--: 50

•s.

40

o

z

30

20

y
>

10

\ I I I I r^

\ I I r^

_i I L_

_i I i_

_1 1 L_

_1 I L_

_] I L.

20

40 60 80

TRUNK LENGTH (MM.)

100

120

Figure 11. — Relation of pelvic fin length to tnnik length in sailfish from the western Atlantic.
YOUNG OF ATLANTIC SAILFISH

187

60

5
5

40

<

z
<

I

z

y 20
>

"T 1 1 1 1 1 1 I I r

±

_L

20

40 60 80

TRUNK LENGTH (MM.)

100

120

FiouKE 12.— Relation of the distance pelvic fin-anal fin to trunk length in sailfish from the western Atlantic.

what with body part and tliat some parts have little
or no inflection. Figure 13, which illustrates the
regression of trunk length on body length, is in-
cluded to show that tliis relation is rectilinear
throughout the size range; the calculated regres-
sion line for specimens with trunk length greater
than 62 mm. has the same slope (b) and is merely
an extension of that for smaller fish.

Subsequent to preparation of plots of data and
calculation of regression lines for western Atlantic
sailfish, I obtained measurements from 34 eastern
Atlantic fish and plotted them on graphs. The data
from the eastern Atlantic are too meager, however,
for making calculations of regressions — the num-
ber of specimens is too small and the size distribu-
tion is poor. Because the greater numbers of west-
ern Atlantic specimens might possibly hide diifer-
ences between the two groups if the data were com-
bined, I plotted them separately on the same
graph, distinguishing the two groups. I shall limit
my conunents to dift'erences this simple comjjarison
suggests.

The individual plots of data for eastern Atlantic
sailfish generally lie within the ranges for fish from
the western Atlantic for eye diameter, body depth,
pelvic fin length, and distance from pelvic fin to

anal fin ; these data are, therefore, not shown on
the figures showing these relations (figs. 8, 9, 11,
and 12, respectively). Measurements of snout
length, liead length, and pectoral fin length, how-
ever, generally lie higher on the graphs for fish
from the eastern Atlantic than for those from the
western Atlantic (figs. 6, 7, and 10). The longer
head (fig. 6) is attributable to the generally longer
snout (fig. 7). The pectoral fin is also generally
longer in eastern Atlantic sailfish (fig. 10).

ACKNOWLEDGMENTS

Staff members of BCF Biological Laboratory,
Brunswick, Ga., helped collect western Atlantic
specimens, made X-ray photographs, and cleared
and stained study material ; they also prepared il-
lustrations and reviewed the manuscript. Person-
nel of BCF Exploratory Fishing and (iear Re-
search Station, Brunswick, Ga., also helped collect
western Atlantic specimens. George C. Miller, of
BCF Tropical Atlantic Biological Laboratory,
Miami, Fla,, made available eastern Atlantic speci-
mens collected off west Africa. Grady W. Reinert
prepared illustrations, and Elbert H. Ahlstrom,
Donald P. de Sylva, and R. Michael Laurs re-
viewed the manuscript.

188

U.S. FISH AND WILDLIFE SERVICE

5

O

z

'^ 60

z
3

-I r 1 1 1 r-

BODY

80
LENGTH

(MM.

FiGUBE 13. — Relation of trunk length to body length in sailfish from the western Atlantic.

LITERATURE CITED

De Sylva, Donalu p.

1957. Studies on the age and growth of the Atlantic
sailfish, Ixtiophorus iimcriraniis (Cuvier), using
length-frequency curves. Bull. Mar. Sci. Gulf
Carib. 7 : 1-20.

1963. Postlarva of the white marlin, Tctrauturus
albidiis. from the Florida Current off the Carolinas.
Bull. Mar. Sci. Gulf Carib. 13 : 123-132.
Geiikinger, Jack W.

1957. Observations on the development of the At-
lantic sailfish I.itioiihoniK (niirriraniiK (Cuvier),
with notes on an unidentified si^ecies of istiophorid.
U. S. Fish Wilill. Serv., Fish. Bull. .")7 : 139-171.

Morrow, James E., and Samuel J. Harbo.

1969. A revision of the sailfish genus Istiophorus.
Copeia 1969: 34-44.
RivAS, Luis Rene.

1956. Definitions and methods of measuring and
counting in the billfishes ( Istiophoridae, Xiphi-
idae). Bull. Mar. Sci. Gulf Carib. 6: 18-27.
Robins, C. Richard, and Doxald P. De Sylva.

1963. A new western Atlantic si)earfish. Tctrup-
tiirus pflttcgcri. with a rede.scription of the Mediter-
ranean spearfish Tctraptiiriin helonc. Bull. Mar.
Sci. Gulf Carib. 13 : S4-122.
Voss, Gilbert L.

19.'53. A contribution to the life history and biology
of the .sailfish, Istioplionis (imeriraiuis Cuv. and
Val., in Florida waters. Bull. Mar. Sci. Gulf Carib.
3: 206-240.

YOUNG OF ATLANTIC SAILFISH

189

MOLLUSKS AND BENTHIC ENVIRONMENTS IN HILLSBOROUGH BAY,

FLORIDA'

BY JOHN L. TAYLOR, JOHN R. HALL, AND CARL H. SALOMAN, FISHERY BIOLOGISTS

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY
ST. PETERSBURG BEACH, FLA. 33706

ABSTRACT

Analysis of benthic mollusks and sediments at 45
stations showed that the diversity and abundance of
mollusks was affected by bottom conditions which were
influenced in varying degrees by domestic and industrial
pollution and dredging. Nineteen stations had no living
mollusks, 18 stations had one or more of the four mol-
lusk species that were predominant, and 8 stations had
mollusks well represented by numerous species and
large numbers of individuals. Stations with no living
mollusks were termed unhealthy, and others were

This rei^ort treats the relation of diversity and
abundance of molhisks to bottom conditions in
Hillsborough Bay, Fla., where dredging and pollu-
tion from domestic and industrial sources now con-
trol the ecology. The data are from benthic and
hydrological surveys by the Bureau of Commercial
Fisheries Biological Laboratory, St. Petersburg
Beach, Fla., during August and September 1963.

The problem of pollution in coastal waters has
stimulated research to establish environmental
quality criteria based on physical, chemical, and
biological components of marine and brackish
water connnunities. Mollusks are useful in such
studies because the group is well described taxo-
nomically and contains species that vary gre4^tly
in habitat selection, mode of feeding, and tolerance
to environmental change. Furthermore, most mol-
lusks are sedentary as adults and the remains of
their shells provide a semipermanent record of
their occupancy.

The ecology of mollusks in natural waters has
been studied by a number of authors. Previous
studies on the ecology of mollusks in natural and
l^olluted waters of the southeastern United States
provided a basis for the interpretation of collec-
tions from Hillsborough Bay. Reports on mollusk
assemblages in unpolluted estuaries included work
by Ladd (1953), Parker (1960), and Brett
(196.']). Within the same geographic area, studies
of mollusks in polluted estuaries include work

' Contribution No. 56, Bureau of Commercial Fisheries Biological Lab-
oratory, St. Petersburg Beach, Fla. 33706.

Published March 1970.

FISHERY BULLETIN: VOL. 68, NO. 2

designated marginal or healthy on the basis of the
mollusks present. From station data, isopleths connect-
ing similar areas indicated that 42 percent of the bay
bottom was unhealthy, 36 percent marginal, and 22
percent healthy. Infrequent occurrence of the American
oyster (Crassostrea virginica) further suggests that the
major portion of Hillsborough Bay was seriously con-
taminated. An appendix has a checklist of the 64 species
of mollusks collected in the bay.

on the ecological effects of petroleum wastes
(Mackin and Hopkins, 1961), pesticides (Butler,
1966), siltation and dredging (Mackin, 1961),
channelization (Chambei-s and Sparks, 1959), and
domestic sewage (McNulty, 1966). The work by
]\IcNulty, and an earlier series of studies with
collaborators, represent a comprehensive study
over a period of 11 years in Biscayne Bay, Fla.,
before and after pollution abatement.

ECOLOGICAL FEATURES OF
HILLSBOROUGH BAY

Hillsborough Bay lies in the upper part of
Tampa Bay. east of Interbay Peninsula and north
of a line between Gadsden Point and Newman
Branch (fig. 1). The 56-km. shoreline encom-
passes a water area of about 10,360 ha. Forty per-
cent of this area is 1.8 m. or less, and except for
dredged ship channels up to 10.5 m. deep, the great-
est depth in the bay is about 5.4 m. Tidal range is
normally 0.9 in. or less, and maximum tidal cur-
rent is under 51 cm./second (1 knot) — see Olson
and iVIorrill (1955) and Taylor and Saloman
(1969). Portions of the bay around Davis Island,
Seddon Island, McKay Bay, and Port Sutton have
l>een dredged for fill material or deepened for
shipping (fig. 1). Other dredging in the bay cen-
ters around oy.ster shell deposits which are used
for the construction industry (Dawson, 1953).
These deposits are extensive and show that the
American oyster, Grassostrea virginica^ once

191

417-060 O - 71

Figure 1. — Tampa Bay and Hillsborough Bay showing channels, stirvei}' transects, collecting .stations, and
environmental conditions at each station — healthy stations (unshaded) ; marginal stations (half-shaded) ;
imhealthy stations (shaded) — August and September 1963.

192

U.S. FISH AND WILDLIFE SERVICE

flourished in Hillsborough Bay as it does today
along most of the Gulf Coast between Cape Sable
and the Rio Grande (Butlei-, 1954). The annual
mean and range of salinity (22.20 and 12.65-27.84
p.p.t.), water temperature (24.96° and 11.65°-
34.00° C), and other hydrological features of the
bay have been reported by Saloman and Taylor
(1968).

In addition to considerable physical alteration
of the bay, water chemistry and resident biota have
changed decidedly as a result of domestic and
industrial sewage. The principal identified pollu-
tants are compounds of phosphorus and nitrogen,
and highly organic suspended .solids. Regional
sanitation plants provide only primary sewage
treatment for 120,000 m.Vday (30 m.g.d.— million
gallons per day) and serve a population of about
300,000. The treated effluent carries more than 50
percent of the suspended solids present before
treatment and adds an enormous load of phos-
phorus and nitrogen.^ The solids are deposited as
sludge, and phosphorus and nitrogen ai-e available
as nutrients for plants and animals. The phosphate
industry provides additional sediment and
phosphorus, and natural land drainage provides
substantial amounts of phosphorus, nitrogen, iron,
copper, and organic compounds (Odum, 1953;
Dragovich and May, 1962; Dragovich, Kelly, and
Goodell, 1968). Dragovich et al. (1968) estimated
that the Hillsborough and Alafia Rivers together
add 557 metric tons of phosphorus to the bay each
year. In the bay the annual mean concentration of
total phosphorus is 19.38 ^g.at./liter, and the total
nitrogen (Kjeldahl) is 80.17 ^g.at./liter. Com-
parative figures for Tampa Bay entrance
(P = 14.39; N = 45.08 /ug.at./liter) and the near-
shore Gulf of Mexico (P = 3.6; 5^^=23.4 ixg.nt./
liter) give some idea of the extraordinary mineral
enrichment that exists in Hillsborough Bay (Sal-
oman and Taylor, 1968). In Biscayne Bay, Fla.,
McNulty, Reynolds, and Miller (1959) and Mc-
Nulty (1966) found that domestic sewage advei-sely
affected the biotic environment. There, daily dis-
charge of 120,000 to 200,000 m.yday (30-50 m.g.d.)
of raw sewage raised the average concentration of
total phosphorus to 3 ^g.at./liter or about one-
sixth of the concentration now in Hillsborough
Bay.

Enrichment of Hillsborough Bay by phospho-
rus and nitrogen causes excessive gro^rth of phy-
toplankton and filamentous algae (Dragovich,
Kelly, and Kelly, 1965). The heavy growth of
algae and the phytoplankton blooms cause marked
fluctuations in dissolved oxygen. In periods of
photosynthetic activity, oxygen concentrations
have exceeded 8 ml./liter but at other times, BOD
(biochemical oxygen demand) may reduce dis-
solved oxygen to 1 ml./lit«r or less at the bottom
(Saloman, Finucane, and Kelly, 1964; Saloman
and Taylor, 1968; FWPCA, personal communi-
cation^).

Other consequences of pollution in Hillsborough
Bay include high water turbidity (annual average,
19.19 Jackson Turbidity Units), low light trans-
mission (annual average, 30.3 percent of incident
radiation at 60 cm. Wow the water surface), and
\-ery little growth of marine grasses (Taylor and
Saloman, 1966; Saloman and Taylor, 1968; and
Taylor and Saloman, 1969). In their comparative
study of macrofauna in major geographic areas
of Tampa Bay, Sykes and Finucane (1966) pro-
vided further biological evidence of pollution in
the bay. From quantitative sampling, their work
showed that catches of fish and crustaceans were
lower in Hillslwrough Bay than in any other re-
gion of the estuary. The gi-eatest catches came
from Old Tampa Bay where environmental con-
ditions differ from those in Hillsborough Bay
mainly in terms of fewer and smaller sources of
pollution, lower turbidity, lower nitrogen concen-
tration, higher dissolved oxygen at the bottom,
more sandy sediments, a more natural shoreline,
and extensive beds of sea gi-asses.

PROCEDURES

We sampled mollusks together with bottom
vegetation and sediments with a bucket dredge
and rigid-frame net at 45 stations between Au-
gu.st 13 and September 5, 1963 (fig. 1). The dredge
dug 5 cm. into the bottom and had a capacity of
15 liters. It filled with sediment after covering
an area of about 30 by 100 cm. The net skinuned
the bottom and had an opening of 30.5 by 91.4 cm.
It was hung with square-mesh netting with open-
ings of 3.2 mm. (Taylor, 1965). At intertidal sta-
tions, the lx)ttom was sampled by sho\'el and the

= Hillsborough County Hcilth Department, Tumpa, Fla. 33601,
personal coninuinication, 1969.

3 Federal Water Pollution Control Administration, Tampa-
Hillsborough Bay Project, Tampa, Fla. 33605, 1968.

MOLLUSKS AND BENTHIC ENVIRONMENTS IN HILLSBOROUGH BAT, FLA.

193

net was pulled by hand. One dredge haul, or a
nearly equivalent volume of sediment collected by
shovel, and one 2-minute net haul were taken at
each station. "We collected water samples at each
station with a Van Dom bottle for determination
of temjjerature, salinity, and pH. Water depth was
measured by handline.

"We removed the mollusks from bottom samples
by sieving sediment and bottom debris on a screen
of 0.701-mm. mesh (Tyler #24 screen*). Before
sieving, we removed a subsample of sediment
(about 300 cc.) fi'om each bottom sample for anal-
ysis at the Sedimentological Laboratory, Florida
State "University. Their analyses included meas-
urements of grain size, calcium carbonate, organic
nitrogen, and organic carbon as well as statistical
characteristics of mean grain size, sorting (as
standard deviation), skewness, and kurtosis (Tay-
lor and Saloman, 1969).

* References to trade names In this publication do not Imply
endorsement of commercial products.

DIVERSITY AND ABUNDANCE
OF MOLLUSKS

"We collected and identified 64 species of mol-
lusks from bottom samples taken in Hillsborough
Bay (Appendix). Of these species only 36 were
represented by living individuals; furthermore,
live mollusks were collected at only 26 of the 45
stations sampled. Samples at all stations where
live mollusks were collected always included one
or more of four species, i.e.: dwarf surf clam
{MuJinia lateralis), paper mussel (Amygdahim
papyria), common eastern nassa {Nassarhis
vibese), and stout tagelus {Tagelus phbems). On
an indi^'idual basis, M. lafernlis was present in 65
percent of the station samples that contained live
mollusks; the incidences of A. papyria, N. vibex.,
and T. pleheius were 58, 54, and 35 percent, respec-
tively (table 1) . The next most numerous mollusks
were the crown conch {Melongena corona) and the
lunar dove-shell {Mitrella lunata) which occurred
at 6 of the 26 stations where live mollusks were
found.

Table 1. — Numbers of living mollusks by species and station collected from Hillsborough Bay, Fla., August and September 1963

(Number of times a station sampled in parentheses]

Station numbers

7-1 7-2
(2) (2)

7-3
(2)

8-1
(2)

(2)

8-3 8-4

(2) (2)

8-5
(2)

8-« 8-7
(1) (2)

(2) (2)

8-10 9-1 9-2 9-3 9-4 9-5
(2) (1) (2) (2) (2) (2)

Mulinia lateralis

AmvQdalum papyria

Nassarius vtber

Taodus plebefus

Melongena corona

Mitrella lunata

Tellina versicolor

•Ensis minor

Mercenaria campeckiensis,

Macoma tenia

Crepidida plana

Bittium rarium

Thracia sp

Modiolus americanus

Anadara transversa

Crassostrea lirginica

Retusa canaliculata

Polinices duplicatus

Odostomia acutidens

Mystella planulata

Epitonium humphreysi

Corbula caribaea

Anachis obesa

Tagelus divisus

Urosalpinz tampaensis. . .

Nucula prozima

Natica pusilla

Laevicarium mortoni

Haminoea succinea

Epitonium angulatum

Crepidula fornicata

Corbula barralliana_

Brachidontes exustus

Polymesoda caroliniana^,.

Acteon punctostriatus

Ischnocliiton papillosus

2 .
40

Total number species

Total number individuals..

800 1
1

122 4

5
69

5
925

194

U.S. FISH AND WILDLIFE SERVICE

Table l.-Numbers of living mollusks by species and station collected from Hillsborough Bay, Fla.. August and September

196S — Continued
[Number of times a station sampled in parentheses]

Species

Station numbers

9-6
(2)

9-7
(2)

9-8
C2)

(2)

9-10
(2)

10-14
(3)

10-16
(2)

10-16
(2)

10-17
(2)

10-18
(1)

10-19

(2)

Mulin ia lateralis

Amygdalum papyria '.\\

Nassanus libez. '."."

Tagelus phbeiua "]'

Melontjena corona /.'.'."

MitTella lunata V.'.V.'.'.V.

TdUna lersicolor ^"11"

Ensis minor... '[^

Mercenaria campechiensis ] "

Macoma tenia '..'.'.'

Crepidula plana. '-'.'.'.'.'.'.'.

Bittium tarium -.'.'.'..'.'.'

Thracia sp '.'.'.'.'.'..'.

Modiolus americanus .'.'.'.'.

Anadara transiersa ',"'"

Crassostrea lirginica

Retusa canalictilata '.'.'..'.'.'.

Polinices duplicatus I![

Odostomia acutidens.

Mysella planulata

Epitonium tiumphreysi '

CoTbula caribaea '.'.'.'.'.

Anachis obesa. ..'

Tagelas diiisus -'.'.'.'.'.'.'

Vrosalpinxtampaensis..

Nucula proxima

Nat ica pusilla __ __'

LaeiicaTium morioni. "'']^

Haminoea siiccinea .,

Epitonium angulatum '.'.'....

Crepidula fornicata

Corbula barratiaiia_

Brachidontes erustus [,

Polymesoda caroliniana

.■Icteon punctostriatus "^

Isclinocltiton papillosus. ..... ...

Total number species

Total number individuals -

10-20
(2)

10-21
(2)

10-22
(2)

10-23
(2)

21
21
9
12 ..

"263"

'""7'..

3

10

63
3

10
......

369
16

3

10
3

1 ....
4 ....
1

35

41

4

300

5

7

"i'

2

io "-'.'.'.'.

3

2

"i'.'"".".'

"i".'.'.'.'.

"22"

3 ....
3"."."."."

4 ..
4 ..

1 ..

2

1

1 ....
1 ....

30
"2

1
10

41

1 .

286

17
612

23

12

71

10

10
353

Station numbers

Species

C

(2)

C-1

(1)

C-2

(2)

C-3
(2)

C-4
(1)

C-5
(2)

C-6

(2)

C-7
(1)

C-8
(1)

C-8-1
(1)

C-8-2
(1)

C-9

(1)

Stations where
collected

Percent-
Stations age of
stations

1
10

1
22

80

Mulinia lateralis ^._ j29

Amygdalum papyria '.'.'.'..'. 26

Nassarius vibex

Tagelus plebeius

Melongena corona...

Mitrella lunata '.'-'.'.'.'.'.'.

Tellina versicolor -...'.'.'.'. "

Ensis minor. _ "1""^! c

Mercenaria campeckiensis '" '

Macoma tenta _ ^

268
16
2

16
4

8 ,
8 .

Number Percent

150
22
16

Crepidula plana.
Bittium varium..
Thracia sp.

6
17

Modiolu

1

17

Hus amertcanus

Anadara transversa ' ' " ' .

Crassostrea virginica 2 2 "

Retusa canaliculata "" ""

Polinices duplicatus. l\\[l]\.[[\\[

Odostomia acutidens ' "

Mysetta planulata l"[[[[\\"]"\ 1 '

Epitonium tiumphreysi .".'. "

Corbula caribaea '.'.'.'.'.'.

Anachis obesa '.'.'.'.'.'. " {'""

Tagelus divisus .-"[[[[]"]"' " "

Urosalpinz tampaensis

Nucula proxima ......

Natica pusilla '..'.'.'.'.". *

Laevicardium jnortoni... l\[\\[[[[y.l][[[[\" "'"

Haminoea succinea '"" X

Epitonium angulatum '"

Crepidula fornicata

Corbula barrattiana V"^^^

Brachidontes exustus """"

Polymesoda caroliniana "[[11]" [[["[[ l"

Acteon punctostriatus lllllll" ]"]["" "

Ischnochiton papillosus '.'.'.'.' '

15

17

65

IS

68

14

54

9

35

6

23

6

23

5

19

5

19

15

15

IS

IS

15

15

3

12

3

12

2

8

2

8

2

8

2

8

2

8

2

8

2

8

1

Total number species 9

Total number individuals ......... 192

4

25

10
328

150

1

4

4

1

1

1

-

13

202

71

142

89

MOLLUSKS AND BENTHIC ENVIRONMENTS IN HILLSBOROUGH BAT, FLA.

195

Live sjiecimens of M. lateral is. A. papyria, N.
vibex, and T. plehehis indicated bottom conditions
by their presence or absence and by their abun-
dance in rehition to otlier live molhisks. On the
basis of tlie occuri-ence and distribution of these
four species, bottom environments were classified
as healthy or marginal. Healthy stations were
those where indicator species were less than 50
percent of all live mollusk species present; at mar-
ginal stations, the indicators represented 50 per-
cent or more of all live species present. Unhealthy
stations were those where no living mollusks were
collected (fig. 1 and tables 2— i). The number of
living mollusks was generally higher at healthy
than at marginal stations except at marginal sta-
tion 9-3 where M. lateralis and TV. vihex were un-
usually abundant. Furthermore, on the basis of
station classification the entire area of the bay

was divisible into healthy, marginal, and unhealthy

zones.

The four species selected as indicators for the
bay, and perhaps the crown conch as well, may be
useful for biological evaluation of the environ-
ment in estuarine water of the southeastem and
Gulf States. Table 5 represents a summary of eco-
logical literature and shows the extreme ranges of
environmental conditions that these five mollusks
can tolerate under natural conditions.

HEALTHY STATIONS

Eight stations, or about 18 percent of those hav-
ing live mollusks, were classified as healthy. The
average incidence of indicator species at these
stations was 27 percent, and the average niunbers
per station were 11 species and 225 individuals
(table 2).

Table 2. — Biotic and physical characteristics of healthy benthic stations in Hillsborough Bay, Fla., August and September 1963

Station

Species ' Individual '

Indicator
species '

Deptli

Mean sediment
grain size

Sediment
sorting

Sediment type Bottom vegetation

Bottom
salinity

Number Number Percent

C 9 192 33

C-2 10 328 40

C-3 9 213 44

10-15 17 512 18

10-16 8 23 13

10-19 12 71 17

10-22 10 88 33

10-23 10 353 20

Mean 11 225 27

Range 13-44

M.

9

1.7

4.05

2.6

4.7

2.28

1.0

2.0

2.78

1.6

3.0

2.74

1.4

6.0

3.15

1.5

3.7

2.02

1.8

2.0

2.84

1.3

1.0

2.59

.8

3.0

2.80

1.5

1.0-6.0

2. 02-4. 05

.^2.6

Coarse silt OraciZarta sp.

Fine sand OracilaTiasp.

Fine sand Oracilaria sp.

Fine sand OraciZarJa sp.

Very fine sand None

Fine sand None...

Fine sand Oracilaria sp..

Fine sand.- QracUaria sp..

Fine sand.

P.p.i.

18.19
18.66
16.36
21.82
22.62
22.95
22.43
21.26

20.52
18. 19-22. 95

• Collected alive.

Table 3. — Biotic and physical characteristics of marginal benthic stations in Hillsborough Bay, Fla., August and September 1963

Station

Species *

Individual Indicator
species '

Depth

Mean sediment
grain size

Sediment
sorting

Sediment type

Bottom
vegetation

Bottom
salinity

Number Number Percent M.

C-1 4 25 50 1.0

C-4 1 2 100 1.0

C-6 4 13 75 4.2

C-6 4 202 76 2.0

C-8 1 71 100 .7

C-8-1 1 142 100 .7

C-8-2 1 89 100 .3

7-1 1 4 100 2.0

8-3 3 13 50 3.6

8-» 1 2 100 3.9

8-8 2 8 60 Z8

8-9 5 57 60 1.0

9-1... 1 1 100 .3

9-3 6 925 60 2.0

9-4 3 6 67 2.4

9-9.. 1 4 100 2.8

10-14 8 267 60 1.0

10-20... 3 6 100 3.9

Mean 3 102 80 1.9

Range 60-100 .3-4.2

2.32
2.95
2.58
2.88
2.61
2.95
6.28
3.04
4.09
5.23
3.14
2.51
2.63
2.38
2.26
3.37
2.68
2.88

1.8

1.2

1.0

1.0

1.1

1.6

2.6

1.1

2.2

2.7

1.4

.5

.7

.8

.7

1.8

.8

1.6

Fine sand

Fine sand

Fine sand

Fine sand

Fine sand

Fine sand

Medium silt

Very fine sand.

Coarse silt

Medium silt

Very fine sand.

Fine sand

Fine sand

Fine sand

Fine sand

Very fine sand.

Fine sand

Fine sand

. None

. None

. None

. None

. None

. None

. None

None

None

None

None

None

None

None

None

None

Oracilaria sp.

None

P.p.t.
18.33
15.69
19.78
18.96
.74
1.16
3.69
17.79
19.78
20.60
16.56
18.78
17.25
18.37
18.51
17.70
20.61
22.92

3.09
2. 25-5. 28

1.4

.5-2.7

Very fine sand.

15.90
. 74-22. 92

' Collected alive.

196

U.S. FISH AND WILDLIFE SERVICE

Table 4.-

-Biotic and physical characteristics of unhealthy benthic stations in Hillsborough Bay, Fla., August and September

1963

station

Depth

Mean sedi-
ment grain
size

Sediment
sorting

Sediment type

Bottom vegetation

Bottom
salinity

C-7....
C-9....

7-2

7-3

8-1

8-2

8-5

8-6

8-7

8-10

9-2

9-5

9-6

9-7

9-8

9-10

10-17....
10-18....
10-21....

Mean.
Range

M.

e

P.p.t.

0.7

-0.95

1.4

Very coarse sand

None

18.33

.7

-.77
6.76

2.1
2.3

Very coarse sand

Medium silt..

None

GraciZaria sp

16.22

4.2

17.79

2.7

17.61

3.9

6.65
2.93

2.5
1.3

Medium silt

None...

None

18.78

3.3

19.04

10.3

7.40

-1.90

4.77

3.31

2.0
2.0
2.8
1.4

Very fine silt

Granule.

Coarse silt

Very fine sand

None

None

None

None.

22.92

6.7

18.60

3.3

19.42

.7

17.94

3.3

5.12

3.2

Medium silt

None.

18.33

4.2

7.55

2.0

Very fine silt

None

19.74

12.1

6.91

o o

Fine silt

None

22.38

3.6

7.84

1.8

Very line silt

None

20.05

4.2

4.35

2.6

Coarse silt..

None..-

19.42

1.0

2.88

1.2

Fine 5 and

None

18.75

10.9

4.46

2.3

Coarse silt.

None

23.77

.7

-.96

2.7

Very coarse sand

None

22. 11

3.6

3.62

1.5

Very fine sand

None

22.81

3.8

'5.37
-1.90-7.84

2.1
1.2-3.2

Medium silt

19. 60

. .7-12.1

. 16. 22-23. 77

' Negative grain size^ excluded.

Table 5. — Range of tolerance in ecological factors and geographical distribution of the five inost commonly collected mollusks in

Hillsborough Bay, Fla., August and September 1963

Species

Temper-
ature

Salinity

pH

Turbidity Depth Current Sediment type

Bottom type

Distribution

Mulinia lateralis ' 2 1-34

Amygdalum papytitt '9-vl6

Nastariua vibex i 3-36

Tagelus plebeius "1-34

Melongena corona 21 1-34

P.p.t. M. Cm.liec.

'1.4-75 26.8-8.7 Tolerant^'.. "1-4.7 59.4-90 Nonselective; fine Unvegetated s Maine to Florida

sand and and Out ol

. silt.' « ' ' Mexico."

'»5-38 26.8-8.7 doJii... 3»l-i.7 ' <90 Fine sand > Unvegetatedi Maryland to Flor-

Vegetated. ida and Qulf of

Mexico.' •

"'9-42 2 6.8-8.7 do2'i'... '2 1-15 "8.6-90 Nonselective; sand Unvegetated "2 Cape Cod to Flor-

and silt. 5 '3 Vegetated. ida and OuU of

Mexico.*

"1-37 26.8-8.7 do2 "21-4.7 "30-90 Nonselective; sand Unvegetated > Cape Cod to Flor-

and silt ' '* Vegetated. ida and Gulf of

Mexico."

i"«8-45 26.8-8.7 do 2 '». . . "0 1-4. 7 « <90 Nonselective; Unvegetated ""' Florida and Gulf

shell, sand and of Mexico.' "

silt » "

' Parker, 1959.

2 Saloman and Taylor, 1968.

2 Breuer, 1962.

' Brett, 1963.

' This report.

« Taylor and Saloman, 1969.

' Hedgpeth, 1954.

« Marland, 1958.

• Abbott, 1954.

'" Tabb, Dubrow, and Manning, 1962.

" Wells. 1961.

"2 Wass, 1965.

'2 Moore, Davies, Fraser, Gore, and Lopez, 1968.

" Allen, 1954.

'i Tabb and Manntog, 1961.

ifl Hathaway and Woodburn, 1961.

" Menzel, 1956.

i« Hedgpeth, 1953.

Most of the healtliy stations (60 percent) were
at the mouth of Hillslxirough Bay along transect
10. The most numerous and diverse molhisk as-
semblage was at station 10-15, where we collected
512 individuals and 17 species. At the upper end of
the bay, conditioiis were healthy at stations C, C-2,
and C-3 where more than average current (C— 2
and C-3) and benthic algae (C, C-2, and C-3)
maintain a favorable environment for many mol-
lusks despite the proximity of effluent discharged

from the Tampa Sewage Treatment plant at
Hooker Point. Throughout the rest of the bay, all
stations were either marginal or unhealthy (fig. 1 ) .

The predominant sediment type at healthy
stations was fine sand (2.80 0). Sediment sorting
was poor (1.5 0), according to the classification
of Folk (1964), and is a reflection of the weak
current system in the bay (Taylor and Saloman,
1969). A number of authors have noted that fine
sand is well suited for colonization by a variety of

MOLLUSKS AND BENTHIC ENVIRONMENTS IN HILLSBOROUGH BAY, FLA.

197

mollusks (Jones, 1950; Pratt, 1953; Thorson,
1956; Sanders, 1958; McNulty, 1961; Brett, 1963).
Another feature of most healthy stations was the
occurrence of a red alga, Gracilaria sp., which is a
source of organic detritus and provides a base foj-
attachment of epiphytic mollusks.

Salinity at healthy stations was between 18 jxp.t.
(upper bay stations C, C-2, and C-3) and 23 p.p.t.
(transect 10). The combination of relatively high
mollusk diversity and reduced salinity at the
upper bay stations indicated that a factor other
than salinity prevented the establislunent of an
equivalent variety of mollusks at most marginal
and unhealthy stations.

MARGINAL STATIONS

At the 18 stations classified as marginal at least
50 percent of the live mollusks were indicator
species, and the average incidence of indicators
at these stations was 80 percent. The average niun-
ber of species per station represented by live ani-
mals was only 3 ; the mean number of individuals
was 102 (table 3) . In comparison with the healthy
stations, marginal stations had about one-fourth
as many species of mollusks and about one-half as
many individuals.

Sediments at marginal stations ranged from fine
sand to medium silt. The average sediment tyi^e
was very fine sand (3.090) — a somewhat finer par-
ticle size than the average size at healthy stations.
Sediment sorting was poor (1.40) and vei"y close
to the figure for liealthy stations.

Bottom vegetation (Gracilar'ia sp.) was found
at only one marginal station. That station liad a
substrate of fine sand and more species of mollusks
than any other station.

Low salinity (less than 4 p.p.t.) near the mouth
of the Alafia Eiver was probably responsible for
fewer species of mollusks at stations C-8, C-8-1,
and C-8-2. The only species present in this area
was Tagelus plebeiu-s.

Data for DO (dissolved oxygen) indicated that
from June through August bottom water in the
bay between transect 10 and McKay Bay becomes
anaerobic (EWPCA, personal commimication ; see
footnote 3). At other times, however, DO values
are generally above 3 ml. /liter and would not prove
limiting. Changes in the DO at stations regarded

as marginal may create a more favorable environ-
ment for mollusks during other seasons.

UNHEALTHY STATIONS

No live mollusks were collected at 19 stations
classified as unhealthy (fig. 1). Two of these sta-
tions were on the eastern shore of the bay (8-10
and 9-10) and adjacent to an extensive area of
gypsum spoil — a byproduct of the phosphate in-
dustry. The gypsum forms a crust on the bottom
that virtually eliminates macrobenthic organisms.

Sediments at other unhealthy stations had a
mean grain size that varied from —1.90
(granule) to 7.84 (very fine silt) — see table 4.
Sediments were coarse at stations near spoil
islands left from channel construction and on a
natural, shelly shoal (C-7). Absence of mollusks
in coarse sediments probably resulted from the
grinding action of large particles powered by wave
action. Stations with fine sediments were in
comparatively deep water. There the sediments
had a high concentration of the toxic compound,
hydrogen sulfide, and are probably anaerobic, or
nearly so, at all times (Florida State Board of
Health, 1965).

ECOLOGICAL ZONES

Isopleths were drawn between similar stations
to represent approximate boundaries of healthy,
marginal, and unhealthy zones in Hillsborough
Bay (fig. 2). Calculation of the area within each
zone showed that only 22 percent of the bay falls
in the healthy categoi-y, 36 percent is marginal,
and 42 percent is unhealthy. Most healthy zones
were near the mouth of the bay where the solid
and soluble products of pollution were least con-
centrated. Marginal zones were on the bottom
slopes between the three unhealthy zones that were
along the eastern and western shores and in mid-
bay ship channels. Observations in Kai'itan Bay
(Dean and Haskin, 1964) and Biscayne Bay (Mc-
Nulty, 1966) suggest that pollution abatement in
Hillsborough Bay would favor progi-essive re-
population of marginal zones by a more normal as-
semblage of benthic plants and animals. In heav-
ily silted areas of the unhealthy zones, however,
biological restoration would probably requii-e a
long period of time.

198

U.S. FISH AND WILDLIFE SERVICE

TAMPA BAY

82 30 W.

FiouBE 2. — Ecol(^cal zones in Hillsborough Bay, Fla., based on the comparative diversity of moUusks — healtliy
zone (uushaded) ; marginal zone ( hatching) ; unhealthy zone (cross hatching) — August and September 1963.

MOLLUSKS AND BENTHIC ENVIRONMENTS IN HILLSBOROUGH BAT, FLA.

199

LITERATURE CITED

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1954. The influence of bottom sediments on the dis-
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Brett, Charles Everett.

1963. Relationships between marine invertebrate in-
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Breuer, Joseph P.

1962. An ecological survey of the lower Laguna Madre
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Butler, Philip A.

1954. Summary of our knowledge of the oyster in the
Gulf of Mexico. In Paul S. Galtsoff (coordinator).
Gulf of Mexico, it origin, waters, and marine life,
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1966. Pe.stieides in the marine environment J. Appl.
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Chambbxs, Gilbert V., and Albert K. Sparks.

1959. An ecological survey of the Houston Ship
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Dawson, Chakles E., Jr.

1953. A survey of the Tampa Bay Area. Fla. State
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Dean, David, and Harolu H. Haskin.

1964. Benthic repopulation of the Raritan River
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Dragovich, Alexander, John A. Kelly. Jr., and H. Grant
Goodexl.

1968. Hydrological and biological characteristics of
Florida's west coast tributaries. U.S. Fish Wildl.
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Dragovich, Alexander, John A. Kexly, Jr., and
Robert D. Kelly.
196.5. Red water bloom of a dinoflagellate in Hills-
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(5002) : 1209-1210.
Dragovich, Alexander, and Billie Z. May.

1962. Hydrological characteristics of Tampa Bay
tributaries. U.S. Fish Wildl. Serv., Fish. Bull. 62:
163-176.
Florida State Board of Health.

1965. A study of the causes of obnoxious odors Hills-
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State Bd. Health, Bur. Sanitary Eng., Jacksonville,
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Folk, Robert L.

1964. Petrology of sedimentary rocks. Hemphill's,
Austin, Tex., 154 pp.
Hathaway, Ralph R., and K. D. Woodburn.

1961. Studies on the crown conch McJongcna corona
Gmelin. Bull. Mar. Sci. Gulf Oarib. 11 : 45-65.
Hedgpeth, Joel W.

1953. An introduction to the zoogeography of the
northwestern Gulf of Mexico with reference to the
invertebrate fauna. Publ. Inst. Mar. Sci., Univ.
Tex. 3(1) : 107-224.

1954. Bottom communities of the Gulf of Mexico. In
Paul S. Galtsoff (coordinator). Gulf of Mexico, its
origin, waters, and marine life. pp. 203-214. [U.S.]
Fish Wildl. Serv., Fish. Bull. 55.

Jones, N. S.

1950. Marine bottom communitie.«. Biol. Rev. (Cam-
bridge) 25 : 283-313.
KsaiN, A. Myra.

1963. Marine molluscan genera of western North
America. Stanford Univ. Press, Stanford, Calif.,
126 pp.
Ladd, Harry S.

1953. Brackish-water and marine as.semblages of the
Texas Coast, with special reference to mollusks.
Publ. Inst Mar. Sci., Univ. Tex. 2(1) : 125-163.
Mackin, John G.

1961. Canal dredging and silting in Ix)uisiana bays.
Publ. Inst. JIar. Sci., Univ. Tex. 7 : 262-314.
Mackin, John G., and Sewell H. Hopkins.

1961. Studies on oyster mortality in relation to
natural environments and to oil fields in Louisiana.
Publ. Inst Mar. Sci., Univ. Tex. 7 : 1-131.
Mabland, Frederick Chap.les.

1958. An ecological study of the benthic macro-fauna
of Matagorda Bay, Texas. M.S. thesis. A & M
College of Texas, 8 -f 75 pp.

McNULTY, J. KNEELAND.

1961. Ecological effects of sewage pollution in Bis-
cayne Bay, Florida : sediments and the distribution
of benthic and folding macro-organisms. Bull. Mar.
Sci. Gulf Carib. 11 : 394-447.
1966. Recoverj' of Biscayne Bay from pollution.
Ph. D. thesis. Univ. Miami. 192 pp., Univ. Micro-
films, Ann Arbor, Mich. (Order No. 66-13,006).
McNuLTY, J. Kneeland, Ernest S. Reynolds, and Sig-
mund M. Miller.

1959. Ecological effects of sewage pollution in Bis-
cayne Bay, Florida : distribution of coliform bac-
teria, chemical nutrients, and volumes of zoo-
plankton. In C. M. Tarzwell (compiler). Biological
problems in water pollution, pp. 189-202. Trans.
Second Seminar Biol. Probl. Water PoUut. held
Apr. 20-24, 1959, at Cincinnati, Ohio.

Menzel, R. Winston (Editor).

1956. Annotated check-list of the marine fauna and
flora of the St. George's Sound-Apalachee Bay Re-
gion, Florida Gulf Coast. Ocean. Inst. Fla. State
Univ., Contrib. 61, iv + 78 pp.

200

U.S. FISH AND WILDLIFE SERVICE

Moore, Hilary B., Leon T. Davies, Thoxias H. Fbaser,
Robert H. Gore, and Xelia R. Lopez.
1968. Some biomass figures from a tidal flat iu Bis-
cayne Bay, Florida. Bull. Mar. Sci. 18: 261-279.
Odum, Howard T.

19.53. Dissolved phosphorus in Florida waters.
Fla. Geol. Surv. Rep. Invest. 9, Pt. I : Miscellaneous
studies, pp. 1-40.
Olson, F. C. W., and John B. Morrill, Jb.

1955. Literature survey of the Tampa Bay area.
Fla. State Univ. Oceanogr. Inst., 66 pp.
PARKEai, Robert H.

1959. Macro-invertebrate assemblages of central
Texas coastal bays and Laguna Madre. Bull.
Amer. Ass. Petrol. Geol. 43 : 2100-2166.

1960. Ecology and distributional patterns of marine
macro-invertebrates northern Gulf of Mexico. In
Francis P. Shepard, Fred B. Phleger, and Tjeerd
H. Van Andel (editors). Recent sediments, north-
west Gulf of Mexico, pp. 302-337. Amer. Ass.
Petrol. Geol., Tulsa, Okla., 391 pp.

Perry, Louise M.. and Jeanne S. Schwengel.

1955. Marine shells of the western coast of Florida.
Paleontol. Res. Inst., Ithaca, New York, 198 pp.
Pratt, David M.

1953. Abundance and growth of Voiiis tncrccnaria
and Callocardia morrhuana in relation to charac-
ters of bottom sediments. J. Mar. Res. 12: 60-74.
Saloman, Carl H., John H. Finucanb, and John A.
Kelly, Jr.

1964. Hydrographic ob.servations of Tampa Bay,
Florida, and adjacent waters, August 1961 through
December 1962. U.S. Fi.sh Wildl. Serv.. Data Rep.
4, ii + 112 pp. on 6 microfiches.
Saloman, Carl H., and John L. Taylor.

1968. Hydrographic observations in Tampa Bay,
Florida, and the adjacent Gulf of Mexico — 1965-
66. U.S. Fish Wildl. Serv., Data Rep. 24, 393 pp.
on 6 microfiches.
Sanders, Howard L.

1958. Benthie studies in Buzzards Bay. I. Animal-
sediment relationships. Limnol. Oceanogr. 3 : 245-
258.
Sykes, James E., and John H. Finucane.

1966. Occurrence in Tampa Bay, Florida, of imma-
ture species dominant in Gulf of Mexico commer-
cial fisherie.s. U.S. Fish Wildl. Serv.. Fi.'ih. Bull.
65: 369-379.
Tabb, Durbin C, David L. Dubrow, and Raymond B.
Manning.

1962. The ecology of northern Florida Bay and ad-
jacent estuaries. Fla. State Bd. Conserv., Tech.
Ser. 39, 81 pp.
Tabb. Durbin C. and Raymond B. Manning.

1961. A checklist of the flora and fauna of northern
Florida Bay and adjacent brackish waters of the
Florida mainland collected during the i)eriod July,
1957 through September, 1960. Bull. Mar. Sci.
Gulf Carib. 11 : 552-649.

Taylor, John L.

1965. Bottom samplers for estuarine research. Ches-
apeake Sci. 6 : 233-234.

Taylor, John L., and Carl H. Saloman.

1966. Benthie project. In Report of the Bureau of
Commercial Fisheries Biological Station, St. Peters-
burg Beach. Florida, fi.scal year 1965, pp. 4-9. U.S.
Fish Wildl. Serv., Circ. 242

1969. Sediments, oceanographic observations, and
floristic data from Tampa Bay, Florida, and ad-
jacent waters, 1961-65. U.S. Fish Wildl. Serv.,
Data Rep. 34, 562 pp. on 9 microfiches.
Thorson, Gunnar.

1956. Marine level-bottom communities of recent
.seas, their temperature adaptation and their
"balance" between predators and food animals.
Trans. X.Y. Acad. Sci., Sect. II, 18: 693-700.
Warmke:, Gebmaine L., and R. Tucker Abbott.

1962. Caribbean seashells. Livingston Publ. Co.,
Xarbertb. Pa.. 348 pp.
Wass, Marvin L.

1965. Check list of the marine invertebrates of Vir-
ginia. Va. Inst. Mar. Sd. Spec. Sei. Rep. 24 (3d
rev. ) , 55 pp.
Wells, Harry W.

1961. The fauna of oyster beds, with special refer-
ence to the salinity factor. Ecol. Monogr. 31 : 239-
266.

APPENDIX

A CHECKLIST OF MOLLUSKS FOUND IN HILLS-
BOROUGH BAY, FLORIDA, AUGUST AND SEPTEM-
BER 1963

We collected and identified 64 species of mollusks
representing 43 families. Determinations were
based on standard taxonomic works (Abbott,
1954; Perry and Schwengel, 1955; Warmke and
Abbott, 1962; Keen, 1963; Abbott, 1968) and by
comparison with specimens in the U.S. National
Mnseuni ( + ) . An asterisk ( * ) indicates that the
species was collected alive.

Class Gastropoda

Family Neritidae

Neritina recJivata (Say)
Family Kissoidae

Rissoina chesneli Michaud
Familj' Vitrinellidae

Cyclost remiscus sp.
Family Cerithiidae

*Bittiumvarium (Pfeiffer)

Sella adamsl ( H. C. Lea )
Family Triphoridae

Triphoranigrocincta (C. B. Adams)

MOLLUSKS AND BBNTHIC ENVIRONMENTS IN HILLSBOROUGH BAY, FLA.

201

Family Epitoniidae

*Epitoniu7n angulatum (Say)

*E'pitonium humphreysi (Kiener)

Efltonium rupicola (Kurtz)
Family Calyptraeidae

*Crepidula fomicata (Limie)

*Crepklula plana Say
Family Naticidae

*Natwa pnsilla Say

*Polinices duplicahos (Say)
Family Muricidae

*Urosalpina; tampaensis (Conrad)
Family Columbellidae

*Anachis obesa (C. B. Adams)

*Anachis semiplicata (Stearns)

*Mitrenalunata (Say)
Family Melongenidae

*Melongena corona (Gmelin)
Family Nassariidae

*Nassarius vibex (Say)
Family Olividae

Olivella perplexa Olsson
Family Marginellidae

Pininum apiclnum (Menke)
Family Atyidae

*Ham,inoea sicccinea (Conrad)
Family Retusidae

*Eetusa canalieuJata (Say)
Family Pyramidellidae

**Odostomia acutidens Dall

Odostoiniaimpu'essa (Say)

"OdostomAaproducta (Dall)

*Turbonilla conradi Bush.
Family Acteocinidae

Cylwhnok iidentata (Orbigny)
Family Acteonidae

*Acteon punctostriatus (C. B. Adams)
Family Ellobiidae

Melampus coffeus (Linne)

Class Amphineura

Family Ischnochitoniidae

* I schnvchiton papnllosus (C. B. Adams)

Class Pelecypoda

Family Nuculidae

*Nucula proxima Say
Family Nuculanidae

Nuculana acuta Conrad
Family Arcidae

*Anadara transversa (Say)

Family Mytilidae

* AmygdaluTn papyria (Conrad)

*Brachidontes exustus (Linne)

*Modiolus americanus (Leach)
Modiolus demissus granosissima
(Sowerby)
Family Pinnidae

Atrlnarigida (Lightfoot)
Family Ostreidae

*Crassostrea virglnica (Gmelin)
Family Carditidae

Cardita ftoridana Conrad
Family Corbiculiidae

*Polymesodacaroliniana (Bosc)
Family Leptonidae

*MyseUa plamdata (Stimpson)
Family Cardiidae

*Laevicardium morfoni (Conrad)
Family Veneridae

Chione cancellafa (Linne)

*Mercenaria campechiensis (Gmelin)

Parastarte trtquetra (Conrad)
Family Petricolidae

PetricoJa phoUidifoiinis Lamarck
Family Tellinidae

MacomaconHtricta (Bruguiere)

*Macoma tenia Say

TeJUna altemata Say

Tellina lineata Turton

*Tellma versicolor DeKay
Family Semelidae

Senieh hellastriata (Conrad)

Semele proficua (Pulteney)
Family Donacidae

Donax variabtlis Say
Family Sanguinolariidae

*Tagelus divhus Spengler

*Tagelus pleheius (Lightfoot)
Family Solenidae

*Ensis minor Dall
Family Mactridae

Mactra fragilis Gmelin

*MvHnia, latcndis (Say)
Family Corbulidae

*Corhula barratiana C. B. Adams

*Corbida caribaea Orbigny
Family Pholadidae

Cyrtopleura costata (Linne)
Family Lyonsiidae

Lyonsia. hyalimt foridann Conrad
Family Thraciidae

*Thracla sp.

202

U.S. FISH AND WILDLIFE SERVICE

MIGRATION OF JUVENILE SALMON AND TROUT INTO BROWNLEE

RESERVOIR, 1962-65

BY RICHARD F. KRCMA AND ROBERT F. RALEIGH, FISHERY BIOLOGISTS

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY

SEATTLE, WASH. 98102

ABSTRACT

Migrations of juvenile chinook salmon (Oncorhynchus
tshawytscha), coho salmon (O. kisutch), sockeye and
kokanee salmon (O. nerka), and rainbow trout {Salmo
gairdneri) from the Snake and Weiser Rivers and from
Eagle Creek were studied. Populations of fish were
sampled with floating traps above the reservoir and a

fixed louver trap in Eagle Creek near the lower end of
Brownlee Reservoir. Age and length of fish, timing of
migration, and numbers of fish of native or hatchery
origin were determined. This information was needed to
evaluate the effect of Brownlee Reservoir on migrations
of anadromous fish.

Brownlee Reservoir was created when a high-
head hydroelectric dam was built in 1958 at the
upstream end of Hells Canyon on the Snake River.
The 92-km. long reservoir forms part of the
boundary between Idaho and Oregon. At full pool,
it is 92 m. deep and less than 1 km. wide ; the upper
end (22 km.) is relatively shallow and essentially
riverine.

BCF (Bureau of Commercial Fisheries) chose
Brownlee Reservoir for an extensive research pro-
gram to determine how a large impoundment af-
fects the i:)assage of salmon and trout. The re-
search, begun in the spring of 1962, comprised five
studies: (1) limnology' of the reservoir system
(Ebel and Koski, 1968), (2) upstream migration
of adult chinook salmon {OncorhyiifiMis tshawi/fx-
rha) througli the reservoir (Trefethen and
Sutiierland, 1968), (8) migration of juvenile
salmon and trout into the reservoir (this report),
(4) distribution and movement of juvenile salmon
in the reservoir (Durkin, Park, and Raleigh,
1970), and (5) migration of juvenile salmon and
trout from the reservoir (Sims, 1970).

Three major streams — the Snake, Burnt, and
Powder Rivers — and more than a dozen minor
streams, most of which have intermittent flows,
are tributaries to Brownlee Reservoir. Previous
investigations had shown that most of the streams
supported local populations of rainbow trout
{Salmo gairdneri) , but chinook salmon and stcel-

Publlshed April 1970.

FISHERY BULLETIN: VOL. 68, NO. 2

head trout (the anadromous form of rainbow
trout) sjDaAvned in only three of the streams.
Spring- and fall-migrating steelhead trout and
spring-migrating chinook salmon spawned in
Eagle Creek, a tributary of the Powder Ri\"er, and
in the Weiser River, a tributary of the Snake
River (fig. 1). Fall-migrating chinook salmon
spawned in the Snake River about 257 km. above
the dam.

Wild (native) salmon and trout fingerlings en-
tered the reservoir during each year of study
(1962-65). From 1963 on, most of the chinook
salmon spawners were diverted to a hatchery. In
1964 and 1965, therefore, hatchei-y-reared progeny
of fall chinook salmon from the lower Cohunbia
Ri\er were released in the Snake River spawning
area above the reservoir. Wo wislied to study the
etfect of a large impoundment on other species of
salmon, so yearling cojio (O. kisutch) from the
lower Columbia River and sockeye salmon {O.
nerka) from the Skeena River were included in
the hatchery releases in 1964 and 1965, respec-
tively. In 196.3, 1964, and 1965, migi-ations of wild
kokanee {0. nerka) entered the reservoir from the
Payette River system.

Tliis report provides estimates of age and
length of fish from each population at the time of
entry into the reservoir, time and duration of
downstream migrations, and numbers of fish of
native and hatchery origin for 1962 through 1965.

203

/

/WASHINGTON jo

xbow Dom i^

1 \Columbia^^— r" TTiS

Louver Sile>
Eogle Cr.j

^f=^-.J^ Da

is

niee
m

1 OREGON -.-m

Burnt Hivtr^y

\ Weiser

''Weiser River

Migrant Di

pper Site S.

N

aV

■"1

=/

Mil

^||"^v.,Payette River

Mori\ng_y\

-Release Siie (1965)

^

10 20

e

,-\j»-Releose Site (1964)

Kilometer
Approximate Scol

J

/V Swon Foils

Figure 1. — Study area showing locations of sampling
equipment used to assess migrations of Juvenile salmon
and rainbow trout to Brownlee Reservoir.

SAMPLING SITES, EQUIPMENT, AND
PROCEDURES

The plan of study was to sample populations of
migrating fish before they entered the reservoir, to
determine their characteristics, and to estimate
their abundance. This plan required the installa-
tion of floating fingerling traps in the Snake River
above the reservoir and a fixed louver in Eagle
Creek, a tributary of the Powder River near the
lower end of Brownlee Reser\'oir (fig. 1) .

Sample catches from the populations of juvenile
Chinook salmon in the Snake and Weiser Rivers
early in the study established that juvenile fall
Chinook salmon migrated from the Snake River
at age 0, whereas juvenile spring chinook salmon
migrated from the Weiser River at age 1. Thus, it
was possible to separate these two populations
on the basis of age or size and to sample them from
a single location below the confluence of the two
rivers.

SNAKE RIVER

The sampling site for the Snake and Weiser
Rivers was about 8 km. below their confluence and
about 4 km. above the reservoir. Flows during the
spring were 383 to 1,372 c.m.s. (cubic meters per
second) and averaged 744 c.m.s. At average flow,
the Snake River channel at this location was about
152 m. wide and had a maximum depth of 7.6 m.

The sampling device in the Snake River was a
modified "migrant dipper" (Mason, 1966) — a self-
cleaning, floating fingerling trap with louvered
leads (fig. 2). The basic unit consisted of a trap
section, 12.2 m. long by 7.6 m. wide by 1.8 m. deep,
with fixed louver leads that extended 9.8 m. up-
stream at a 10° angle to the flow. A self-cleaning
traveling screen formed the rear of the trap, and
a metal screen floor extended upstream to the two
fixed louver sections. The louvers guided the fish
into the trap area where a continuously rotating
scoop dipped the fish and deposited them into a
trough. The fish were then flushed into a holding
pen at the side of the trap.

Fish were captured in traps from 1962 through
1965. We carried out feasibility tests with one trap
in 1962 and examined the horizontal distribution
of downstream migrants at the same time. In the
spring of 1963, two migrant dipper traps were
attached to an overhead cable and positioned in
the main current. Floating louver extensions were
added to the fixed louver sections to increase the
sampling capability. In attempts to increase the
catch, the louver angle and lengths were altered
each year (table 1). In 1962, the traps were oper-
ated continuously from mid-April until early July
and then intermittently until December. On the
basis of tliese early experiments, the operations in
1963-65 began in mid-March and ended in July.

Table 1. — Traps used in the Snake River and configuration
of attached louver arrays

Year

Traps

Details of louver leads

Angle

Length

Width at
mouth

Number

Degreet

M.

M.

1962....

1

10

9.7

13.7

1963....

2

30

22.0

30.6

1964....

2

15

22.0

21.4

1965....

1

16

47.6

30.5

Fish captured in the traps and subsequent esti-
mates of the magnitude of migration were classi-

204

U.S. FISH AND WILDLIFE SERVICE

Figure 2. — FloaJting traps (migrant dippers) used to sample migrations of juvenile salmon and rainbow
trout in the Snake River above Brownlee Reservoir.

fied by age group on the basis of lengths
determined by daily sampling. The length-age re-
lation was established by scale analysis. Finger-
lings in their first year of life are termed age-
group 0; these fish become age-group I on Janu-
ary 1 of the succeeding year.

Marked fish were used to estimate the propor-
tion of the migration captured by the traps. The
proportion varied with trap design and position,
size and species of migrants, and flow and tur-
bidity of the river. A portion of the daily catcli
of fish was marked, transported 3.2 km. upstream,
and released for recapture. They were marked by
age group and released at scheduled intervals dur-
ing the day and night.

Fish marked to assess the migration from the
Snake River were tattooed (Volz and "Wlieeler,
1966). This method provided many combinations
of marks that were durable and could be easily
detected. Juvenile salmon from each population
were fin-clipped or jaw-tagged each year for sub-
sequent identification as they moved through the
reservoir.

EAGLE CREEK

The sampling site at Eagle Creek was 183 m.
upstream from its confluence with the Powder
River and about 460 m. from the reservoir (fig. 1) .
The stream at this point was 15 m. wide at noiTnal
flows. Except during maximum ninoft' in the
spring, floAvs seldom exceeded 57 c.m.s.

Samples of downstream migi'ants were obtained
with a stationary louver device (Bates and Vin-
sonhaler, 1057) — see figure 3. In 1962, the louver
(18.3 m. long and 0.9 m. high) was positioned at
a 30° angle to the stream bank. In 1963, to increase
the catch and eliminate selectivity for larger fish,
the angle was decreased to 15° and the length
extended to 36.6 m. In 1964, the channel was al-
tered above the louver to straighten the approach
flow.

Fish from Eagle Creek were collected from
three sources and marked in a variety of ways.
Most fish were stained with Bismark Brown Y
dye^ (Deacon, 1961) and released above the sam-

1 Trade names referred to In this publication do not imply
endorsement of commercial products by the Bureau of Com-
mercial Fisheries.

JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR

205

f:.a3-

FiGTTRE 3. — Stationary louver used to estimate the number of juvenile salmon and rainbow trout migrating

into Brownlee Reservoir from Eagle Creek.

pling site to determine trapping efficiencies of the
louver. Fish to be stained could be held in the
cooler waters of Eagle Creek with little difficulty,
whereas they could not be kept alive for sufficient
time to stain them in the warmer waters of the
Snake River. We obtained test fish mainly from
irrigation bypass traps and fyke nets located sev-
eral kilometers ui>stream. "Wlien sufficient numbers
of migrating fish were not availalble from these
sources, we used fingerlings captured at the louver.
Periodically, groups of migrants from Eagle
Creek were marked by fin-clipping, jaw tags, or
plastic thread tags - for identification in the
reservoir.

DOWNSTREAM MOVEMENT, AGE,
LENGTH, AND TIME OF ENTRY INTO
THE RESERVOIR OF JUVENILE SALM-
ON AND TROUT

The characteristics of the migrations into
Brownlee Reservoir were determined from catches

= Developed by the Fish Commission of Oregon.

at the sampling sites. Timing and peaks of runs
are expressed as weekly percentages of the esti-
mated numbers of fish in the migrations. About 10
percent of each daily catch was examined for data
on length and age.

MIGRATIONS OF WILD SALMON AND TROUT

Migrations of wild chinook salmon and steel-
head trout juveniles entered tlie reservoir from
three tributaries. Fall chinook entered from the
Snake River, whereas spring chinook and steelhead
entered from Eagle Creek and Weiser River.

Fall Chinook Salmon

The movement of juvenile fall chinook salmon
fi-oni the Snake River to Brownlee Reservoir be-
gan about mid-Ai^ril and peaked in mid-May in
1962 and 1963 (fig. 4). About 75 i^ercent of the
migration took place during a 2-week period, and
nearly all of the fish liad migrated by mid-June.
Principal movement was between sunrise and
10 a.m. and from 3 to 7 p.m.

206

U.S. FISH AND WILDLIFE SERVICE

1962

I f

I 234 I 23451 2341 234
APRIL MAY JUNE JULY

-f^ — I — I — I — I — I — 1 — I — I — I — I — I — I — I
[2 I234I2345I234I234

APRIL MAY JUNE JULY

WEEKS
FiGUKE 4. — Timing of migration of native juvenile fall
ehinooli; salmon (age-group 0) from the Snake River to
Brownlee Reservoir by weekly periods, 1962-63.

The size of native juvenile fall chinook salmon
increased throughout the migration period (table
2). Early migrants in 1962 averaged 52 mm.; by
the final week, average length had increased to 71
mm. The migrants averaged larger in 1963 — 73
mm. at the start and 81 mm. at the end of the
migration period.

Spring Chinook Salmon

Spring chinook salmon enter Brownlee Reser-
voir from Weiser River and Eagle Creek; their
season of spawning is similar, but the sizes and
seasons of migration of the juveniles into the reser-
voir are substantially ditl'erent.

Weisei' River pojmlafion. — Juvenile spring chi-
nook salmon from the Weiser River first appeared
at the Snake River trap in early April and peaked
in late April or early May (fig. 5). The migration
was nearly complete ])y late May in all years. Daily
catches of spring chinook salmon were greatest
between 7 and 11 a.m. and .'5 and 7 p.m. except
during the peak when diurnal liighs were not

1234! 234 123451 234
MARCH APRIL MAY JUNE

WEEKS
Figure 5. — Timing of migration of juvenile spring chinook
salmon from the Weiser River to Brownlee Reser\-oir
by weekly i>eriocl.s, 1962-65.

clearly defined. Daily catches were lowest between
10 p.m. and 4 a.m.

The size of spring chinook salmon from the
Weiser River differed from that of wild fall chi-
nook salmon from the Snake River in 1962-63;
spring fish were age-group I and distinctly larger
than fall fish, which were age-group O. In 1964
and 1965, however, the difference between these
wild spring chinook salmon and the hatchery-
reared fall chinook salmon was less apparent by
late April when the length ranges merged. In

.JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR

207

417-060 O - 71

Table 2. — Lengths of mid juvenile fall chinook salmon from
the Snake River during migration past sampling site,
1963-64

Length of fish at stage of migration
Year Early > Late 2

Fisli Mean Range Fisli Mean Range

Number Mm. Mm. Number Mm. Mm.

1962 76 62 33-80 434 71 47-103

1963 - -... 97 73 48-99 133 81 67-98

1964 (») - 146 79 61-90

' Mid-April to mid-May.

2 Mid-May to mid-June.

3 No discernible fish of this group in sample.

1964 and 1965, bhe two populations were separated
by the percentajie of each age group in the daily
sample as estimated from scale analysis.

The average length of spring chinook salmon
varied from 106 mm. in 1962 to 149 mm. in 1964
(table 3). Each year the average size increased
from the beginning to the end of the migration.

A few large individuals (215-260 mm.) were
captured in 1963 and 1964, but the total constituted
less than 1 percent of the catch. These fish (age-
group III) appeared at the trap early in the season
during extremely high flows from the Weiser
River.

Table 3. — Lengths of juvenile spring chinook salmon from
the Weiser River during migration past sampling site in
the Snake River, 1962-65

Length of fish at stage of migration
Year Early ' Late 2

Fish Mean Range Fish Mean Range

Number Mm. Mm. Number Mm. Mm.

1962 8 106 95-117 104 134 125-161

1963 438 108 94-140 62 142 116-165

19&4 249 112 100-146 81 149 126-166

1966 19 119 101-130 22 140 120-165

1 April to pealc of migration (late April or early May).

2 From peak of migration through May.

Eagle Creek population. — Juvenile spring chi-
nook salmon from Eagle Creek migrated down-
stream most of the year except during the summer
when flows averaged less than 1 c.m.s. (fig. 6) . The
principal migration was in the fall when flows at
the trapping site exceeded 1.5 c.m.s. As irrigation
was reduced at this time, most of the flow re-
mained in the stream dhannel, and water tempera-
tures ranged from 0° to 13° C. Winter migrations
were small and occurred only during short-term
increases in water temperature and flow. A sec-
ondary migration took place in the spring as water
temperature and flows again increased. The migra-
tion declined just before liigh flows from spring
rain and melting snow (fig. 6). Periodic sampling
during the high flows .suggested that few chinook
salmon were migrating. As water levels receded,
however, fish were taken in limited numbers imtil
the upstream diversion of water for irrigation
greatly reduced the flows at the louver. Water
temperatures increased in the spring from near
freezing to about 8° C.

Chinook salmon of age-group O dominajted the
migration in the fall. These fish emerged from
the gravel in the spring and were the offspring of
adults that had spawned in late summer and early
fall of the previous year. The size of the 0-group
fish varied slightly from year to year and through-
out the migi'ation period (table 4).

Juvenile chinook salmon that moved down-
stream from January into late spring were
primarily age-group I fish. A small number of age-
group (average, 60 mm.; range, 41-80 mm.) was
sampled from April through June 1963. Some age-
group II fish — less than 3 percent of the total

Table 4. — Lengths of juvenile spring chinook salmon at beginning and end of spring and fall migrations at Eagle Creek, 196S-65

Year

Spring migration

Fall migration

Age-group

Age-group I

Age-group

Age-group I

Beginning
Aver- Range

End

Beginning
Aver- Range

End

Beginning
Aver- Range

End

Beginning
Aver- Range

End

Aver-

Range

Aver-

Range

Aver-

Range

Aver-

Range

age

age

age

age

age

age

age

age

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

Mm.

1962.

... (•)

(')

(')

(')

m

C)

(')

(')

78

63-109

84

60-111

119

112-120

132

2115-168

1963.

... C)
- (')

W

61

46-80

86

68-106

93

71-98

87

64-118

89

60-116

144

130-162

(')

(')

19B4.

m

66

68-78

90

72-108

94

72-130

102

76-121

103

78-126

168

-158

W

m

1966.

... (■)

(')

«

(2)

100

86-118

111

83-119

108

83-119

C)

(■)

(')

(')

C)

C)

1

Not in

operation.

2
3

Few fish sampled.
Not in catches.

205

U.S. FISH AND WILDLIFE SERVICE

40

30

20

z 10

UJ

o
UJ

0-40
o
o 30

UJ

^20

>-

OD

10

<
o

I-
o

40
30
20
10

1962
lAGE GROUP

4-x
,-.X

1963

19 64

1963

AGE GROUP I

/^

^^ci.-'-y 1

.-<•..

1964

Age 1

Temp. "C.

Flow CMS.

/X

/-v /

/\ 1 ^ 1

r^ - V

.v,.^,..--'S--x

./•^

'

1965

/"

-^---^^'>''

A'

-r-"-* — T^ r

-I-

20 -

10 -

6-\

o

UJ

o:

H
<

o:

UJ

20 0. -I

2
ui

10 i-H

UJ

o

<H

oc

UJ

>
<

20 -

dio -

—

20
10

en
uf

20

lOuJ
o

<

UJ
>
<

20
10

OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUNE JULY

Figure 6. — Timing of migration of spring chinook salmon (age-groups O and I) frooi Eagle Creek to
Brownlee Reservoir in relation to water temijerature and flow, 1962-65 (x indicates i>eriods of no
data).

catch — were taken each spring. These fish averaged
140 mm. (126-180 mm.) and were scattered
tliroughout the migration.

Most hsli moved downstream past the louver at
night — between 6 and 12 p.m. Few fish were
caught through the rest of the 24:-hour period ex-
cept during higli flows and turbid water; at these
times fish moved downstream throughout the day
and night.

Kokanee

Kokanee sahnon from tlie Payette River system
appeared at the Snake River sampling site in
mid-June in 1963-65. The migration was evident
for 3 or 4 weeks, but most of the fish moved down-
stream during a 1-week period (fig. 7). Kokanee
averaged 118 to 120 mm. long through the 1964
migration and 93 to 108 mm. through the 1965
season (table 5).

JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLBE RESERVOIR

209

1964

Rainbow Trout

Anadromous rainbow trout spawned in the same
tributaries as spring chinook salmon. Offspring of
the anadromous form could not be separated from
resident native and planted rainbow trout that
complete their life cycle in fresh water. Studies
on the enti-y of trout into the reservoir included
young from all three groups.

Table 5. — Lengths of juvenile kokanee salmon during
migration past sampling site in Snake River, 1963-66

Year

Length of fish at stage of migration

Early

Late:

Fish

Mean Range

Fish

Mean Range

1963..
1964..
1965..

Number
7
... 279
166

Mm. Mm.
(3) 100-110
118 88-140
93 80-110

Number
3
107
151

Mm. Mm.
(3) 128-142
120 104-146
108 70-165

Figure 7. — Timing of migration of kokanee salmon
from tbe Snake River to Brownlee Reservoir,
1964-65.

' First week.
- Last week.
' Insufficient sample.

Trout migrated from the Snake River in the
spring (fig. 8) at the same time as the chinook
salmon i:)opulations. Time of peak migration
varied but was in late April or May 1962-65. Age
groups were from O to IV, but most were age-
group I and II. Size overlap was considerable
among age-groups I and II. Table 6 shows the age
groups and length-frequency ranges for 1963.

The movement of rainbow trout from Eagle
Creek (fig. 9) also took place primarily in the
spring; about 75 percent of the fish migrated in
late spring, at a time of high flows. A smaller run
peaked in the fall. Fish of age-groups I and II
dominated the run in the spring. Age-groups O
and I were dominant in the fall ; however, all age-
groups O through IV were represented. Table 7
shows the size ranges.

MIGRATIONS OF HATCHERY-REARED SALMON

Most of the chinook salmon spawners were di-
verted to hatcheries from 1963 through 1965. In
1964 and 1965, hatchery-reared fingerling salmon
were released at the Snake Eiver spawning area,
88 to 120 km. above the reservoir. Chinook salmon
fingerlings from fall migrating adults were re-
leased in 1964 and 1965. Coho salmon fingerlings
were released in 1964 and sockeye salmon finger-
lings in 1965.

210

U.S. FISH AND WILDLIFE SERVICE

30

20

10

30 -

-20

10

;30

o 20

10

30 -

1962

1963

1964

1965

Figure 8. — Timing of migration of juvenile rainbow trout
to Brownlee Reservoir from the Snake River, 1962-65.

Table 6. — Age groups and lengths of juvenile rainbow
trout captured in the migrant dipper traps in the Snake
River above Brounlee Reservoir in 1963

Age group

Fish

Mean
length

Range

0...
I...
II..
III.
IV..

'umber

^ Mm.

Mm.

2

(')

95-100

502

177.1

125-210

276

239.8

190-286

34

294.1

275-340

1

(1)

382

1 Insufficient sample.

Table 7. — Age groups and lengths of juvenile rainbow
trout from Eagle Creek during migration past sampling
site in fall 1962

Age group

Fish

Mean
length

Range

0...

I...
II..
III-

rv..

Number

Mm.

Mm.

119

78.0

52-109

228

141.7

90-183

16

200.0

180-265

3

(')

225-270

1

(')

285

Fall Chinook Salmon

Hatchery-reared juveniles of fall cliinook
salmon were released in the Snake River above
the re.sei-voir in 1964 and 1965 to supplement the
dwindling smolt migrations of wild fall chinook
salmon. About 250,000 fall chinook salmon were
released 120 km. above the reservoir from
March 30 to April 3, 1964, wlien water tempera-
tures averaged 9.5° C. In 1965, 592,000 juvenile fish
were released 88 km. upstream from tlie reservoir
from March 15 to 25, when the water temperature
averaged 9.8° C. A tank truck transported the
fish from hatcheries on the lower Columbia River.
Tlie fish were released during daylight.

The migrations of liatchery chinook salmon
overlapped with migrations of wild spring chi-
nook (age-group I) from the Weiser River. In
1964, juvenile chinook salmon from hatchery re-
leases were recovered at the Snake River sampling
site within 3 days after the first release. Down-
stream migration continued until late June, but
catches were highest in mid-May (fig. 10). The
migration in 1965 was longer and the peak less well
defined.

The lengths of hatchery-reared chinook salmon
increased as the season progressed and by late
April were the same size as those of the age-gi'oup
I wild chinook salmon from Weiser River. The
hatchery fisli captured at the migrant dipper in
1964 averaged 74 mm. (56-100 mm.) early in the
season and 112 mm. (91-135 mm.) near the end of
the migration (table 8). In 1965, the hatchery fish
averaged 69 mm. (46-90 mm.) at the start of
migration and 112 mm. (96-125 mm.) at the end.

Table 8. — Lengths of hatchery-reared juvenile chinook
salmon during migration past sampling site in Snake
River, 1964-66

Year

Length of fish at stage of migration

Early i

Late 2

Fish Mean Range

Fish Mean

Range

1964.
1965..

Number Mm. Mm.
264 74.5 56-100
125 69.3 46-90

Number Mm.
220 112
124 112

Mm.
91-135
96-125

' March through mid-May.
2 Mid-May through June.

> Insufficient sample.

Coho Salmon

The introduction of 375,000 juvenile coho
salmon into the Snake River in 1964 provided an

JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR

211

z
o

UJ

0.

X

o
o

o

40

30

20

10

40

30

20

10

40

30

20

10

1962

1963

1964

1963

1964

Trout Migration
Temperature "C.
Flow C.M.S.

30
20

10

H
d

.,« , — a— ^ 1 1 r

1965

OCT NOV DEC. JAN. FEB. MAR. APR. MAY JUNE JULY

UJ

302H30

30
20
10

a:
20^

UJ

10 '-H

UJ

o

Ui

>
<

' - 10 - 10

203

10 o

UJ

0^

30
20

FiouEE 9. — Timiag of migratioii of juvenile rainbow trout to Brownlee Reservoir from Eagle Greek in
relation to water temperature and flow, 1962-65 (x indicates period of no data).

opportunity to study the migration of a nonin-
digenous species. These fish were obtained from a
hatchery in the lower Columbia River, trans-
ported 120 km. above the resen'oir, and released
from March 15 to 30 in wat«r that averaged 9.4°
C. They did not appear in the Snake River trap
until mid- April (fig. 11). The run peaked in mid-
May and ended in early June.

The mean lengths of trap samples of coho
salmon increased throughout the migration. Mi-
grants averaged 112 mm. (71-140 mm.) early in
the season; by the end of the migration period
they averaged 131 mm. (110-166 mm.).

Sockeye Salmon

About 473,000 sockeye salmon fingerlings were
released in 1965 in the Snake River 88 km. above

212

U.S. FISH AND WILDLIFE SERVICE

12 3 4 12 3 4
MARCH APRIL

Figure 10. — Timing of migration of juvenile hatchery-
reared fall Chinook salmon (age-group 0) to Brownlee
Reservoir from the Snake River, 1964r-65.

the reservoir. These fish were reared from eggs
obtained in the fall of 1963 from Babine Lake,
British Columbia. The eggs were eyed at a
hatchery at Mavirice Lake, British Columbia, and
transpoi'ted to Leavenworth National Fish Hatch-
ery in Washington, wliere they were reared until
their release in 1965. Releases of 20,000 to 30,000
fish were made 5 days each week from March 15
to April 8, 1965; river water temperatures aver-
aged 9.8° C. The sockeye salmon moved rapidly
downstream; the first migrants were recovered
within 2 days after the initial release. Peak migra-
tion was during the first week of April (fig. 12) ;
by mid-April the migration was nearly complete.
Sockeye salmon migrants averaged 121 mm. long
(86-175 mm.).

UPSTREAM MOVEMENTS OF JUVENILE
CHINOOK SALMON

A late group of chinook salmon fingerlings ap-
peared at the Snake River trap near the end of
June or in early July of each year. Because the
migrations of fall- and spring-run chinook salmon
were essentially completed by this time, the origin
of these fish was of interest. Their length was
similar to that of age-group I fish from the Weiser
River, but examination of their scales revealed
tliat they were fingerlings of age-groups O and I.
Growth patterns on their scales showed an area
of rapid growth at the margin typical of fish from

DU

—

H

Z

uj40

-

o

cr

^30

-

— '

UJ

H20

-

S

wlO

-

UJ

_i

.<

— 1=

-1 1 1 r-i 1 1 1

12 3 4
APRIL

I 2 3
JUNE

Figure 11. — Timing of migration of juvenile hatchery-
reared coho salmon from the Snake River to Brownlee
Reservoir, 1964.

the reservoir. This scale structure indicated they
had moved upstream from the reservoir. This
movement was confirmed in 1963 when 12 fin-
clipped individuals were caught that had been
marked as emigrants from Eagle Creek in the
fall of 1962. In 1964, 2.7 percent of the fish cap-
tured from this July migration were fall chinook
salmon that had been previously tagged and re-
leased in the upper reservoir.

According to Durkin et al. ( 1970) , this upstream
movement of fish into the Snake River may be
related to the environment of the reservoir. The
reservoir was rapidly filled early in the 1963 sea-
son, and, excejjt for a minor drawdown of 3 m.
in May, it was at full pool. Some Eagle Creek fish
moved up the reservoir in 1963, possibly because
surface currents frequently moved toward the up-
stream end of the reservoir. Late arrivals may
have been attracted upriver by the relatively
cooler, oxygenated water as the smolting phenom-
enon (Hoar, 1963; Conte, "Wagner, Fessler, and
Gnose, 1966) attenuated and reservoir tempera-
ture and oxygen conditions deteriorated (Ebel
and Koski, 1968). As the river temperature in-
creased to 20° C, the fisli returned to the reser-
voir. In 1964, when the surface level of the
reservoir was lower, Eagle Creek fish were not
captured in the Snake River: however, recovery
of fall chinook salmon that had been marked and
released in the upper reservoir again suggested an
upstream response to cooler water.

JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR

213

T 1 1 1 1 I I 1 1 I

1234 123412345
MARCH APRIL MAY

Figure 12. — Timing of migration of juvenile liatchery-
reared soelveye salmon from the Snake River to Brown-
lee Reservoir, 1965.

ESTIMATES OF IMMIGRATION

Recruitments by age-group and popiUation were
estimated each year from data on release and re-
capture of marked fish. Estimated recruitment
(N) was obtained by dividing the recaptures of
marked fish (R) into tlie number of marked fish
released (M) and multiplying by the catch (C).

In 1962. personnel of the Idaho Department of
Fish and Game working upstream from the
Bureau's migrant-dipper trap marked fall ohinook
juveniles and released them in the Snake River.
These marked fish were used for the 1962 estimate.
The marked fish group far exceeded the total catch
of the migrant dipper. As a result, a single esti-
mate was made for the Snake River population
over the entire season. The 1962 estimate of re-
cruitment for Weiser River chinook salmon was
based upon the total catch by the scoop traps of
the Idaho Department of Fish and Game and the
estimated efficiency of these traps.

In 196.3-65, the Snake and Weiser River fish that
passed our trap were estimated each week and the
values summed to yield the estimated total immi-
gration. Fish for marking were obtained from the
migrant dipper catches.

It was sometimes necessary to supply informa-
tion by extrapolation when reliable data were lack-
ing. Wlien data on catch, recovery of marked fish,
or marked fish released were unreliable or lacking,

reliable data for 1 or 2 weeks preceding, bracketing,
or following were used to supply an approxima-
tion of the needed data.

Studies on fish distribution in the Snake River
in 1964 indicated that fingerling salmon were more
concentrated near the surface during the day than
at night (Monan, McConnell, Pugh, and Smith,
1969). Moreover, the increased length of louver
leads in 196.5 accentuated the difference between
the percentage of the migration captured by the
traps by day and by night. This difference necessi-
tated the use of two catch figures in estimating the
1965 i-ecniitments. Table 9 shows yearly differences
in the ability of the migrant dipper traps to cap-
ture fish during the peak of migration.

SNAKE AND WEISER RIVERS

Tlie number of juvenile native chinook salmon
that entered Brownlee Reservoir after 1962 de-
creased each year. One of the reasons was that the
adult spawners were intercepted and diverted to
hatcheries downstream from Brownlee Dam. Our
highest estimate of recruitment was in 1962 when
529,000 young chinook salmon enteretl from the
Snake River (table 10) ; these fish were offspring
of adults that had been transported past the dam
and spawned in the fall of 1961. The highest num-
ber of juvenile chinook salmon from Weiser River
(122,500) was also in 1962; these fish were off-
spring of spring migrants that had spawned in
1960.

The number of kokanee increased each year;
nearly one-half million entered the reservoir in
1965.

Of the hatchery-i-eared fish released in the Snake
River, sockeye salmon had the highest survival to

Table 9. — Ability of migrant dipper traps to capture
juvenile salmon during peak migration from the Snake River
into Brownlee Reservoir, 1962-65

Year of

migration

Chinook

Cohoi

Sockeye

I

1962

1963

1964

. ..^(a.m.-

Percent
.. 2.36
. 3.66
. 8.13
- 6.97
. 2.35

Percent

(?)
16.70
16.86

«

Percent
(')
(')
13.46
(')
C)

Percent

(')

C)
9.17
7.10

Percent
(')
«
6.2
6.31

'5'55{p.m.3;"

1.10

I All age-group I.

! 6:00 a.m.-6:00 p.m.

3 6:00 p.m.-6;00 a.m.

* Not present in migration.

> Not tested.

214

U.S. FISH AND WILDLIFE SERVICE

Table 10. — Estimates of juvenile salmon that entered
Brownlee Reservoir from the Snake River system, 1962-65

Year

Native species Hatcher

y-reared
Coho

species

Fall Spring :
chiuoolf Chinook

Kolianee FaU
Chinook

Sockeye

19621

1963

1964

1965

- 629,000 122,500

- 374. 000 15, 000

(2) 6, 800
(2) 3, 200

Number
m (?)
500 (J)
5, 500 111, 600
506,800 162,800

69.000

m

360,000

1 Calculated from data supplied
Department.
- Negligible numbers.
3 Not present in migration.

in part by Idaho

Fish and Game

the reservoir, and coho salmon the lowest. Sur-
vivals from release point to reservoir were in-
versely coiTelated with time spent in the river but
not to distance traveled (table 11) .

Table 11. — Time in river and survival of hatchery fish from
release site to Brownlee Reservoir, 1964 and 1965

Estimate

Year

Species

Median

Migration

Time

Re-

offish

Sur-

and

of

release

peak

in

leased

passing

vival

distance

salmon

time

river

collection
facilities

Weeks Number Number

1961 (Coho

120 km. (Chinook.

1965 (Chinook.
88 km.. (Sockeye..

Mar.
Apr.
Mar.
Mar.

Mid-May..

Mid-May..
Mid-May..
Early
AprU.

375,000
250,000
592,000
473,000

69,000
111,500
162, 800
360,000

Per-
cent
18.4
44.6
27.5
76.1

EAGLE CREEK

Estimates of migi-ation from Eagle Creek were
based on average efficiencies of the louver facility
throughout the year (table 12). In 1962, the aver-
age efficiency was 10.2 percent but the louver was
selective for larger fish. Alteration of the structure
in 1963 increased the efficiency to 57.5 percent and
eliminated selectivity. Straightening of the river
channel above the louver in 1964 pro\-ided a
straighter angle of approach for the current and
further increased the efficiency of the louvers to
91.3 percent during the fall migration. In the
spring of 1965, efficiency was less (85.2 percent)
as a result of ice and high flows, which created
currents that varied in velocity and direction of
approach across the face of the louver.

Juvenile fish that entered the reservoir from
Eagle Creek in 1962-63 (table 13) were progeny
of native adults that were transported around

Brownlee Dam in 1960-62. Thereafter natural
production in the creek declined markedly because
the policy of passing fish changed. Juvenile mi-
grants in 1964-65 were primarily from adults that
were surplus to hatchery needs and werB trans-
ported from a collection facility at Oxbow Dam
( 19 km. downstream from Bro%vnlee Dam) tx>
liolding ponds near the spawning area. Prespawn-
ing fish were held in these ponds imtil nearly
mature and then released into Eagle Creek.

T.4.BLE 12. — Collection efficiencies of the louver system at
Eagle Creek, 1962-65

Efficiency of collection
by period of migration

Year

Spring Fall

Percent Percent

1962 10.2

1963 14.7 57.5

1964 42.0 91.3

1965 85.2 (1)

' Not in operation.

Table 13. — Estimates of juvenile spring chinook salmon
that entered Brownlee Reservoir from Eagle Creek, 1962-65

Estimated recruitment by season
and age-group

Year of migration Total

Spring migration Fall migration

I II I

1962 (1) (I) (1) 116,000 1,200 117,200

1963 600 13,600 (?) 7,500 (!) 22,300

1964.. (2) 6,700 (!) (2) (2) 7,200

1966 (!) (!) (!) (I) (I)

' Not in operation. ! Negligible numbers.

SUMMARY AND CONCLUSIONS

Movements of juvenile salmon and rainbow
trout from tributary streams into Brownlee Reser-
voir were examined in 1962-65 as part of a study
on the effect of a large impoundment on the mi-
gration and survival of anadromous fish. Esti-
mated numbers of migrant juvenile salmon were
determined by sampling of juvenile fish popula-
tions that were en route to the reservoir from the
Snake and Wei.ser Rivers and Eagle Creek, the
three tributaries supporting indigenous popula-
tions of salmon and anadromous rainbow trout.
Juvenile fall and spring chinook salmon, kokanee
salmon, and rainbow trout entered the upper reser-
\'oir ^-ia the Snake River. Hatchery-reared fall

JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR

215

chinook and coho salmon were released in the
Snake River in 1964 and fall chinook and sockeye
salmon in 1965. Migrations from Eagle Creek near
the lower end of the reservoir included native
spring chinook salmon and rainbow trout.

Progeny of spring chinook salmon from the
Weiser River were fish of age-group I that ranged
from 94: to 165 mm. long. This migration began
before but partially overlapped a migration of fall
chinook juveniles from the Snake River. The mi-
gration usually peaked in late April and early
May. Estimated numbers of fish were: 1962 —
122,500: 1963—15,000: 1964—6,800; and 1965—
3,200.

The migration of juvenile fall chinook salmon
(age-group O) from the Snake River began in
mid-April, peaked in mid-May, and was almost
complete by mid-June. The fish were 33 to 103 mm.
long. Estimated recruitments to Brownlee Reser-
voir in 1962 and 1963 were 529,000 and 374,000.
Because few fish were passed above Brownlee Dam
after 1962, migrations of wild fish in 1964—65 were
negligible.

Migrant salmon from Eagle Creek were of wild
populations of spring chinook salmon. The prin-
cipal migration of juvenile chinook salmon (age-
group 0; 53-125 mm.) was in the fall as irrigation
decreased and water flows correspondingly in-
creased. Temperatures ranged from 0° to 13° C.
A lesser migration of age-groups 0, I, and TI
(45-168 mm.) occurred in the spring. Estimated
recruitments from Eagle Creek were: 1962 —
117,200 (fall migration only) ; 1963—22,300; and
1964—7,200.

Native juvenile kokanee salmon (70-155 mm.)
were observed in the Snake River each year in
June and July, except in 1962. Their migrations
were relatively short; most fish migrated in a
1-week period in late June or early July. Esti-
mated recruitment of this species was 500 in 1963,
5,500 in 1964, and 506,800 in 1965.

Juvenile rainbow trout migrating from the
Snake River and Eagle Creek were wild steel -
head trout and wild and hatchery-reared rainbow
trout. The Snake River populations (95-382 mm.)
migrated in the spring from mid-March to late
July, peaking from mid- April to mid-May. Juve-
nile trout, 52-285 mm. long, migrated from Eagle

Creek in the fall and spring, but the principal
movement coincided with high spring flows.

Juvenile fall chinook salmon, reared in a hatch-
ery (age-group 0; 46-135 mm. long), were re-
leased in the Snake River above the reservoir
during March and April, 1964-65. Some moved
downstream past the trapping site within 3 days
after release, but the migration peaked in mid-
May, which was comparable to native migrations.
The migration ended in late June in 1964 and in
early July in 1965. Of 250,000 juvenile fall chi-
nook salmon released in 1964, 111,500 were esti-
mated to have entered the reservoir. In 1965, the
estimated recruitment was 162,800 of the 592,000
fish released.

Hatchery-reared coho salmon yearlings (71-
166 mm.) released in middle to lat« March 1964,
migrated slowly; they appeared at the trap site
4 weeks after the first release, peaked during the
first week of May, and continued to migrate until
mid-June. Of the 375,000 coho salmon released,
69,000 entered the reservoir.

Hatchery-reared sockeye salmon (86-175 mm.)
appeared at the Snake River trap 2 days after
their release in mid-March ; the migration peaked
in the first week of April and was complete by the
end of April. An estimated 360,000 of 473,000 fish
released entered the reservoir.

Survival to the reservoir of hatchery -reared
salmon varied inversely with time spent in the
Snake River but was not related to distance of
planting site above Brownlee Reservoir.

LITERATURE CITED

Bates, Daniel W., and Russell Vinsonhaler.

1957. Use of louvers for Riding fish. Trans. Amer.
Fish. Soc. 86 : 38-57.
CoNTE, F. p., H. H. Waoner, J. Fessleb, and C. Gnose.
1966. Development of osmotic and ionic regulation in
juvenile coho salnuxn Oncorhynchus kisutch.
Oomp. Biochem. Physiol. 18 : 1-15.
Deacon, James E.

1961. A staining method for marking large numbers
of small flsih. Progr. Fish-Cult. 23 : 41-42.
DuKKiN, Joseph T., Donn L. Park, and Robert F.
Raleigh.
1970. Distribution and movement of juvenile salmon
in Brownlee Reservoir, 1962-65. U.S. Fish Wildl.
Serv., Fish. Bull. 68 : 219-243.
Ebel, AVesley J., and Charles H. Koski.

1968. Physical and chemical limnology of Brownlee
Reservoir, 1962-64. U.S. Fish Wildl. Serv., Fish.
Bull. 67 : 295-335.

216

U.S. FISH AND WILDLIFE SERVICE

Hoar, William S.

1963. The endocrine regulation of migrating behavior
in anadromous teleosts. Proc. 16th Int. Congr. Zool.
3: 14-20.
Mason, James E.

1966. The migrant dipper: a trap for downstream-
migrating fi.sh. Progr. Fish-Cult. 28 ; 96-102.
MoNAx, Gerald E., Robert J. MoConnell, John R. Pugh,
and Jim Ross Smith.
1969. Distribution of debris and downstream migrat-
ing salmon in the Snake River above Brownlee
Reservoir. Trans. Amer. Fisli. Soc. 98 : 239-244.

Sims, Cabl W.

1970. Emigration of juvenile salmon and trout from
Brownlee Reservoir, 1963-65. U.S. Fish Wildl.
Serv., Fish. Bull. 68 : 24&-259.
Trefethen, Parker S., and Doyle F. Sutherland.

1968. Passage of adult Chinook salmon through
Brownlee Reservoir, 1960-62. U.S. Fish Wildl.
Serv., Fish. Bull. 67 : 35-45.
VoLz, Charles D., and Chester O. Wheeler.

1966. A portable fish-tattooing device. Progr. Fisih-
Cult. 28 : 54-56.

JUVENILE SALMON AND TROUT MIGRATION INTO BROWNLEE RESERVOIR

217

DISTRIBUTION AND MOVEMENT OF JUVENILE SALMON IN BROWNLEE

RESERVOIR, 1962-65

BY JOSEPH T. DURKIN, DONN L. PARK, AND ROBERT F. RALEIGH, FISHERY BIOLOGISTS
BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY
SEATTLE, WASH. 98102

ABSTRACT

Juvenile salmon — chinook {Oncorhynchus tshawy-
tscha), coho (O. kisutch). and sockeye and kokanee
(O. nerka) — were studied. Their rates and direction of
movement, spatial distribution, and successful passage
to the outlet varied in relation to surface currents,
water temperature, and dissolved oxygen concen-
trations.

Some juvenile salmon stayed in Brownlee Reservoir
through the summer, fall, and early winter; the per-
centage varied between years. The percentages were
highest in years with high water level and retarded,
disoriented flows during the spring migration. Salmon

Figure 1. — Brownlee Reservdir, Snake River, and major
tributaries.

Published April 1970.

FISHERY BULLETIN: VOL. 68, NO. 2

that held over eventually concentrated in rather re-
stricted areas of the reservoir through the summer and
early fall, owing to high epilimnion temperatures and
to low concentrations of dissolved oxygen that extended
into the epilimnion from the hypolimnion.

When the water level was low and reservoir currents
were oriented downstream, loss of orientation by
juvenile salmon was least and movement through the
reservoir was most rapid. These reservoir conditions
varied, but salmon populations that migrated early In
the year were most likely to encounter them.

The completion in 1958 of Brownlee Dam on the
middle Snake River (Soule, Heikes, Mitchell, and
Schaufelberger, 1959) created a long, narrow res-
ervoir along the path of migrating Pacific salmon
(genus Oncorhynclms) and anadromous rainbow
trout (steelhead) Sahno gairdneri (fig. 1). At full
pool the impoundment is 92 km. long, less than
0.8 km. wide, and nearly 92 m. deep. The upper
24-km. of the reservoir is relatively shallow, slow
moving, and forms a river-run impoundment. The
lower 68 Ian., which thermally stratifies, lies
within an arid mountainous terrain. Powder River
Arm, a prominent appendage on the Oregon side,
joins the reservoir 17 km. above the dam and
extends westward for 15 km. The upper 5 km. of
the arm forms a wide, shallow, unstratified pond
when the reservoir is full. Juvenile salmon enter
the reservoir from the Snake and Powder Rivers
en route to the sea.

When Brownlee Reservoir was completed, de-
tailed knowledge was lacking on the passage of
Pacific salmon and steelhead trout through large
resorvoii-s; therefore, BCF (Bureau of Coimner-
cial Fisheries) conducted detailed research at
Brownlee in 1962-65. Tliese studies covered native
stocks of steelhead trout, spring and fall chinook
salmon {0. tshaioytscha) , and kokanee (land-
locked sockeye salmon, 0. nerka) in addition to

219

hatchery-reared fall chinook, sockeye, and coho
{0. kisutch) salmon. The research, which began
in the spring of 1962, consisted of five studies : (1)
limnology of the reservoir system (Ebel and
Koski, 1968), (2) upstream migration of adult
chinook salmon through the reservoir (Trefethen
and Sutherland, 1968), (3) migration of juvenile
salmon and trout into the reservoir (Krcma and
Raleigh, 1970), (4) distribution and movement of
juvenile salmon in the reservoir (this report), and
(5) migration of juvenile salmon and trout from
the reservoir (Sims, 1970) .

Our report gives an account of movements and
distributions of the juvenile salmon in relation to
their environment. Data on the movements of
juvenile st«elhead trout were difficult to analyze
and report, as we were unable to clearly distin-
guish them from the nonanadromous wild and
hatchery-reared rainbow trout that were also in
the reservoir.

EQUIPMENT AND PROCEDURES

To obtain the desired information, it was neces-
sary to sample the juvenile fish in the lower 68 km.
of the reservoir. This sampling involved both gear
and marking efforts.

FISHING EQUIPMENT

Studies had indicated that four types of fishing
equipment were needed to capture juvenile fish :
floating traps, gill nets, purse seines, and two-boat
trawls. These, together with the fingerling col-
lection facility (skimmer net) of the Idaho Power
Company 1.5 km. above the dam, provided basic
data on the movement of juvenile salmon within
the reservoir. The sampling equipment was de-
ployed to intercept migrants in the upper, middle,
and lower reservoir from early in the year until
late fall (fig. 2).

Floating Traps

Floating traps were the most effective fishing
gear for capturing age-group salmon (fig. 3).
The dimensions of the trap, mesh size, and fishing
methods were similar to those described by Roth-
fus, Erho, Hamilton, and Remington.' From one

' Lloyd O. Rothfus, Michael Erho, J. A. R. Hamilton, and Jack
D. Remington. 1964. A study of reservoir rearinR of coho salmon
in Lake Merwin, Washington. State Wash. Dcp. Fish., Res. Div.,
18 pp. (Processed.)

to seven of these units were used. The traps were
tended every other day early in the year and each
day between mid-March and early July. There-
after, as fish became less available, the traps were
operated with diminishing frequency and in most
years were removed by late July.

Gill Nets

The number of gill net stations fished depended
on the water level and its effect on the length of the
reservoir. At each site, two or three parallel sec-
tions of multifilament net, 30 m. long by 4.5 m.
deep, were fished at predetermined depths in a
manner similar to that described by Rees (1957).
The mesh sizes were 1.9, 2.5, 3.1, 3.8, 5.1, and 6.3 cm.
stretched mesh, of which the 2.5- to 3.8-cm. sizes
were most effective. The nets were most efficient on
salmon over 90 mm. fork length and at night.

Purse Seines

Two purse seines (Durkdn and Park, 1967) were
used as mobile sampling gear on fish concentra-
tions throughout the limnetic environment of the
reservoir. One of the seines was 180 m. long and
10.5 m. deep; the other was 210 m. long and 16.5
deep. Both were set from a barge. Purse seines
were used in the main resei-voir during spring and
early summer and in the Powder River Arm dur-
ing fall.

Two-Boat Trawls

Surface trawls (Johnson, 1956) were used to
locate concentrations of salmon and to determine
their relative abundance. The trawls were 3.0 m.
high, 5.4 m. wide at the mouth, and 7.8 m. long.

MARKING

Various types of marks were placed on captured
juvenile fish for identification at recapture. The
type of mark depended on the size of fish. Fish less
than 100 mm. long were marked with vinyl thread
tags (developed by personnel of the Fish Ommis-
sioii of Oregon). A jaw tag clamped to the left
mandible marked the fish (100 to 250 mm. long) ;
fish over 250 mm. had a plastic dart tag. Color
coded tattoos, used in 1962, were discontinued
when the vinyl thread tag became available. Other
groups of fish were marked by clipping fins before
they entered the reservoir (Krcma and Raleigh,
1970).

220

U.S. FISH AND WILDLIFE SERVICE

Brownlee Dam
Skimmer

Powder River Arm

\

Legend

Floating traps
Purse seining area
Gill net station
Trawling area

FiGUEE 2.— Location of sampling areas and types of fishing gear used in Brownlee Reservoir, 1962-65.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

221

r-gsn.-

Figure 3. — Floating trap used to capture juvenile salmon moving near the shore. Salmon were diverted
to the trap by a lead extending from the shoreline.

A combination of length-frequency ranges and
the above marks identified specific populations and
individual fish and, thus, yielded data on direction
and rat« of movement, spatial distribution, gro^vth,
and survival of the populations of salmon that
entered the reservoir.

Upon capture, the fish were anesthetized, meas-
ured (fork length) to the nearest millimeter, ex-
amined for marks, and tagged if not previously
marked. Scales for age determination were taken
each month from a sample of up to 10 fish in each
5-mm. length group in the catches. All fisli were
released near the capture site.

THE ENVIRONMENT OF THE RESERVOIR

Apparently, the conditions
effect on the environment of
were the size and timing of
drawdown and fillui> and
through the impoundment,
reservoir, filling, spillway

exerting the greatest
Brownlee Reservoir

the annual reservoir

the volume of flow
Water level of the

discharge, and flow

varied consideraibly during the 4-year study (fig.
4). The drawdown was least (6.4 m.) in 1963 and
greatest (28.3 m.) in 1965. Drawdown typically
began in December or January. Filling began
each year in early April except in 1965 when it was
delayed until mid-May. Filling was nearly com-
plete by late June 1962, mid-April 1963, mid-Juno
1964, and mid-June 1965. The extent of drawdown
or fill determined the length of the reservoii-, and
the time of filling determined tlie quality of thn
water through which the fish migrated.

SURFACE CURRENTS

The volume of inflow and outflow, together with
the water level of the reservoir, determined the
orientation and stability of currents and the ve-
locity of flow. Figure 5 shows typical currents
under different reservoir conditions.

The stability, velocity, and orientation of the
reservoir surface cui'rents varied considerably over
the study yeai-s (1962-65). Surface currents near

222

U.S. FISH AND WILDLIFE SERVICE

JAN. FEB.* MAR.' A PR.' MAY ' JUN.' JUL ' AUG.' SEP. ' OCT." NOV." DEC.

PiouKE 4. — Seniimcmthly averages of resen-oir water level, turbine and .spillway discharges, and Snake
River flow into Brownlee Reservoir, 1962-65. Flow is in cubic meters per second.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

223

417-060 O - 71 - 4

Stotions

Reservoir conditions :

Reservoir conditions :

s s

Surfoce level ot minus 27.1 to Il5.5nr>. ond filling-, inflow 511 c.m.s.,
outflow 424 c.m.s., spill dischorge 0.

N. N.

S. ° S

Surface level at minus 13. I m. and filling; Inflow 595 c.m.s.,
outflow 693 c.m.s., spill dischorge 371 c.m.s.

Reservoir conditions: Surfoce level oi full pool ond steody; inflow I,l85c.m.s
outflow 1,219 c.m.s., spill disct)orge 1,008 c.m.s.

Velocity ni p s
Direction % of time
Downstream direction

FiGTJBE 5. — ^Direction (percentage of time, indicated by scale between center and upper margin of each figure) and
average velocity (m.p.s. scale between center and lower margin) of currents recorded at 3-m. depth in Brownlee
Reservoir. Direction of current reads toward point of wedge. Percentages of time (if any) during which no flow
was detectable are given mthin each circle ; when flow was in a particular direction more than 50 percent of the
time the percentage is given outside of the circle. Adapted from Bbel and Koski (1968) .

224

U.S. FISH AND WILDLIFE SERVICE

the dam were affected mainly by the presence or
absence of spillway discharges even when the
reservoir level was down 27.1 to 15.5 m. (fig. 5).
Surface currents in the middle and upper sections
of the reservoir, however, appear to be little af-
fected by spillway discharges. Reservoir level and
volumes of flow liad the greatest effect on the
orientation and stability of the surface currents in
these areas (fig. 5).

TEMPERATURE CYCLE

The volume of flow and water level of the reser-
voir also influenced the characteristics of tempera-
ture and oxygen in the impoundment. Figure 6
shows a generalized annual tliermal cycle in the
reservoir. From January to mid-March, isotlierms
of 1° t« 6° C. were vertically aligned. Horizontal
alignment of isotherms began in late March, and
thermal stratification developed by early June. A
sharp convergence line (not shown in fig. 6) was
formed in the upper reservoir in late spring of
1963 when cold, dense river water sank below the
warmer surface water (Ebel and Koski, 1968). In
late June, the temperatures of the river water and
surface water were similar and the line disap-
peared. By mid-July the entire reservoir was
usually stratified with well-defined epilimnion,
thermocline, and hypolimnion. In late summer,
water temperatures ranged from 5° C. in the liy-
polimnion to as high as 24° C. at the surface. In
mid-October a convergence line was again formed
by rapidly cooling water from the Snake River
and the thermocline was gradually eroded. Ver-
tical alignment of isotherms began again in early
December.

DISSOLVED OXYGEN CYCLE

The dissolved oxygen content of the reservoir
followed a similar cycle each year (fig. 7). The
reservoir was near saturation and relatively stable
from January to mid-March, at which time oxy-
gen concentrations began to decline in the deeper
parts. Depletion of oxygen continued through the
summer until August when all water below 30 m.
had less than 3 p.p.m. In September, the cooler,
oxygenated water from Snake River began to sink
below the surface of the upper reservoir. By No-
vember, most of the water had 7 to 9 p.p.m. of
oxygen.

These seasonal changes occurred each year, "but
with certain differences. In 1965, a drawdown of
28.3 m. and a late filling period caused: (1) late
formation of a thermocline, (2) higher average
temperatures from top to bottom, (3) lower oxy-
gen concentrations during August and September,
and (4) currents that were consistently oriented
downreservoir through May. Drawdown was sig-
nificant in 1964 (26.7 m.), but the filling began
earlier and volumes of inflow and outflow were
smaller. Temperatures were lower and concentra-
tions of dissolved oxygen were higher in 1964 than
in 1965, but conditions were less favorable for fish
than in 1962 or 1963. A reservoir drawdown suf-
ficient to allow sustained downreservoir current
velocities can prevent a sharply defined conver-
gence line from forming. For this reason, no con-
vergence line formed in the upper reservoir in the
spring of 1962, 1964, or 1965.

Generally, the temperatures and dissolved oxy-
gen in the reservoir were within acceptable limits
for survival of salmon during their spring migra-
tion (March- June). These conditions, however,
began to deteriorate by late June and were mar-
ginal to restrictive until late September. A more
detailed report of the environment was presented
by Ebel and Koski (1968) .

DISTRIBUTION AND MOVEMENT OF
NATIVE STOCKS OF SALMON

Juvenile salmon from four populations were
indigenous to Brownlee Reservoir: Two were
progeny of spring chinook salmon, one of fall
Chinook salmon, and one of kokanee. The account
of movement and behavior of juvenile salmon
while passing through the reservoir environment
is presented by species and population.

SPRING CHINOOK SALMON

Offspring of spring chinook salmon enter the
reservoir from two areas : the Weiser River, a trib-
utary of the Snake River, and Eagle Creek, a
tributary of the Powder River (fig. 1). Migrants
from Weiser River must traverse the entire reser-
voir on their seaward migration, whereas Eagle
Creek migrants have less than one-half of the
reservoir to negotiate. The two populations also
differ in average age, size, and season of entry.
Table 1 gives yearly estimates of the numbers of
young fish that entered the reservoir in 1962-65.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

225

STATION NUMBERS

2 4 6 8 10 12 14 16 18 20

10
20
30-
40
50
60
70
80

0- ? . ? . f . 6 8 10 12 , 14 ^ 16 18 20

2 4 6 8 10 12 14 16 18 20

MARCH 11-14

Figure 6. — ^Water temperature profile and stratlflcatioQ cycle at Brownlee Reservoir, 1963, modified from Bbel

and Koski (1968).

Table l.—Estimaled numbers of juvenile spring chinook
salmon that entered Brownlee Reservoir, 196S-66 (from
Krcma and Raleigh, 1970)

Welser River origin

Eagle Creek origin

Year

Age- •
group I

Spring migrants

Age-group
I

Fall migrants
Age-group
I

Number Number Number Number Number Number

1962 122,600 (>) (i) (>) 116,000 1,200

1963 16,000 600 13,600 P) 7,600 (!)

1984. 6,800 (!) 6,700 (!) (!) (l)

1968 3,200 (!) (1) (!) (1) (1)

Not estimated.

' Negligible numbers.

Weiser River Population

Spring chinook salmon from the Weiser River,
106 to 176 mm. long, entered the reservoir as
yearlings from early April until late June. The
migration peaked from late April to early May
each year.

Through late May, spring chinook salmon from
the Weiser River that were in the reservoir could
be distinguished from fall chinook salmon of age-
groups O and I on the basis of length ; they were
longer than age-group O but shorter than age-
group I of the fall stock. After late May, as length

226

U.S. FISH AND WILDLIFE SERVICE

STATION NUMBERS

10
20
30
40
50
60
70
80

10 12 14 16 18 20

JULY 8-11

16,18 20

SEPTEMBER 3-6

SEPTEMBER 30"
OCTOBER 1-3

,8 10 12 14 16 16 20

? . f , ^

NOVEMBER 4-8

10 12 14 16 18 20

FiouKE 6. — Continued

measurements overlapped, the populations were
separated on the basis of marked fish in the catch.
By late May, however, the peak of migration from
the Weiser River had usually passed through the
reservoir.

A comparison of the timing of peak catches in
the Snake River above the reservoir and at Brown-
lee Dam provided rough estimates of the time re-
quired for passage tlirough the reservoir — about 2
weeks in 1962 and 3 weeks in 1963 (fig. 8). Differ-
ences in flow and length of reservoir between the
2 years appear to account for the more rapid move-
ment in 1962. From early May through early

June 1962 the reservoir was drawn down 9 m. and
was about 75 km. long. Over the same period in
1963 it was nearly full and 92 km. long (fig. 4).
Because of decreased depth and length in 1962,
the average movement of the water mass through
the reservoir was more rapid and conducive to
passage of fish.

On the basis of the comparison of peak catches,
the movement through the reservoir of yearling
chinook salmon from tlie Weiser River averaged
6.4 km. per day in 1962 and 4.8 km. per day in
1963. Recapture of 334 marked individuals in 1962
and 1963 indicated that these fish moved through

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLBB RESERVOIR

227

STATION NUMBERS
Q 2 4 6 8 10 12 14 16 18 20 2 4 G 8 10 12 14 16 IS 20

* r' ' ' ' surface' frcJ;

iZEN

2 4 6 8 10 12 14 16 18 20
-H — ji — r-l ' *— ; — I 1 — V"" *— 1 — '

^ ----6 ^ ^6-

2 4 6 8 10 12 14 16 18 20

JUNE 4-10

PiotTBE 7. — DisaolTed oxygen (p.p.m.) profiles from Brownlee Reservoir, 1963, modified from Ebel and Koeki

(1968).

the reservoir with little wandering and corrobo-
rated the estimated rates of movement.

In 1962, about 3,200 fish from the Weiser River
population were marked as they were entering the
reservoir. Six were recaptured the following
spring (1963) in the reservoir. In 1963, about 1,900
fish were marked during their migration into the
reservoir; in late June and July, 23 were recap-
tured in the Snake River. A study of growth
patterns on their scales showed that they had re-

turned upstream from the reservoir. These recap-
tures indicate that some fish of the Weiser River
population become disoriented and hold over in the
reservoir, but this behavior did not appear to be
a major factor in the general movement of this
early migrating population of large yearling fish.
In general, the Weiser River chinook salmon
passed through a more benign environment in the
reservoir than did populations migrating later in
the season ( figs. 6 and 7 ) .

228

U.S. FISH AND WILDLIFE SERVICE

STATION rNiwMP.FRS

2 4 6 8 10 12 14 16 18 20

DECEMBER 9- ,2

PiQUBE 7. — Continued

Eagle Creek Population

The principal migration of spring cliinook salm-
on from Eagle Creek into the reservoir was in
the fall and consisted of age-group O fish, 53 to
125 mm. long. This movement was followed by a
second lesser migration of age-group I fish, 65 to
138 mm. long, from February to May (Krcma and
Raleigh, 1970). Only chinook salmon tliat had
held over from the spring migrations were foimd
in significant numbers in the reservoir at that time
of year. These populations were separable by size
(fig. 9).

Continuous recovery from the upper Powder
River Arm and the main reservoir of marked age-
group O fish from the fall migration from Eagle
Creek indicated that not all these fingerlings con-
tinued to move through the reservoir. Further evi-
dence was obtained by comparing mean lengths of
fish caught leaving Eagle Creek with those of fish
from the reservoir. Fish that remained in the
stream grew little through the fall and winter,
whereas those in the reservoir continued to grow.

Incidental movement of Eagle Creek fish from
the reservoir began in November, but a sustained

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLiEE RESERVOIR

229

APRIL

Cotches
N= 2,412 I I ADO»e reservoir
N- 281 SS Skimmer net

neor dam

a1

Cotches
N= 15,000 I I Above reservoir
N= 620 ^J Sliimmer net
near dam

a R

JUNE

JULY

Figure 8. — -Percentages of the total catch of juvenile spring chinook salmon from Weiser
River, taken during different weeks at the upper and lower ends of Brownlee Reservoir,
1962-63.

outmigration did not occur until after the first
of the year (Sims, 1970). Tliere were two major
migrations of Eagle Creek fish from the reservoir
each year; the first consisted of fish that entered
the reservoir in the fall and overwintered, and
the second consisted of spring migrants that moved
directly from the stream to the dam (fig. 10). The
first group migrated from the reservoir primarily
from late January to April and the second group
from late March to June ( fig. 11 ) .

We investigated the possibility that the reservoir
might be delaying the seaward migration of the
fall migrants. Tagging data showed that most fall
migrants spent about 3 months in the reservoir,
whereas most spring migrants moved through the
reservoir in a much shorter time. In 1964 and 1965,
groups of Eagle Creek fall migrants were marked,
transported around Brownlee and Oxbow Dams,
and released in the Snake River. Sampling at Ice
Harbor Dam (442 km. downstream from Brown-
lee) showed that fish released in the river below
the dams overwintered in the Snake River and
arrived at Ice Harbor Dam at about the same time

as the group that passed through the reservoir.^ It
appears, therefore, that Brownlee Reservoir did
not unduly delay the fall migration from Eagle
Creek and tliat these fish nonnally overwinter be-
fore going to sea.

Although Brownlee Reservoir did not appear
to cause an appreciable delay in the seaward mi-
gration of the fall migrants, some fish from Eagle
Creek became disoriented in the reserv'oir imder
certain conditions. In 1962 and 1964, fish from
Eagle Creek moved consistently downstream to-
ward the dam. In 1963, however, a segment of the
population moved upreservoir. This movement
was proven by capture of 12 marked individuals
in the Snake River 4 km. above the reservoir in
late June and July 1963. Drawdown of the reser-
voir exceeded 14 m. in 1962 and 1964 but was only
6.4 m. in 1963. Figures 4 and 5 indicate that these
conditions would provide weak downstream cur-
rents in 1962 and 1964 but disoriented curi-ents in

' Personal communication, Howard Raymond, Fishery. Biol-
ogist, BCF Biological Laboratory, Seattle, Wash,, June 1065.

230

U.S. FISH AND WILDLIFE SERVICE

CO

480 p
440 -
400-
360-
320-
280-

I I Unmarked fish
H Marked fish

HOLDOVERS FROM SPRING MIGRATION
(MOSTLY SNAKE RIVER AGE-GROUP 0)

FALL MIGRANTS FROM
EAGLE CREEK

I I 1 — r

80- 90-
84 94

100- 110- 120- 130- 140 150- 160- 170- 180" 190- 200- 210" 220" 230- 240-
104 114 124 134 144 154 164 174 184 194 204 214 224 234 244

LENGTH (MM.)

FrouRE 9. — Len^hs of juvenile spring Chinook salmon from Eagle Greek that entered Brownlee Reservoir in the
fall and lengths of holdover Chinook salmon from populations that entered in the spring, in samples collected
September through December 1962.

1963. We presume that some Eagle Creek fish
moved upreservoir in 1963 because of frequent up-
reservoir currents. The fish that arrived at the
upper end of the reservoir in late June and July
as the "smolting'' condition (Hoar, 1963; Conte,
Wagner, Fessler, and Gnose, 1966) was attenu-
ating and reservoir temperature and oxygen con-
ditions were deteriorating (figs. 6-7) may have
been attracted upstream by the relatively cooler,
oxygenated wat^r of tlie Snake River.

FALL CHINOOK SALMON OF AGE-GROUP O

Juvenile fall chinook salmon entered the reser-
voir as age-group O and at a smaller length (33-
105 mm.) than other ijopulations. They began their
migration from spawning grounds in the Snake
River about 120 km. above the reservoir. Table 2
gives estimates of fall chinook juvenile salmon that
entered the reservoir.

We studied the offspring of native popidations
in 1962 and 1963; hatchery-reared juvenile fish
from otlier sources were released in the spawning

area for study as they passed through the reservoir
in 1964 and 1965.

Table 2. — Estimated numbers of fall chinook salmon that
entered Brownlee Reservoir, 1962-66 {from Krcma and
Raleigh, 1970)

Year

Native Hatchery-
reared

Numbtr offith

1962.. 629,000 (')

1963 374,000 (')

1964 (!) 111,600

1965 (') 162,800

' None released.

' Negligible numbers.

Juvenile native fall chinook salmon entered the
reservoir from late April through June in 1962
and from late April through mid-June in 1963.
Mean lengths of age-group O fish in the reservoir
were 56 to 85 mm. through the 1962 season and 75
to 195 mm. in 1963.

Peak catches above the reservoir and at the
fingerling collection facility near Brownlee Dam

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

231

z
o

<

a

z
<

a.

3
O

q:

03

Z

o

s

<3

1963

D FALL MIGRATION INTO RESERVOIR

E SPRING MIGRATION INTO RESERVOIR

El COMBINED MIGRATION FROM RESERVOIR

SEP.

OCT

NOV.

DEC.

JAN.

FEB.

MAR.

APR.

MAY

JUN.

Figure 10. — Percentage of total catches of juvenile spring chlnook salmon from Eagle Greek that entered and that left
B^o^vnlee Resen'oir in different months, 1962-64. Fish entering the reservoir were caught in a louver trap at Eagle
Greek (Krcma and Raleigh, 1970) ; fish leaving the reservoir were caught in skimmer net traps in tie forebay
(1963) or in scoop traps below the dam (1964).

• FALL

MIGRANTS

1963

o SPRING MIGRANTS 1

X

iZ

u.
O

1

1 ° 1

Of)

o:

10 20 30

9 19

1

II 21 31 10 20 30

10 20 30

9 19 29

UJ
CD

JAN.

FEB.

MAR. APR.

MAY

JUN.

2
Z>
z

1964

•I^<t

P . »

-tM-

_, , 9 tf88ja8,8ap ^ ,8 b, — ,_o,-

P 1 1 . .

10 20
JAN.

9 19

FEB.

10 20 30

MAR.

19 29

APR.

19 29
MAY

JUN.

Figure 11. — Date of arrival at Brownlee Dam of juvenile spring chinook salmon tagged at
Eagle Greek during the fall and spring migrations of 1962-64. Each circle represents
one recovery.

showed that juvenile fall cliinook salmon passed
through the reservoir in about 2 weeks in 1962 and
in about 7 weeks in 1963 (fig. 12). Figures 4 and 5
indicate that the currents would have been of low
velocity but moderately well oriented downstream
during the 1962 migration. In 1963, the migrant

fall chinook salmon entered the reservoir a week
later than in 1962 (fig. 12). At that time the reser-
voir was drawn down only 3 m. and was being
filled. Although volumes of inflow and outflow
were moderate to high, the currents were disori-
ented (figs. 4 and 5).

232

U.S. FISH AND WILDLIFE SERVICE

40

X

u
^ 30

UJ

o 20

t-
z

UJ

o
q:

10

1962 CATCH

D CATCHES ABOVE THE RESERVOIR

CATCHES IN UPPER RESERVOIR TRAPS

Q CATCHES IN FOREBAY BY SKIMMER NET TRAPS

Jl

I

1963 CATCH

(56)

40

I
o

o

Ul

30

o 20

IT
UJ
Q.

10

I

I

2 3
APRIL

PlOUBE

512 34 123 412345
MAY JUNE JULY

12. — Oatehes of naibLve juvenile fall chinook salmon in the upper reservoir and at Brownlee Dam, 1962-63.

Trap and surface trawl catches in 1963 indicated
tliat most of the migrants were remaining in the
upper reservoir. They were in the Snake River
water mass upstreajn from the point where the
colder river water sank below the reservoir surface
(Ebel and Koski, 1968; Raleigh and Ebel, 1967).
Gill net sampling showed the fish were near the
surface of the reservoir through mid-June. By late
June, however, they were captured at all depths.
At this time the river water began to warm and
mix with the reservoir water mass; the convergence
line disintegrated, and the juvenile fish began to
move through the reservoir. Peak catches by traps

in the upper reservoir and at Brownlee Dam
showed that after the initial 5-week delay the fiSh
migrated through the reservoir in about 2 weeks
(fig. 12).

In 1963, the capture of a number of large finger-
lings in the Snake River above the impoundment
indicated a pronounced upreservoir movement of
young fall chinook salmon (Krcma and Raleigh,
1970). Growth patterns on the scales ^owed that
these fish had lived in the reservoir. The identifica-
tion of marked fish indicated that most of the fish
that moved upstream had migrated from Eagle
Creek and the Snake River in the spring of 1963.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BEOWNLEB RESERVOIR

233

KILOMETERS FROM DAM

20 -

40
60

80

20h
40
60
80

JUNE I- 15

4

II

24 34

-^-^^

^ y

*:

^;^

II

JUNE 16 - JULY 20
24 34

u

u

u

u

- D

a

B

B /

B

B

B

B /

" a

a

a

^ /

- D

a

X

:

^DECE^

^BER

i^

FISH

CAUGHT

PER

NET

DAY

TEMPERATURE

OXYGEN

a

1 1

Less

thon 21°

C.

1 1

More

thon

2

p.p.m.

1
2

or
to

less
5

\=>-K^

21"' C

or more

t=l

Less

thon

2

p.p.m.

6

to

45

FiouKE 13. — Distribution of juvenile fall chinook salmon in Brovvnlee Resen'oir in relation to critical oxygen
and temperature regimes. Fish caught in gill nets in 1963.

234

U.S. PISH AND WILDLIFE SERVICE

We presume that these fish were attracted up-
stream by the cooler water of the Snake River ( 14r-
22° C), wliich averaged 2 to 3° C. less than the
reservoir. The subsequent downstream migration
coincided with an increase in river temperatures to
over 18° C. and the breakdown of the convergence
line.

In most years, after the migration of smolts
ended in late Jime or July, some chinook salmon
remained in the reservoir as holdovers. In 1963,
most of the migrants did not leave the reservoir
even though the outmigration continued into Au-
gust (Sims, 1970). The holdover fish were from all
salmon ix>pulations but were mainly progeny of
fall cliinook salmon. They were easily distin-
guished from more recent arrivals by their large
size; in addition, some had identifying fin clips or
tags.

Gill net catches showed that the holdover salm-
on had a restricted spatial distribution through
the summer and early fall. By late June or early
July, surface temperatures exceeded 20° C. and
oxygen depletion progressed upward from the bot-
tom. These conditions were especially prevalent in
the upper end of the reservoir (figs. 6 and 7) . In-
creasing epilimnion temperatures and decreasing
liypolimnion levels of dissolved oxygen eventually
confined the holdovers into restricted areas un-
favorable for juvenile salmon (fig. 13). By late
September and October, conditions began to im-
prove and the surviving juvenile salmon dispersed
tliroughout tlie reservoir.

This same sequence of events occurred each year,
but with modification. According to Raleigh and
Ebel (1967), the amovmt of reservoir drawdown
and the time and duration of the subsequent filling
period appeared to be most significant in creating
large differences in temperature and oxygen from
year to year. In 1965, the large drawdown (28 m.)
and prolonged filling (fig. 4) caused late forma-
tion of a thermocline, high temperatures, and low
oxygen concentrations during late summer. In
1964, drawdown was significant (27 m.) but the
filling period was shorter. Water temperatures and
oxygen concentrations through the summer were
more favorable than in 1965 but less favorable
than in 1963, when the drawdown was small (3m.)
and tlie filling period was early and short.

Estimates of movement of juvenile fall cliinook
salmon into Brownlee Reservoir (Krcma and Ra-

leigh, 1970) and later escapement (Sims, 1970)
verified that the survival of holdover salmon was
extremely poor. Fortunately, the conditions that
brought about the harshest summer environment
(large drawdown and delayed fill) were also the
conditions that facilitated rapid passage of finger-
lings through the impoundment (Ebel and Koski,
1968; Sims, 1970).

Holdovers of salmon were encountered in the
Powder River Arm in October 1962 when 75 chi-
nook salmon were caught. Two of these fish bore
fin clips that identified them as progeny of fall
chinook salmon from the Snake River that had
entered the reservoir in the spring. One fish of this
group was also recaptured at the upper end of
the main reservoir in the spring of 1963.

In early summer of 1963, fall chinook salmon
were captured in gill nets in the lower Powder
River Arm. As the environment improved in the
fall, many fish moved into the upper arm. From
mid-September to mid-December, 561 chinook
salmon were captured; of these 444 were tagged
and released. The subsequent capture of 28 marked
fish in the area of release provided evidence that
some fall chinook salmon remained in the upper
arm until drawndown in December. On the basis of
captures of tagged and untagged fish in the Pow-
der River Arm, a population estimate (made by
the technique of Schnabel, 1938) of chinook
salmon in the arm ranged from 2,631 to 6,521 ; the
average of 22 estimates was 3,883.

The movement of holdovers from Brownlee Res-
ervoir in 1963 began in January and peaked in
February. A total of 5,396 fish were caught in the
skimmer net and in scoop traps below the dam.
The exodus in 1964 started in November, peaked in
January, and was completed by mid-May (Sims,
1970) . The total catch of the skimmer net (partial-
ly deactivated in February) and the scoop traps
was 1,275 fish. This early outmigration appeared
to be a displacement because of the approach of a
cold water mass through the reservoir (fig. 14).

The recapture of marked holdover fall chinook
salmon within the reservoir in 1963 provided in-
formation on movements of these fingerlings.
Early in the year (before April) most of the fish
moved toward the dam, but many moved upstream
and a few were recaptured in the area of release.
The recapture of fish in all areas of the reservoir
and the relatively slow rates of movement indi-

JUVBNILB SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

235

DECEMBER 1963

MARCH 1964

DIRECTION OF FLOW

PERCENTAGE OF TOTAL
5 10 15 20

WEEKS

25

— I —

FiQTJEE 14. — Movement of holdover fall Chinook salmon from Brownie© Reservoir in relation to water temper-
ature. (The early outmigration coincided with the approach of a mass of cold water.)

cated that these fish were wandering. As the season
progressed, however, the increases in the propor-
tion and rate of movement downreservoir suggest
the onset of a directed migration (fig. 15).

The holdover of fingerling salmon in Brownlee
Reservoir was evident during each year of study,
but the percentage of the total involved, as indi-
cated from reservoir recruitment and escapement
estimates (Krcma and Raleigh, 1970; Sims, 1970),
fluctuated significantly. The percentage of hold-
overs seemed to be smallest in 1965, intermediate
in 1964, and highest in 1963. The yearly percent-
age of holdovers varied inversely with reservoir
conditions conducive to good passage of fish (figs.
4 and 5).

KOKANEE OF AGE-GROUP I

A few kokanee were caught in the reservoir in
1963 and 1964, and large numbers entered the

reservoir in 1965 (table 3) . The fish were probably
from the Payette River system (Payett« Lakes and
Cascade and Deadwood Reservoirs). The migra-
tion appeared each year in early June, peaked in
mid- to late June, and continued into July. Too
few fish were present in 1963 or 1964 to determine
movement within the reservoir. In 1965, however,
it was evident from gill net catches and the
recapture of tagged fish that through June the mi-
grants consistently moved downreservoir. By mid-
July, when the reservoir was full and the outflow
was greatly diminished, fish were moving upres-
ervoir and downreservoir in about equal numbers.
Kokanee were captured near the surface early
in the migration, but as the season progressed and
the environment deteriorated, the population
was concentrated near the dam at depths of 18 to
47 m., as were other salmon species that held over
(fig. 13).

236

U.S. FISH AND WILDLIFE SERVICE

Table 3. — Estimated length and numbers of kokanee that
entered Brownlee Reservoir, 1963-66 (from Krcma and
Raleigh, 1970)

Year

Fish -

Length

Mean Range

Number
500 .

Mm. Mm.

5,500

120 104-146

1965

506,800

108 70-155

Kokanee populations that passed through
Brownlee Reservoir did not do well. The fish that
we observed did not leave their nursery area until
late spring. They arrived at Brownlee Reservoir
when the impoundment was filling or full, the
temperatures were rising, and spillway flow was
reduced. If they did not move through the reser-
voir, the harsh environment in late summer prob-
ably caused almost total mortality. Emigration

estimates made by Sims (1970) suggested that
losses were large in 1964 and 1965. These fish ap-
parently were unable to survive through the sum-
mer — a few holdovere of the 1962 migration were
captured in 1963, but none were observed in later
years.

DISTRIBUTION AND MOVEMENT OF
HATCHERY-REARED SALMON

To bolster the dwindlmg numbers of native salm-
on and to observe the effect of the reservoir on
the passage of other salmon species, we placed
hatchery-reared fall chinook and coho salmon
juveniles in the Snake River about 120 km. above
the reservoir in 1964 and introduced hatchery-
reared sockeye and fall-chinook juvenile salmon
about 88 km. above the reservoir in 1965 (Krcma
and Raleigh, 1970).

>■
<

O

> 6
tc
iij
in

iLl

tE 4

3

5 2

UJ

S 8

u. O ^

o > 6

cr.

z ^

if UJ .

I- oc 4

UJ >

? o

Q Q 2

N=23
AVG. = 0.79 KM./ DAY

N=34
AVG.: 0.56 KM. /DAY

N= 15
AVG. = 1.35 KM. /DAY

N = 60
AVG. = 2.65 KM. /DAY

3-9 10-16 17-23 24-30 31-6 7-13 14-27 21-27 28-4 5-11 12-18
MARCH APRIL MAY
I*— PRESMOLTING SEAS0N-*|« SMOLTING SEASON *\

FlGUBE 15. — -Numbers of tagged juvenile chinook salmon holdovers recovered in Brownlee
Reservoir, March 3 to May 18, 1963, showing direction and rate of movement.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

237

FALL CHINOOK SALMON OF AGE-GROUP

Hatchery- reared fall chinook salmon were re-
leased in the Snake River about 120 km. above
Brownlee Reservoir in March 1964 and 1965. Al-
though released over a period of only 10 days, their
movement into the reservoir extended over 3
months. Early and late migrants were 46 mm. and
130 mm. long in 1964 and 67 mm. and 135 mm. in
1965.

In 1964 and 1965, tagged hatchery chinook
salmon moved primarily toward the dam until
mid-May. After mid-May in 1964, some tagged
fish were recaptured moving upreservoir; four
tagged fish were recaptured in traps in the Snake
River about 4 km. upstream from the head of the
reservoir (Krcma and Raleigh, 1970). This up-
stream movement involved fewer fish in 1965.
According to Sims (1970), 50 percent of the esti-
mated migration of hat^heiy-reared chinook salm-
on into Brownlee Reservoir had left by the end
of June 1964 and over 97 percent in 1965.

The movement upstream into the Snake River
in 1964 might have been related to temperature,
as noted previously for populations of native juve-
nile chinook salmon.

The ability of these fish to move through the
reservoir to the river below Brownlee Dam (50
percent in 1964 and 97 percent in 1965) appeared
to vary with volume of flow, direction of current,
and length of reservoir. The drawdown lasted 6
weeks longer in 1965 than in 1964 and was accom-
panied by spillway discharges of large volume and
duration and high volumes of inflow from the
Snake River (fig. 4). During the 1965 migration
this condition produced not only a smaller im-
poundment (45-50 km. long) but currents of
higher velocity that were more consistently toward
the dam than in 1964.

The rate of movement of tagged chinook salm-
on in the reservoir was similar in 1964 and 1965
even though the enviromnents were different. The
rate for all chinook salmon that moved toward

the outlet averaged 3.0 and 2.9 km./day, respec-
tively (table 4) . Fish tagged through the first half
of May generally moved faster than those tagged
later. Upreservoir movement for nine chinook
salmon averaged 0.89 km./day in 1964 and 2.0
km./day in 1965.

Chinook salmon recaptured downriver at Ice
Harbor Dam averaged 19.9 kmyday in 1964 and
18.8 km./day in 1965 through the reservoir and
river.

Fish captured early in the season in midreser-
voir and along both banks indicated that fall
chinook salmon of age-group O were distributed
throughout the surface area. Gill net catches
showed that juvenile chinook salmon moved both
up and down the reservoir during darkness. This
observation implies that most directed movement
may have occurred during daylight and that
fish milled or were carried by currents during
darkness.

The distribution of hatchery-reared fall chinook
salmon through the summer was similar to that
of native fall chinook salmon (fig. 16). In the
spring the fish were generally distributed through-
out the epilimnion of the reservoir. As the surface
temperature increased the fish moved into deeper
water and downreservoir. Temperatures above
21° C. at the surface and low oxygen concentra-
tions (less than 3 p.p.m.) at depths where the
water was cooler forced the fish to move into re-
stricted areas. The increased catches of fish in gill
nets in the upper reservoir in Jime and July were
probably the result of fish returning from a tem-
porary upstream movement into the Snake River.

Some hatchery-reared chinook salmon from the
1964 release remained in Brownlee Reservoir dur-
ing the winter. Sims (1970) estimated that only
about 85 percent of the hatchery-reared fall chi-
nook salmon that entered the reservoir in 1964
migrated out that year. Also 17 fish from this
group were captured in the reservoir in February
and March 1965.

Table 4. — Summary of direction and rale of movement of tagged age-group O hatchery-reared fall chinook salmon in Brownlee

Reservoir, 1964-6S

Direction of movement

Rate of movement

Year

Recaptured Upreservoir

Down-
reservoir

No move-
ment

Upreservoir

Range

Down-
reservoir

Range

Brownlee
Reservoir to
Ice Harbor

Range

1964..
196S..

Number Number
..60 9
277 14

Number
37
237

Number
14
46

Km.lday
0.89
2.0

0.0&-1.86
.08-9.76

Km.lday
3.0
2.9

0.31-9.7
.06-a7

Km.lday
19.9
18.8

12.6-33.8
8. 0-42.

238

U.S. FISH AND WILDLIFE SERVICE

KILOMETERS FROM DAM

X

I-

0.
bJ
O

20
40

1 II

i 1

24 34

60
80

A^''

JUNE 13- JUNE 26

JULY 25 - AUGUST 7

B^':-^-\^^:^^■::/:V^:•■.;v:■■•'••^•■"■•:•^■•!;;:••:v

AUGUST 8 - AUGUST 21

JUNE 27 - JULY 10

AUGUST 22- SEPTEMBER 4

FISH CAUGHT

PER NET DAY

TEMPERATURE

OXYGEN

O

(ZZI Less ihon 21° C.

1 IMore fhon 2 p.am.

LiKj 21° C. or more

SLess thof) 2 ppm.

^H 6

Figure 16. — Distribution of hatcheory-reared fall ehinook salmon in Brownlee Reservoir in relation to critical
oxygen and temperature regimes as determined from gill net catches, 1965.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

239

417-060 O - 71 - 5

COHO SALMON OF AGE-GROUP I

Of 375,000 juvenile coho salmon released in the
Snake River 120 kin. above the reservoir from
March 15 to 30, 1964, an estimated 69,000 entered
the reservoir (Krcma and Raleigli, 1970). Early
in the migration these fish averaged 112 mm. long;
by the end they averaged 131 mm.

On the basis of peak catches at the Snake River
trapping site above the reservoir and at the dam,
passage time through the reservoir was 2 weeks
(fig. 17). The reservoir was only 64 km. long at
the beginning of the migration as a result of a
13.5-m. drawdown ; the distance between the reser-
voir and the trapping site in the river was about
35 km.

Recapture data from 26 tagged fish indicated
that the rate of movement changed during the
migration (fig. 18). Before May 20 when the res-
ervoir was drawn down about 13 m. and the out-
flow volume was large (about 850 c.m.s.), 17
tagged migrants averaged 1.8 km./day. As the
outflow was curtailed and the reservoir began to
fill, the migration i-ate of nine tagged fish then
dropped to 0.9 km./day. At this time the propor-

tion of fish moving upreservoir also appeared to
increase.

In early May most coho salmon were near the
surface in the upper reservoir, but by the end of
the month most had shifted to the vicinity of the
dam at greater depths. As the migration rate
slowed in late May and recruitment from the
Snake River continued, catches were again good
in the upper reservoir. In July the greatest con-
centration appeared to be in midreservoir at
depths of 18 to 31 m. Catches declined through
July, and only a few fish were captured thereafter.

SOCKEYE SALMON OF AGE-GROUP I

In 1965, 473,000 yearling sockeye salmon were
released in the Snake River, 88 km. aJbove Brown-
lee Resei-voir. Krcma and Raleigh (1970) esti-
mated that 360,000 had entered the reservoir. The
salmon were from Babine Lake, British Ck}liunbia
and reared to yeai"ling stage at the Leavenworth
National Hatchery, Wash. The left ventral fin
was clipped on all fish. Migrants in March aver-
aged 121 mm. ; later migrants averaged 130 mm.
by mid-May.

35
30
25
20
15
10
5 5

S

fe45
^40
z 35

UJ

o
a: 30

UJ

■^25

20

15

10

5

MIGRANT DIPPER TRAP CATCHES IN THE
SNAKE RIVER ABOVE THE RESERVOIR

SCOOP TRAP CATCHES BELOW THE DAM

-18 19-25 26-2 3-9 10-16 17-23 24-30 31-6 7-13 14-20 21-27 28-4 5-11 12-18 19-25 26-1 2-8 9-15 16-22
APRIL MAY JUNE JULY AUGUST

FiouBE 17.— Weekly cafjches of juvenile hateheiy-reared coho salmaa above Brownlee Reservoir and below Brownlee

Dam, 1964.

240

U.S. FISH AND WILDLIFE SEBVICK

MIGRATION RATE

1.8 KM. PER OAY-

-0.9 KM. PER DAY-

WATER LEVEL V

OUTFLOW

20
MAY

20
JUNE

1,500

i
c

1,000 1
i

500

30

FiouBE 18. — Rate of downstream movemenit of tagged hatchery-reared echo salmon in
relation to water level and outflow in Brownlee Reservoir, April 1 to June 30, 1964.

These fish moved rapidly downstream after re-
lease. The first sockeye salmon were captured in
the reservoir on March 17^ — 2 days after the initial
release. Catches above the reservoir reached a peak
during the first week of April and below the reser-
voir the following week. During the ensuing 2
months, 44 sockeye salmon were recaptured at Ice
Harbor Dam and two at Bonneville Dam. The
capture of fish in gill nets in the reservoir indi-
cated that the fish moved consistently downreser-
voir. No sockeye salmon were observed in the
Powder River Arm, and no delay within the reser-
voir was evident.

The average daily rate of movement for 117
tagged sockeye salmon that moved toward the out-
let was 5.2 km./day. On the basis of this rate and
the length of the reservoir (45-50 km.) in late
March and early April, sockeye salmon required
an average of about 8 or 9 days to move through
the reservoir.

Most sockeye salmon were captured within 4.5 m.
of the surface, some were between 4.5 and 13.5 m.,
and a few were taken as deep as 22.5 m. (table 5).

Data on catch per unit of effort at three gill net
stations indicated that the vertical distribution
was similar throughout the reservoir.

Sockeye salmon were captured near shore and
offshore in the upper reservoir. In the lower reser-
voir they were captured almost exclusively off-
shore. The recovery of tagged sockeye salmon
indicated that fish tagged near the shore even-
tually moved to the open water, whereas those
tagged offshore remained offshore.

During the migration period from March
through mid-May 1965, the environment was
favorable for fish passage. Dissolved oxygen con-
centrations were 6 to 11 p.p.m. until early May,
and temperatures ranged from about 5° C. in late
March to 15° C. in late April. The reservoir level
was 24 to 30 m. below full pool through mid-May,
and its length was reduced to about 45 km. Spill
discharge at Brownlee Dam was continuous, rang-
ing from a weekly average of 424.5 to 1,440.3 c.m.s.
Current monitors, operated by persomiel studying
the limnology of the reservoir, revealed that sur-
face currents were oriented toward the outlet. Ac-

Table 5. — Depth distribution of sockeye salmon yearlings as indicated by the catch per gill net day at different depths in Brownlee

Reservoir, March 17 to April 26, 1965 •

Depth

MUel

MUe24

Sets

Sockeye

Catch per
unit effort

Sets

Sockeye

Catch per
unit effort

Sets

Sockeye

Catch per
unit effort

No.
7
2
6

No.

247
3
4

3

No.
35.3

1.5

0.8

0.0

0.6

0.0 .

No.
4
3
4
3
1

No.

312
8
3
3
4

No.

78.0
2.7
0.8
1.0
4.0

No.
6
3
6
4
4

No.
205
10
10
3
3

No.

34.2
3.3
1.7

2

0.8

6

0.8

2

M

.<1.4

1.6- 4.1

4.2-13.7

13.8-18.3

18.4-22.9 -

23.0-27.6

'Mesh sizes used were 1.9, 2.6, 3.1, and 3.8 cm. stretched mesh.
JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWI>rLEE RESERVOIR

241

cording to Sims (1970), nearly 100 percent of the
sockeye salmon migration had passed through
Brownlee Reservoir.

SUMMARY

The distribution and movement of juvenile salm-
on that migrate through Brownlee Reservoir, a
large impoundment on the Snake River, was
studied from 1962 to 1965. The study included na-
tive spring and fall chinook salmon and kokanee
and hatchery-reared fall chinook, coho, and sock-
eye salmon.

Each native salmon population had a character-
istic age, size, and time of entry into the reservoir.
Most spring chinook salmon from Eagle Creek
entered the reservoir in the late fall as age-group
O, 53 to 125 mm. long. These fish overwintered in
the reservoir, primarily in the Powder River Arm.
They resumed their seaward migration in the
spring just before the peak of a second outmigra-
tion from Eagle Creek in March and April of age-
group I fish, 65 to 138 mm. long. The migration
of juvenile spring chinook salmon from the Weiser
River entered the reservoir in peak numbers in late
April or early May; it consisted of age-group I
fish, 106 to 176 mm. long. This movement was
closely followed by that of age-group O fall
chinook salmon from the Snake River, 33 to 105
mm. long, which entered the reservoir in peak num-
bei-s in mid-May. Kokanee migrants entered the
reservoir latest in the season ; age-group I fish, 70
to 155 mm. long, arrived in mid-June.

Hatchery-reared groups of salmon migrated into
the reservoir as follows: fall chinook salmon of
age-group O (46-135 mm.) in mid-May of 1964
and 1965; coho salmon of age-group I (71-166
mm.) in mid-May 1964; and sockeye salmon of
age-group I (86-175 mm.) in early April 1965.

Migrants from all populations were near the
surface as they entered. As the season progressed
and the juvenile fish moved downreservoir, the}'
tended to move into deeper water.

Migration peaks from the reservoir varied from
year to year, depending on reservoir conditions,
but were sequential by stock. Fish (mainly fall
chinook salmon) that remained in the reservoir
from the previous year's migration left the reser-
voir early (late January or February) at the ap-
proach of a cold water mass that moved through

the reservoir. This migration was followed in late
February and early March by fish (mainly fall
chinook salmon) that had overwintered in the
Powder River Arm. Spring migrants from Eagle
Creek and Weiser River arrived at the dam in
large numbers in April and May. Fall chinook
salmon from the Snake River arrived in late May
to early July and kokanee, in July or August.
Hatchery-reared fall chinook salmon left in Ma}'
1964 and in April 1965, coho salmon in late May
1964, and sockeye salmon in April 1965.

Juvenile fish that did not leave the reser-
voir by late June or July were confined to re-
stricted areas of the reservoir by high epilimnion
temperatures and low concentrations of dissolved
oxygen, which extended into the epilimnion from
the hypolimnion. Wlien this process began, juve-
nile salmon in the upper end of the reservoir usu-
ally reentered the slightly cooler waters of the
Snake River. They returned to the reservoir when
temperatures in the river began to approach 20° C.
The survival of holdover salmon through the sum-
mer and early fall was extremely poor.

The differences in success of passage through the
reservoir were more closely related to the physical
conditions of the resei-voir than to behavioral dif-
ferences between species of salmon stocks. Success
of passage for all populations was poorest in 1963
when the reservoir was nearly full throughout the
migration. Under this condition, the reservoir was
92 km. long and surface currents were either weak
or nonexistent and often moved upreservoir. Pas-
sage through the reservoir was intermediate in

1962 and 1964 when drawdown was 6 to 14 m.
through May and the reservoir averaged 70 km.
long. The most successful passage was in 1965
when the drawdown was large (26-28 m. through
May), the reservoir was relatively small (45-50
km. long) , and currents were consistently oriented
downstream. Loss of orientation and upreservoir
movement of the juvenile salmon were correlated
with conditions in the reservoir most prevalent in

1963 and least prevalent in 1965.

Early entrance into the reservoir appeared to
improve the chances of successful passage. In gen-
eral, early fish encountered the best combination
of reservoir length, current conditions, and envi-
ronment. Late migrants, such as the kokanee, en-
tered a rapidly deteriorating environment, and
their success of passage was extremely poor.

242

U.S. FISH AND WILDLIFE SERVICE

ACKNOWLEDGMENTS

Many individuals contributed to this study, par-
ticularly the late Joe Dunatov, master fisherman,
and crew chiefs Lawrence Davis, Maurice Laird,
Lawrence Logan, Nathan Roe, and Philip Weitz.
Employees of fishery agencies of Idaho, Oregon,
and Washington and of the Idaho Power Com-
pany provided assistance and background infor-
mation. We are also indebted to James Graban
and the late Wayne Klaveno of the Idaho Fish and
Game Department, Robert Gunsolus and Lawrence
Koni of the Fish Commission of Oregon, Lloyd
Rothfus of the Washington Department of Fish-
eries, and Wendell Smith, biologist of the Idaho
Power Company.

LITERATURE CITED

CoNTE, F. P., H. H. Waoneb, J. Fessleb, and C. Gnose.

1966. Development of osmotic and ionic regulation
in juvenile coho .salmon Oncorhynchus kuutch.
Comp. Biochem. Physiol. 18 : 1-15.

DuBKiN, Joseph T., and Donn L. Pabk.

1967. A purse seine for sampling juvenile salmonids.
Progr. Fish-Cult. 29 : 56-59.

Ebel, Weslhts- J., and Charles H. Koski.

1968. Physical and chemical limnology of Brownlee
Reservoir, 1962-&1. U.S. Fish Wildl. Serv., Fish.
Bull. 67 : 295-335.

HOAB, Wn-LIAM S.

1963. The endocrine regulation of migrating behav-
iour in anadromous teleosts. Proc. 16th Int. Congr.
Zool. 3 : 14-20.

Johnson, W. E.

1956. On the distribution of young sockeye salmon
(Oncorhynchus nerka) in Babine and NUkitkwa
Lakes, B.C. J. Fish. Res. Bd. Can. 13:695-708.

Kbcma, Richard F., and Robert F. Raleigh.

1970. Migration of juvenile salmon and trout into
Brownlee Reservoir, 1962-65. U.S. Fish Wildl.
Serv., Fish. Bull. 68 : 203-217.

Raleigh, Robert F., and Wesley J. Ebel.

1967. The effect of Brownlee Reservoir on migrations
of anadromous salmonids. Amer. Fish. Soc., Res-
ervoir Fisheries Resources Symposium, Athens,
Ga., Apr. 5-7, 1967, pp. 415-443.

Rees, William H.

1957. The vertical and horizontal distribution of sea-
ward migrant salmon in the forebay of Baker Dam.
Wash. Dep. Fish., Fish. Res. Pap. 2(1) : 5-17.

Schnabel, Zoe E.

1938. Estimation of the total fish population of a
lake. Amer. Math. Hon. 45 : 349-352.
Sims, Carl W.

1970. Emigration of juvenile salmon and trout from
Brownlee Reservoir, 1963-65. U.S. Fish Wildl.
Serv., Fish. Bull. 68 : 245-259.
Soule, G. B., T. R. Heikes, W. B. Mitchell, and O. F.

SCHATJFELBEBGEB.

1959. Design, construction and operation of Brown-
lee Hydroelectric Development. Trans. Amer. Inst.
Elec. Eng., Pap. 59-921, 18 pp.
Teefethen, Pabkek S., and Doyle F. Sutheeland.

1968. Pas.sage of adult chinook salmon through
Brownlee Reservoir, 1960-62. U.S. Fish Wildl.
Serv., Fish. Bull. 67: 35-45.

JUVENILE SALMON DISTRIBUTION AND MOVEMENT IN BROWNLEE RESERVOIR

243

EMIGRATION OF JUVENILE SALMON AND TROUT FROM BROWNLEE

RESERVOIR, 1963-65

BY CARL W. SIMS, FISHERY BIOLOGIST

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY

SEATTLE, WASH. 98102

ABSTRACT

Floating scoop traps below Brownlee Dam captured
samples of marked and unmarked salmon and trout
that had left the impoundment from July 1963 through
August 1%5; estimates of emigration were based on
these samples.

Success of passage varied among years and popula-

tions and was affected by the environment in the
reservoir during outmigration. Downstream migrants
that entered the reservoir early in the season were more
successful than those that entered later. Emigration
was also more successful when the reservoir level was
low.

Brownlee Reservoir was chosen for an extensive
research program by BCF (Bureau of Commercial
Fisheries) to determine how a large impoundment
affects the passage of salmon and trout. The
research, begun in the spring of 1962, consisted
of five studies: (1) limnology of the reservoir
system (Ebel and Koski, 1968); (2) upstream
migration of adult chinook salmon (Oncorhynchus
tshawytscha) through the reservoir (Trefethen and
Sutherland, 1968); (3) migration of juvenile salm-
on and trout into the reservoir (Krcma and
Raleigh, 1970); (4) distribution and movement of
juvenile salmon in the reservoir (Durkin, Park,
and Raleigh, 1970); and (5) migration of juvenile
salmon and trout from the reservoir (the present
report) .

Brownlee Reservoir, on the middle Snake River,
lies at the southern end of Hells Canyon along the
border between northeast Oregon and western
Idaho. The reservoir is about 92 km. long and
averages slightly less than 800 m. wide. Brownlee
Dam (constructed by the Idaho Power Company)
is a high-head structure, the primary function of
which is hydroelectric power production. It is
396 m. wide on the top, has a single spillway and
four Francis turbines with vertical shafts, and
creates 83 m. of head at full pool. The dam dis-
charges directly into Oxbow Reservoir, formed by
Oxbow Dam about 19 km. downstream.

In an attempt to provide facilities for the passage
of juvenile salmon and trout past Brownlee Dam,

Published April 1970.

FISHERY BULLETIN: VOL. 68. NO. 2

the Idaho Power Company installed a fingerHng-
collection system in 1959 in the forebay of the
reservoir about 3 km. downstream from the dam
(Soule, Heikes, Mitchell, and Schaufelberger,
1959). The system, consisting of a shore-to-shore
barrier net and surface collection traps, proved
only partly successful.' Many fingerlings passed
under or through the barrier net and left the
reservoir via the turbines or spillway. Idaho
Power Company removed the system in February
1964, after which all fish that left the reservoir
passed through the turbines or spillway.

Native populations of anadromous salmon and
trout affected by Brownlee Reservoir include fall-
and spring-run chinook salmon {Oncorhynchus
tshawytscha) and steelhead trout (Salmo gairdneri) .
Before the construction of Brownlee Dam in 1958,
the largest population was fall-run chinook salmon,
which spawned in the Snake River upstream from
what is now the upper end of Brownlee Reservoir.
The Fish Commission of Oregon estimated annual
fall chinook salmon spawning runs of as many as
20,000 fish in the late 1950's. By 1963 this popula-
tion was greatly reduced. Before 1963, spring-run
chinook salmon spawned in the Weiser River (a
tributary of the Snake River above the head of
the reservoir) and in Eagle Creek (a tributary of
the Powder River, which enters near the lower
end of the reservoir). Steelhead trout were native
to Weiser River and Eagle Creek as well as several

' Oraben, James E. 1964. Evaluation of fish facilities, Brownlee and Oibow
Dams, Snake River. Idaho Department of Fish and Game, Boise, Idaho,
60 pp. (Processed.)

245

streams above Brownlee Dam. Several impound-
ments in the Snake River system above Brownlee
Reservoir support populations of kokanee (0.
nerka) ; these fish periodically move into the
Brownlee area.

After the decline of the native runs, hatchery-
reared Chinook, coho (0. kisutch), and sockeye
salmon were released in the Snake River above
Brownlee Reservoir by the BCF in 1964 and 1965
to provide additional fish for study.

The study on the passage of juvenile salmon and
trout from Brownlee Reservoir began in July 1963
and continued through the summer of 1965. I
report here the number and size of emigrants and
the time of emigration.

TECHNIQUES OF SAMPLING AND
ANALYSIS

The sampling area (fig. 1) was immediately
below Brownlee Dam. About 180 m. below the
powerhouse the turbine tailrace channel enters

the original river channel, which carries the inter-
mittent discharges from the spillway of the dam.
The Interstate Bridge crosses Oxbow Reservoir
about 600 m. downstream from the dam. At that
point, the reservoir is about 160 m. wide and 3.5
m. deep at midchannel when Oxbow Reservoir
is at full pool.

The primary sampling site was in the turbine
tailrace, about 150 m. below the powerhouse. The
turbine tailrace is about 76 m. wide; the water is
about 4 m. to 7 m. deep, depending on the level
of Oxbow Reservoir and the discharge from Brown-
lee Dam. Because fish that passed over the spillway
could not be sampled at the tailrace site, an addi-
tional sampling site was established downstream
at the Interstate Bridge for use during periods of
spillwdy operation.

The analyses of the data involved an evaluation
of (1) equipment, (2) procedures, (3) tests of
sampling efficiency, and (4) methods of computing
emigration.

Figure 1. — Turbine tailrace (foreground) at Brownlee Dam with scoop traps in position below right
bank. Spillway (not in operation in this photo) enters original river channel on extreme left.

246

U.S. FISH AND WILDLIFE SERVICE

Figure 2. — Scoop traps in operation in the turbine tailrace.

EQUIPMENT

Three scoop traps (fig. 2) were used to collect
juvenile migrants.^ Each trap was 3.0 m. wide
by 3.2 m. long and fished at a depth of 1.2 m. A
pontoon-type barge, 5.5 m. by 7.5 m., supported
the individual traps and winch equipment. In the
turbine tailrace, the traps were close to the right
(Idaho) bank. At the Interstate Bridge, one trap
was in the center of the channel and the other two
were about 30 m. from the right and left banks.

PROCEDURES

The traps were emptied of fish and cleared of
debris at 8 a.m. and 4 p.m. Additional checks
were made at noon and at midnight during peak
outmigration and at any time that excessive debris
accumulated. During special studies, the traps
were emptied of fish and debris at intervals of 1,
4, and 6 hours.

> Bell, Robert. 1969. Time, slje, and estimated numbers of seaward migra-
tions of Chinook salmon and steelhead trout in the BrownleeOibow section
of the middle Snake River. Idaho Department of Fish and Game, Boise,
Idaho, 34 pp. (Processed.)

All salmon and trout were identified, examined
for marks or tags, and measured for fork and
standard length. All live salmon and trout were
anesthetized before examination and then were
released unless needed for special studies. Scale
samples were taken from dead and injured fish
when possible.

TESTS OF TRAP EFFICIENCIES

Fish marked by partial fin clip, tattoo, or ther-
mal biand were used to evaluate the efficiency of
the scoop traps at both sampling sites. Hatchery-
reared juveniles were used for marking in all
years, except in 1964 when a few tests were made
with native age-group I spring and fall chinook
salmon from scoop trap catches. Hatchery-reared
age-group chinook salmon were used in 1964 and
1965, age-group I coho salmon in 1964, and
sockeye salmon in 1965.

Tests at the Interstate Bridge required that
test fish be released into the spUlway and into the
turbine penstocks; tests at the turbine tailrace site
required releases only into the penstocks. Pen-

JUVBNILE SALMON AND TROUT EMIGRATION FROM BROWNLEB RBSEHIVOIR

247

stock releases were made by pumping the test fish
down the penstock air vent through a 76-mm.
hose.

In 1964, about 1,570 hatchery-reared juvenile
Chinook salmon and an equal number of juvenile
coho salmon were released into the spillway and
turbine penstocks to determine efficiency of the
traps at the Interstate Bridge (table 1). Fifteen
chinook and 15 coho salmon were recaptured,
(0.95-percent return for each species). Trapping
eflSciency for chinook salmon was slightly higher
in 1965 when 1,171 hatchery-reared test fish were
released and 15 fish (1.28 percent) were recaptured
(table 2). Recovery efficiency of the traps for
hatchery-reared sockeye salmon fingerlings re-
leased in 1965 was significantly higher than for
chinook salmon; 2,670 test sockeye salmon were
released and 71 (2.66 percent) were recaptured at
the bridge site (table 3).

The scoop traps were more efllicient in the tur-
bine tailrace than at the Interstate Bridge. In
1964-65, 8,471 test fish (hatchery-reared juvenile
chinook, coho, and sockeye salmon) were released
into the various turbine penstocks for recovery
in the turbine tailrace. Differences in average
recovery between years and among species were
so slight that the data were combined. Recoveries
for daylight releases (8:00 a.m. to 4:00 p.m.) were
0.5 to 7.5 percent and averaged 4.1 percent (table
4). Recaptures of fish from night releases (4:00
p.m. through 8:00 a.m.) were 4.5 to 29.7 percent
and averaged 11.3 percent (table 5).

METHODS OF COMPUTING EMIGRATION

Estimates of emigration were based on live and
dead fish caught in the scoop traps. Identity of
the various populations was determined from fish
that had been marked in the tributary drainages
and subsequently recovered in the scoop traps.
Length-frequency data and scale samples were
also used to determine the origin of different
populations of fish emigrating at various times of
the year.

Estimates of emigration during periods of
sampling at the Interstate Bridge were computed
with the general formula (Chapman, 1948) :

where

j^_CiM±l)
'"'- (R+1)

A7^= population estimate
6*= sample size
Af =number of marks
i2=marked recaptures in C

(1)

Table 1. — Numbers of marked juvenile chinook and coho
salmon recovered in scoop traps at the Interstate Bridge
after release in the spillway (S) or turbines {T) of Brown-
lee Dam, April S4 to June SO, 1964

Date (1964)

Fish Release Average
released site spill

Fish recovered

Number

April:

24 101 S

25 100 S

26 103 8

27 95 S

28 100 S

29 100 S

May;

7 106 S

7 89 T

8 100 S

8 100 T

15. 100 T

16 100 T

20 102 S

20 100 T

21 116 T

27 106 T

June:

11 79 8

14 179 8

15 189 S

16 200 S

16. 200 T

17 100 T

18 100 T

19 100 T

23 100 S

24 100 S

25 100 S

30 100 S

Total 3,165

(M .>/»«.) Number Percent

177
185
279
405
458
452

548
548
642
642
510
510
579
579
551

332

706

737

795

795

978

1,100

1,136

1,189

1,137

961

170

0.99
1.00
.97
.00
.00
1.00

3.77
4.49

.00
1.00

.00
2.00

.98

.00
1.72

.94

1.27
.56
1.06
1.00
.60
.00
1.00
1.00
.00
1.00
1.00
.00

30

.95

Table 2. — Numbers of marked juvenile chinook salmon
recovered in scoop traps at the Interstate Bridge after
release in the spillway (S) or turbines (T) of Brownlee
Dam, April 9 to May 20, 1966

Fish

Release

Average

Date (1965)

released

site

spUl

Fish recovered

Number

(MMiec.)

Number Percent

April.

9...

160

3

409

1

0.6

13..

102

T

566

2

2.0

13..

... 121

8

566

.0

15..

107

8

512

2

1.9

21..

... 122

T

1,338

1

.8

25..

164

T

1,657

2

L3

May:

14..

101

S

958

1

1.0

14-.

... 106

T

968

2

L9

20..

101

S

622

3

3.0

20..

>tal

97

T

622

1

1.0

T

... 1,171

16

1.28

To compensate for the variation in efficiency of
traps in the turbine tailrace, I computed emigra-
tion during periods of sampling at that site with
an alternate method:

N,=

trap catch

percentage of efficiency

(2)

248

Upper and lower limits were computed for esti-
mates of emigration at both sampling sites. For
estimates based on sampling at the Interstate

U.S. FISH AND WILDLIFE SERVICE

Table 3. — Numbers of marked juvenile sockeye salmon
recovered in scoop traps at the Interstate Bridge after
release in the spillway (S) or turbines (T) of Brovmlee
Dam, March 31 to May IB, 1966

Date (1965)

Fish
released

Release
site

Average
spill

Fish recovered

Number

March:

31 241 T

April:

1 95 S

2 109 T

5 177 S

5 275 T

6 140 S

7 211 T

8 238 S

9 lOB T

10 218 S

10 103 T

11 124 S

12 180 S

14 110 T

16 140 S

May:

15... 207 S

Total 2,670

CM.Vkc.) Numbtt Percent
2.5

487

459
425
448
448
519
338
357
409
610
510
511
499
448
511

2.1
1.8
2.3
2.9
1.4
1.9
2.1
4.9
1.8
2.9
4.8
1.1
3.6
3.6

4.3

2.66

Table 4. — Numbers of marked juvenile salmon {chinook,
coho, and sockeye) recovered in scoop traps in the Brownlee
Dam tailrace between 8 a.m. and 4 p.m., 196^-66

Total

fish

released

Number released at Turbine
turbine number dis-

charge Fish recovered

12 3 4

1964:

July 3..

July 3..

July 4..

July 4..

July 6.-

JulyS..

July 5. .

July 7-.

July 7..

July 7..

July 8..
1965:

June 6..

June 6..

June 6..

June7..

Total.

Number

200
200
200
200
200
200
200
200
200
200
200

350
371
392
384

Number offish

100 .
100 .
100
100 .
100 .
100 ,
100

100 100

100 100

100 100

100 100

96 99 76

99 100 79

106 99 87

95 92 105

(.M.'laee.)

618
612
439
448
379
399
375
387
443
417
536

79 472

93 472

100 409

92 547

Num- Per-
ber cent

100
100
100
100
100
100
100

5
7
14
7
6
1
3
15
10
10
9

13
17
22
12

2.5
3.5
7.0
3.5
3.0
.5
1.5
7.5
5.0
6.0
4.5

3.7
4.6
5.6
3.1

3,697 1,096 790 747 1,064

Bridge, these limits represent the 95-percent con-
fidence limits as computed by Chapman's formula :

m, 7n=R-f

1.96^

where

v>

±1.96-»/R-F

1.96*

(3)

m and m are the upper and lower values of R,
respectively.

Upper and lower estimates at the turbine tail-
race site were based on the 95-percent confidence
interval of the means of the frequency distributions
in the respective day-night tests of efficiency
(Wilkes, 1948). These values were computed ac-
cording to the formula:

where

n

ti= population mean
.X'= sample mean
<„= confidence coefficient
s= standard deviation
n= number of tests

Table 5. — Numbers of marked juvenile salmon {chinook,
coho, and sockeye) recovered in scoop traps in the Brownlee
Dam tailrace between 4 p.m. and 8 a.m., 1964-66

Date

Total

fish

released

Number released at
turbine number

Turbine
dis-
• charge Fish recovered

1964:

Julys..

July 4. -

July 6...

July?.-.

July 11--

Julyll..

July 12..

July 12..

July 14..

July 15..

July 15..

July 15..

July 16..

July 17..

July 18. .
1965:

June 5..

June 5..

June 6..

June 7..

Total.

Number

200
20O
200
100
300
300
200
200
200
100
800
200
300
200
300

Number offish

100

100

100

100

100

100 .
100 .

100

100

100

100

100

100

100

100 .

100

100 .

100

100 .

100

100

100

100

100
100

100

lOO

100

100

100 .

100

100

100

(.M.'Isec.)

577
378
349
364
268
263
228
294
301
84
343
214
339
303
408

409 110 100 99 100 553

364 61 99 99 105 168

381 94 96 101 90 159

320 98 98 59 65 358

Num-
ber

10
9
13

7
25
26
34
34
15

6
27
28
89
12
34

36
54
52
30

Per-
cent

5.0
4.5
6.5
7.0
8.3
8.7
17.0
17.0
7.5
6.0
9.0
14.0
29.7
6.0
11.3

8.8
14.8
13.6

9.4

4,774 1,363 793 1,458 1,160

11.33

Estimates of annual emigration were based on
scoop trap catches from May 1963 tlirough Au-
gust 1965 (table 6). No tests of efficiency of scoop
traps were made in 1963; therefore, estimates of
emigration for that year were based on efficiency
tests in 1964. In the estimates of emigration,
catches by the Idaho Power Company barrier net
in 1964 were also included. Estimates of immigra-
tion used to compare with estimates of emigration
were from Krcma and Raleigh (1970).

ESTIMATES OF EMIGRATION

EMIGRATION OF NATIVE SALMON

The migration of juvenile salmon and trout
from Bro\\'Tilee Reservoir included three native
and three hatchery-reared salmon populations and
a trout population of unknown origin. Estimates
of emigration were made for each population.

Native juvenile salmon migrating through
Brownlee Reservoir included fall chinook salmon
and kokanee from the Snake River and spring
chinook salmon from Eagle Creek and the Weiser
River.

JUVENILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR

249

Table 6. — Catches of juvenile salmon and rainbow-steelhead
trout by scoop traps below Brownlee Dam, May 1, 1963 to
August 31, 1966 '

Date Chinook Coho Sockeye Kokanee Rainbow-

(year and salmon salmon salmon salmon steelhead

month) t™u'

1963:

May

June

July

August

September..

October

November..

December..
1964:

January.

Number
2
194
62
82
16
8
49
101

Number Number Number Number

13
1
1
1

247

February 273

-- 370

885

506

621

56

114

25

7

8

2

March -

Aprtl

May

June

July

August

September..

October

November..
December. -
1965:

January

February.. -

March

AprU

May

June

July

August

256

262

124

84

3

2

11

90

2

1

14
11

28

114

79

76

61

32

3

4

4

3

2

2

2

14

2,214

9

2 198

8,162

338

'900

8

392

1,802

80

193

. 3,077

142

111

34

208

128

Total 8,864

729

10,384

3,466

1,480

' Catches by scoop trap reported by Graben, 1964 (see teit lootnote 1).

Fall Chinook Salmon

An estimated 54,800 native fall chinook salmon
from the Snake River left the reservoir in 1963 as
age-group and in 1964 as age-group I (table 7).
Of these fish, 2,700 were captured by the Idaho
Power Company barrier net in the forebay of the
reservoir and transported below Oxbow Dam and
released. Total emigration of the 1963 year class
was about 15 percent of established immigration
to the reservoir (table 7) .

Age-group-0 fish from the 1963 year class first
appeared in the scoop traps below the dam in
May 1963 (fig. 3); peak migration was in June.
Except for one period in 1963 (late September to
early October), some fish moved past the dam
throughout the summer and fall. About 75 percent
of age-group I fish in 1964 (1963 year class) left
the reservoir in late January; a second peak ap-
peared in early April.

Spring Chinook Salmon

Emigration of juvenile spring chinook salmon
of the 1963 year class was 5,900 fish or about 16
percent of the estimated immigration from the
Weiser River and Eagle Creek to the reservoir
(table 8). A small number from Eagle Creek began

«/)
o

z
<

o

X

I

8-

6-

4-

ul 3-

OD

2

Z

I-

1

I 1 l-p-. - ^ I I I I r-jJ 1-'-^-

V^u

.rft,.

MAY JUN. JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR.APR. MAY JUN. JUL,
1963 1964

Figure 3. — Estimated emigration from Brownlee Reservoir of juvenile native fall chinook salmon (1963
year class), from the Snake River, May 1963 to August 1964.

250

U.S. FISH AND WILDLIFE SERVICE

2,000-

X

«2 1,500-
u.

u.
O

_

a: 1,000-

UJ

o

S

Z

500-

r

"h r

P

— =f

^

^..d

t-,-I-

" -f>>^, , ,

,-T^^ rf|M^ ,

-A-

iJiin-^TTr^.

NOV. DEC. JAN. FEB. MAR. APR. MAY JUN. JUL. AUG. SEP. OCT. NOV. DEC. JAN.FEB.MAR. APR.MAY JUN. JUL.
1964

1963

1965

Figure 4. — Estimated emigration from Brownlee Reservoir of juvenile native spring chinook salmon from
Eagle Creek and Weiser River, November 1963 to July 1965.

Table 7. — Estimated immigration of juvenile native fall
chinook salmon into Brownlee Reservoir from the Snake
River and estimated emigration from the Reservoir, May 1,
1963 to August 1964 (all fish of 1963 year class)

Estimated
immigration

Years ot
emigration

Estimated emigration

Range of estimated
emigration

Low

High

Number
374,000

1963-64

Number Percent
■54,800 16

Number
39,600

Number
72,600

> Includes 2,700 fish captured at the Idaho Power Company barrier net.

to leave the reservoir as age-group fish in
November 1963, and the emigration continued
through June 1964 (fig. 4). Distinction between
fish from the Weiser River and those from
Eagle Creek was not always possible, but knowledge
of the age of fish at the time of downstream
migration to the reservoir provided a basis for
their identification at certain times of the year.
Krcma and Raleigh (1970) have shown that fish
from the Weiser River do not enter the reservoir
until spring 1 year after hatching, whereas fish
from Eagle Creek enter at age in the fall and
again as age-group I in the spring. Spring
chinook salmon that left the reservoir in the fall.

winter, and early spring, therefore, were probably
from Eagle Creek; fish leaving later in the spring
and in early summer could be from either the
Weiser River or Eagle Creek.

The emigration of the 1964 year class of spring
chinook salmon was estimated at 14,000 fish,
51 percent of estimated immigration. Most of these
fish were from Eagle Creek. Additional catches of
juvenile migrants from Eagle Creek were made in
the stream, transported downstream below Oxbow
Dam, and released (Krcma and Raleigh, 1970).
Juvenile spring chinook salmon that entered the
reservoir in late March and early April 1964
migrated rapidly through the impoundment. Peak
emigration was in mid-April, and the migration
ended in late July (fig. 4).

Kokanee

The origin of, or reasons for, some migrations of
juvenile kokanee into Brownlee Reservoir are not
completely understood, but most fish observed
during the present study were probably from the
Payette River system (Payette Lakes and Cascade
and Deadwood Reservoirs). Kokanee periodically
migrate however, and rather large numbers of
fingerlings entered Brownlee Reservoir in 1964

Table 8. — Estimated immigration of juvenile native spring chinook salmon into Brownlee Reservoir from Eagle Creek and
the Weiser River and estimated emigration from the Reservoir, November 1, 1963 to August 1966

Year class

Estimated immigration

Years of
emigration

Estimated emigration "

Range ot estimated
emigration

Weiser River

Eagle Creek

Total

Low

High

1963.

1964

Number

16.000

6,800

Number

22,300

7,200

Number
37,300
14,000

1963-64
1964-66

Number Percent
6,900 16
7,200 81

Number
4,700
4,600

Number
8,600
11,300

JUVENILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR

251

and 1965. In 1964, 2,100 kokanee fingerlings
(1963 year class) were estimated to have left the
reservoir, representing about 38 percent of the
estimated recruitment to the reservoir (table 9).
The outmigration started during the latter part of
June 1964, reached a peak in early August, and
ended by the first week in September.

Table 9. — Estimated immigration of juvenile kokanee into
Brownlee Reservoir from the Snake River system and esti-
mated emigration from the Reservoir, May 1964. and 1966

Year class

Estimated
Immigration

Year ot
emigra-
tion

Estimated Range of estimated
emigration emigration

Low High

1963

1964

Number

6,600

506,800

1964
1965

Number Percent Number Number

2,100 38 1,700 2,900

62.100 10 4,200 73,200

An estimated half million age-group I kokanee
entered Brownlee Reservoir in 1965, but only 10
percent (52,100 fish) are estimated to have
left the reservoir. According to Durkin et al.
(1970), the poor success of the migration of
kokanee can be attributed to the high reservoir
level and its attendant lack of downstream-
orienting currents. These fish did not enter the
reservoir until June and did not begin to leave
until late June. The outmigration was greatest in

late August and was completed by early Septem-
ber (fig. 5) . Fish remaining in the reservoir in late
July, August, and September were subjected to
high temperatures in the epilimnion (above 21"
C.) and oxygen-deficient water in the hypolim-
nion. These factors forced fish into unfavorable
habitats where survival was poor (Durkin et al.,
1970).

EMIGRATION OF JUVENILE HATCHERY-REARED
SALMON

About 250,000 age-group juvenile fall chinook
salmon and 375,000 age I juvenile coho salmon
were released in the Snake River above Brownlee
Reservoir in late mnter and early spring of 1964.
Additional releases of 592,000 age-group fall
chinook salmon and 473,000 age-group I juvenile
sockeye salmon were made in the spring of 1965.
Chinook and coho salmon fingerlings were from
hatcheries on the lower Colimabia River; sockeye
salmon fingerlings were from the Leavenworth
National Fish Hatchery, where they had been
reared from eggs obtained from Babine Lake in
British Columbia.

Fall Chinook Salmon

About 85 percent (94,500) of the estimated
111,500 hatchery-reared juvenile fall chinook
salmon that entered the reservoir in 1964 passed

20

tn
o

z

o

5 10

UJ

z

1 1 r

Ldt

T^^^ i' ■!■ 1 1 1 r

JUL. AUG. SEP. OCT. NOV. DEC. JAN. FEB. MAR. APR. MAY JUN. JUL. AUG. SEP.

1964

1965

Figure 5. — Estimated emigration from Brownlee Reservoir of juvenile native kokanee from the Snake

River system, 1964-65.

252

U.S. FISH AND WILDLIFE SERVICE

Brownlee Dam in 1964 (table 10). These fish first
appeared at the traps below the dam in early
April (9 days after release in the Snake River
above the reservoir) and their numbers peaked in
the second week of May. Small numbers of fish
moved out of the reservoir through the summer
until the emigration of the 1964 year class was
completed on September 1 (fig. 6).

An estimated 275,200 hatchery-reared fall
chinook salmon (1965 year class) left the impound-
ment in 1965 — more than were estimated to have
entered the reservoir. The discrepancy between
the two estimates is probably due to different
sampUng methods. Nevertheless, such a compari-
son is useful when one recognizes that the low
range emigration estimate (175,000 fish) is within
the 95-percent statistical confidence range of the
immigration estimate. Fish of the 1965 year class
were first taken in the scoop traps below the dam
in late March (fig. 6), 12 days after release in the
Snake River above the reservoir. Peak migration
was in mid-April, and a few fish were still leaving
the reservoir when the experiment terminated at
the end of August.

Coho Salmon

Emigration of juvenile hatchery-reared coho
salmon (1963 year class) in 1964 was estimated
at 51,600 fish or about 75 percent of immigration
to the reservoir (table 11). The emigration of
coho salmon began on May 16, 1964, about 6 weeks

Table 10. — Estimated immigration of juvenile hatchery-
reared fall chinook salmon into Brownlee Reservoir from
the Snake River and estimated emigration from the
Reservoir, 1964-65

Year
class

Estimated
immigration

Year

otemi-
gration

Estimated emi-
gration

Range of estimated
emigration

Low High

1964

1965

Number

111,600

. 162,800

1964
1965

Number Percent

94,500 85

■275,000 ■>100-t-

Number Number
68,600 133.400
175,000 432,000

' Disci«pancy between estimates of immigration and emigration probably
due to differences in sampling techniques in the Snake River and below
Brownlee Reservoir.

after their release in the Snake River above the
reservoir. The run reached a peak 1 week later
and continued until the end of August (fig. 7).

Sockeye Salmon

Juvenile hatchery-reared sockeye salmon (1964
year class) released in 1965 had little difficulty
in passing through the reservoir. Emigration in
1965 was estimated at 408,000 fish, more than
100 percent of the estimated immigration (table
11). The range of the two estimates overlap,
however. The first sockeye salmon appeared in
the scoop traps 6 days after the first releases on
March 15, 1965. The emigration was relatively
short, beginning on March 21 and ending by the
second week of May (fig. 8) . Peak was during the
week of April 4 to 10, when 175,000 fish are
estimated to have left the reservoir.

60

55

50-

Q

z

< 45

t/5

o 40
^ 35
^ 30

u. 25
o

20
q:

CD 15.
I 10-

5H r

■' ' ' h * M" -'-v-

"1 r

-r

^U-i-hyr-rTK

T

APR MAY JUN. JUL. AUG. SEP OCT NOV. DEC. JAN. FEB. MAR. APR. MAY JUN. JUL. AUG.SEP
1964 1965

Figure 6. — Estimated emigration from Brownlee Reservoir of juvenile hatchery-reared fall chinook
salmon from the Snake River, April 1964 to September 1965.

JUVENILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR

253

20

z
<
m

O

X

15

5 10-

5-

"T~n->-p-r-,-^^

JAN. FEB MAR APR MAY JUN JUL
1964

AUG SEP OCT NOV. DEC.

Figure 7. — Estimated emigration from Brownlee Res-
ervoir of juvenile hatchery-reared coho salmon from
the Snake River, 1964.

200

5 150
o

•a 100-

50

L

— I 1 1 1 1 1 r

JAN. FEB. MAR. APR MAY JUN JUL. AUG. SEP OCT NOV. DEC

1965

Figure 8. — Estimated emigration from Brownlee Res-
ervoir of juvenile hatchery-reared sockeye salmon from
the Snake River, 1965.

Table 11. — Estimated immigration of juvenile hatchery-
reared coho and sockeye salmon into Brownlee Reservoir
from the Snake River and estimated emigration from the
Reservoir, May 1, 1963 to August 31, 1965

Year
class

Species

Esti-
mated
Immi-
gration

Year
ol emi-
gra-
tion

Estimated emi-
gration

Rangeot esti-
mated emigration

Low High

1983...
1964...

Coho

Sockeye..

III

1984
1965

Numbtr Percent

61,800 78

1408,000 i>100-f

Number Number

37,900 72,600

324,000 613,800

1 Discrepancy between estimates of ImmlgtBtlon and emigration probably
due to dlSerences In sampling techniques In Snake River and below Brownlee
Reservoir.

EMIGRATION OF JUVENILE TROUT OF UNKNOWN
ORIGIN

Because anadromous rainbow trout (steelhead)
could not be separated from native and hatchery-
reared resident rainbow trout, the data on emi-
gration include all populations of rainbow trout.
For the same reason, Krcma and Raleigh (1970)
did not attempt to estimate immigrations of rain-
bow steelhead trout. Comparisons of emigration
and immigration, therefore, were not possible.
Juvenile rainbow trout emigrated from Brownlee
Reservoir each year during this study. An esti-
mated 24,800 rainbow-steelhead trout (table 12)
left the reservoir from August 1963 through De-
cember 1964. The major emigrations were in
May and June. In 1965, emigration was esti-
mated at 73,600 fish, and the major outmigrations
were in April and May.

Table 12. — Estimates of emigration of juvenile native and
hatchery-reared resident rainbow trout and anadromous
rainbow {steelhead) trout from Brownlee Reservoir, May 1,
1963, to August 31, 1966

Year of emigration

Estimated
emlgiBtlon

Range of estimate

Low

High

1963-64

1986

Number

24,800

73,800

Number
17,900
48,600

Number
35,000
118,000

LENGTHS OF EMIGRANTS

The sizes of the juvenile fish in various stocks
that emigrated from Brownlee Reservoir generally
increased as the season progressed. The fork
length of fall chinook salmon caught below the
dam from August 1963 through December 1964
was 45 to 240 mm. (table 13). Two distinct length
groups were evident from November 1963 through
June 1964. The larger fish (age-group I) were
from the 1963 year class of fall chinook salmon
from the Snake River; these fish dominated the
catch through March 1964. Beginning in April
1964, the smaller native spring chinook salmon
of the 1963 year class and the hatchery releases
of fall chinook salmon of the 1964 year class
dominated. Holdover of fish was slight in 1965;
the entire emigration was of native kokanee and
spring chinook salmon (age-group I) of the 1964
year classes and hatchery releases of sockeye
salmon (age-group I) and fall chinook salmon
(age-group 0) of the 1964 and 1965 year classes.

Hatchery-reared coho salmon increased from
an average length of 125 mm. (90-155 mm.) in
May 1964 to 200 mm. (155-245 mm.) in August
1964 (fig. 9).

254

U.S. FISH AND WILDLIFE SERVICE

30

20-

10-

N=3I8
X=I25

rTT rr

tu

MAY

20-

N=237
)?=I30

JUNE

10-

J-

,.llIW_

I — 1 1

o 30-1

Q.

20-1

10-

N= 133
X=173

30-1

20-

10-

AL

JULY

fdltfl^

N: 74
X = 201

AUGUST

T
75

100

125

— r
150

JW

51

175 200 225 250
FORK LENGTH (MM.)

Figure 9. — Length-frequency distribution of 762 juvenile hatchery-reared coho
salmon from the Snake River collected below Brownlee Dam, May 16 to Au-
gust 31, 1964. (N= number of fish; X indicates average length.)

JUVENILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR

417-060 O - 71 - 6

255

Table 13. — Length-frequency distribution of 6,697 juvenile fall chinook salmon from the Snake River collected below

Brownlee Dam, August 1, 1963 to August 31, 1965

Number of fish by year and month

Fork length

1963

1964

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July

Mm.
240..
235..
230..
225..
220..
215..
210..
205..
200..
195..
190..
186- .
180..
176..
170..
166..
160..
165..
160..
146..
140..
136..
130..
125..
120..
115..
110..
106..
100..
95...
90...
86...
80...
75...
70...
65...
60...
55...
50...
46...

1

3

8
13
36
42
16 .

4 .

1 .

1 .

2
12
21
13
13

2

3

2 .

1

1

7

13

14

22

7

2

1

1

7
13
41
48
43
23
12

6

2 .

3

1

2

8
25
47
55
26
21

4

4

6

1

2

16

2

3

25 ..

3

24 ..

2

10

1

1

9

2

6

2

1

7

1

2

6

1

4

3 ..

3

8

1 .

3
2
14
7
4
2
6
1

12

8
10

2

4

2 .

2 .

1
4
7
10
13
15
32
29
IS

1

4

11

7

12

28

60

45

61

55

56

68

74

104

102

98

31

19

1

1

Total.

124

20

70

108

219 262 361 934

773

86

16

89

62

66

Ill

68

158

65

131

62

68

76

20

55

12

43

1

44

1

32 .

21

8 .

1

668

51

The average lengths of kokanee differed little
in the early and late runs in 1964 (about 5 mm.),
but in 1965 the average increased from 105 to
138 mm. during a 90-day period in June, July,
and August (fig. 10).

Hatchery-reared sockeye salmon migrated
through the reservoir during such a short period
in 1965 that size of the fish changed little. The
lengths of these fish were 75 to 170 mm. (fig. 11).

Length-frequency distributions for juvenile
rainbow-steelhead trout are given in table 14.
Lengths of trout below the dam were 65 to 368
mm. The larger fish probably were native rainbow
trout rather than the offspring of anadromous
steelhead trout.

EFFECT OF ENVIRONMENT ON
EMIGRATION

The environment significantly affected the pas-
sage of juvenile salmon and trout through Brown-
lee Reservoir. In 1963, emigration from the
reservoir was low when (1) reservoir drawdown
in the spring was small, (2) the reservoir was filled
early, and (3) maximum discharge was late.

30 n
20-

10-

30i

z 20

u

o

a

ui 10 .

a.

1964

JUNE

N=65
X= 144

L

4ll

N= 185
ji=l28

L.

30-

N= 63
5i= 149

20-

10-

n

^

Kl

AUGUST

Ji

H= 661
H: 138

k

100 125 150 175
FORK LENGTH (MM.)

r30

20 •-

z

uj
u

-10 «:

1-30

20

100 125 150 175
FORK LENGTH (MM.)

Figure 10. — Length-frequency distribution of 1,043
juvenile native kokanee from the Snake River collected
below Brownlee Dam, 1964 and 1965. (N= number of
fish; 5C indicates average length.)

256

U.S. FISH AND WILDLIFE SEEVICE

Table 14.

-Length-frequency distribution of 1,381 juvenile rainbow-steelhead trout collected below Rrownlee Dam, August 1

1963 to August 31, 1966

Number of fish by year and month

Length (mm.)

1963

Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mar. Apr. May June July

3S0-349..
340-349..
330-339..
320-329..
310-319..
300-309..
290-299..
280-289..
270-279..
260-269..
2SO-2i9..
240-249..
230-239..
220-229..
210-219..
200-209..
190-199..
180-189..
170-179..
160-169..
160-189..
140-149..
130-139..
120-129..
110-119..
100-109..

90-99...

80-89...

70-79...

60-69...

1
3
2
14
2
1

1

1

1

5

2

6

2

9

13

14

11

9

3

3

2

4
1

11
3

9
12
13
19
29
22
16
14
8
1

S

7

21

13

IS

7

1

1

1
1
6
11
9
8
4

Total 10

178

80

48

Table 14.-

— Length-frequency distribution

of 1,381 juvenile rainbow-steelhead trout collected below Brownlee Dam,
1963 to August 31, 1965 — Continued

, August 1,

Length (mm.)

Number offish by year and month

1904

1968

Aug.

Sept.

Oct.

Nov.

Dec.

Jan.

Feb.

Mar.

Apr.

May

June

July

Aug.

360-369

1
1
1

2 .

i"

2"

1

1 .

2"'

1 .

.......

3W-369

1

340-349

1

330-339

2

320-329

1

1

310-319

1
2

1
1

3

1

3

1

3

8

18

24

32

24

. 34

19

22

32

43

27

13

9

3

1

1

300-309

3

290-299

1
2
4
6
. 12
. U
3
4
1

2
4

9
7
12

16
20
18
17
18
30
26
26
22
14
4
4
........

12

280-289

1

2 .
3

2

3

1

8

7

8
12
16
16
11

6 .

1 .
1

3 .

2 .

"i"

8
6
6
3

10

270-279

13

260-269 ,

1
1

24

260-269

17

240-249

16

230-239

2

1

g

220-229

210-219

2

200-209

1

190-199

1
2

180-189

1

1

170-179

1

160-169

1

160-189

140-149

1

1

130-139

1

120-129

1 .

110-119

100-109

1

1

90-99

1
1

1

1

3

80-89

1

3

70-79

60-69

1

Total...

. 48

3

4

3

1

2

12

326

264

99

31

113

JUVE3NILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR

257

- 3001

m

a

z

4
(/)

3
O

X

200-

X

in

O 100

o

Z

-^F-^t

th^

25 50 75 100 125 150 175 200
FORK LENGTH (MM.)

Figure 11. — Length-frequency distribution of 1,626
juvenile hatchery-reared sockeye salmon from the
Snake River collected below Brownlee Dam, March 21
to May 13, 1965.

Emigration was notably more successful in 1964
and 1965 when the reservoir level was low through
most of the downstream migration, and discharges
were high during early and midspring.

Fish that entered the reservoir after the middle
of June, as kokanee did in 1964 and 1965 (fig. 5),
had poor success of passage. In both years, emi-
gration of kokanee was less successful than that
of other species of fish migrating earlier in the
season. Kokanee did not enter the reservoir until
late June when the reservoir was fuU and currents
were weak and not clearly oriented in any direc-
tion. Those fish remaining in the reservoir through
the summer encountered low oxygen concentra-
tions (0-3 p.p.m.) below the thermocline and high
water temperatures (24° C. or above) near the
surface (Ebel and Koski, 1968). Few kokanee sur-
vived the harsh summer.

MORTALITY RELATED TO TURBINES

Because.many fish were found dead in the scoop
traps, the mortality attributable to the traps and
the turbines was examined. A detailed investiga-
tion was beyond the scope of this study, but
mortality was assessed at the turbine tailrace site
in June 1965. During a 6-day period (June 1-6),
all scoop traps were emptied twice daily — at 8:00
a.m. and 4:00 p.m. In a second 6-day period
(June 7-12), all fish were removed as soon as they
entered the traps (table 15). All fish caught during
both periods were hatchery-reared chinook salmon
of the 1965 year class.

258

Mortality during the two periods was as indi-
cated in table 15: 88 percent of the fish were
dead in the traps in the first period, and 16 per-
cent were dead when they entered the traps in
the second period. Because the fish were removed
immediately in the second period, they died of
causes other than trapping or handling.

To assess delayed mortality, samples of live
fish taken from the traps during the second period
were held in a holding tank in circulated water for
an additional 24-hour period. Hatchery-reared
chinook fingerlings collected in the reservoir
above the dam were held with these fish to serve
as a control (table 16). At the end of 24 hours,
67.5 percent of the fish taken from the traps and
17.5 percent of the control fish were dead. Thus,
the delayed mortality of fish passing through the
turbines was 50 percent.

Thus, on the average under test conditions, 16
of every 100 fish passing the sampling site were
already dead. Of the 84 survivors, 42 died within
24 hours, which indicated a total turbine-related
mortality of 58 percent.

Table 15. — Mortality of juvenile hatchery-reared chinook
salmon taken by scoop traps at the turbine tailrace sampling
site, June I-IS, 1966

Turbine Water Fish In
Date discharge temper- total catch Mortality

ture

MMuc. °C. Number Number Percent

Period A;' .„ ,., „ «,

Junel 481 " ^25 SS m

June 2 484 13 8^ 77 M

JmeS 478 18 167 160 96

June4 470 18 230 216 94

Junes ... 472 14 160 146 91

juHe o::::::: 410 18 323 274 ss

Totals 1,068 939 88

^f^,l' 847 18 148 26 18

juS68::..:.:.:... 823 w es 12 »

June9 440 18 23 1 4

June 10 - 433 16 18 1 6

Junen 423 16 4 J ?S

June 12 334 17 16 2 13

Totals 273 43 16

1 Normal operathig conditions. Trap emptied at %-S» a.m. and 4:00 p.m.
dally.
» Fish removed from trap Immediately upon entry.

Table 16. — Delayed mortality of juvenile hatchery-reared
chinook salmon taken from the tailrace scoop traps,
June 7-12, 1966

Group

Fish In Mortality at the
trap end of 24 hours

Number

ExperimentaL ,^

Control »•»

Number Percent
66 67.8

18 17.8

U.S. FISH AND WILDLIFE SBBVICE

SUMMARY AND CONCLUSIONS

Estimates of emigration of juvenile salmon and
trout from Brownlee Reservoir from July 1963
through August 1965 were based on catches in
floating scoop traps below Brownlee Dam and on
estimates of efficiency of the traps.

Emigration of native fall chinook salmon of the
Snake River was estimated at 15 percent of im-
migration into the Reservoir in 1963 (1963 year
class). Hatchery-reared fall chinook salmon (age-
group 0) were planted in the Snake River in 1964
and 1965. Estimates of emigration were 85 percent
of immigration in 1964 and 100 percent in 1965.

Emigration of native spring chinook salmon
(Eagle Creek and the Weiser River) was estimated
at 16 percent of immigration in 1964 and at 51
percent in 1965.

Emigration of native kokanee of the Snake River
system was estimated at 38 percent of immigration
in 1964 and at 10 percent in 1965.

Hatchery-reared coho and sockeye salmon were
planted in the Snake River in 1964 and 1965, re-
spectively. An estimated 75 percent of the coho
salmon (1963 year class) that entered the reservoir
in 1964 passed through. Emigration of sockeye
salmon (1964 year class) in 1965 was estimated at
100 percent of immigration.

Because anadromous rainbow trout (steelhead)
could not be separated from populations of native
and hatchery-reared resident rainbow trout, I did
not compare emigrations and immigrations. About
24,800 rainbow trout left the reservoir from August
1963 through December 1964. Emigration was
estimated at 73,600 fish in 1965.

The environment in the reservoir during the
time of outmigration clearly affected success of
passage. In general, fish that entered the reservoir
early in the spring, when the reservoir was drawn
down and water temperature and oxygen concen-
trations were favorable, passed through more suc-
cessfully than did those that entered during the
summer, when water temperatures were high, cur-
rents were weak, and concentrations of oxygen
were low.

The fish of the various stocks that emigrated
from Brownlee Reservoir showed a general increase" \
in length as the season progressed.

The following general conclusions were reached :

1. Downstream migrants that entered the
reservoir early in the season passed through
more successfully than those that entered
later.

2. Emigration was more successful when the
reservoir level was low during the time of
migration than when the reservoir was
filled before completion of the migration.

3. Because of time of emigration, size of the
fish at time of entry into the reservoir, and
the shorter distance traveled by the fish,
one would expect what happened : Progeny
of native spring chinook salmon migrated
through the reservoir more successfully
than native fall chinook salmon.

LITERATURE CITED

Chapman, D. G.

1948. Problems in enumeration of populations of
spawning sockeye salmon. 2. A mathematical
study of confidence limits of salmon populations
calculated from sample tag ratios. Int. Pac. Salmon
Fish. Comm., Bull. 2: 67-85.
DiTRKiN, Joseph T., Donn L. Park, and Robert F.
Raleioh.

1970. Distribution and movement of juvenile salmon
in Brownlee Reservoir, 1962-65. U.S. Fish WUdl.
Serv., Fish. BuU. 68: 219-243.
Ebel, Weslet J., and Charles H. Koski.

1968. Physical and chemical limnology of Brownlee
Reservoir, 1962-64. U.S. Fish Wildl. Serv., Fish.
BuU. 67: 295-335.
Krcma, Richard F., and Robert F. Raleigh.

1970. Migration of juvenile salmon and trout into
Brownlee Reservoir, 1962-65. U.S. Fish Wildl.
Serv., Fish. BuU. 68: 203-217.
SouLE, G. B., T. R. Heiees, W. B. Mitchell, and
O. F. Schaufelberqer.

1959. Design, construction, and operation of Brown-
lee Hydroelectric Development. Trans. Amer.
Inst. Elec. Eng., Pap. 59-921: 1-18.
Trefethen, Parker S., and Dotle F. Sutherland.

1968. Passage of adult chinook salmon through
Brownlee Reservoir, 1960-62. U.S. Fish WUdl.
Serv., Fish. BuU. 67: 35-45.
Wilkes, S. S.

7^^j^48. Elementary statistical analysis. I*rinceton
^s^'OUniversity Press, Princeton, N.J., 284 pp.

JUVBINILE SALMON AND TROUT EMIGRATION FROM BROWNLEE RESERVOIR

259

CHARACTERISTICS OF SOME LARVAL BOTHID FLATFISH, AND
DEVELOPMENT AND DISTRIBUTION OF LARVAL SPOTFIN FLOUNDER,
CYCLOPSETTA FIMBRIATA (BOTHIDAE)i

BY ELMER J. GUTHERZ,^ FISHERY BIOLOGIST
ABSTRACT

Pertinent literature on larval flatfish of the family
Bothidae and some of the characters helpful in identi-
fying these larvae are discussed. Helpful characters
are of two types; transitory, those which are lost, and
permanent, those which are retained. Transitory
characters include larvae pigmentation, elongate
dorsal and pelvic fin rays, and spina tion; permanent
characters include meristic counts, placement of
pelvic fin bases and fin rays, and caudal osteology.

Developmental changes in general growth patterns,
formation of fins, larval spinatlon, pigmentation,

migration of the right eye, and sequence of ossification
based on 171 larvae (1.7-14.5 mm. SL) collected oft the
south Atlantic coast of the United States is presented.
Several sizes of larvae showing spinatlon, pigmentation,
and elongate fin rays are illustrated, and one
illustration shows the degree of ossification.

Spawning appears to occur between April and October
in waters of about 50 m. or less. Fertilized eggs have
not been seen, but their size at hatching is estimated
to be about 1.5 mm.

Five families of flatfish occur off the south-
eastern coast of the United States (Bothidae,
Scophthalmidae, Pleuronectidae, Soleidae, and
Cynoglossidae). Species of bothids are common in
the inshore waters south of Cape Hatteras, N.C.,
and are more numerous (13 genera and 49 species)
than are species of the other four families (Cyno-
glossidae, 1 genus and about 15 species; Soleidae,
3 genera and 5 species; Pleuronectidae, 1 genus
and 3 species; Scophthalmidae, 1 genus and 1
species) .

The spotfin and other floundei-s discussed in this
paper are taken in industrial fish catches or are
caught incidentally in shrimping. Of these floim-
ders, only the fluke {Paralickthys) is removed from
the catch and its flesh utilized. Flukes are also
fished for sport or commercially along much of the
east and Gulf coasts of the United States. Several
other species of large flounders may be fished
commercially in the future if stocks of sufficient
size can be found.

Larvae of flatfish along the southeastern coast
of the United States are jDoorly known; however,
a few authors have illustrated and described some

1 Contribution No. 102, Bureau of Commercial Fisheries Biological Lab-
oratory, Brunswick, Ga. 31520.

' Present address: Bureau of Commercial Fisheries Exploratory Fishing
and Gear Research Base, Pascagoula, Miss. 39567.

Published May 1970.

FISHERY BULLETIN: VOL. 68, NO. 2

of these fish taken off North Carolina. Goode and
Bean (1896) identified an AncylapseUa diUcta
larvae (listed as Notosema dilecta, Bothidae) ;
Hildebrand and Cable (1930) had larvae of Para-
lickthys (Bothidae) ; and Deubler (1958) showed
the postlarvae of Paralickthys. Hildebrand and
Cable illustrated and described larvae of Sym-
pkwus plagiusa (Cynoglossidae) in 1930, and the
larvae of Trinectes maculatus (listed as Ackirus
fasciatus, Soleidae) in 1938 from off North
Carolina.

I discuss the literature pertaining to the larvae
of Syacium (Bothidae) in some detail, because of
the many similar external features between the
larvae of Cyclopsetta and Syacium. Both genera
have many elongate dorsal and pelvic fin rays, a
single sphenotic spine, and heavy preopercular
spines, but larvae of Cyclofsetta have more num-
erous elongate dorsal fin rays, and the sphenotic
and preopercular spinatlon is smaller.

This paper reports on development of larvae of
spotfin flounder, Cyclopsetta fimbnata, that U.S.
Fish and Wildlife Service vessels Theodore N.
GiU and Oregon collected off the south Atlantic
coast of the United States (fig. 1). It describes
growth changes in the head length, body depth,
eye diameter, snout length, and upper and lower

261

FiouBE 1. — Collection sites of Cyclopsetta fimbriata larvae from cruises of U.S. Fish and Wildlife Service vessels

Oill and Oregon.

262

U.S. FISH AND WILDLIFE SERVICE

jaw lengths, and the development of fins, spi-
nation, pigmentation, sequence of ossification, and
migration of the right eye.

REVIEW OF PERTINENT LITERATURE
CONCERNING BOTHID LARVAE

In their description of Ancylofsetta dilecta
(three-eyed flounder), Goode and Bean (1896)
did not mention the larva they illustrated or any
of its larval characters. The following characters
are taken from the illustration: about 70 dorsal
fin rays, the 9 anteriormost elongate ; about 60 anal
fin rays; 6 pelvic fin rays, the first three are elon-
gate and extend almost to the caudal peduncle;
ocular-side pelvic fin on median line; small eye;
large mouth ; origin of dorsal fin anterior to ante-
rior edge of eyes ; migrating (right) eye appears to
move under the dorsal fin or through the head. All
of these characters except the number of fin rays
are present on large larvae of Cyclopsetta. Well-
developed preopercular spines and a single sphen-
otic spine are present on larval Cyclopsetta but
are not shown on Goode and Bean's illustration.
Despite the lack of spines on their illustration, I
believe their specimen is a Cyclopsetta.

In Ancyloj)setta, the ocular-side pelvic fin is
above the median line ; the origin of the dorsal fin
is above the anterior part of the eye, not in advance
of it; the eyes are large, and the right side eye
probably migrates over the median dorsal ridge
anterior to the origin of the dorsal fin, not under
it. I do not know if larvae of Ancylofsetta have
elongate dorsal and pelvic fin rays.

Many species of Bothidae have elongate dorsal
and pelvic fin rays in the larval stage, but larvae
of Syacium are the only other bothid larvae to have
numerous elongate dorsal (more than five) and
pelvic (generally three) fin rays. Symphurus
larvae (family Cynoglossidae) also have elongate
dorsal rays, that can number up to seven. The num-
bers of dorsal and anal fin rays that Goode and
Bean (1896) show are too low for Syacium, and
the elongate pelvic fin rays they show are too long
for Syacium.

I am unaware of any published accounts of
Ancylopsetta larvae except those in which Sya-
cium, Cyclopsetta, Cithanchthys, or Etropus lar-
vae have been misidcntified as Ancylopsetta. Kyle
(1913) described and illustrated (fig. 27) a 6- to
7-mm. larva he called Ancylopsetta sp. Regan

(1916) illustrated (plate 9, fig. 3) a specimen iden-
tified as A. qvudrocellata that he said resembles
Kyle's (1913) Ancylopsetta; Regan's second illus-
tration (plate 9, fig. 4) is a 4-mm. larva that he
called Ancylopsetta sp. Both of Regan's (1916)
larvae as well as the larva figured by Kyle (1913)
are larvae of Syacium. Aboussouan (1968) dis-
cussed in detail the relation of Kyle's (1913) An-
cylopsetta and Regan's (1916) Ancylopsetta to
Syacium. Dannevig (1919) and Hsiao (1940) re-
corded Ancylopsetta larvae from eastern Canada
and along the outer edge of Georges Bank that are
similar to Kyle's Ancylopsetta sp. and these also
are larvae of Syacium, — warm- water species of ver-
tebrates and invertebrates in this area are not un-
common (Bigelow, 1926, and Colton, 1961).
Pearson (1941) listed .4 ncy?o/>5e^to sp. in plankton
collections from Chesapeake Bay, but these are
probably Etropus or Citharichthys. Pearson
(1941: 84) stated, "The most characteristic fea-
tures of the two fish are the pronounced elongation
of the first two dorsal rays, the latter reaching
nearly a quarter the length of the body, and the
elongation of one of the ventral fins into a filament
extending to the vent." These larval characters
are found on larvae of Etropus and Citharichthys,
and species of these two genera are known from
Chesapeake Bay. Cyclopsetta and Syacium have
not been reported north of Cape Hatteras, N.C.,
except for larvae of Syacium referred to as An-
cylopsetta by Dannevig (1919) and Hsiao (1940).

Known larvae of Etropus have 2 elongate dorsal
fin rays, and Citharichthys larvae have to 3
elongate dorsal fin rays (5-10 in Cyclopsetta and
Syacium) and 1 or 2 elongate pelvic fin rays (3
in Cyclopsetta and Syacium) .

S. guineensis (Bleeker, 1862) probably is a syn-
onym of S. micrurum Ranzani 1840; if so, the
larvae described by Aboussouan (1968) from off
Dakar are those of S. micrurum. Norman (1934)
listed S. guineensis in the synonymy of S. micru-
rum and gave its distribution as "Atlantic coast of
tropical America from Florida to Rio de Janeiro,
tropical West Africa." Distinguishing between
adult S. guineensis and S. mierurum is difficult,
and they are separated by their distribution; S.
guineensis off west Africa and S. micrurum, off
Florida, the Antilles, through the Gulf of Mexico
and the Caribbean Sea, and off the Atlantic coast
of South America to Rio de Janeiro.

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

263

Three species of Syaciwm occur in the western
North Atlantic. S. papillosimi (Linnaeus, 1758)
and S. micrurum, are difficult to separate as juve-
niles and can be separated as adults only by the
width of the interorbital space. All other meristic
and morphometric characters overlap. S. gtmteri
Ginsburg, 1933 can usually be separated from the
other two species of Syacmm in the western North
Atlantic by the number of dorsal and anal fin rays.
Syacium papillosum, and S. micrurum rarely have
fewer than 85 dorsal fin rays or fewer than 68 anal
fin rays, whereas S. gunteri rarely has more than
84 dorsal fin rays and more than 67 anal fin rays
(Gutherz, 1967).

Aboussouan's (1968) description of larval S.
micrurum (listed as S. guineensis) is of greatest
value for workers in the area off Dakar where only
one species of Syacium, is known. His paper is val-
uable in separating Syacium, larvae from the lar-
vae of other genera.

Aboussouan (1968) implied that Kyle's Cith-
arichthys B. (Kyle, 1913; fig. 29) is a Syacium
rather than a Cithanchthys^ but I disagree for the
following reasons: At this stage of development
larvae of Syacium have numerous elongated dor-
sal and pelvic fin rays but the known larvae of
Oitharichthys have only a few, if any, elongate fin
rays ; S. gunteri has fin ray counts similar to those
given by Kyle for Oitharichthys^ but our larvae of
S. gu/nteri have the heavy preopercular spination
and the large sphenotic spine seen on the larvae of
the other species of Syacium; the preopercular
armature of Syacium is not reduced or blunted
until the right side eye has reached the middorsal
ridge or is turning onto the left side ; the mouth of
Syacium, larvae is larger than that shown by Kyle,
and the origin of the dorsal fin is more anterior;
the larvae of several species of bothids have pig-
ment patterns similar to Oitharichthys B. I believe
this specimen probably represents a Oitharichthys
or Etropus.

ParaZichthys sp. and P. olivaceous larvae have
been figured and described by Hildebrand and
Cable (1930) ; Deubler (1958) ; Chang, Xo, and
Sha (1965) ; and Okiyama (1967). These descrip-
tions are based on larvae collected off the Atlantic
coast of the United States, off Japan, and on lab-
oratory-reared specimens. A high degree of simi-
larity in the developmental pattern is noted except

for Okiyama's P. olivaceous, which have longer
elongate dorsal fin rays that seem to persist longer
than the elongate dorsal fin rays on the larvae
described by Chang et al. (1965). Characteristics
common for the eggs and larvae of Paralichthys
and a discussion of the relation between the mi-
grating eye and the anterior portion of the dorsal
fin are given by Chang et al. (1965) .

Hippoglossina ohlonga larvae have been illus-
trated and described by Agassiz (1879, listed as
Pseudorhomhus ohlongus), Perlmutter (1939),
and Miller and Marak (1962, listed as Paralich-
thys oilongus).

Oitharichthys larvae have been figured by Ahl-
strom (1965), and Kyle (1913, fig. 29) has illus-
trated what is probably a Oitharichthys or
Etrop^is.

Bothus larvae have been illustrated and de-
scribed by Kyle (1913), Colton (1961), and Ochiai
and Amaoka (1963) among others. These descrip-
tions and figures of larvae collected off the Atlantic
coast of the United States, the mid-Atlantic re-
gion, and off the Japanese coast show a high degree
of similarity. All have only one elongate dorsal
ray.

Ohascanopsetta larvae have been illustrated and
described by Kyle (1913) and Bruun (1937). Kyle
was unable to refer his larva to any known Atlan-
tic species, but Bruun placed it in Ohascanopsetta.

Illustrations and descriptions of larvae in the
closely related Scophthalmidae can be found in
Smith (1904), Moore (1947), and Bigelow and
Schroeder (1953).

MATERIALS AND METHODS

The original sampling procedures used on
cruises of the FWS (U.S. Fish and Wildlife Serv-
ice) vessel Theodore N. Gill were reported by
Anderson, Gehringer, and Cohen (1956) and An-
derson and Gehringer (1957).

Additional plankton samples were collected in
January and June 1967 on cruises of the FWS
vessel Oregon. Plankton and nekton samples were
collected in depths of 14.6 to 45.7 m. (8-25 fath.)
by 1-m. plankton and nekton nets (1-mm. mesh)
and i/^-m. plankton nets (1-mm. and 0.33-mm.
mesh), which were towed for 15-minute periods.

A size series of specimens was cleared and
stained by the procedure given by Taylor (1967).

264

U.S. FISH AND WILDLIFE SERVICE

All measurements were made with an eyepiece
micrometer and a stereoscopic microscope and re-
corded to the nearest 0.01 mm.

MEASUREMENTS

Measurements used when working on larval flat-
fish require definition, because they differ signifi-
cantly from those used on adult flatfish.

Standard length (SL) : Tip of snout to that point
on notochord where dorsal flexture takes place
(dorsal and anal finfolds have a slight inden-
tation where the notochord turns dorsally, ac-
tinotrichia are visible in the caudal region of
the finfold immediately posterior to this in-
dentation) ; or tip of snout to base of median
caudal fin rays if these rays are developed ; or
tip of snout to distal end of hypurals if cau-
dal fin rays are developed.

Head length (HL) : Tip of snout to posterior edge
of cleithrum on a horizontal line through cen-
ter of left eye on small larvae ; or tip of snout
to origin of dorsalmost part of pectoral fin
base ; or tip of snout to posteriormost part of
opercle on large larvae.

Body depth (BD) : "Wlien left side pelvic fin base
is not developed, vertical depth is taken im-
mediately posterior to the cleithrum ; or from
origin of left side pelvic fin base to dorsal
margin of body (excluding finfold or rays).

Origin of pelvic fin base to cleithrum : Least dis-
tance from origin of pelvic fin base to ventral
tip of cleithrum, both left and right sides.

Eye diameter (ED) : Horizontal distance across
the left eye.

Upper jaw length (UJL) : Anterior tip of pre-
maxillary to distal edge of maxillary.

Lower jaw length (LJL) : Symphysis of lower
jaw to posterior edge of angular.

Snout length (SN) : Anteriormost part of pre-
maxillary to anterior edge of left eye.

COUNTS

Dorsal, anal, caudal, and pelvic fin rays: Total
number of fin rays in which the basal portion
is distinguishable.

PROBLEMS ENCOUNTERED IN WORKING
WITH LARVAL FLATFISHES

The wide variation in measurements and counts
of larval flatfishes may be due to distortion by

preservation or to differing rates of development.
When killed and preserved the larvae often curl;
the pectoral fins may harden in an extended posi-
tion ; the mouth may open and distort some head
features ; and the eyes often distend, shrink, or fall
out. Larval fish are fragile, and fin rays are often
broken, particularly the elongate rays. Poor pre-
serving and collecting teclmiques often damage
or distort specimens. Fresh, well-preserved, flat-
fish larvae can be held in place for examination
by a cover slide, but older, softer, or poorly pre-
served material may be damaged if handled in this
manner. Older, softer specimens are often difficult
to measure; however, they are often partially or
completely bleached, so that tlie fin rays and myo-
meres or vertebrae are easier to count than in the
fresh firmer specimens. Much of the material from
the Theodore N . Gill is soft, but that from more
recent Oregon cruises is in excellent shape.

Pigment patterns fade and are lost in preserva-
tive, so a knowledge of wlien specimens were col-
lected is important; also the rate of development
is not the same for all individuals. Larvae col-
lected over a wide geographic area and an ex-
tended period of time may show differing rates of
development. Within a species, fishes that meta-
morphose at small sizes probably liave different
rates of development from those that metamor-
phose at larger sizes. These differences must be
recognized when working with larval flatfish.

CHARACTERS USEFUL IN IDENTIFYING
BOTHID LARVAE

Characters that can be used to identify bothid
larvae fall into two categories: (1) transitory,
those which are present during part or all of the
larval period but eventually are lost and (2) per-
manent, those which develop during the larval
period and are retained in the juvenile and adult
stages.

Transitory characters include larval pigmenta-
tion, elongate fin rays, and head and body spina-
tion. Type and intensity of these transitory char-
acters may be of generic or specific significance.
Many of the bothid genera in the western North
Atlantic have elongate dorsal and pelvic fin rays
in the larval stages: Paralichthys (Hildebrand
and Cable, 1930) ; some Citharichthys (Ahlstrom,
1965; O. stigmaeus has no elongate dorsal fin
rays) ; Syacium (Aboussouan, 1968) ; Bothus and

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

265

Ohascanopsetta (Kyle, 1913) ; and Cydopsetta
(Goode and Bean, 1896). Many bothid larvae in
the western North Atlantic have spines. These are
more frequently seen on the preopercular margin
than on the head or body. Most bothids have a
swim bladder during the larval stage. Those larvae
with a protracted larval stage retain the swim
bladder longest. The migrating eye moves over the
middorsal ridge anterior to the origin of the dorsal
fin or through the head between the dorsal fin and
the supraorbital bars of the cranium.

Permanent characters include meristic counts,
relation of the origin of the pelvic fin bases to
each other and to the cleithrum, and the arrange-
ment of the caudal fin rays with respect to the
other caudal fin rays and the bones of the hypural
plate. Size at metamorphosis is important in dis-
tinguishing between genera.

MERISTIC CHARACTERS

The most important characters for identifica-
tion of bothid larvae are meristics. Myomeres,
which correspond in number to vertebrae, are the
first countable item to develop. Those near the
anterior and posterior portions of the body are
difficult to count in the early stage larvae. Abdom-
inal vertebrae usually number 10, but can be 11
{Chascanopsetta has 16 or 17). Caudal vertebrae
are much more variable, ranging from 23 to 42.
The vast majority of bothid larvae have between

34 and 40 total vertebrae or myomeres. Dorsal and
anal fin ray numbers are also variable and overlap
widely between species of Bothidae. The adult
complements of dorsal and anal fin rays are dis-
tinguishable in larval O. fiTribriafa by about 8-mm.
SL (fig. 2). The rate of fin ray development and
the fin ray numbers at the various sizes may have
generic or specific value. Although much meristic
overlap is evident among species of bothids, sev-
eral species can be separated by meristic values.

PELVIC FIN

Pelvic fin characteristics helpful in determining
a genus or generic group are : the position of the
fin bases in relation to the median line, size of
larvae when the left fin base and rays first appear,
relation of the origins of the right and left side
fin bases to the cleithrum, and the number of
elongate fin rays.

Four of the 13 genera of bothids in the western
North Atlantic {Parcdichthys, Ancylopsetta, Gas-
tropsetta, and Hippoglossina) have the left and
right side fin bases above the median line; all other
western North Atlantic bothid genera have the left
side fin base on the median line and the right side
fin base above the median line.

I have only seen Parcdichthys of the four genera
with left and right side pelvic fin bases above the
median line. In Paralichthys the left side fin base
does not appear until the larvae are about 7 mm.

u. so

o

i <o

DORSAL-O
ANAL-X
CAUDAL - it

O O O O

o<b

X X '^

OOO « °

o *

** * ***♦ • *

*****

II 13 13

STANDARD LENGTH (MM.)

FiGDBE 2. — Relation of number of dorsal, anal, and caudal fin rays to standard len^h of

Cydopsetta fimhriata larvae.

266

U.S. FISH AND WILDLIFE SERVICE

SL. I have not seen the larvae of Aovcyhpsetta,
Gastrofsetta^ or Hippoglossina, but an ilhistration
of a 5.7-mm. SL Hiffoglossina oblotigus by Perl-
mutter (1939) ; and illustrations of a 6.5-mm. spec-
imen and a larger one by Agassiz, (1879, plate 9,
figs. 4 and 5) do not show a left side pelvic fin. The
pelvic fins of H. oblongvs appear very much later
than do the dorsal and anal fins (Agassiz, 1879).

At 5 mm. SL Syaciiim, Cyclopsetta, Githarich-
thys, and Etropus have a well-developed pelvic fin
on the left side. The left side fin base appears at 2
to 3 mm. SL and is better developed than the right
side base, which develops later.

I do not know at what size the pelvic fin bases
first appear in Engyophrys, Trichopsetta^ or Mon-
olene (I have assigned larvae exceeding 8 mm. SL
with well-developed pelvic fin bases to Engyoph^ys
and Monohne) . The origin of the left side fin base
of adults is adjacent to the cleithrum or slightly
anterior to it in Engyophrys, Trichopsetta, and
Monolene, but the origin of the right side fin base
is slightly posterior to the cleithrum.

The origins of the left and the right side pelvic
fin base are posterior to the cleithrum in Para-
lichthys, Aneylopsetta, Gastropsetta, Hippoglos-
sina, Syacium^ Cyclopsetta, Citharichthys, and
Etropus. In Bothus and Chascanopsetta the origin
of the left side pelvic fin base is on the urohyal,
which is well in advance of the cleithrum. The
right side fin base of Bothus and Chascanopsetta
is short, and its origin is well posterior to the
cleithrum.

CAUDAL OSTEOLOGY

From late stage larvae to adults, the bothids
show a correlation between caudal Osteology and
position of the pelvic fui bases (table 1). Species
of Paralichthys, Ancylopsetta, Gasfropsetta, and
Hippoglossina have the dorsalmost principal cau-
dal fin ray associated with an epural ; the ventral-
most principal caudal fin ray has a spur associated
with it, and it is associated with the haemal spine
of the penultimate vertebra. The count of principal
caudal fin rays in this group, starting with the
epural and ending with the haemal spine of the
penultimate vertebra, is 1-2-6-4-3-1 or 1-2-6-5-
2-1 in Paralichthys. In these genera neither of the
plevic fin bases is on the median line and the origins
of both pelvic fin bases are well behind the clei-
thrum.

Species of Syacium, Cyclopsetta, Citharichthys,
and Etropus have all 17 principal caudal fin rays
associated with the four hypural elements. The
dorsal-to-ventral count of principal caudal fin rays
on each hypural is 4-5-4-4. In these genera the left
side pelvic fin base is on the median line, and its
origin is well behind the cleithrum.

Table 1. — Four generic groups which show a relation be-
tween the origins of the pelvic fin bases and number of
principal caudal fin rays associated with caudal elements

lAsterlsks Indicate the genera for which I have no Identified larvae]

Genera

Number of

prtaolpal

Pelvic fin (PJ) caudal fin rays

associated with

caudal elements

Paralichthys

ATicylopsetta'

Oastropseita'

Hippoflosaina'

SyaciUTn

1-2-6-5-2-1
Neither pelvic fin base on median

line, both short-based; origins 1-2-6-4-3-1

well behind cleithrum.
Ocular-side P* base on median line; 4-5-1 1

Cydopsetta

origin posterior to cleithrum.
Blind-siae P> base above median
line; origin posterior to cleithrum.

Cilharkhthyt

Etropus ....

Trichopsetta'

Monolene

origin slightly anterior to or below
clelthral tip. Blind-side P> base

Bothus

above median line; origin posterior
to cleithrum.
Ocular-side P^ base on median line, 1-4-4-3-4-1

Chascanopsetta'

extending onto urohyal; origin
anterior to cleithrum. Blind-side
P> base above median line, short-
based; origin posterior to
cleithrum.

Species of Engyophrys, Trichopsetta, and Mon-
olene have the dorsalmost and ventralmost prin-
cipal caudal fin rays associated with the neural and
haemal spines of the penultimate vertebra and
have a count of 1-3-5-4-3-1. In these genera the
left side pelvic fin base is on the median line and
its origin is slightly anterior to the cleithral tip
and to the origin of the right side base.

In Bothus and Chascanopsettathe count of prin-
cipal caudal fin rays associated with the caudal
elements is 1 11 3-4^1, starting at the neural
spine and ending at the haemal spine of the pe-
nultimate vertebra. In Bothus and Chascanopsetta
the left side pelvic fin base is on the median line
and its origin is on the urohyal, on the right side
the base is short, above the median line, and its
origin is behind the cleithrum.

The number of principal caudal fin rays asso-
ciated with caudal elements shows some variation,
because a fin ray may be supported in part by two
elements, such as hypurals, epurals, or neural or
haemal spines.

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

267

DEVELOPMENT OF CYCLOPSETTA
FIMBRIATA LARVAE

No information is available on the fertilized eggs
or the yolk sac larvae of C. fimbriata; however, I
do have certain observations on the larger larvae,
including their identification, patterns of general
growth, formation of fins, spination, pigmenta-
tion, migi-ation of eyes, and sequence of
ossification.

IDENTIFICATION OF LARVAE

Larvae of O. fi7n'briata are identifiable at very
small sizes. The smallest larva in my sample (1.72
mm. SL) has a large head with a well-developed
mouth. Hatching size is probably about 1.50 mm.
SL or slightly smaller. Larvae of this species have
two prominent transitory features (they may be
generic) that are readily seen on the smallest lar-
vae (fig. 3) : a small, single spine on the sphenotic
region of the cranium and several small single
spines on the preopercle {Syacium has larger
sphenotic and preopercular spines) . These spines
persist throughout the larval stages (figs. 3-7)
and are still evident during metamorphosis (that
period when the eye is migrating) . No fin rays are
discernible in the finfold of the smallest larva
(1.72 mm. SL). At about 2.10 mm. SL the first
three elongate dorsal fin rays appear. Elongate
dorsal fin rays (8-11 in the large larvae) persist
throughout the larval stages (figs. 4-7). At about
3.00 to 3.30 mm. SL one to three elongate pelvic
fin rays appear (fig. 4) and persist throughout the
larval stages (figs. 4-7).

The right side eye is migrating in the largest
larva in my sample (14.51 mm. SL). The dorsal

edge of the migrating eye is above the middorsal
ridge of the cranium. During metamorphosis the
eye moves under the dorsal fin which is attached
anteriorly to the ethmoid region of the cranium.
The migrating eye had not yet begun to turn onto
the left side, but it appeared about ready to move
under the dorsal fin. Elongate dorsal and pelvic
fin rays and head and preopercular spination per-
sist (fig. 7).

Four transitory larval features help differenti-
ate C. fimbriata and Syacium larvae from all other
bothid larvae found along the southeastern coast
of the United States: (1) a single spine in sphen-
otic region of the cranium, (2) several single pre-
opercular spines, (3) relatively high numbers of
elongate anterior dorsal fin rays, and (4) three
elongate pelvic fin rays (figs. 3-7). Compared to
Cyclopsetta, Syacium has larger and heavier
spines, fewer elongate dorsal fin rays, and rela-
tively shorter elongate pelvic fin rays. The sphen-
otic spine is surrounded by concentric rings on
large Cyclopsetta larvae but by a crenulated cap on
Syacium larvae. The origins of the pelvic fin bases
in relation to each other and to the cleithrum and
the transitory larval characters provide the
generic identity of Cyclopsetta larvae.

Three species of Cyclopsetta occur in the west-
ern North Atlantic Ocean (Gutherz, 1967). C. fim-
hriata is the only species known from the Atlantic
coast of the United States, C. decu^ata is known
only from the type, and C. chittendeni is found
along the coast of the United States only in the
Gulf of Mexico. The distribution of these species
excludes all known species of Cyclopsetta except
fimbiiata from consideration for my larvae.

FiouBE 3.— Larva of Cyclopsetta fimbriata, 1.8» mm. SL. Note sphenotic and preopercular spinaUon. Pectoral fin is

omitted to show swim bladder and gut.

268

U.S. FISH AND WILDLIFE SERVICE

GENERAL GROWTH PATTERNS

Head length and body depth show a uniform
rate of increase with standard length throughout
the size range of my sample (figs. 8-9) .

Upper jaw length shows a uniform rate of in-
crease with standard length in larvae longer than
about 4 mm. SL, but smaller larvae have a faster
rate of increase (fig. 10) .

Lower jaw length increases at a uniform rate
with standard lengtli in larvae between about 4
and 13 mm. SL; but larvae smaller than about
4 mm. SL and longer than 13 mm. SL have a
faster rate of increase (fig. 11) .

/

Snout length increases only slightly in speci-
mens up to about 2.7 mm. SL; between about 2.7
and 4 mm. SL snout length increases at its fastest
rate ; and larvae larger than about 4 mm. SL have
a uniform but slower rate of increase with stand-
ard length (fig. 12).

Eye diameter increases at a uniform rate with
standard length in larvae longer than about 3.5
mm. SL; the rate is faster in smaller larvae (fig.
13). Eye diameter as a percentage of head length
decreases throughout the size range in my sample
(fig. 14) ; the fastest decrease is between head
lengths of about 0.5 and 1.5 mm. (1.8 to about 4
mm. SL).

/

/

/ /

i /

/

Figure 4. — Larva of Cyclopsetta flmbriata, about 3.0 mm. SL. Note sphenotic and preopercular spination, elongate dorsal
and pelvic fin rays, and pigmentatiom. Pectoral fin is omitted to show swim bladder, gut, and pigmentation on dorsal
portion of swim bladder and gut.

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

269

M

vX

®

\

\

FiQUBB 5. — Larva of Cyclopsetta flmibriata, 6.9 irnn SL. Note sphenotic and preopercular spination, elongate dorsal and

peMc fin rays, and pigmentation. Pectoral fin Is omitted.

270

U.S. FISH AND WILDLIFE SERVICE

H i„rjy

Figure 6. — Larva of Cyclopsetta flmhriata, 12.9 mm. SL. Note sphenotlc and preopercular spination, elongate dorsal and
pelvic fln rays, pigmentatian, and area under anterior portion of the dorsal fin through which the right side eye will
migrate.

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

271

417-nfif) O - 71 - 7

FiGtJBE 7. — Larva of Cyolopsetta fimbriata, 14.0 mm. SL. Larva has been cleared and stained, and all bone that has
absorbed alizarin red S is shaded. Note sphenotic and preopercular spination, elongate dorsal and pelvic fin rays,
right aide eye under anterior part of dorsal fin will migrate through head. Ossification is not yet complete.

z

STANDARD LENGTH (MMj

FiQUBE 8. — Relation of head length to standard length of Cyolopsetta fimbriata lan-ae. Dots represent individual
si>ecimens, and open circles represent means (see app. tables 1 and 2).

272

U.S. FISH AND WILDLIFE SERVICE

a
O

-J L_

..y- -■

_] L I I 1 I I I I 1_

-J 1_

« 7 8 9 10

STANDARD LENGTH (mmO

FiouEE 9. — Relation of body depth to standard length of Cyclopsetta fimbrwta larvae. Dots represent Individual
specimens, and open circles represent means (see app. tables 1 and 2).

1.0 .

_] I I L.

6 7 8 9

STANDARD LENGTH (AAMJ

FiQUBE 10. — Relation of upper jaw length to standard length of Cyclopsetta flmbriata larvae. Dots represent individual
specimens, and open circles represent means (see app. tables 1 and 2).

STANDARD LENGTH (MM.)

PioimE 11. — Relation of lower jaw length to standard length of Cyclopsetta flmbriata larvae. Dots represent individual
specimens, and open circles represent means (see app. tables 1 and 2).

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

273

^ I.OL

z>
O

z

:..... a..-.

_I L_

STANDARD LENGTH (MM.)

E^ouBE 12. — Relation of snout length to standard length of Cyclopsetta flmbriata larvae. Dots represent indlTidiial
specimens, and open circles represent means (see app. tables 1 and 2).

1.5

-

ae

^ IJ>

-

o

ut

D '

i

<

: t>

•o. •

a

a

. o

u .5

,

;(^"..'

.tf-'

>-

.;.«•. ji*-='

'••. p

:,tfT-'^

#

1

'

•

1

1

'

,

I I J J 4 5 6 7 e 9 10 n 12 13 li 15

STANDARD LENGTH (MMJ

FiQiTEE 13. — Relation of eye diameter to standard length of Cyclopsetta flmbriata larvae. Dots represent individual

specimens, and open circles represent means (see app. tables 1 and 2).

50

-

X

.

1—

O

•

2 40

.

o «• •

—t

«• •

1 . *
o ..

a

A..

<

' , ,

*

UJ

•

<»"

.

X

*.. • 'O-

■~^ 10

-

,

. - .. . - .

1

i.

o-

*

<

•o

a

•

^

*

UJ

o.

• o •

>-
lu 20

>

1

1

»

1.0 2.0 3.0 4.0 5.0

HEAD LENGTH (MM.)

FiouEE 14. — Decrease in eye diameter relative to head length of Cyclopsetta flmbriata larvae. Dots represent eye
diameter as percentage of head length of individual specimens, and open circles represent means (see app. tables
land2).

274 U.S. FISH AND WILDLIFE SERVICE

Gill rakers begin to develop as elevations on the
dorsal surface of the ceratobranchial. They are
first seen when the larvae are about 8 mm. SL.
Four or five lower-limb gill rakers are first seen on
larvae about 9 mm. SL. They are short, blunt, well
separated, and located on the ceratobi-anchial. By
10.0 mm. SL the number of lower-limb gill rakers
has increased to seven and they are found on the
ceratobrancliials and hypobranchials. The adult
complement of 8 to 10 gill rakers on the lower limb
is reached at about 13.5 mm. SL. Gill rakers are
first seen on the epibranchial in 13.5 mm. SL
larvae, which have a single gill raker located im-
mediately above the angle.

FIN FORMATION

In the development of C. fmhriata the pectoral
fin is the first to appear and the last to complete
its development. The caudal fin completes develop-
ment first, followed in order by the dorsal, anal,
and pelvic fins. By about 8 mm. SL the adult
complement of fin rays is present in the caudal,
dorsal, and anal fins (fig. 2) .

Pectoral Fin

The pectoral fin is present on my smallest larva
(1.72 mm. SL) and is not fully developed on my
largest specimen (14.5 mm. SL). Initially it is
large and rayless.

Caudal Fin

The fully formed caudal fin has 17 principal fin
rays associated with the four hypural elements.
The dorsal and ventralmost caudal fin rays are
simple; the remaining rays are branched. Princi-
pal caudal fin rays are separable into two groups.
The nine upper rays are associated with the two
superior hypurals and the eight lower rays with
the two inferior hypurals (4-5 1 1 ). No caudal
fin rays are associated with neural and haemal
spines of the penultimate vertebra. A ventral
thickening near the posterior end of the notochord
is seen on specimens about 3.5 mm. SL. This thick-
ened tissue develops into the two median hypural
plates and their associated caudal fin rays. The first
four caudal fin rays to develop are seen first on a
5.44 mm. SL specimen and appear simultaneously
(fig. 2). They develop at an oblique angle to the
notochord and are divided into two groups, upper
and lower. This division separates the caudal fin

into superior and inferior components. By about
8 mm. SL the notochord lias turned dorsally, the
hypurals and caudal fin rays are arranged parallel
to the axis of the body, and all principal caudal
fin rays are developed (fig. 2) , but the caudal oste-
ology is not fully developed until a larger size.

Dorsal Fin

Dorsal fin ray development is an important tax-
onomic character in larval flatfish. These fin rays
begin to develop in a thickened area above the
nape on specimens of about 2 mm. SL. My small-
est specimen with doi-sal fin rays (three elongate
rays) is 2.08 mm. SL (see app. table 1) . The origin
of the dorsal fin base moves anteriorly on the lar-
vae until the fin base is over the eye ; at this time
dorsal fin rays begin developing posterior to the
nape. All elongate dorsal fin rays develop first.
The origin of tlie dorsal fin continues to shift an-
teriorly until it becomes attached to the ethmoid
region of the cranium ahead of the eye. The first
three fin rays must develop simultaneously ; all but
three of the specimens between 2 and 3 mm. SL
have three or four fin rays (one with two, and two
with five). The number of fin rays on all but four
specimens between 3 and 5 mm. SL does not ex-
ceed 10 (one with 11 and three with 14), and most
of the rays are elongate. The number of fin rays
increases rapidly between 5 and 8 mm. SL; at 8
mm. SL the adult complement of 78 to 87 fin rays
is present (fig. 2) . Three of my 19 larval specimens
exceeding 8 mm. SL had 77 fin rays, and one had
76.

Anal Fin

Fifteen anal fin rays were present on a 5.9 mm.
SL specimen; none were discernible on smaller
specimens (fig. 2; app. table 1). Tlie number of
fin rays increased rapidly, as in the dorsal fin, and
the adult complement of 59 to 67 fin rays was de-
veloped by about 8 mm. SL (fig. 2). Four of 19
specimens exceeding 8 mm. SL had fin ray counts
of 58, three had fewer than 58, and the others had
counts between 59 and 67 (see app. table 1).

Pelvic Fins

Pelvic fin bases develop early. The left-side fin
base and its three elongate anterior fin rays de-
velop earlier than the right-side fin base. The left-
side fin base is first noted on specimens of about

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

275

2.5 mm. SL as a thickening on the ventral edge of
the body immediately anterior to the gut, but the
right-side base does not appear until about 3.5 mm.
SL. My smallest specimen with pelvic fin rays (left
side, and elongate rays) was 3.0 mm. SL. The first
right-side fin ray is seen on a 5.3 mm. SL specimen.
The three elongate pelvic fin rays on the left side
develop simultaneously. They are present on all
specimens but two (one with a single fin ray and
one with two fin rays) . The fourth left fin ray de-
velops at about 5 mm. SL, and the fifth and sixth
rays by about 10 mm. SL. Each fully developed
pelvic fin has six fin rays. The three elongate fin
rays of the left side are thickened and heavier than
the other pelvic fin rays and extend posteriorly to
about the caudal peduncle; they are often broken.
None of the other pelvic fin rays is elongate. The
origins of the pelvic fin base are equidistant behind
the cleithrum.

LARVAL SPINATION

A single sphenotic spine and a series of preoper-
cular spines (figs. 3-7) persist throughout the size
series of my larval specimens (1.72-14.51 mm.
SL) . These spines are smaller but similar in posi-
tion and shape to those reported for Syacium
by Kyle (1913) and Aboussouan (1968). The
sphenotic spine becomes relatively smaller as the
larvae grow. The spine is surrounded by concentric
rings that are first noted on specimens of about

4.6 mm. SL. Four to six small sharp spines are
present on the preopercular margin ; two or three
of these are on the ventral edge, a larger single
spine is at the angle, and two more small spines
are on the posterior edge. The large spine at the
angle of the preopercle thickens, and a spur devel-
ops on the upper posterior edge of the spine on
larger larvae. These spines do not alter position
or shape but become relatively smaller with in-
creasing size of the larvae. The sphenotic and
preopercular spines can be traced through the
developmental series and are important in identi-
fying this group of larvae (figs. 3-7) .

PIGMENTATION

Pigment on all of the Theodore N. Gill material
is faded, but pigment patterns are readily seen on
the fresh Oregon material. In my sample, pig-
ment is first seen on a 2.8 mm. SL specimen — a
large melanophore over the base of each sphenotic

spine, and another melanophore on the gular re-
gion between the posterior end of the lower jaws
and the tip of the cleithrum. The dorsal portion
of the swim bladder and the dorsal loop of the gut
are heavily pigmented. On a 3.2 mm. SL specimen
the melanophores at the bases of the sphenotic
spines have faded, but those on the gular region
and along the dorsal aspect of the gut remain.
Three clusters of melanophores are present on the
dorsal edge, and two are on the ventral edge of the
body. The anteriormost is on the dorsal edge of
the body over the pectoral fin base (there is no
corresponding ventral cluster of melanophores).
The other two dorsal clusters of melanophores
have corresponding ventral clusters. The middle
spots are immediately behind the gut region, at
about the midpoint of the body (TL), and the
posterior spots are slightly anterior to the caudal
peduncle (fig. 4). A series of small melanophores
can be seen on the ventral edge of the gut between
the vent and the anterior portion of the gut cavity.
Pigmentation is essentially the same on specimens
up to about 4 mm. SL, but the number of melano-
phores increases. Specimens between 4 and 5 mm.
SL have a large melanophore on each opercle be-
hind the eye and another on the median line at the
origin of the pelvic fin base. The dorsal portion of
the gut has two areas of dark pigment ; the ante-
riormost is on the upper half of the swim bladder
and the other is above the loop of the intestine.

At about 5 mm. SL the melanophore on the
gular region has disappeared, but additional clus-
ters of melanophores have appeared, one dorsal
and one ventral, between the middle and posterior-
most cluster but nearer the posteriormost cluster.
The two new clusters are of equal size and are
smaller than those nearest to them. The remaining
pigment is similar to that seen on the smaller
larvae. Shortly after appearance of the third ven-
tral pigment cluster the posteriormost ventral
cluster increases in length and becomes longer than
its corresponding dorsal area.

By 7 mm. SL a fifth dorsal cluster has appeared
between the first two clusters. Two pigment clus-
ters have developed along the lateral septum, cor-
responding in position with the two posterior
dorsal and ventral clusters. Pigment is present
over the entire swim bladder on the left side and
absent on the right side. Pigmentation remains
essentially the same through the rest of the larval

276

U.S. FISH AND WILDLIFE SERVICE

series in my sample, except for darkening and the
appearance of pigment at the distal edge of the
caudal peduncle, in the branchial chambers, and
around the urohyal (figs. 5 and 6).

MIGRATION OF THE EYE

Specimens of 7 mm. SL are symmetrical; the
right eye has not begun to migrate (fig. 5). The
dorsal fin continues its development anteriorly,
and its origin is over the anterior edge of the eye.
The supraorbital bars on the cranium have not
begun to become modified.

By about 8 mm. SL the right eye has moved
only slightly ; the origin of the dorsal is above and
posterior to the ethmoid region of the cranium and
the origin of the fin base remains unattached. Tis-
sue between the ventral edge of the anterior por-
tion of the dorsal fin and the frontal region of the
cranium is becoming thin, and the supraorbital
bars have begun to shift onto the ocular sides as
an accompanying depression begins to form above
the left eye.

By 10.5 mm. SL the right eye has migrated
dorsoanteriorly but its upper edge is not yet level
with the supraorbital bars ; the origin of the dorsal
is attached to the ethmoid region of the cranium
and its point of attachment has shifted onto the
right side of the head, over the nostrils. The right
side is the blind side in the adult. The area of thin
tissue between the dorsal fin and the supraorbital
bars is wider. The supraorbital bars continue their
shift to the left side, and the depression of the
cranium above the left eye is larger.

On a 14 mm. SL specimen the upper edge of
the right side eye is visible through the thin tissue
below the dorsal fin (fig. 7). The shifting of the
supraorbital bars has created a large depression
over the left eye. The origin of the dorsal fin re-
mains attached. The right eye has not yet begim
to move through the head onto the left side. In
larger specimens the eye will move through the
head in the area between the dorsal fin and the
depression created by the shift of the supraorbital
bars.

SEQUENCE OF OSSIFICATION

I cleared and stained several specimens to de-
termine the sequence of ossification. The degree of
ossification can be assessed by the intensity of the
stain (alizarin red S) absorbed by the bone. In

this discussion I consider any bone that absorbed
stain to be ossified.

On a 1.7 nun. SL specimen only the cleithrum,
the distal edges of the preopercle and preopercular
spines, and the sphenotic spine and its base showed
any ossification.

By 3 mm. SL some ossification is seen in the
cranial cap, lower jaw, premaxillary, and the four
elongate dorsal fin rays. By 3.5 mm. SL the three
elongate pelvic fin rays, the maxillary, four bran-
chiostegal rays, and six elongate dorsal fin rays are
ossified. The palatine and parasphenoid are stained
and extend from the symphysis of the upper jaw
to the cleithrum ; these bones will form part of the
floor of the neurocranium. At this size all stained
areas are in the head and pelvic fin region. Six
canine teeth are present in the lower and four in
the upper jaw, but none are stained. A slight
thickening on the ventral edge of the posterior
part of the notochord is the rudimentary hypural,
and it is only slightly ossified, if at all.

Ossification is still restricted to the head and
pelvic fin base region at 4.1 mm. SL. All seven
branchiostegal rays, the urohyal, and the preoper-
cle and opercle in the opercular series are now
ossified. The vertebrae and neural and haemal
spines have not begim to ossify. Ossification at 4.9
mm. SL is essentially similar to that of the 4.1 mm.
SL specimen; again the anterior neural and hae-
mal spines are visible but are not stained. They are
not attached to the vertebrae and appear as thin
lines between the vertebrae and the dorsal and
anal fin rays.

At 5.5 mm. SL the right pelvic fin base, three or
four caudal fin rays (but not the hypural ele-
ments), the dorsal aspect of the subopercle, and
some vertebrae and associated neural and haemal
spines have begun to ossify. The 16 anterior neural
spines and the anterior seven haemal spines, and
the dorsal rim and sides of the neural arch on the
second, third, and fourth vertebrae are lightly
stained. The first vertebra and its neural spine
are not stained. The occipital region of the neuro-
cranium and the scapula have begun to ossify.

The areas of ossification, as determined by ab-
.sorption of alizarin red S stain, are larger and the
color is more intense at 6.4 mm. SL than on smaller
specimens. At this size the notochord is upturned
and two hypural elements are differentiated. Ten
caudal fin rays are stained, and five are associated

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

277

with each hypural element. The notochord has
neural and haemal spines on nearly its full length.
Most neural arches, but only the anterior haemal
arches, are stained. Pterygiophores of the anterior
elongate dorsal fin rays are developing. About 40
dorsal and 24 anal fin rays are stained. The in-
teropercle has begim to ossify, and all four opercu-
lar elements show some ossification. The supra-
orbital bars are stained and are visible as anterior
extensions of the neurocranium. The auditory re-
gion of the neurocranium is partially stained, and
the post cleithrum is ossifying.

By 10 mm. SL ossification has progressed con-
siderably, and many bones in the head, vertebrae,
and caudal fin can be recognized. At about 10 mm.
SL ossification is noted in the hypural elements,
the basal part of the urostyle, and the parapophy-
sis of the last abdominal (precaudal) vertebra.
The dorsal aspects of the posterior 14 and the an-
teriormost 3 or 4 vertebrae are lightly stained ; the
remaining vertebrae are not stained. All neural
and haemal spines and arches are ossified except
for those on the penultimate vertebra. There are
16 caudal fin rays : Four are associated with each
of the two inferior hypurals, the superior hypurals
are indistinguishable. Four to six pelvic fin rays
have developed on each fin base, and the pelvic
bone is beginning to ossify. The supraorbital bars
extend forward; their anterior edge is above the
nostril. The entopterygoid, which is immediately
above the pterygoid, is lightly stained. Bones of
the lower jaw suspension can be identified; the
quadrate, hyomandibular, and pterygoid are
lightly stained. The supracleithrum and post-
temporal region of the cranium can be distin-
guished. The upper jaw now has about 10 teeth
and the lower 16; those near the symphysis are
relatively small and close together. A "cartilagi-
nous" bar extends posteriorly along the ventral
median edge of the gut from the distal edge of
the pelvic fin base to below the liver. The anterior
ventral edge of the urohyal is hooked and pointed
forward.

Ossification has changed little at about 14 mm.
SL except on the vertebrae (fig. 7). The first ab-
dominal (precaudal) vertebra is completely ossi-
fied, and the dorsal aspect and one-third to one-
fourth of the lateral surfaces of the other abdom-
inal vertebrae are ossified. The parapophyses of
the last four abdominal vertebrae are also ossified,

but no ribs are seen. Ossification of the parapophy-
ses begins with the last abdominal vertebra and
proceeds anteriorly to the fifth vertebra, the last
one with a parapophyses. The first through the
18th caudal vertebrae show the same degree of
ossification ; posteriorly they become progressively
more ossified until ossification is complete on the
last four vertebrae. Interneurals and interhaemals
are developing between the fifth and 10th neural
and haemal spines. The enlarged pterygiophore,
which is associated with the first 10 to 12 anal fin
rays, is now lightly stained.

My largest larva (14.5 mm. SL) is stained and
shows essentially the same degree of ossification as
the 14 mm. SL specimen. The vertebral column,
pterygiophores of the dorsal and anal fins, and all
bones of the neurocranium and branchiocranium
are not completely ossified. The supraorbital bars
extend forward onto the ethmoid region and form
the frontals. The right side supraorbital bar ap-
pears to be partially reabsorbed as suggested by
its upturned anterior medial edge in the sphenotic
region and its position and thimiess. The left su-
praorbital bar lias moved closer to the left eye.
After movement of the supraorbital bar is complete
the left side bar and part of the right side bar form
the interorbital bar, and the remaining part of the
right supraorbital bar is reabsorbed. At a larger
size the right eye will move under the dorsal fin
and stop at the interorbital bar. The sphenotic and
preopercular spines are still present at 14.5 mm.
SL but will eventually be reabsorbed or broken off
and leave the surface smooth.

SPAWNING AND DISTRIBUTION

Larvae were collected between Jupiter Inlet,
Fla., and Cape Hatteras, N.C. (fig. 1) in surface
waters over depths of 11 to 2,510 m. (6-1,372
fath.) ; 21 stations were in depths greater than
183 m. (100 fath.) and 54 stations in depths less
than 183 m.

Specimens were collected primarily north of lat.
30° N. (70 collecting sites were north and only 5
were south of lat. 30° N.). Sixty-nine larvae were
taken at 35 stations occupied at night, and 102 were
taken at 38 stations occupied during the day. No
larvae were collected between November and
April ; one lan^a was taken in April and one in No-
vember; and the rest in May to October (fig. 15).

278

U.S. FISH AND WILDLIFE SERVICE

14

-

'

r

-

_

12

.

—

, ^

5

5 „

-^10

_

.

X

,

t-

/

\
\

O

~

r /

z

/

\

/
/
/
/

\

lu 8

—J

-

/

/

\

\
\

\
\
\

-

/

\

/

O

/

\

/

\

Oi

-

r /

V

/

\

< 6

_

/

\

1

_

a

1

-

- \

1

\

z

1

\

\
\

1

\

\ -
\

<

1

t

1-

10 4

-

.

1

1

1
-1
1

<

\
\
\
\

1
1
1

\

\

-

~~~

L

i..

/

\

2

_

/-J

—

\

_

/ ^ J

L \

/ \

/ \

/ \

/ \

/ N

1 1 1 1 I 1 1 I

M

J A

MONTHS

50

40

<
>

-30 <

20

. 10

00

Z

FiouBE 15. — Size range and mean size of larvae collected from April to November. Frequency

of larvae per month also shown.

The Theodore N. Gill data by themselves show
a single spawning peak in September, but the
combined Theodore N. Gill and Oregon data sug-
gest a bimodal spawning period with peaks in June
and September. The first larvae appear in April,
and numbers increase sharply until June; after
September the numbers decrease sharply to No-
vember. Larvae 2.6 mm. SL and smaller were col-
lected each month from May through October. I
estimate that hatching size is about 1.5 mm. SL;
therefore, spawning must occur throughout this
period. The mean size of the larvae increases
through July and then decreases in September.
This size decrease is correlated with a spawning
peak (fig. 15). My samples contain no larvae ex-
ceeding 9 mm. SL until the last week in June, but
larvae of this size are present in succeeding months
through November (fig. 15). These size data sup-
port the supposition that spawning begins in the
spring.

I have not seen spawning fish, but I have ex-
amined gonads from G. fimhriata taken tlirough-
out the year off Cape Kennedy, Fla. None of the
gonads were ripe, but the ovaries enlarged pro-
gressively from spring to fall. In the winter the
ovaries are very thin and flat. My examination of
gonad development indicates a spawning period
from early spring to late fall — again supporting
conclusions based on the samples of larvae.

I tried to determine where C. fimhriata spawns
by analyzing the collection data for 28 smaller
larvae (1.7 mm.-3.0 mm. SL). These specimens
were collected at 17 stations on Theodore N. GiU
and Oregon cruises. Ten of the 17 stations were
occupied during daylight ; of these six were in 46
m. (25 fath.) or less. Three of the seven nighttime
stations were in depths of 46 m. (25 fath.) or less.
Small larvae were collected from May through
October from Florida to North Carolina. Because
hatching size is estimated to be about 1.5 mm. SL,
specimens less than about 2.0 mm. SL must have

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

279

been collected close to the spawning area, but this
view may be erroneous because the time required
for hatching of the eggs is unknown. Six speci-
mens (1.72-2.01 mm. SL) were collected from five
stations, at the surface in 22 to 450 m. (12-246
fath.) during both day and night. These small
larvae were caught from July to September from
Georgia to North Carolina. It appears that C.
f/mhriata spawns from April to October through-
out the entire collection area on the Continental
Shelf and that most spawning is in waters of 46
m. (25 fath.) or less. Delineation of the spawning
area of C. pmbriata must await the collection or
observation of .snawning fish.

ACKNOWLEDGMENT

Elbert H. Ahlstrom of the BCF Fishery-Ocean-
ography Center, La Jolla, Calif., reviewed the
manuscript and made many helpful suggestions.
Assistance by various staff members of the labo-
ratory included review of the manuscript, prepara-
tion of figures 3 through 7, and preparation of
stained material.

LITERATURE CITED

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1879. On the young stages of some osseous fishes.
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Ahlstrom, Elbebt H.

1965. Kinds and abundance of fishes in the Cali-
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1957. Physical oceanographic, biological, and chemi-
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1956. Physical oceanographic, biological, and chemi-
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1926. Plankton of the offshore waters of the Gulf
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BiGELOw, Henry B., and William C. Schboedeb.

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1937. Chas canopsetta in the Atlantic ; a bathypelagic
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Colton, John B., Jr.

1961. The distribution of eyed flounder and lantern-
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1961 : 274-279.
Dannbvig, Alf.

1919. Canadian fish-eggs and larvae. In Johan
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74 pp.
Deubler, Eabl E., Jr.

1958. A comparative study of the postlarvae of thre.e
fiounders (Paralichthys) in North Carolina. Co-
pela 1958: 112-116.
GooDE, George Brown, and Tableton H. Bean.

1896. Oceanic ichthyology, a treatise on the deep-sea
and pelagic fishes of the world, based chiefly upon
the collections made by the steamers Blake, Alba-
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with an atlas containing 17 figures. U.S. Nat.
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Guthebz, Elmeb J.

1967. Field guide to the flatfishes of the family Both-
idae in the western North Atlantic. U.S. Fish
Wildl. Serv., Circ. 263, iv -|- 47 pp.
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1930. Development and life history of fourteen tele-
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U.S. Bur. Fish. 48 : 505-642.
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1940. A new record of two flounders, Etropus crosso-
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(Goode and Bean), with notes on postlarval char-
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Kyle, H. M.

1913. Flat-fishes (Heterosomata). Rep. Dan.
Oceanogr. Exped. Mediter. 2 : 1-150.
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MOORB, Emmexine.

1947. Studies on the marine resources of southern
New England. VI. The sand flounder, Lophopsetta
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NOBMAN, J. R.

1934. A systematic monograph of the flatfishes ( Het-
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OcHiAi, Akira, and Kunio Amaoka.

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APPENDIX

Table 1. — Selected measurements and counts of larval Cyclopsetta fimbriata

Measurements

Counts

standard
length

Head
length
(HL)

Body
depth
(BD)

Eye

diameter

(ED)

Upper Jaw
length
(UJL)

Lower jaw
length
(UL)

Snout
length
(SN)

Pelvic fin

origin to

tlpot

clelthrum '
bUnd-tide

ocular.«lde

Dorsal
fln
rays

Anal
fin
rays

Urn.

1.72

Mm.
0.64

HL

SL

32

Mm.

BD
SL

Mm.

0.20
.20
.22

ED
HL

37
46
37

Mm.

UJL
HL

LJL
Mm. HL

Mm.

SN
HL

Percent

Number

Number

1.76

0.42
.49

24

27

o.tn

.10

16
17

1.79

.69

33

1.89

2.01

.64
.69
.76
.69
.74
.74
.86
.76
.78
.81
.78
.73
.93
.76
.86
.86
.88

32
29
37
30
32
30
33
29
30
30
29
27
34
28
31
30
31

.64

32

.24
, .27
.29
.29
.29
.29
.34
.29
.29
.29
.27
.32

37
48
38
42
39
39
40
38
37
36
36
14

.07

11

2.01

Z08

.18
.12
.12

.12

20
17

16 .
16

3

2.33

4

2.33

4

2.46

4

2.60

4

2.60

.07
.12
.12
.10

9
16
15
13

3

2.64

.76
.81
.81
.73
.96
.64
.86
.91
.98

29
30
30
27
36
23
31
32
34

0.27
.27

36
33

0.42 64
.39 48
.34 44
.37 61
.42 46

3

2.72

3

2.72

3

2.72

4

2.72

3

2.76

.29
.29
.34
.34

38
34
40
39

.10
.17
.16
.16

13

20 .

17

17

2

2.79

4

2.83

.32
.32

37
36

.44 61

.47 63

3

2.87

83

6

2.91

4 . .

2.91

.83
.78
.93
.88
.86
.83
.83
.98

29
27
32
30
29
28
27
32

.86
.71
.98
.83
.86

30
24
34
29
29

.32
.29
.37
.34
.34
.32
.34
.37

39
37
40
39
40
39
41
38

.27
.24

33
31

.39 47
.42 64
.47 61
.44 60
.37 43
.39 47
.37 46
.42 43

.17
.12
.17
.12
.16
.12
.12
.12

21

IS .

18

14

17

14

14

12

3

2.91

3

2.91

120
86
83

6 . .

2.91

.37

42

3

2.96

4

2.96

.24
.27

29
33

3

3.03

.78
L03

26
34

3

3.03

4

3.10

4

3.10

.44

.32
.37
.39
.49
.37
.39
.37
.32
.39

37
34
41
40
48
38
39
35
36
38

.49
.34

42

37

.61 62
.41 47
.37 41
.49 60
.66 64
.42 43
.61 61
.49 47
.47 62

.34

.24
.12
.17

.22
.22
.24

29

26

13

17

21

22 .

24

e

3.10

.93
.91
.98

1.03
.98

1.00

L06
.91

1.03

30
29
32
34
31
31
33
28
31

100
100
100

4

3.10

.91
1.03
1.23
1.03
1.26
LIO

29
33
39
33
39
34

4

3.10

.34
.34

.32

36
33
33

3.14

7

3.14

6

3.22

6

3.22

.29
.32

28
36

6

3.30

.20
.16

22 .
16

4

3.30

LIO

33

100

6

See footnote at end of table.

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

281

Table 1. — Selected measurements and counts of larval Cyclopsetta fimbriata — Continued

standard
length

Measurements

Head
length
(hL)

Body
depth
(BD)

Eye

diameter

(ED)

Upper ]aw
length
CUJL)

Lower Jaw
length
(LJL)

Snout
length

(SN)

Pelvic fln

origin to

tip of

cleltnnun •
blind-tide

ocular-side

Counts

Dorsal
fln
rays

Anal
fln
rays

Mm.

3.34
3.36
3.38
3.41
3.42
3.48
3.48
3.48
3.48
3.49
3.49
3. M
3.54
3.64
3.64
3.61
3.61
3.67
3.67
3.73
3.76
3.80
3.80
3.88
3.88
3.88
4.06
4.06
4.06
4.11
4.11
4.11
4.24
4.24
4.24
4.24
4.30
4.37
4.43
4.43
4.43
4.43
4.49
4.66
4.62
4.62
4.62
4.62
4.76
4.76
4.76
4.81
4.81
4.87
4.87
4.94
4.94
4.94
4.94
6.00
6.06
5.06
6.06
5.06
6.19
5.32
6.32
5.32
6.44
6.44
5.44
5.67
5.89
6.01
6.01
6.08
6.14
6.29
6.39
6.39
6.50
6.60
6.70

Mm.
1.06

1.03

1.26

1.22

1.27

1.30

1.00

1.36

1.13

1.37

1.30

1.16

1.27

1.18

1.13

1.20

1.47

1.32

1.32

1.16

1.25

1.16

1.30

1.18

1.42

1.32

1.42

1.40

1.40

1.30

1.27

1.36

1.27

1.37

1.30

1.45

1.30

1.32

1.35

1.59

1.42

1.45

1.45

1.52

1.69

1.47

1.47

1.54

1.42

1.62

1.79

1.59

1.47

1.72

1.62

1.72

1.52

1.64

1.67

1.54

1.69

1.49

1.64

1.69

1.62

1.76

1.81

1.81

1.72

1.91

2.08

1.89

1.89

1.84

1.96

2.08

2.08

2.20

2.07

1.94

2.20

HL

SL

31

29

29

30

37

36

37

37

29

39

32

39

37

33

36

33

31

33

40

36

36

30

33

30

34

30

35

33

36

34

34

32

30

32

30

32

30

33

29

30

30

36

32

32

31

33

34

32

31

32

30

32

37

33

30

35

31

36

31

33

33

30

31

29

32

30

30

33

34

33

32

34

36

31

31

30

32

33

33

34

32

30

33

Mm.

1.10
.98
1.13
.98
1.45
1.30
1.22
1.30
1.16
1.36
1.27
1.67
1.35
1.25
1.47
1.30
1.22

1.47
1.64

1.64
1.62
1.15
1.35
1.40
1.64
1.69
1.49
1.46
1.64
1.35

1.64
1.69
2.11

1.89
1.76
1.86
1.67
1.59
1.72
1.98
1.79

2.25
1.72
1.81
1.64
1.91
1.96
1.67
1.72
1.81
1.96
1.86
1.74
2.16
2.33
2.08
1.94
2.16
2.46
2.13
2.13

2.20
2.20
2.45
2.87
2.60
2.23
2.35

BD

SL

33
29
33
29
42
37
35
37
33
39
36
47
38
36
42
36
34

40
44

41
43
30
36
36
40
39
37
36
37
33

1.69

38

1.67

39

1.42

33

1.72

39

1.57

34

1.64

36

2.08

47

36
34
46
41
38
39
33
33
36
41
37

46
36
37
33
38
39
33
34
36
38
35
33
41
43
38
37
39
42
35
35

36
35
38
46
40
34
36

Mm.

0.42
.34
.37
.37

ED
HL

40
35
38
36

Mm.

0.39
.32

UJL
HL

37
33

Mm.

0.61
.42
.49

LJL
HL

58
43
60

Mm.

0.17
.17
.20
.20

SN
HL

16
17
20
19

.42

34
30

.61
.54

49
44

.22
.34

18

.37

.42

34

28

.37

28

.44

34

.64

42

.29

22

.39
.37
.39
.39
.42
.44
.42

29
33
28
30
37
35
36
36

.39
.42
.69
.49
.34
.49
.37

29
37
43
38
30
39
31

.51
.64
.69
.56
.61
.59
.64
.49

37
48
60
43
44
46
46
43

.29

21

.37
.27
.24
.27
.27
.22

27
21
21
21
23
19

.39
.47
.39
.44

.42
.44
.42
.39
.47
.49
.47

.44
.47
.44
.39
.44
.49
.42
.47
.42
.47
.39

.47
.51
.44
.54
.47
.49
.54
.47
.47
.49
.64
.49
.49
.66
.61
.49
.49

.49
.47
.61
.49
.47
.49
.49
.54
.66
.54
.61
.54
.66
.66
.66
.61
.49
.49
.69
.69
.56
.66
.54

27
36
30
38
34
38
32
33
33
37
33

31
36
36
29
35
36
32
32
32
36
29

33
36
30
36
30
33
37
31
33
32
30
31
33
33
34
28
32

29
31
32
33
29
31
30
31
30
30
30
28
27
30
30
33
25
24
28
27
27
29
25

.56
.51

38
39

.64
.66

44

60

.61
.51

44
41

.66
.64

.59

67
51
61

.64

.44
.61
.54
.44

31
44
39
34

.69
.66
.64

.78
.86
.56

49
60
45
56
61
43

.47
.54

36
37

.64
.64

47
49
46

.34

.34
.32
.29
.32
.29
.24
.24
.32
.27
.34
.42
.32
.27
.20
.32
.20
.30
.32
.32

23

26
24
25
26
25
18
20
23
20
24
30
23
21
16
24
16
22
25
22

.37

.61

46
41

.32
.20

24
15

.49

35

.66

46

.22

16

.47
.56

32
37

.42
.39
.61
.61

.69

27
27
34
34
37

.64
.73
.73
.69
.69
.56
.59
.71
.78

44

48
54
47
47
36
42
47
44
43

.34
.39
.37

23
26
23

.61
.49
.49

40
34
28
32

.81
.71
.64
.61

47
47
37
40

.27
.29
.22
.32
.39
.37
.32
.39
.24
.34
.32

18
19
15
21
22
23
22
23
16
20
21

.61
.49
.51
.61
.61
.51
.64
.64
.66
.51
.66
.61
.69
.69
.61
.52
.64
.73

31

32
32
34
37
32
33
36
36
28
38
32
33
37
32
28
28
35

.73
.64
.61
.64

33
31
31

29

.76
.64
.69
.66
.76
.66
.71
.81
.91
.69
.78
.78

.81
.74
.74
.81

.78
.83

46
42
43
44
46
42
44
46
49
38
46
41
41
46
43
40
38
39
41
45
43
40
38

.49
.32
.32
.27
.39
.37
.34
.39
.47
.37
.44
.39
.47
.66
.51
.37
.49
.42
.49
.66
.47
.42
.44

29
21
20
19
24
23
21
22
26
20
26
20
23
30
27
20
25
20
24
25
23
22
20

Percent
100

71

88

100
71
76
88

125
83
83

88

"77'

113

71
88

82

"77'

80

71
80

80

76

77

77
100

77
'77"

126

77
85

80

83
86
71

77
85
83
76
85
92
77
83

Number

Number

8

8

6

9+

7

6

7+
14

7

8

7
14

9

8

8

7

6

3
14
10

8

8
10
11
7
10
7
8
9
12
9
8
20

16
16
46
20
60
63

66
74
66
68
66

68

16
2S
36

33
42
38
42

35

See footnote at end of table.

282

U.S. FISH AND WILDLIFE SERVICE

Table 1. — Selected measurements and counts of larval Cyclopsetta fimbriata — Continued

Measurements

Counts

Pelvic fin

Head

Body
depth

Eye

Upper law
length

Lower law

Snout

origin to

Dorsal

Anal

standard

leu

iKth

diameter

length

length

tip of
clelthmm •
blind-aldt
ocular-side

fln

fln

length

(HX)

(BD)

(ED)

(UJL)

(LJL)

(SN)

rays

rays

HL

BB

ED

UJL

LJL

SN

Mm.

Mm.

SL

.Mm. SL

Mm.

HL

Mm.

HL

Mm. HL

Mm.

HL

Perctnl

Number

NumbtT

6.70

2.08

31

2. 72 41

0.64

31

0.78 38

0.42

20

69

64

44

6 80

2.08
2.16

31
31

2.45 36
2. 45 36

.49
.66

24
26

. 86 41
.93 43

.42
.42

20
19

100

77

6.91

.71

33

39

7.01

2.20

31

2. 72 39

.66

25

.74

34

.93 42

.66

25

83

73

50

7.01

2.28

33

2.83 40

.61

27

.81

36

.98 43

.49

21

78

66

46

7.63

2.38
2.38
2.66

32
31
32

2.83 38
3.03 40
3.22 40

.69
.66
.69

29
28
27

.81

34

1.03 43
1. 03 43
1.10 43

.56
.69
.61

24
25
21

75
84
88

7 63

72
79

60

8.04

.93

36

62

8.04

2.64
2.83
2.91

33
34
33

3. 14 39
3.49 42
3. 69 42

.74
.74
.71

28
26
24

.91
1.00
1.00

34
36
34

1.10 42
1.22 43
1.15 40

.59
.74
.66

22
26
23

83
88
71

8.76

79

66

9.18

2.79

30

3. 30 36

.69

26

. .69

25

74

81

87

9.38

3.38

36

4.30 46

.71

21

1.00

30

1.35 40

.86

26

71

79

60

9.38

2.95

31

3.80 41

.74

25

1.03

36

1.22 41

.74

25

78

82

63

9.S9

3.49

36

4.24 44

.69

20

1.00

29

1.30 37

.81

23

92

77

64

9.79

2.91

30

3. 61 37

.71

24

.91

31

1. 18 41

.74

25

66

76

60

10.21

3.03

30

4. 11 40

.66

22

.98

32

1.15 38

.73

24

71

81

61

10.31

3.65
3.10

35

30

4. 62 45
4. 24 41

.81
.71

22
23

. 1.52 42
1.36 44

.88
.73

24
24

69
61

77
78

68

10.31

1.10

36

60

10.31

3.18

31

4.11 40

.74

23

1.10

36

1.32 42

.74

23

74

79

69

11.08

3.67

32

4.43 40

.78

22

1.16

32

1.42 40

.91

26

100

82

62

12.06

3.80

32

4.66 38

.86

23

.98

26

1. 35 36

.86

23

79

77

68

1Z23

3.99

33

4. 89 40

.91

23

1.32

33

1.71 43

.91

23

78

82

K

13.20

4.49

34

6.38 41

.86

19

1.42

32

1.84 41

1.18

26

73

82

61

13.63

4.18

31

6.26 39

.93

22

1.35

32

1.72 41

.98

22

82

84

81

13 g6

4.30
4.62

31
33

. .91
.98

21
21

1.25
1.69

29
34

1.71 40
1. 98 43

.98
1.05

23
23

66

92

14.02

5.61 39

80

60

14.18

4.76

33

6.01 42

.93

20

1.49

31

2.03 43

1.22

26

73

83

61

14.61

4.75

33

6.87 40

1.22

26

1.40

29

1.84 39

1.10

23

78

80

68

> Distance between the origin of the right side pelvic fln base and the tip of the cleltbnim divided by the distance between the origin of the left side pelvic
fln base and the tip of the clelthmm.

Table 2. — Average values for selected measurements and counts {y2~mm. size intervals to 5.0 mm. SL; 1-mm. intervals for
larger sizes) ; all specimens in a given size series were not necessarily used to compute the mean

Measurements

Counts

Pelvic fln

Head

Body

Eye

Upper Jaw

Lower law

Snout

origin to

Dorsal

Anal

Standard length

Specimens

length

depth

diameter

ieni

?th

length
(LJL)

length

tip of

fln

fln

(HL)

(BD)

(ED)

CUJL)

(SN)

clelthrum '
blind->lde
ocular-side

rays

rays

Range

Mean

Mean

nr.

Mean

BD

Mean

ED

Mean

UJL

Mean

LJL

Mean

SN

Mm.

Mm.

Number

Mm.

SL

Mm.

SL

Mm.

HL

Mm.

HL

Mm.

HL

Mm.

HL

Perceni

Number

Number

L60-L9fl

1.79
2.20
2.80
3.28
3.68

4

6
18
23

0.60
.69
.83
1.06
1.25

28
32
30
32
M

0.62
.64
.84
1.12
1.42

29
32
30
34
39

0.21
.28
.32
.38
.42

40
40
38
37
34

. 0.09

. .12

.13

.21

.29

17
16
16
20
?3

2. 00-2. 49

'6.'28'
.37
.49

"33
35

38

"o.'ii"

.60
.60

"49"

47
48

93

92

86

3.8
3.4
5.2
6.6

2. 60-2. 99

3 00-3 49

3. 60-3. 99

4. 0O-4. 49

4.25
4.78
6.30

1.37
1.65
1.70

32
32
32

L59
1.79
1.98

37
38

38

.44
.50
.51

33
32
,30

.48
.62
.57

35
33
,33

.66
.68
.76

48
44
44

.29
.33
.,39

21
21
23

78
88
81

7.5
12.1
14.3

4.50-4.99

6.00-5.99

16.0

8.00-6.99

6.42

2.04

.32

2.40

37

.66

28

.64

32

.84

41

.46

•a

81

64.8

37.0

7.00-7.99

7.30

2.31

32

2.85

39

.63

27

.79

35

.99

43

.65

24

80

70.3

48.6

8.00-8.99

8.27

2.74

33

3.38

41

.72

26

.96

;«

1.14

42

.65

24

82

79.0

59.0

9.0O-9.99

9.46

3.10

33

3.85

41

.71

Zi

.98

31

1.26

40

.77

25

76

79.0

58.8

10. OO-IO. 99

10.28

3.24

32

4.27

42

.73

22

L06

,34

i.M

42

.77

24

69

78.8

69.6

11.00-11.99

11.08

3.57

.12

4.43

40

.78

22

1.15

32

1.42

40

.91

2,')

100

82.0

62.0

12.00-12.99

12.14

2

3.90

32

4.72

39

.88

23

1.15

30

1.53

40

.88

23

78

79.5

58.0

13.00-13.99

13.63

3

4.32

,12

5.32

40

.90

21

1.34

31

1.76

41

1.05

24

73

83.0

8L0

14.00-14.99

14.24

3

4.71

33

5.80

40

1.04

22

1.49

31

1.95

42

1.12

24

81

8L0

69.7

> Distance between the origin of the right side pelvic fln base and the tip of the clelthmm divided by the distance between the origin of the left side pelvic
fln base and the tip of the clelthmm.

LARVAL BOTHID FLATFISH AND SPOTFIN FLOUNDER

283

CONTROL OF OYSTER DRILLS, EUPLEURA CAUDATA AND
UROSALPINX CINEREA, WITH THE CHEMICAL POLYSTREAM

BY CLYDE L. MACKENZIE, JR., FISHERY BIOLOGIST

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY
MILFORD, CONN. 06460

ABSTRACT

Five experimental and 10 commercial treatments of
oyster beds In four States were made with Polystream.
On a typical bed, where water currents were less
than 2.7 km. per hour, Polystream killed about 85
percent of the thick-lipped drill, Eupleura caudata,
and 66 percent of the Atlantic oyster drill, Vrosalpinx
cinerea. A significantly higher percentage of oyster
drills was killed by treatments made in late April and
early May rather than later in the summer. Oyster

drills that survived did not feed for several months.
The number of drills remained low for at least 2 years.
Polystream treatments killed only small percentages of
fish, small clams, Mercenaria mercenaria, crabs, and
other Invertebrates. After a treatment, oysters, Crassos-
trea virginica, clams, and other organisms had small
residues of Polystream In their tissues but gradually
lost these residues. Growth of oysters was normal on
treated beds.

Boring gastropods, known as oyster drills, and
starfish, Asterias forhesi, are the most, serious pred-
ators of oysters in Long Island Sound. The drills
prey heavily on oysters, Crassostrea virginica,
along the entire Atlantic Coast, from Canada to
Florida, and in certain areas of the Pacific Coast.
Where they are extremely numerous, oyster drills
destroy nearly all oysters on commercial beds. In
Long Island Sound, however, drills usually reduce
the number of oysters to such a level that most
beds are of marginal value commercially.

This article summarizes laboratory and field
experiments made during the development of a
control method of oyster drills for use on com-
mercial oyster beds in southern New England and
New York; it includes the results of ,15 treatments
during 1961-67.

HISTORY OF DEVELOPMENT OF METHOD

All early phases of work on the development
of a method of control of oyster drills by use of
Polystream, including the initial testing of chem-
icals, was done by the biological laboratory at
Milford, Conn. Field tests and commercial appli-
cations of Polystream were made under the
inspection of the author in the States of Connecti-
cut, New York, Rhode Island, and Massachusetts.
Additional independent laboratory and field stud-
ies were later made in Virginia.

Published May 1970.

FISHERY BULLETIN: VOL. 68, NO. 2

EXPERIMENTAL WORK AT MILFORD

In 1946, the Fish and Wildlife Sfervice biologi-
cal laboratory, Milford, Conn., began a program
of screening organic chemicals with the goal of
eventually developing a method to control oyster
drills (Loosanoff, 1960). A method was sought
that would kill oyster drills, but would not harm
oysters, clams, Mercenaria mercenaria, and other
organisms on a shellfish bed, and also would not
leave residues in tissues of shellfish that would be
harmful to man. Tests were made in the laboratory
and the field.

Laboratory Tests

Loosanoff, MacKenzie, and Shearer (1960a,
1960b) reported that chlorinated benzenes, such as
monochlorobenzene, orthodichlorobenzene, para-
dichlorobenzene, trichlorobenzene, tetrachloro-
benzene, and their mixtures, are toxic to several
species of marine gastropods, including the thick-
lipped drill, Eupleura caudata, and the Atlantic
oyster drill, Urosalpinx cinerea. These chemicals
were- selected for further tests because they were
toxic to snails, virtually insoluble in sea water,
and of sufficient density to settle to the bottom of
the Sound. The last two characteristics reduced
the chance of damage to any but bottom-dwelling
organisms whose soft parts contact the chemicals
directly. Small quantities of Sevin (1-naphthyl-

285

N-methylcarbaraate) were added to the chlorin-
ated benzenes to increase their killing effect on the
snails. In laboratory experiments, orthodichloro-
benzene mixed with dry sand in the ratio of 1 to 19,
by volume, and then spread over shallow pans
killed most oyster drills ; and when used to form a
barrier in small troughs it prevented them from
crossing the barrier for several months.

Ijoosanoff, MacKenzie, and Davis ' stated that
for 14 months small barriers consisting of ortho-
dichlorobenzene and sand continued to affect oys-
ter drills on contact but were not toxic to larvae
and juveniles of sea squirts, Molgula manhattensh,
common shipworms. Teredo sp., Atlantic oyster
drills, eastern white slippers, Cr&pidiila plana,
and mud blister worms, Polydora sp., which set
and grew within 2.5 cm. (1.0 inch) of the barriers.
These observations showed that orthodichloroben-
zene was only a contact poison. In large outdoor
troughs siltation reduced the effectiveness of chlo-
rinated benzenes by forming a covering layer that
kept the oyster drills from touching the chemicals.

Field Tests

Loosanoff (1961) reported that oyster drills can
be greatly reduced in numbers by spreading chem-
ically treated sand over shellfish beds. The combi-
nation that gave good results consisted of 95
percent dry sand and 5 percent orthodichloroben-
zene containing 1 to 3 percent, by weight, of Sevin.
The chemicals were mixed with the sand in large
commercial cement trucks. The treated sand,
loaded on the deck of a boat, was then spread over
the oyster bed by a Iiigh-pressure stream of water.

Davis, Loosanoff, and MacKenzie ^ reported the
results of treatments of several small oyster beds.
They emphasized the effects of chemical treat-
ments on organisms other than oysters and clams.
On July 16, 1961, a bed of about 1.6 ha. (4 acres)
in Great South Bay, Long Island, N.Y., was
treated with 9.5 kl. jjer hectare (5 yards per acre)
of sand mixed with 1.9 hi. (50 gallons) of ortho-
dichlorobenzene containing 6 kg. (13 pounds) (2
percent by weight) of Sevin. As the sand'de-

I Loosanoff, V. L., C. L. HacEenzle, Jr., and H. C. Davis.

1960. Progress report on chemical methods of control of moUnscan
enemies. Bur. Commer. Pish. Blol. Lab., Mllford, Conn., Bull 24
(8). 20 pp.

•Davis, H. C, V. L. Loosanoff, and C. L. MacKenzie, Jr.

1961. Field tests of a chemical method for the control of marine
gastropods. Bur. Commer. Fish. Blol. Lab., Mllford, Conn., Bull.
26 (3), 9 pp.

scended, several small fish were killed and common
jellyfish were carried to the bottom. Shortly after
tlie sand reached the bottom, sea squirts were
found partially contracted ; oyster drills and other
snails were greatly swollen; and a number of
liermit crabs, Pagumn sp., and mud crabs, Neo-
panope texana, were dead. They did not determine
whether this experimental treatment eventually
killed the oyster drills. Another bed, which was off
the east end of Long Island in 9 m. of water, was
treated in like manner. Because of strong water
currents over the area, little sand actually reached
the bottom that was to be treated and, as a result,
the treatment was not effective. This failure indi-
cated that in an area with strong currents it was
very difficult to control oyster drills with sand
treated with a chlorinated benzene.

In treatments along the Connecticut shore the
effects of the chemicals on animals inhabiting the
bottom varied somewhat depending on location of
the bed. In open waters, divers noticed only a small
effect on fish, hermit crabs, mud crabs, and anne-
lids. In ai-eas where waters were shallower and
currents slower, however, the effect was greater.
In all tests, fish, hermit crabs, and mud crabs fed
and moved normally in an area within a few days
after a treatment. Fish, perhaps attracted by the
exposed white feet of swollen gastropods, were
more numerous after a treatment. Most pelagic
common shrimp that were in the immediate area
at the time the treated sand was spread were ap-
parently killed. Once the chemicals were on the
bottom, however, shrimp moved in again and re-
mained uninjured. Oysters and mussels, Mytilus
edidis, when present, were pumping normally with-
in an hour of the treatment. Starfish, Asterias for-
besi, were irritated by treated sand falling on their
aboral surface, and small sores soon appeared. In
a number of treated areas starfish consumed swol-
len oyster drills and northern moon shells, Poli-
nices sp. Davis et al.' also reported that the treat-
ment did not reduce the intensity of setting of
oyster and starfish larvae in the area.

Polystream* (trademark of Hooker Chemical
Corporation for a mixture of polychlorinated ben-
zenes containing a minimum of 95 percent total of
active triclilorobenzene, tetrachlorobenzene, and

' See footnote 2.

< Trade names referred to In this publlcatloD do not Imply
endorsement of commercial products.

286

U.S. FISH AND WILDLIFE SERVICE

pentachlorobenzene, and having a last crystal point
of 18° C. ± 3° C), a less expensive product than
oithodichlorobenzene, was used for the first time on
experimental beds in New Haven Harbor, Conn.,
in the summer of 1961. I made field tests to com-
pare the effectiveness of orthodichlorobenzene and
Polystrcam and to determine the minimum quan-
tity of chemically treated sand needed to control
oyster drills. Sevin was added to both types of
polychlorinated benzenes at the rate of 2 percent
by weight, and a total of 1.9 hi. of either ortho-
dichlorobenzene or Polystream was mixed with
each 9.5 kl. of sand. The two chemical-sand mix-
tures were spread over eight 0.4-ha. beds at rates
of 1.9, 5.1, 9.5, and 19 kl. per hectare. Drill traps
were used to estimate the effects of treatments on
populations of oyster drills and mud crabs.

SCUBA divers studied the effects of these
treatments. Their observations indicated that
treatments of 9.5 and 19.0 kl. per hectare of either
orthodichloi'obenzene and Sevin or Polystream and
Sevin caused all visible gastropods, including
thick-lipped drills, northern moon shells, knobbed
whelks, Biisycon carica^ channeled whelks, Busy-
con ccmalietdatum, and New England nassas, Nas-
sarius trivittatvs, to become swollen (snails listed
in order of importance as shellfish predators; the
New England nassa is not a predator). Appar-
ently, the latter three species of predators were
compelled to emerge from their usual position
buried in the bottom. A number of pipefish,
Syngnathus fusc^is, mud crabs, and shrimp were
either partially paralyzed or behaved abnormally.
Small flounders, Pseudopleuronectes americanus,
however, swam around apparently unliarmed.
Three days later these effects wei'e more evident;
all visible gastropods were either swollen and being
eaten alive by starfish or they had already died.
The pipefish, mud crabs, and shrimp, nevertheless,
had either recovered or had been replaced by otiiers
from surrounding areas. Subsequent observations
revealed that starfish were gradually consuming
the remaining swollen gastropods. Thus, the area
was left with a large number of empty gastropod
shells which gradually disappeared ; a lot with 42
shells of the northern moon shell per 50 m.^ of
bottom on July 3, for example, had none by July
18. Presumably, the shells had been occupied by
hermit crabs and carried away.

Catches of oyster drills on traps indicated that

CONTROL OF OYSTER DRILLS WITH POLYSTREAM

applications of 9.5 and 19.0 kl. of treated sand
per hectare had killed nearly all drills and that
the mixture of Polystream and Sevin was more
effective than the mixture of orthodichlorobenzene
and Sevin. The numbers of mud crabs on traps
before and after treatments indicated that they
were not harmed by the treatments. As a result,
we thereafter used Polystream exclusively, aban-
doned orthodichlorobenzene, and standardized the
treatment rate at 9.5 kl. per hectai'e.

Increased catches of drills, along the borders of
lots several weeks after the treatment, indicated
that drills were migrating into the lots from sur-
rounding areas. This observation suggested that
to ensure protection of an oyster bed from oyster
drills, a zone perhaps 25 or more meters wide out-
side the bed, as well as the bed itself, should be
treated, and that treatment of a single large bed
would be more efficient than treatment of a number
of small beds.

Polystream was used to treat beds inhabited by
oysters and clams that are later consumed by
humans. It was necessary, therefore, to determine
whether these shellfish retained any residues of this
chemical. In practice, however, only those beds
with seed oysters on them are treated with Poly-
stream. These oystei-s are transplanted to untreated
beds at least 4 months before harvest. It was also
desirable to know whether other organisms inhab-
iting treated beds, particularly those that might
be taken by sport or commercial fishermen, retain
residues of Polystream.

To determine whether oysters, clams, or other
animals or plants accumulated and then lost resi-
dues of Polystream, I studied specimens that were
collected from treated beds by divers or by dredg-
ing. I also studied northern lobsters, Homurus
americanus, in cages to determine whether residues
would be lost after a period of time in water free
of Polystream. The U.S. Testing Company of
Hoboken, N.J., determined the quantity of Poly-
stream in tissues of the plants and animals through
use of a technique developed by Schwartz, Gaffney,
Schmutzer, and Stefano (1963).

In 1961 and 1962, 1 determined the quantities of
Polystream in oysters and clams from a 0.4-ha. lot,
treated with 1.9 hi. of this chemical. In oysters the
residue was 1.8 p.p.m. (parts i^er million) 8 days
after the treatment. It diminished slowly until
none was detected 119 days later. Residues in clams

287

417-060 O - 71 - 8

Table 1. — Residues of Polyslream in oysters and clams on
a 0.4-hectare bed in New Haven Harbor, Conn., after it
was treated with Poly stream-sand, June S7-S9, 1966

Table 2. — Residues of Polyslream in oysters collected at
various distances from lot 42, Norwalk, Conn. Lot was
treated on August 24, 1966

Time after treatment

Residues

In oysters

In clams

8

Dayi

P.V-m.
1.8

P.p.™.

14

2.3

1.7

28

0.2

0.6

56

0.3

0.3

77

0.7

0.7

119

<0.1

<0.1

33«

<0.1

<0.1

455

0.1

0.1

were at similar levels and were lost at similar rates
(table 1).

Oysters removed from a treated bed and re-
jjlanted on an untreated area lost any residue of
Polystream within a Aveek. Nevertheless, the first
few times oysters that had once grown on a treated
bed were to be harvested, they were analyzed for
any possible residue of Polystream before clear-
ance for marketing. None of these oysters had
residues.

In 1966, 1 determined the rates of loss of Poly-
stream in oysters at several distances from lot 42,
Norwalk, which was treated on August 24, 1966,
and where strong currents had washed many gran-
ules off the lot. After 8 days, residues were as high
as 0.3 p.p.m. in oysters 150 m. from the lot and
were higher in oysters closer to the lot. On October
13, however, only those oysters 15 m. or closer to
the lot showed any residue. At this distance the
level had dropped from 1.7 p.p.m. in September
to 0.2 p.p.m. On December 8, 106 days after the
treatment, no residues were detected in any oysters
outside the treated lot (table 2) .

To determine the quantity of Polystream in tis-
sues of other organisms inhabiting an oyster bed,

Distance from lot 42

Date of collection (1966)
Sept. 1 Oct. 13 Dec. 8

15

A/.

P.p.m.
1.7

P.p.m.
0.2
<.l
<.l
<.l

P.p.m.
<0. 1

30

0.4

<.l

75

0.2

<.l

150

0.3

<.l

I made periodic collections from treated beds. All
species of animals or plants collected within a year
had accumulated a small quantity of Polystream.
Residues of Polystream eventually diminished in
those species, namely, the bay scallop, Pecten irra-
(liaTis, hermit crab, and sea lettuce, Ulva sp., where
comparisons between time intervals were made
(tables).

By holding northern lobsters in a cage for a
week in the center of a bed 45 days after it was
treated, I found that they do accumulate a small
residue of Polystream (1.4 p.p.m.) when retained
in a treated area. A group of lobsters held on the
treated lot for a week and then held on an un-
treated area for another week did not have any
residue. Thus, lobsters may accumulate a small
quantity of Polystream while they inhabit a
treated bed, but they lose it soon after they leave
the bed.

To determine mortality rates of oysters because
of possible predation by oyster drills on treated
beds, divere collected oysters periodically on sev-
eral beds. The divers either swam across the center
of beds for a distance of perhaps 150 m., gathering
about 30 clusters of oysters randomly, or they col-
lected oysters and all other material from within
a metal ring enclosing either 1 or 1.5 m.= of bottom
from 10 different sections.

Table 3. — Residues of Polystream in animals and plants inhabiting oyster beds in Conn, and N.Y. treated with Polystream

Animal or plant

Location

Time art«r Residue
treatment

Northern puffer {SphatToides maculaius) New Haven (State spawning bed).

Sea robin {Prionotua carolinus) New Haven (State spawning bed).

Sand shark (.Carcharias taurue) _ _. New Haven (lot 152)

Starflsh (Asteri<u forbesi) New Haven (lot 16)

Bay scallop {PecUn irradiant) Sag Harbor (lot S)

Bay scallop Sag Harbor (lot S)

Northern moon shells iPolinictB sp.) Northport Got 1) ,

Hermit crab (Pojurus sp.) New Haven Oot 162)

Hermit crab.

Mud crab (Neopanope teiana) __ New Haven (lot 152).

Red sponge (Microciona proliftrd) New Haven (lot 13)..

Spaghetti grass (Codium fragile) Sag Harbor (lot S)...

Sea lettuce (Wcasp.).. New Haven (lot 162).

Sea lettuce. Sag Harbor OotS)...

Days

P.p.m.

31

6.9

26

8.4

8

S.0

30

1.8

6

13.6

260

0.9

1 hour

60.0

1

12.3

26

2.2

1

20.6

26

2.3

260

0.1

1

8.9

6

0.3

288

U.S. FISH AND WILDLIFE SERVICE

EXPERIMENTAL RESULTS IN OTHER AREAS

Wood and Roberts (1963) reported that in the
laboratory Polystream alone killed 50 to 78 percent
of large Atlantic oyster drills from the Eastern
shore of Virginia and that a mixture of Poly-
stream and Sevin killed 66 to 77 percent. Thus,
they felt that Sevin was not needed. They also in-
dicated that if oyster drills are in poor condition,
they are more easily killed by Polystream. There-
fore, they recommended that treatments should be
made in the early spring when oyster drills are
emerging from winter dormancy.

Haven, Castagna, Chanley, Wass, and Whit-
comb (1966) reported the results of a field test in
Hog Island Bay, Va. A 0.4-ha. section of bottom
was treated with 9.5 kl. of sand mixed with Poly-
stream containing 2 percent of Sevin. The oyster
drills were not killed by the treatment, they depos-
ited egg cases at a normal rate, and they destroyed
as many oysters on the treated plots as on un-
treated control plots. I believe the reason for the
ineffectiveness was that the treated sand soon sank
as deep as 4 cm. into a layer of silt on the bed ; thus,
the drills could move over the bottom without
contacting significant quantities of the chemicals.
Haven et al. (1966) also reported that the Poly-
stream-Sevin treatment had a deleterious effect on
other living organisms and that growth of oysters
and clams was apparently retarded.

RESULTS OF COMMERCIAL
TREATMENTS

I used se\ eral methods to evaluate the effective-
ness of treatments in killing oyster drills and their
effects on organisms inhabiting oyster beds. Ten
commercial treatments of oyster beds are described.

METHODS USED IN EVALUATION

Oyster companies used a standard rate of 1.9 hi.
of Polystream per hectare (50 gallons per acre) of
oyster bed. In early treatments, they mixed Sevin
with Polystream at the rate of 2 percent by weight.
The Polystream was mixed with either dry sand or
a granular clay [the mixture is termed Polystream
(Granular)] which carried it to the bottom and
dispersed it.

Several techniques were used to evaluate the
effects of treating commercial oyster beds with

Polystream and Sevin. On numerous occasions
SCUBA divers examined each bed carefully for
20 to 30 minutes to determine the gross effects of
the chemicals on all visible living animals and
plants. Often they made the first examination
within an hour of a treatment and followed it by
many subsequent periodic examinations during the
next 2 to 3 years. They examined certain beds once
a month during collections to determine survival
rates of oysters.

In 1961-63, drill traps were used to estimate the
effectiveness of treatments in controlling oyster
drills. Because mud crabs enter drill traps in large
numbers, I estimated the effect of treatments on
these populations.

From 1964^67 I made quantitative determina-
tions of the number of drills per unit area with a
hydraulic sampler, which pumps through a mesh
bag all bottom material from within a ring enclos-
ing areas of 1 or 1.5 m.^ All coarse material is
retained within the bag, carried to the surface, and
sorted. This sampling method, which is carried out
by divers, provides an accurate measure of the
density of oyster drills and other mollusks on a
shellfish bed if enough samples are taken. I took
about 25 random samples on beds 2 to 6 ha. in size
a few days before and again about a month after
a treatment. I determined the percentage of oyster
drills killed by comparing their densities before
and after treatments. Actually, the Atlantic oyster
drills on many beds were too few in number for
me to determine the precise percentage of this
species killed.

EFFECTS OF TREATMENTS IN DIFFERENT AREAS

Ten commercial treatments in four States were
made with Polystream. Each treatment will be
described separately by areas.

Area 1: Lewis Gut, Bridgeport, Conn., 1962

Lewis Gut is a long narrow arm of Bridgeport
Harbor. The water is about 1 to 3 m. deep at low
tide, and maximum currents run at about 4.5 km.
per hour (2.5 knots). On June 27 and 29, 1962,
an oyster company treated 12 ha. of this area with
a mixture of Polystream-Sevin and sand.

Eifect on gastropods. — Divers observed that
within an hour after the treatment nearly all thick-
lipped drills, Atlantic oyster drills, northern moon
shells, and both knobbed and channeled whelks

CONTROL OF OYSTER DRILLS WITH POLYSTREAM

289

were swollen ; a few weeks later most of these gas-
tropods, as well as mud snails, were dead.

To evaluate the number of oyster drills killed,
I used drill traps. The catch per trap per week fell
from 16 drills before the treatment to 0.4 drill
afterwards. One year later the average catch of
oyster drills increased, primarily by recruitment
of young drills, to about two per trap per week.
In 1964, the average catch rose to about 5 per trap
per week, again as a result of recruitment by young
oyster drills; by July 1965 it rose to 13 per trap
per week (fig. 1).

E-ffect on associated animals. — During 1961,
divers observed that only a small number of fish —
primarily sea robins, Prionotns caroUnus; pipe-
fish; flounders; mummichogs, FundvZus heterocli-
tus; and eels, Anguilla rostrata — were present in
Lewis Gut before or after the treatment. Immedi-
ately after the application of chemicals only the
pipefish appeared to be affected, i.e., more slug-
gish than usual. A few hours later, however, mum-
michogs were dying along the shore as some of the
finer sand coated with Polystream was churned up
in the water by wave action.

This treatment had a slight effect on several

organisms. Hermit crabs were affected to some
degree. A number of them had no shells; appar-
ently, a small quantity of treated sand entered the
shell and caused enough irritation to compel them
to leave. The abdomens of a number of these crabs
had been bitten off. Most mud crabs were unaf-
fected, but between 5 and 10 percent were twitch-
ing abnormally immediately after the treatment.
The treatment also compelled many nereids and
nemerteans to emerge from their burrows. A few
weeks later all animals not killed by the initial
treatment appeared to be normal.

Catches on drill traps indicated that the treat-
ment did not reduce the population of mud crabs.
The weekly catch of these crabs on drill traps fol-
lowed the same pattern each year: Each trap
caught an average of about 15 crabs per week in
May, June, and July ; about 10 crabs during Au-
gust; and (because of recruitment of young crabs)
18 to 23 crabs in the fall (fig. 2) .

Effect on predation. — In midsummer of 1962 an
oyster company planted 3,500 hi. ( 10,000 bushels)
of seed oysters in Lewis Gut. Periodic examination
of the oysters through early winter showed little
loss from predation by oyster drills.

290

JUNE JULY AUG. SEPT. OC

1962
Figure 1. — Catches of oyster drills on traps in treated area of Lewis Gut, Bridgeport, Couu.

U.S. FISH AND WILDLIFE SERVICE

MAY JUNE JULY AUG, SEPT. OCT. NOV.

1962

MAY JUNE JULY AUG. SEPT. OCT.

1963

JULY AUG. SEPT. OCT.

1964

Figure 2. — Catches of mud crabs on traps in treated area of Lewis Gut, Bridgeport, Conn.

Area 2: Northport Harbor, N.Y., 1963

Noithpoit Harbor on the north shore of Long
Island is about 6.5 km. long. The oyster beds are in
water 4.5 to 7.5 m. deep at low tide, and water cur-
rents rarely exceed 1.8 km. per hour.

On May 21 and 28, 1963, 1 made a series of com-
parative treatments. The i^urpose was to determine
whether Drillex (a mixture of Polystream and 2
percent by weight of Sevin) is more lethal to oyster
drills than Polystream alone. The experiment had
four 2-ha. lots. Two lots received an application
of 11.5 kl. of treated sand per hectare. They were
designated as 1 (for Polystream) and 1 x (for
Drillex). The remaining two lots which received
19.0 kl. of treated sand per hectare were desig-
nated as 2 and 2 x.

Effect on gastropods. — -The treatments had a
very deleterious effect on gastropods. A few hours
after the treatments, divers observed that nearly
eveiy visible gastropod on all four lots was
swollen ; on lots treated with Drillex, however, the
drills expanded faster and sooner. Ten days after
tlie treatments, most thick-lipped drills were
drawn deeply into their shells but some were still

swollen. Northern moon shells were observed in
tliree conditions — partially expanded, dormant
with their operculum flush with their aperture,
and dead. Twenty-three days after the treatments
divers noted that all visible thick-lipped drills
were dead on lots 2 and 2 x, and only a small num-
ber were alive on lots 1 and 1 x. No northern moon
sliells were observed either dead or alive; even
their shells were gone. Hermit crabs had probably
carried them off the bed.

Because many flounders were swimming over
the beds and crabs were numerous when the snails
were swollen, these fish had ample opportunity to
feed on the paralyzed drills. I observed no snails
being consumed, however; instead, they appeared
to die directly from the toxic effects of the
chemicals.

Examination of the bottom showed that Poly-
stream alone killed almost as many oyster drills as
Drillex.

Effect on associated animals. — Divers observed
that during the applications of Drillex-sand a
small number of flounders, many hermit crabs,
sin-imp, and annelids were killed; however, 10

CONTROL OF OYSTER DRILLS WITH POLYSTREAM

291

days later they saw a large number of healthy
flounders (only about 1 percent were still affected)
and mud crabs on the two treated beds.

Polystreaih was used m all later commercial
treatments because these experiments showed it
was much less toxic than Drillex to associated
animals, particularly arthropods.

Effect on predation. — I made no careful quanti-
tative determinations; however, periodic observa-
tions of the lot indicated that predation by oyster
drills on oysters on the treated lots during 1963
was slight.

Area 3: Northport Harbor, N.Y., 1%5

On April 28, 1965, which was 2 years after the
initial treatment, lot 1 was treated again with
Polyst ream-sand.

Effect on gastropods. — Eight days after the
treatment divers observed that every snail was
swollen.

The treatment killed 64 percent of the oyster
drills (77.2 percent of the thick-lipped drills and
8.6 percent of the Atlantic oyster drills) and re-
duced their numbers from 31.5 to 11.4 per m.*
(table 4).

Effect on associated animals. — Nine days after
the treatment divers found 6 stunned adult floim-
ders and one dead juvenile on the bed among about
50 healthy floimders of mixed ages. The only her-
mit crab they saw was healthy.

Before treatment the number of young clams
(5-7 mm. long) on the bed was 158 per square
meter ; 28 days after the treatment the number of
clams was 125 per square meter. Thus, apparently
only about 20 percent were killed.

Effect on predation. — I made no quantitative de-
terminations. Periodic observations of the lot indi-
cated, however, that predation by oyster drills
during 1965 was slight.

Area 4: Northport Harbor, N.Y., 1966

On May 9, 1966, 3 years after the initial treat-
ment, lot 2 was treated again, this time with Poly-
stream (Granular).

Effect on gastropods. — ^Three days after the
treatment divers found that all thick-lipped drills,
Atlantic oyster drills, northern moon shells, and
New England nassas were swollen.

The treatment killed 92 percent of the oyster
drills (94.5 percent of the thick-lipped drills and
71.7 percent of the Atlantic oyster drills) and re-
duced their numbers from 27 to 2.1 per square
meter (table 4).

Effect on associated animals. — No observations
were made by divere.

Effect on predation. — I made no careful quan-
titative determinations. Several observations of
the lot indicated, however, that predation by oyster
drills during 1966 was slight.

Table 4. — Density of oyster drills, before and after treatments with Polystream and sand or Polystream (Granular), on oyster

lots in N.Y., Conn., R.T., and Mass., 1966-67

Lot DO. and area

Date of
' (hectares) treat-
ment

Formulation

Drills per m.'

Before treatment

After treatment

Killed •

E. caudttta U. cinerea E. eaudata V. clnerea

E. caudata U. cinerea

Both

species

combined

25(3.2) 4/30/65

1(2.4-3.2) 4/28/65

2(2.0) 6/0/66

208(1.8) 9/15/66

I8» 4/ ?/67

40» 4/29/67

49> 4/29/67

42(2.8) 5/ 1/87

50> 6/ 1/67

19 Control

RI(0* 6/ 1/67

FP(0.08) - 5/29/67

FP Control

Poly-sand.-.
Poly-sand.-.
Poly (Qran.)
Poly (Oran.)
Poly (Oran.)
Poly (Gran.)
Poly (Oran.)
Poly (Gran.)
Poly (Qran.)

None

Poly (Gran.)
Poly (Gran.)
None

Number Number Number Number Percent Percent Percent

3.3 0.9 0.0 0. S 100.0 4&6 88.7

25.2 6.3 5.7 5.7 77.2 8.6 64.0

24.1 2.9 1.3 0.8 94.5 71.7 92.3

14.0 J0.9 77.5

7.6 0.9 2^4 1.6 68.0 520

12.0 4.7 2.2 1.6 82.2 66.7 77.8

6.6 0.7 a 9 0.0 84.6 100.0 86.4

3.0 0.3 0.9 1.0 66.7 .. 43.6

12.6 1.3 1.7 a 6 86.4 65.6 83.6

188 0.7 19.6 1.7

ao 6.5 ao ao loo.o 100.0

0.0 40.8 0.0 2.2 94.5 94.6

0.0 37.2 0.0 33.2

'Lot25,OysUrBay,N.Y.;Lotsl,2, Northport, N.Y.; Lots 205, 18,40, 49,42,50, and 19, Norwalk.Conn.; RI, Charlestown Pond, R.I.; FP, Fresh Pond

Mass.

' Actual number of hectares treated on these beds Is unknown, bat I estimated that areas treated ranged between 1.2 and 6.0 hectares.

• Both species.

< If count increased, no perceutage is given for tbi? species

292

U.S. FISH AND WILDLIFE SERVICE

Area 5: Sag Harbor, N.Y., 1963

A 0.4-ha. lot along the eastern shore of Shelter
Island in Sag Harbor was treated. The water over
tliis lot is about 3 m. deep at low tide, and maxi-
mum curi'ents are about 2.7 km. per hour.

On September 27, 1963, Polystream (Granular)
was used for the first time to control oyster drills.

Effect on gastropods. — Within an hour of tlie
treatment divers noticed that all visible snails were
at least partially swollen. A week later divers ol)-
served many affected thick-lipped drills, Atlantic
oyster drills, northern moon shells, and both knob-
bed and channeled whelks.

Ten drill traps were placed on the treated lot and
an adjacent area before the treatment. The traps
in each area collected between 200 and 300 oyster
drills. After the treatment, traps were examined
only once. They collected only 10 oyster drills on
the treated area but gathered 127 on the control
area. I did not count the two species of drills
separately.

Effect 011 nxsockifed anbmds. — Divers observed
that the treatment did not affect associated animals
and plants, such as flounders, bay scallops, mud
crabs, and sea lettuce.

Effect on predation. — No determinations were
made.

Area 6: Oyster Bay Harbor, N.Y., 1965

Oyster Bay Harbor on the north shore of Long
Island is about 8 km. long. The oyster beds are
in water from 3.5 to 10 m. deep at low tide and
water currents do not exceed 2.7 Imi. per hour.

On April 30, 1965, lot 25, 3.2 ha., was treated
with Polystream-sand.

Effect on gastropods. — The divers made no ob-
servations. The treatment killed 89 percent of the
oyster drills (100 percent of the thick-lipped drills
and 46.6 percent of the Atlantic oyster drills) and
reduced their numbers from 4.2 to 0.5 per square
meter (table 4).

Effect on associated animals. — The divers made
no observations.

Effect on predation. — Lot 25 was planted with
small oysters in 1965, 1966, and 1967. Each year
oysters were grown on the bed during their first
summer of life and then transplanted to another
bed the following spring. WTien first planted in
June, July, August, and early September, the oys-
tei-s were about 5 to 10 mm. long. By late Novem-
ber most of them had grown to 40 to 60 mm.

Predation on the oysters w-as light in each of the
3 years. On October 1, 1965, examination of the
bed showed that less than 5 percent of the oysters
had been killed by oyster drills and starfish com-
bined. On July 22, 1966, divers observed that no
oystei-s had been drilled. By October 9, 1967, oys-
ter drills and starfish had killed 4.3 percent of the
oysters on one section of the lot and 8.1 percent
on another section. Predation by starfish was re-
sponsible for most of the mortality.

Area 7: Norwalk Harbor, Conn., 1966

Norwalk Harbor is interspersed with se\'eral
small islands that protect oyster beds in channels
and bays from storms. Water over the beds is from
2 to 6 m. at low tide, and the strongest currents
run about 3.5 km. per hour.

Lot 42 in Norwalk Harbor was treated with
Polystream (Granular) on August 24, 1966. Depth
of water at mean low tide averages about 3 m.;
maximum current is 3.5 km. per hour. Divers re-
ported that strong currents carried off the lot a por-
tion of the granules.

Effect on gastropods. — Before the treatment,
divers counted up to five oyster drills of both spe-
cies on each cluster of oysters. Within an hour after
the treatment all visible thick-lipped drills and
Atlantic oyster drills on clusters of oysters were
swelling.

On September 8, 1966, 14 days after the treat-
ment, divers observed that most oyster drills at-
tached to clusters of oysters had fallen to the bot-
tom. In a few instances, however, one or two oj'ster
drills that were protected by being attached on
the underside of clusters were unaffected and some
were feeding on oysters.

On frequent inspections of the lot divers found
that most oyster drills remained stunned, in a
semiswollen condition, until November. A small
number of drills may have recovered before the
water dropped below 10° C, the temperature at
which they normally become dormant.

As far as divers coidd determine, the treatment
of lot 42 on August 24 did not kill many oyster
drills but only immobilized them and prevented
them from feeding. I suspected that a higher per-
centage would have been killed if the treatment
with Polystream had been made in late April or
early May.

To determine more precisely the effect of Poly-
stream in the summer, however, an oyster comjiany

CONTROL OF OYSTER DRILLS WITH POLYSTREAIM

293

treated lot 205, in a moi-e protected area. Tidal
currents over this lot run at no more than 0.9 km.
per hour and, therefore, did not carry off the Poly-
stream (Granular). The water is about 2 m. deep
at low tide. On September 15, when the lot was
ti'eated, the water temperature was about 21° C.

A month later determinations with the hy-
draulic sampler showed that the treatment killed
78 percent of the oyster drills (no separation of
species was made) (table 4).

Effect on associated animals. — On lot 42, divers
reported that a large number of pipefish, juvenile
flounders, mud crabs, and shrimp were stunned by
the chemical an hour after the treatment, but these
animals a]3peared to be normal later. They made
no observations on lot 205.

Effect on predation. — In early May 1966, lot 42
was planted with 350 hi. of 1-year-old oysters
(5,000-6,000 individuals per bushel). On June 17,
7 weeks later, oyster drills had killed 4.3 percent
of the oysters and had reduced the number of live
oysters per cluster from 19 to 18.2.

By July 25, 12 weeks after the planting, the
I'ate of kill by oyster drills had increased tremen-
dously. For example, 34 percent of the oysters had
been killed around the edges of the bed and 26 per-
cent in the center. Thus, during the period of 5
weeks, from June 17 to July 25, the average kill
was 4.8 oysters per cluster, or nearly one oyster per
cluster per week.

On August 24, the day the lot was treated, a
third sampling was made. In areas around the
edges of the lot, where oysters were planted thinly,
clusters avei-aged only two live oysters each. In the
center of the lot the number of live oysters per
cluster averaged between 9 and 10. Thus, even in
the main portions of the lot about 50 percent of
the oysters had been destroyed. Oyster drills
caused almost all the mortality; starfish caused
only a small amount.

The fourth sampling was made on September 8.
In the main portion of the lot, clusters had an av-
erage of ten 1-year-old oysters and, in addition,
18.3 live spat had attached to each cluster. By
counting small oyster scars I determined that the
original 1966 oyster set had averaged about 30
per cluster. Thus, even in the center of the lot,
oyster drills had destroyed more than a third of
the 1966 oyster spat by the time of treatment,
August 24.

By observing these oystei-s through the fall of
1966 and into the spring of 1967, I found that
virtually no additional oysters were killed by oys-
ter drills. On March 31, 1967, clusters in the main
portion of the lot averaged 9.3 2-year-olds (in 1966
they were 1-year-olds) and 21.5 1-year-olds of the
1966 oyster set. No careful determinations were
made on lot 205. Later periodic observations indi-
cated, however, that predation by oyster drills was
slight.

In the spring of 1967, when these oysters were
transplanted to another lot, their volume had in-
creased to 2,100 hi., a sixfold increase during one
growing season. I did not determine the increase
in size of individual oysters.

Area 8: Norwalk Harbor, Conn., 1967

Five lots in Norwalk were treated with Poly-
stream (Granular) between April 29 and May 13,
1967. Lot 42 was treated again and two lots along-
side, lots 40 and 50, were treated for the first time.
Depths of water and current velocities are about
the same over these three lots. Lots 18 and 49 were
also treated for tlie first time. The depth of water
over these lots at low tide is about 2.5 m. and cur-
i-ent velocities do not exceed 0.9 km. per hour. Lot
19, adjacent to lot 18, was not treated and served
as a control.

Effect on gastropods. — Divers made no observa-
tions during or immediately after these treatments.

On lot 18 the treatment killed 52 percent of the
oyster drills (68 percent of the thick-lipped drills
and apparently none of the Atlantic oyster drills —
again, numbers of Atlantic oyster drills were too
low for significant comparisons) and reduced their
numbers from 8.4 to 4.0 per square meter (table
4).

On lot 40 the treatment killed 78 percent of the
oyster drills (82.2 percent of the thick-lipped drills
and apparently 66.7 percent of the Atlantic oyster
drills — again, numbers of the latter species were
too low for accurate appraisal) and reduced their
numbers from 16.7 to 3.8 per square meter (table

4).

On lot 42 the treatment killed 44 percent of the
oyster drills (66.7 percent of the thick-lipped drills
and apparently no Atlantic oyster drills — numbers
of Atlantic oyster drills were too low for reliable
comparisons) and reduced their numbers from 3.3
to 1.9 per square meter (table 4). Because most

294

U.S. FISH AND WILDLIFE SERVICE

oyster drills were killed on this lot by the second
treatment and not by the first in 1966, I believe
that treatments in early May are much more effec-
tive tlian those made later in the summer.

On lot 49 the treatment killed 86 percent of the
oyster drills (84.6 percent of the thick-lipped
drills and apparently all of the Atlantic oyster
drills) and reduced their numbers from 6.3 to 0.9
per square meter (table 4) .

On lot 50 the treatment killed 84 percent of the
oyster drills (86.4 percent of the thick-lipped drills
and 55.6 percent of the Atlantic oyster drills) and
reduced their numbers from 13.9 to 2.8 per square
meter (table 4).

Lot 19, which served as a control, was sampled
at the same time as the other lots. The density of
oyster drills per square meter was about the same
on each date; on May 10 it was 19.5, and on June
30 it was 21 .2 (table 4).

E-ffect on associated animals. — Divei-s did not ex-
amine these lots closely during or immediately
after treatment. At intervals during the summer
of 1967, however, they observed that healthy
flounders, young starfish, mud crabs, and other
animals were numerous on the beds. They saw no
affected animals. In fact, most animals were more
numerous on treated lots than on areas barren of
oysters nearby. The divers did not count the young
starfish on unplanted areas, but on October 6 they
counted 8.8 young-of-year starfish per square meter
on lot 18, and 35.3 per square meter on lot 40.

Effect on predation. — I carefully recorded mor-
talities of oysters on these lots from the time they
were planted through November when oyster drills
became dormant. In May 1967, 1- and 2-year-old
oystei-s were planted on lot 40 and 1-year-old
oysters were planted on lots 42, 49, and 50; and
from June through early September, 1967-year-
class hatchery-reared seed oysters about 5 nnn. in
length were planted on lot 18. Losses of oystei-s
because of predation by oyster drills did not ex-
ceed 1.5 percent on any of these lots by late Novem-
ber (table 5). Because enough drills were present
on some lots to cause higher mortalities — lot 40,
for instance, had 3.8 oyster drills per square meter,
and lot 50 had 2.3 i^er square meter — most live
oyster drills must have been sufficiently "stunned"'
by the Polystream to prevent their feeding. This
apparent "stunning" effect was also evident on lot
42 in 1966.

CONTROL OF OYSTER DRILLS WITH POLYSTREAM

Oysters planted on these lots freshly treated
with Polystream grew normally. For example, the
1-year-old oysters on lot 50 increased in volume
from an average of less than 1 cc. to about 15 cc.
each during the 1967 growing season. My determi-
nations of growth of oysters planted on untreated
bottoms show that this amount of growth is about
normal.

Area 9: Foster's Cove, R.I., 1967

Foster's Cove on tlie south shore of Rhode Is-
land, about 4 ha. in area, is a tidal pond connected
to Charlestowa Pond by a narrow inlet. Depth of
water over the oysters ranges from to 2 m. at low
tide. There is little exchange of water between the
two areas; thus, the principal water currents in
the cove are caused by winds. Examination of three
sections of Foster's Cove on November 10, 1966,
indicated that oyster drills had killed about 75
percent of the oysters.

On May 31, 1967, two areas totaling 0.8 hectare
were treated with Polystream (Granular) .

Effect on gastropods. — Divei-s made no observa-
tions during or immediately after treatment. My
later observations showed that the treatment killed
all Atlantic oyster drills (no thick-lipped drills
were present) in both areas and reduced their
numbers from 9.5 and 3.6 to 0.0 per square meter
(table 4).

Effect on associated aninuds. — On June 8, 8 days
after the treatment, I examined the areas by walk-
ing along the shores and divers also examined
them. Along the north shore, perhaps 15 m. from
one of the treated areas, there were 4 dead toad-
fisli, Opsanus tau; 50 dead silversides, Menidia
menidia; 500 to 1,000 dead niunimichogs; 4 dead
blue crabs, Callinectcs sapidus; 50 dead shrimp;

Table 5. — Percentage of oysters killed hii oijs'er drills and
starfish in center areas of lots in Norwalk, Conn., 1967

lAccumulatcd niontlily totals ']

Lot number May June July Aug. Sept. Oct. Nov.

Perunt

182 0.0 0.0 O.n 0.6 0.4 1.0 0.2

40< .0 0.0 1.0 0.0 0.0 .5

42' .0 0.0 0.5 I.O 0.0 .5

4(1' .0 0.0 0.0 0.3 1.5 .0

50> .2 1.0 0.0 1.0 0.7 .0

' Sampling errors account for slight variation In numbers.

• Oysteis niised in hatcheries in 1967.
' l-year-old oyslcrs.

• Mixture 0(1065 and l'J66oystor set (1 and 2 years old).

295

and 10 dead polychaetes. On the inspections made
along the shoreline, just inside the other treated
section, there were only two dead toadfish and one
dead blue crab. Undoubtedly, a high percentage of
fish, blue crabs, and shrimp was killed at the time
of treatment. Divers did not see any fish or shrimp,
live or dead, either on or off treated areas.

Effect on predation. — No determinations were
made.

Area 10: Fresh (Quahog) Pond, Falmouth, Mass., 1%7

Fresh Pond, about 2.0 ha., is a tidal pond on the
east shore of Buzzard's Bay. It is connected with
the Bay by a long, narrow creek only about 1 m.
wide and 0.3 m. deep at the entrance of the pond.
The area for growing oysters is from to 2 m.
deep. Winds generate the principal currents in the
pond.

On May 29, 1967, a 0.08-ha. section of the pond
was treated with Polystream (Granular) .

Effect on ga.stropods.—^N\th.\n an hour of the
treatment divers observed that all snails were
beginning to swell.

By July 11, the treatment had killed 95 percent
of the Atlantic oyster drills (no thick-lipped drills
were present) and reduced their numbers from
40.8 to 2.2 per squai-e meter (table 4) .

An untreated area in another section of the pond
that served as a control for the treatment had an
average on May 29 of 37.2 Atlantic oyster drills
per square meter. On July 11 this control plot
had 33.2 drills per square meter.

Effect on associated animals. — Because the
treatment extended to the shoreline of the pond, a
number of observations could be made by walking
along the shore. An hour after the treatment I
observed 2 flounders (5 cm. long), 5 green crabs,
Carcinus maenas, and 200 shrimp all dying, and
100 mummichogs stunned. I also observed three
small schools of silversides swimming through the
area; all these fish were healthy. New England
nassas and mud snails, Nassarius obsoletus, were
begimiing to swell.

On July 11, 1967, divei-s examined the area
again. The only animal affected other than snails
was a tautog which weighed about 1.8 kg. All New
England nassas and mud snails were dead.

Effect on predation. — The area had no oysters.

RECOMMENDATIONS FOR USING
POLYSTREAM

During this study I made a number of observa-
tions on the use of Polystream (Granular), the
form now most commonly used on commercial oys-
ter beds to control oyster drills. These observations
are listed below and should be emphasized for
those who might wish to use this product :

1. The bed to receive a treatment should have a
firm bottom, free of silt.

2. Treatments should be made in late April or
early May when oyster drills first become active
after a period of winter dormancy.

3. Polystream (Granular) should be spread at
slack current.

4. Most successful treatments have been made in
water less than 6 m. deep, where currents are less
than 2.7 km. per hour. Wliere currents are stronger
than this, planted oysters appear to prevent the
Polystream (Granular) from being carried off a
bed.

5. Polystream (Granular) treatments are suc-
cessful on beds planted with seed oysters.

6. In certain shallow areas, where little or no
current flows, a smaller quantity of Polystream
(Granular) may be successful.

SUMMARY

1. Five experimental and 10 commercial treat-
ments of oyster beds were made with Polystream
in the States of Connecticut, New York, Rhode
Island, and Massachusetts.

2. Immediately after a treatment, oysters, clams,
and other organisms accumulated small residues
of Polystream in their tissues. These residues, how-
ever, were gradually lost or greatly diminished.
For instance, oysters and clams lost the residue of
Polystream within 119 days. If they were trans-
planted from a treated to an untreated bed, how-
ever, they lost the residue within a week.

3. All oyster drills were killed in areas where
water current velocities were low. On a typical
bed, in an area where current velocities were be-
tween 0.9 and 2.7 km. per hour, liowever, about
85 percent of thick-lipped drills and 66 percent of
Atlantic oyster drills were killed. Apparently, no
oyster drills were killed where current velocities
were strong.

4. On treated beds where current velocities were
low, significant percentages of fish, small clams.

296

U.S. FISH AND WILDLIFE SERVICE

and other invertebrates were killed. On treated
beds where current velocities were between 0.9 and
2.7 km. per hour, treatments killed only small per-
centages of fish, small clams, crabs, and other
invei-tebrates. A few hours after the treatment the
area appeared to be nontoxic to these animals.

5. A higher percentage of oyster drills was
killed by treatments made in late April and early
May than later in the summer.

6. Oyster drills were killed by the toxic action
of Polystream, not by fish or crabs after they be-
came swollen. In a small number of instances, how-
ever, they were consumed by starfish.

7. Oyster drills that survived a treatment ap-
peared to be affected by the treatment to the extent
that they did not feed significantly for a few
months and, thus, did not kill many oysters.

8. The number of oyster drills on a bed where
seed oysters were planted and removed each year
remained low for at least 2 years.

9. Oyster drills killed less than 2 percent of
young oysters during the first year on most treated
beds.

10. Growth of oysters appeared to be normal on
treated beds. For example, on one bed 1-year-old
oysters increased in volume from less than 1 cc.
to 1,5 cc. in one growing season.

ACKNOWLEDGMENTS

Barry Baiardi, Russell Clark, Otis C. Lane,
John J. Manzi, and Nicholas Penchuck provided
technical assistance. Hillard Bloom and the Bloom
Brothers Oyster Company; J. Richards Nelson

and the former F. Mansfield and Sons Oyster
Company; Lester Johnson and G. Vanderborgh,
Jr., of G. Vanderborgh and Sons Oyster Com-
pany; and Arnold Carr, Division of Marine Fish-
eries, Mass., also helped me.

LITERATURE CITED

Haven, Dexteb, Michael Castagna, Paul Chanley,
Mabvin Wasb, and James Whitcomd.

1966. Effects of the treatment of an oyster bed with
Polystream and Sevin. Chesapeake Sci. 7 : 179-188.
LoosANOFP, Victor L.

1960. Some effects of pesticides on marine arthro-
pods and mollusks. Biological problems in water
pollution. In Transactions of the 1959 Seminar,
pp. 89-93. U.S. Dep. Health Educ. Welf., Public
Health Serv.

1961. Recent advances in the control of shellfish
predators and competitors. Proc. Gulf Carib. Fish.
Inst, 13th Annu. Sess., pp. 113-127.

LoosANOFP, V. L., C. L. Mackenzie, Jr., and L. W.
Shearer.
1960a. Use of chemicals to control shellfish pred-
ators. Science (Wash.) 131: 1522-1523.
1960b. Use of chemical barriers to protect shellfish
beds from predators. Fish., Wash. State Dep. Fish.
3 : 86-90.
Schwartz, N., H. E. Gaffney, M. S. Schmutzer, and
F. D. Stefano.
1963. A method for the analysis of chlorinated ben-
zenes in clams (^[ercrnaria mcrcenaria) and oys-
ters {Crassostrea vh-ginica). J. Ass. Off. Agr.
Chem. 46 : 893-898.
Wood, Langley, and Beverly A. Roberts.

1963. Differentiation of effects of two pesticides upon
Vrosalpinx cinerea Say from the Eastern Shore of
Virginia. Proo. Nat. Shellfish. Ass. 54: 75-85.

CONTROL OF OYSTER DRILLS WITH POLYSTREAM

297

COMPARATIVE DISTRIBUTION OF MOLLUSKS IN DREDGED AND UN-
DREDGED PORTIONS OF AN ESTUARY, WITH A SYSTEMATIC LIST
OF SPECIES >

BY JAMES E. SYKES AND JOHN R. HALL, FISHERY BIOLOGISTS

BUREAU OF COMMERCIAL FISHERIES BIOLOGICAL LABORATORY

ST. PETERSBURG BEACH, FLA. 33706

ABSTRACT

A survey of benthic mollusks In Boca Clega Bay, Fla.,
showed a much smaller number and variety of species
in the soft sediments in dredged canals than in the
predominantly sand and shell sediments in undredged

areas. Samples contained an average of 60.5 live mollusks
and 3.8 species in undredged areas and I.l individuals
and 0.6 species in dredged canals. A list of mollusks
collected in this survey and in past studies Is appended.

This report compares the numbers and vari-
eties of mollusks in fine sediments of dredged
canals with those found in undisturbed bottoms
of sand and shell in Boca Ciega Bay, Fla. The
bay is a shallow coastal lagoon of about 70 km.*
which connects with Tampa Bay at its southern
end (fig. 1). Some of the previous investigations
in the lagoon included studies of sediments
(Goodell and Gorsline, 1961; Taylor and Saloman,
1969); hydrology (Saloman and Taylor, 1968);
submerged vegetation (Pomeroy, 1960; Phillips,
1960) ; fishes (Springer and Woodburn, 1960; Sykes
and Finucane, 1964) ; and benthic invertebrates
(Hutton, Eldred, Woodburn, and Ingle, 1956;
Bullock and Boss *).

A recent evaluation of the effects of dredging
and filling has documented a large loss of estu-
arine resources in Boca Ciega Bay (Taylor and
Saloman, 1968). It was here that scientists and
conservationists were finally successful in sup-
pressing a dredge-fill proposal of 202 ha. (Sykes,
1967). Tliis is also the bay in which the U.S.
Army Corps of Engineers denied a dredge-fill
application for the first time on the basis of
fish and wildlife values, thus providing a stim-
ulus for more comprehensive assessments of the

' Contribution No. 57, Bureau oJ Commercial Fisheries Biological Labora-
tory, St. Petersburg Beach, Fla. 33706.

> Bullock, R., and C. Boss. 1963. Ecological distribution oJ marine mol-
lusks In Boca Ciega Bay, Florida. Winter term project. Mimeographed
report on file at Florida Presbyterian College, St. Petersburg, Fla. 33733.

biological and recreational aspects involved in
future bayfill developments.

Thorson (1956) and others have concluded
that sediment composition is a cardinal factor
in controlling the settlement and viability of
many marine invertebrates. The distribution
of sessile benthic mollusks indicates to the marine
ecologist the ability of the environment to sup-
port life. Marked deficiencies in abundance and
variety indicate abnormality of the environment,
and the degi-ee of deficiency is roughly propor-
tional to the degree of abnormahty.

PROCEDURES

Between September 1963 and August 1964, we
took 107 bottom samples at 31 stations in Boca
Ciega Bay (figs. 1 and 2). Seven stations were
in canals between finger fills (1-7), and the other
24 (8-31) were m relatively undisturbed areas
of the bay. We collected algae, sea grasses, and
benthic animals with a bucket dredge and bot-
tom drag (Taylor, 1965). In water less than
1 m. deep, three shovelfuls of bay bottom (about
15 1.) were substituted for the dredge haul. One
station sample consisted of the combined catch
from one bucket dredge (or three shovelfuls)
and one bottom drag. At each station a sub-
sample of sediment was taken from the dredge
or shovel and was later analyzed at Florida
State University.

Published May 1970.

FISHERY BULLETIN: VOL. 68, NO. 2

299

ST. PETERSBURG

AREA

OF

STATIONS

KILOMETERS
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or

SUIVEY

Xtg?^^

»f4S'Vt.

Figure 1. — Collecting stations 20 to 31 and area of stations 1 to 19 (see fig. 2), Boca Ciega Bay, Fla.
300 U.S. FISH AND WILDLIFE SERVICE

■."Si

PETERSBURG

82°46W.

Figure 2. — Collecting stations 1 to 19, Boca Ciega Bay, Fla., between Johns Pass and Corey Causeway.

We washed samples for benthic organisms on
a24-mesh sieve which had an opening of 0.701 mm.
and fixed the material retained by the sieve in a
10 percent sea-water Formalin ' mixture. A
protein stain (rose bengal) was added to fa-
cilitate the separation of small organisms from
debris. Identified animals were preserved in 70
percent isopropanol.

' Trade names referred to in this publication do not Imply endorsement
of commercial products.

We identified 168 species of mollusks repre-
senting 69 families; of these, representatives of
156 species were collected live. We based deter-
minations on standard taxonomic works (Clench,
1941-69; McLean, 1951; Olsson, Harbison, Fargo,
and Pilsbry, 1953; Abbott, 1954, 1968; Perry
and Schwengel, 1955; Warmke and Abbott, 1962;
Keen, 1963; Wagner and Abbott, 1967; an un-
published report by Bullock and Boss (see foot-
note 2), and collections at the University of

DISTRIBUTION OF MOIXUSKS IN AN ESTUARY

301

Table 1. — Depth, bottom type, and number of live mollusks
collected at stations in dredged canals in Boca Ciega Bay,
Fla., 1963-64

Canal
station

Depth

Bottom type

Species

per
sample

Individual
per sample

Sand size
and larger

SUt and
clay

1..
?

M.
4
3

Percent
6

7

6
60

7

6
14

Percent
94
93

96
40
93
94
88

Number
1.0
1.0

1.0

.6

.6

Number
1.0
1.8

3..
4..

6-.
f,

4

3
6
4

2.0

1.0

7..

Average

4

2.6

... 4

16

85

.6

l.l

South Florida * and the U.S. National Museum.
Specimens from this study were deposited in the
invertebrate reference collection of the BCF
(Bureau of Commercial Fisheries) Biological
Laboratory, St. Petersburg Beach, Fla.

MOLLUSK-SEDIMENT RELATIONS

Comparison of mollusks and bottom types

showed that species and individuals were much

less numerous in soft sediments of canals than in

sandy sediments in undredged areas of Boca Ciega

Bay (tables 1 and 2). Canal sediments, which

averaged 85 percent silt and clay, had 16 live Tablk f.-Depth, bottom type and ""'"^f «/f'''«.'"«""f;
= ' , ^. . •'.' 11 i J collected at stations m undredged areas of Boca Ciega Bay,

mollusks m 14 samples. Living specimens collected pi^,^ 1963~64

at the seven canal stations were the gastropods

Nassarius inbex and Haminoea antillanim, and the

pelecypods Brachidontes exustus, Anoinalocardia

cuneimens, and Mercenaria campechiensis. These

species and 151 others were collected live from the

24 stations in undredged areas of the bay. Sedi-
ments from natural bottom, which averaged 91

percent sand and shell, yielded 5,631 live mollusks

in 93 samples.

Pratt (1953) suggested that soft sediments and

associated hydrological conditions may be limiting

because (1) rapid deposition has a smothering

effect, (2) high organic content of soft sediments

depletes dissolved oxygen, and (3) weak currents

in areas of deposition are insufficient for the re-
moval of toxic metabolic wastes. Comparisons of

sediments and environmental factors (Taylor and

Saloman, 1968) in dredged and undredged areas at

sampling stations lead us to conclude that the soft

sediment is the principal factor luniting the abun- LITERATURE CITED

dance and diversity of benthic mollusks in bayfiU

canals of Boca Ciega Bay. Such sediments are as Abbott, R. Tuckeb. >t . ^ n„

*i • 1 A • i tu f A .^A^^A 1 1; 1954. American seashells. D. Van Nostrand Co.,

tliick as 4 m. in waterways that were dredged 15 Princeton, N.J., 541 pp.

years ago. 1963 geashells of North America. Golden Press,

N.Y., 280 pp.
Clench, William J. (Editor).

1941-69. Monographs of the marine mollusks of the
Western Atlantic. Johnsonia, vols. I-IV. Dep.
Mollusks, Mus. Comp. Zool., Harvard Univ.,
Cambridge, Mass.
Draqovich, Alexander, and John A. Kelly, Jr.

1964. Ecological observations of macro-inverte-
brates in Tampa Bay, Florida, 1961-1962. Bull.
Mar. Sci. Gulf Carib. 14: 74-102.
GooDELL, H. G., and D. S. Gorsline.

1961. A sedimentologic study of Tampa Bay,
Florida. Rep. Int. Geol. Congr., 21 Sess., Pt. 23,
pp. 75-88. Int. Ass. Sediment., Copenhagen, 1961.

Bottom type

Stations In

Depth

Species

Individual

undredged areas

Sand size

Silt and

per

per sample

and larger

clay

sample

M.

Percent

Percent

Number

Number

8

2.6

98

2

3.6

8.0

9

1.0
.5

99
89

1
11

3.0

.6

7.3

10 .

.6

11

1.5
.6

97
96

3
4

4.0
.5

25.0

12-

2.5

13

2.0

96

4

3.6

18.0

14

1.7

88

12

.6

2.0

16

.6

92

8

2.6

20.6

16 .

.7

99

1

.3

..7

17

5.0
1.5
1.0

83
96
84

17
4
16

1.0
6.6
1.6

2.5

18

68.0

19

24.0

20

.6
1.0
2.0

99
98
98

1
2

6.6
3.4

2.8

140.0

21

67.8

22

71.8

23

7.0
2.0

.7
7.0

.7

98
79
97
99
97

2
19
3

1
3

4,3
11.7
3.2
4.0
5.0

66.6

24

316.0

25

8.4

26 . ...

16.7

27

11.0

28

3.0

2.0

.3

12
87
98

88

12

2

4.7
6.7
6.2

56.3

29

89.0

78.0

31

2.0

95

5

4.0

86.5

Average

1.9

91

9

3.8

60.6

ACKNOWLEDGMENTS

The authors gratefully acknowledge confirma-
tions and corrections of identifications made by
Harry W. Wells, Department of Biology, Univer-
sity of Delaware, Newark, Del. ; Joseph Rosewater,
Division of Mollusks, U.S. National Museum,
Washington, D.C. ; and George Radwin, San Diego
Natural History Museum, San Diego, Calif.

• HiUnian Collection, University of South Florida, Tampa, Fla. 33620.

302

U.S. FISH AND WILDLIFE SERVICE

Hdtton, Robert F., Bonnie Eldred, Kenneth D.
WooDBURN, and Robert Ingle.

19.36. The ecology of Boca Ciega Bay with special
reference to dredging and filling operations. Fla.
State Bd. Conserv., Tech. Ser. 17(1), 86 pp.
Keen, A. Myra.

1963. Marine moUuscan genera of western North
America. Stanford Univ. Press, Stanford, Calif.,
126 pp.

McLean, Richard A.

1951. The Pelecypoda or bivalve mollusks of Porto

Rico and the Virgin Islands. Scientific Survey

of Porto Rico and the Virgin Lslands. N.Y.

Acad. Sci. 17, 183 pp.

Olsson, Axel A., Anne Harbison, William G. Farooi

and Henry A. Pilsbry.

1953. Pliocene MoUusca of southern Florida.
Monogr. Acad. Nat. Sci. Philadelphia 8, 458 pp.
Perry, Louise M., and Jeanne S. Schwengel.

1955. Marine shells of the western coast of Florida.
Palaeontological Research Institute, Ithaca, N.Y.,
318 pp.
Phillips, Ronald C.

1960. Ecology and distribution of marine algae
found in Tampa Bay, Boca Ciega Bay, and at
Tarpon Springs, Florida. Quart. J. Fla. Acad.
Sci. 23: 222-260.
Pomeroy, Lawrence R.

1960. Primary productivity of Boca Ciega Bay,
Florida. Bull. Mar. Sci. Gulf Carib. 10: 1-10,
Pratt, David M.

1953. Abundance and growth of Venus mercenaria
and Callocardia morrhuana in relation to the char-
acter of bottom sediments. J. Mar. Res. 12: 60^74.
Saloman, Carl H.

1965. Bait shrimp {Penaeus duorarum) in Tampa
Bay, Florida — biology, fishery economics, and
changing habitat. U.S. Fish Wildl. Serv., Spec.
Sci. Rep. Fish. 52C, iii + 16 pp.
Saloman, Carl H., and John L. Taylor.

1968. Hydrographic observations in Tampa Bay,
Florida, and the adjacent Gulf of Mexico — 1965-
1906. U.S. Fish Wildl. Serv., Data Rep. 24, 39
pp. on 6 microfiches.
Springer, Victor G., and Kenneth D. Woodburn.

1960. An ecological study of the fishes of the Tampa
Bay area. Fla. State Bd. Conserv., Prof. Pap.
Ser. 1, 104 pp.
Sykes, James E.

1967. The role of research in the preservation of
estuaries. Trans. 32d N. Amer. Wild!. Natur.
Resourc. Conf., pp. 1.50-160.
Sykes, James E., and John H. Finucane.

1964. Occurrence in Tampa Bay, Florida, of imma-
ture species dominant in Gulf of Mexico commercial
fisheries. U.S. Fish Wildl. Serv., Fish. Bull. 65:
369-379.

Taylor, John L.

1965. Bottom samplers for estuarine research.
Chesapeake Sci. 6: 233-234.

DISTRIBUTION OF MOLLUSKS IN AN ESTUARY

Taylor, John L., and Carl H. Saloman.

1968. Some effects of hydraulic dredging and coastal
development in Boca Ciega Bay, Florida. U.S.
Fish Wildl. Serv., Fish. Bull. 67: 213-241.

1969. Sediments, oceanographic observations, and
floristic data from Tampa Bay, Florida, and adja-
cent waters, 1961-65. U.S. Fish WUdl. Serv.,
Data Rep. 34, i -^ 561 pp. on 9 microfiches.

Thorson, Gunnar.

1956. Marine level-bottom communities of recent

seas, their temperature adaptation and their

"balance" between predators and food animals.

Trans. N.Y. Acad. Sci., Sect. 2, 18: 693-700.

Wagner, Robert J. L., and R. Tucker Abbott

(Editors).

1967. Van Nostrand's standard catalog of shells.
2d ed. D. Van Nostrand Co., Inc., Princeton,
N.J., 303 pp.
Warmke, Germaine L., and R. Tucker Abbott.

1962. Caribbean seashells. Livingston Publishing
Co., Narberth, Penn., 348 pp.

APPENDIX

A Checklist Of Mollusks From Boca Ciega
Bay, Florida

We identified 168 species of mollusks repre-
senting 69 families from BCF collections in Boca
Ciega Bay. Of these, members of 156 species were
alive. The number was increased to 72 families
and 188 species by including mollusks recorded in
other studies. The additions are coded within the
list by surname initials of the authors who re-
ported them: B. and B. — ^Bullock and Boss (see
footnote 2); H. — Hutton et al. (1956); D. and
K. — Dragovich and Kelly (1964). Mollusks not
collected alive in this investigation are denoted
by an asterisk (*). We identified some specimens
only after comparison with specimens in the U.S.
National Museum (+). Classifications are based
on Abbott (1954, 1968) and Warmke and Abbott

(1962).

CLASS GASTROPODA

FissurelUdae

Diodora cayenensia (Lamarck)
Trochldae

*Calliostoma jujubinum tampaense (Conrad)
Turbinidae

Arene tricarinata (Stearns)
Turbo castaneus (Gmelin)

Neritldae

*Nerilina reclivata (Say)

303

417-060 O - 71 - 9

Melanellidae

Melanella bilineata (Alder)
Melanella intermedia (Cantraine)

Epitoniidae

Epitonium angulatum (Say)
Epitonium hympreysi (Kiener)
Epitonium rupicola (Kurtz)

Rissoidae

Risaoina chesneli (Michaud)

VitrinelUdae

CydostTemiscus beaui Fisher — further verification

pending.
Cyclostremiscus suppressus Dall — futher verification

pending.
+ Teinostoma cryptospira (no author on specimen) —

further verification pending.

Truncatellldae

*Truncatella pulchella Pfeiffer

Turrltellldae

Vermicularia fargoi Olsson

Caecldae

Caecum cooperi S. Smith
Caecum pulchellum Stimpson
Meioceras nitidum (Stimpson)

ModuUdae

Modulus modulus (Linn6)

Cerithlidae

Bittium varium (PfeifiFer)

Cerithiopsis emersoni (C. B. Adams) — B. and B.

Cerilhiopsis greeni (C. B. Adams)

Cerithium muscarum Say

Cerithium floridanum Mfirch

Seila adamsi (H. C. Lea)

Triphoridae

Triphora nigrocincta (C. B. Adams)

Potamididae

Batillaria minima (Gmelin)

Calyptraeldae

Calyptraea centralis Conrad
Crepidula aculeata (Gmelin)
Crepidula fornicata (Linn6)
Crepidula maculosa Conrad
Crepidula plana Say

Strombidae

Strombus alalus Gmelin — B. and B.
Natlcldae

Nalica pusilla Say

Polinices duplicatus (Say)

Sinum perspectivum (Say) — B. and B.

Murlcidae

Eupleura sulcidentata Dall

Murex cellulosus Conrad

Murex pomum Gmelin

Thais haemastoma floridana (Conrad) — B. and B.

Urosalpinx perrugata (Conrad)

Buccinidae

Buaycon contrarium (Conrad)
Busycon spiralum (Lamarck)

Columbellidae

+ Anachis semiplicata Stearns

Anachis obesa (C. B. Adams)

Anachis ostreicola Sowerby

Columbella ruslicoides Heilprin — B. and B.

Mitrella lunata (Say)

Melongenidae

Melongena corona (Gmelin)
Nassarildae

Nassarius vibex (Say)
Fasciolarildae

Fasciolaria hunleria (Perry)
Fasciolaria tulipa (Linn^)
Pleuroploca giganlea (Kiener) — H.

OUvldae

Oliva sayana Ravenel
Olivella perplexa Olsson
Olivella mulica (Say)
Olivella floralia Duclos

Marginellidae

Bullata ovuliformis (Orbigny)
Hyalina avenacea (Deshayes)
Marginella aureocincta Stearns
Persicula lavalleeana (Orbigny)
Prunum apicinum (Menke)

Conidae

Conus floridanus Gabb — H.
Conus jaspideus Gmelin — H.
*Conus slearnsi Conrad

Terebridae

Terebra concava vinosa Dall
Terebra dislocala Say
Terebra protexta Conrad

Turridae

*Glyphoturris rugirima (Dall)
*Monilispira leucocyma (Dall)
Pyrgocythara hemphilli Bartsch and Rehder
Stellatoma slellata (Stearns)

BulUdae

Bulla striata Bruguifere

Atyldae

Haminoea antillarum (Orbigny)
Haminoea succinea (Conrad)

304

U.S. FISH AND WILDLIFE SERVICB

Retusidae

Retusa canaliculata (Say)
Pyramidellidae

Odostomia acutidens Dall
Odoslomia impressa (Say)
Odostomia producta Dall
Odostomia seminuda C. B. Adams
Odostomia sp.

Pijramidella crenulala (Holmes)
+ Sayella hemphilli (Dall)
Turbonilla conradi Bush (Dall)
Turhonilla dalli Bush

Acteocinldae

Cylichna bidenlala (Orbigny)
Acteonidae

Acleon punclostrialus (C. B. Adams)
Aplysildae

Bursatella leachi plei Rang
Ellobildae

Melampus coffeus (Linn^)

CLASS AMPHINEURA

Ischnochitonldae

Chaetopleura apiculata (Say)
Ischnochiton papillosus (C. B. Adams)

Chitonldae

Chiton tuberculalus Linn^ — H.

CLASS SCAPHOPODA

Dentaliidae

Dentatium eborcum Conrad

Denlalium antillarum Orbigny

Dentalium sp. (resembles D. texasianum Philippi)

CLASS PELECYPODA

Solemyacidae

Solemya occidenlalis Deshayes
Nuculidae

Nucula proxima Say
Nuculanldae

Nuculana acuta Conrad
Arcidae

Anadara transversa (Say)
*Arca zebra Swainson
Barbatia cancellaria (Lamarck)
Barbatia Candida (Helbling) — D. and K.
Noetia ponderosa (Say)

Glycymerldidae

Glycymeris pe