CALIFORNIA
FISH-GAME

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u

0

V

VOLUME 50

APRIL 1964

NUMBER 2

Published Quarterly by

THE RESOURCES AGENCY OF CALIFORNIA
CALIFORNIA DEPARTMENT OF FISH AND GAME

SACRAMENTO

STATE OF CALIFORNIA

EDMUND G. BROWN, Governor

THE RESOURCES AGENCY OF CALIFORNIA

HUGO FISHER, Administrator

FISH AND GAME COMMISSION

HENRY CLINESCHMIDT, President, Redding

THOMAS H. RICHARDS, JR., Vice President WILLIAM P. ELSER, Member

Sacramento San Diego

DANTE J. NOMELLINI, Member JAMIE H. SMITH, Member

Stockton Los Angeles

DEPARTMENT OF FISH AND GAME

WALTER T. SHANNON, Director

722 Capitol Mall
Sacramento 95814

CALIFORNIA FISH AND GAME
Editorial Staff

JOHN E. FITCH, Editor-in-Chief Terminal Island

JAMES H. RYAN, Editor for Inland Fisheries Sacramento

CAROL M. FERREL, Editor for Game Sacramento

JOHN L. BAXTER, Editor for Marine Resources Terminal Island

DONALD H. FRY, JR., Editor for Salmon and Steelhead Sacramento

TABLE OF CONTENTS

Page

Annual Abundance of 5Toung striped Bass, Eoccus saxatilis, in the
Sacramento-San Joaquin Delta, California Harold K. Ckadwick 69

Some Observations on Factors Associated with Survival of striped
Bass Eggs and Larvae Arnold l>. Albrechi 100

Partyboat Logs Show How Skindivers Fared during 1960, 1961,
and 1962 William /•'. Wood 114

Recent Occurrences of Intergeneric Hybrid Flounders, Inopsetta
ischyra (Jordan and Gilberl i, from California and Oregon..

Paul II Ueed 118

Northward Movement of the < ialifornia Sea ( Itter

Robert T. Orr and Thomas C. Poulter 122

NoU

Grass Rockfish, Seoastodes rastrelliger (Jordan and Gilberl .
from the Yaquina Bay Area. Oregon

William C. Van Arsdel, III and Carl /•'. Bond 125

Reviews 126

i 67 )

ERRATUM

Abramson, Norman J., Estimating the number of angling license pur-
chasers, vol. 48, no. 4. pp. 253-255.

The expression following the equal sign on line 3. page 254 should
read

N — - „ . ./•■■ rather than ., . r-. .

n (n — 1) n ( n — 1 )

The author is indebted to Maurice I. Gershenson, California Division of
Labor Statistics and Research, for noting this error.

(68)

ANNUAL ABUNDANCE OF YOUNG STRIPED BASS,
ROCCUS SAXATILIS, IN THE SACRAMENTO-
SAN JOAQUIN DELTA, CALIFORNIA1

HAROLD K. CHADWICK

Inland Fisheries Branch

California Department of Fish and Game

INTRODUCTION

A reliable index of striped bass spawning success would serve two
important management purposes. First, it would enable us to determine
if recruitment is directly related to spawning success. It' it is, we could
predict important changes in the fishery three years in advance.

Second, it would give insight into environmental factors responsible
for good and poor year-classes. Besides increasing our understanding of
tin; bass population, this knowledge might be used to improve recruit-
ment by modifying water development plans in the Sacramento-San
Joaquin Delta under the State Water Resources Development System.

Fyke net samples provided the earliesl information on young bass
distribution (Hatton, 1940). They were qo1 promising for estimating
abundance, and subsequent sampling of eggs and larvae with plankton
nets also had important Limitations (Calhoun and Woodhull, 1948; Cal-
houn. Woodhull, and Johnson. 1950).

An exploratory survey with tow nets in the early summer of 1947
(Calhoun and Woodhull. l!Ms found bass about an inch long dis-
tributed throughout the lower Sacramento-San Joaquin River system
except in the Sacramento River above Lsleton. This suggested the best
index of spawning success would be the abundance of bass about an
inch long, measured by tow netting.

In 1948 and 1949 extensive tow net surveys were made to measure
the relative abundance of young bass in the Delta between Rio Vista
and Pittsburg (Erkkila et al., 1950). In 1951, The actual size of the
young bass population was estimated twice during the summer (Cal-
houn. 1953). since 1953, the Department has made more limited sur-
veys annually.

This paper reports results of these animal surveys for 1953 through
1962. It also reports results of two types of studies to evaluate their
accuracy. First, more intensive surveys (Delta-wide surveys), explora-
tory tow net sampling, and beach seining were used to learn if annual
surveys accurately measured abundance throughout the nursery
grounds, and throughout the time when young bass were vulnerable to
the tow net. Second, the net's size selectivity, the vertical and horizontal
distribution of young bass, the effects of tidal stage on catch, and the

1 Submitted for publication September 1963. This work was performed as part of
Ding-ell-Johnson Project California F-9-R. "A Study of Sturgeon and Striped Bass,"
supported by Federal Aid to Fish Restoration funds.

(69)

70

( \l.in>i;\i\ PISB AND GAME

relationship between water transparency and net efficiency were exam-
ined to determine bow accurately tow netting measures abundance in
the immediate water mass bein^- sampled.

DESCRIPTION OF STUDY AREA

California's only large striped bass population inhabits the estuary
of the Sacramento-San Joaquin River system (Figure 1 I and adjacent
coastal waters. Tidal movement dominates the estuary, with flow re-
versal occurring in summer tip to Courtland on the Sacramento River
and above Mossdale on the San Joaquin River. However, the Delta is
essentially fresh water, with salinities seldom exceeding 1,000 ppm
chlorides a few miles above the confluence of the two rivers. Down-
stream, salinity increases rapidly, sometimes approaching 90 percent
of seawater in San Pablo Bav in late summer

r? ^~"h

- fooihef Ri*er

$coie in Miles

FIGURE 1. The study area showing tow net and seining stations and areas represented by

Delta-wide survey stations.

JUVENILE STRIPED BASS ABUNDANCE 71

Waters throughout the Delta are turbid, with Secchi disk readings
seldom over a foot, except in the Sacramento River above Rio Vista. In
the bays west of Pittsburg the water is clearer.

METHODS
Description of Nets

Most sampling was with a tow net mounted on skis, as described by
Calhoun (1953). The net cone was made of J-ineh stretched mesh #6
medium-laid cotton webbing, and nylon bobbinet with openings approxi-
mately 0.1 inches in diameter (Pattern No. 281, Marion Textiles. Inc.,
New Fork). A 9-foot cone of cotton webbing was attached directly to
the frame, and a 7-foo1 nylon bobbinel cone was sewed to the cotton
webbing, so that the cotton webbing formed a 2-foo1 fyke inside the
bobbinet. The overall length of the net was approximately 14 feet. A
quart Mason jar was tied in the apex of the bobbinet cone.

Size selectivity, vertical distribution, and some horizontal distribution
measurements were determined with modified nets. In measuring size
selectivity, the bobbinet of the standard net was replaced with bobbinet
having holes approximately 0.04 inches in diameter (Pattern 1400,
Marion Textiles).

In measuring vertical distribution, we used circular nets, 3 feet in
diameter. These had an 8-fool cone of the same cotton webbing joined
to a 6^-foot cone of No. 281 bobbinet to form a 2-foot fyke inside the
bobbinet. One of these nets was mounted on skis to measure horizontal
distribnt ion during 196] .

Fishing Procedures

The standard net was towed from the 28-foo1 research boat Striper,
on a {-inch steel cable passing from a winch amidship through a block
suspended from an "A" franc at the stern (Figure 2 .

All samples were taken towing into the current at 1.000 rpm engine
speed giving a velocity through the water of approximately 2.7 feet per
second. Calhoun found this an efficient speed (Calhoun and Warren,
1949).

Fishing depth was estimated from the length of cable released. The
relationship between fishing depth and cable length was established
by measuring cable deflection angle, and from readings made with
Moeller Chemical Sounding Tubes suspended by rubber stoppers inside
an aluminum tubing capsule attached to the net frame.

Three circular nets were fished simultaneously to measure vertical
distribution. Each was attached with a swivel safety hook to a swivel
clamped on the towing cable. A 2-foot-square wooden kite weighted with
concrete blocks was attached to the end of the cable to depress it, so
less cable was needed to fish a given depth. The nets could be retrieved
so rapidly that the difference between fishing times of the top and bot-
tom nets was less than 5 percent.

Lateral distribution of small bass in various channels was measured
during 1961 with a circular net mounted on skis, towed from a 40 hp
outboard skiff.

72

CALIFORNIA PISH AND GAME

*

FIGURE 2. Tow net being pulled

aboard Striper at end of a tow. Photograph by William
Heuhach, July 1962.

Annual Survey Procedures

Tn 1953, stations were selected in the lower San Joaquin River (I),
and in the Sacramento River several miles above and below the mouth
of the San Joaquin River (II and III); in 1954, two stations were
added in Snisnn Bay (IV and V) (Figure 1). We believed these sta-
tions represented the area inhabited by almost 90 percent of the esti-
mated young bass population in early July 1951 (Calhoun, 1953).

These localities were sampled during the week of minus tides (water
height at low tide at Golden (Jate, San Francisco, below mean sea
level) closest to the time that young bass at Antioch reached a mean
length of 1-inch. This was to compensate for annual variations in
spawning time and growth rate. Stations were sampled in numerical
order — one station a day — on successive days. Fifteen 15-minute sam-
ples were taken at each station during the minus ebb tide. At the start
of each tow. 185 feet of cable was released and it was retrieved during
odd-minute intervals, thus all depths to about 30 feet were sampled
equally.

Procedures were changed in 1957. Stations III, IV, and V were
dropped, and stations were selected in Spoonbill Slough (VF and Mon-
tezuma Slough (VII) (Figure 1). The same minus tides were sampled,
but each station was sampled on three different days with five, 15-
minute tows per day. Stations 1 and II were sampled during ebb tides
on days 1, 3, and 5, and 2, 4, and 6, respectively. Stations VI and VII
were sampled during flood tides on days 1, 3, and 5, and 2, 4, and 6,
respectively. Sampling started 2^, 2, i, and 1 hour after slack water

JUVENILE STRIPED BASS ABUNDANCE 73

at Stations I, II, VI, and VII, respectively, and subsequent samples
were taken at J-hour intervals, so any correlation between catch and
tidal stage would not bias the results. Only 100 feet of cable were re-
leased at Station VI ; it was shortened to 75 and 50 feet after 5 and 10
minutes, since the water was considerably shallower there, other pro-
cedures remained the same.

Delta-wide Survey Procedures

Thirty stations (Stations 1-30, Figure 1 I were selected to sample tin-
area between upper San Pablo Bay and Isleton on the Sacramento River
and Mossdale on the San Joaquin River as extensively as could be done
in f) days with one boat. Three 10-minute samples were taken at each
station every other week. Days of least tidal fluctuation were sampled
to minimize any biases associated with tidal stage. Sampling was con-
ducted from the time substantial numbers of bass over 0.7 inches long
appeared until the mean bass size approached 2 inches.

Previous work indicated most bass were in the top 10 feet of water
(U. S. Dept. of Interior, 1957) ; hence, towing procedures were designed
to sample equally all depths to 12 feet. This was done by releasing 100
feet of cable at the start of each tow. and retrieving 25 feet at 3-minute
intervals. Data collected in 1960 showed the vertical distribution of bass
was not constant, so in 1961 towing procedures were modified to sample
all depths equally. We released enough cable to reach the bottom at the
start of towing and pulled in 25 feet nt appropriate intervals. Selected
stations had a 30-f6o1 maximum depth, since deeper water could not he
sampled with available gear. During 1961, one tow at each station was
made in the old manner each period, so a ratio of catches by the new
method (diagonal tows) to the old method (surface tows) could be
calculated.

In Phil. Stations !». ID. 21. 22. and 24 were abandoned, because few
fish had been caught there, and five stations (31-35) were added to
cover the San Joaquin Delta more thoroughly. In 1962, Stations 20, 23,
and 32 were abandoned so Stations 11a, 13a, 27a. and 30a could be
added to increase sampling in areas of greatest water volume.

Seine Survey Procedures

Seine collections were made with a 100- by (i-foot, J-inch stretched
mesh beach seine during October or November 1956-1959. Sites were
selected wherever suitable beaches were found from western San Pablo
Bay to the mouth of the Feather River on the Sacramento River and
about 10 miles above Mossdale on the San Joaquin River (Stations
A-BB, Figure 1). Up to three hauls were made at each station.

Procedures Used to Evaluate Accuracy of Local Abundance Estimates

The minimum size selectivity of the standard tow net was measured
by comparing lengths of bass caught in the standard net with lengths
of bass caught in the net with the Pattern 1400 bobbinet cod end.

We measured vertical distribution at several localities having water-
depths of approximately 30 feet, by fishing the three circular nets si-
multaneously at 5, 15, and 25 feet.

74 CALIFORNIA PISH AND GAME

Between L957 and 1959, we measured horizontal distribution by com-
paring catches nexl to shore and al mid-river on alternate tows. Shore
tows were in water less than 10 feel deep with 75 Peel of cable, so the
nel rode on the bottom excepl al Stations 1 and 5, where the water was
20 to 30 feel deep adjacenl to shore. Mid-river tows were taken follow-
ing annual survey procedures. In 1961, comparisons were made by
simultaneously taking a sample nexl to shore with the small tow ael
pulled by a skiff and a sample at mid-river using the procedure de-
signed to measure vertical distribution. The mean catch of the three
nets fished in mid-river was compared with the catch near shore.

Statistical Methods

Catches were analyzed with standard statistical procedures. In most
experiments variables were analyzed by factorial design analysis of
variance, which requires normally distributed measurements. It was
impossible to determine the type of distribution of sample eatches,
since the population sampled was constantly changing because of tidal
movement and fish behavior. However, trawl net eatches generally
have some type of contagious distribution, so the logarithms of the
catches, or the catches plus one in samples with zero catches, are suit-
able for most statistical analyses (Gulland, 1956). Logarithmic trans-
formations have been used commonly in other similar studies (Winsor
and Clarke, 1940; Silliman, 1946; and Bagenal, 1958), and I used them
in all analyses.

For the annual surveys, simple aggregate indices of abundance were
calculated by dividing the sum of the mean catches per tow at several
stations during a given year by the sum of the mean catches per tow
at those stations during the base year. This gives each station an im-
portance proportional to the magnitude of its catch. This is preferable
to other ways of calculating indices, since the fraction of the population
present at each station cannot be estimated.

A simple aggregate index was also calculated for the Delta-wide sur-
veys. In addition, a weighted index was calculated by multiplying the
catch at each station by the water volume represented by the station
(Appendix A). These volumes were determined by setting boundaries
midway between stations or at a distance of 2.5 miles from stations on
the area's periphery and estimating the water volume present at mean
half-tide to the nearest 1,000 acre-feet.

Striped bass were measured to the nearest 0.1 -inch, fork length.

RESULTS

Annual Surveys
1953-1956 Surveys

Catches during 1953 and 1954 were considerably greater than those
during 1955 and 1956, and catches were generallv greatest at Stations I
and II (Table 1).

The 1954-1956 results were analyzed by analysis of variance to test
the hypothesis that these stations sampled the population adequately.
The 1953 results were not included, since only three stations were
sampled. I assumed the first tow each day was made at the same tidal
stage, and the other tows followed at equal time intervals. Thus, the

JUVENILE STRIPED BASS ABUNDANCE

to

TABLE 1
Summary of Striped Bass Catches Made During Annual Surveys

Date

Sta-
tion

7/26-28
1953

6/28-7/2
1954

7/4-8
1955

7/19-23
1956

7/13-16
1957

7/26-8/1
1958

6/20-25
1959

7/6-11
1960

6/26-7/1
1961

7/1-6
1962

I

Catch/tow . . .
Mean lengthf.

85.0
1.0

117.1
1.0

73.5
1.1

48.9
1.0

*23.9
1.2

37.6
1.1

13.1
1.5

42.1
1.3

157.8
1.1

*277.8
0.9

II

Catch/tow ...
Mean length..

110.7
1.0

96.2
1.0

35.5

1.0

21.3
1.0

•27.3
1.3

17. it
1.3

9.3
1.4

117.3
1.2

235.6
0.9

417.9
1.1

III

Catch/tow ...
Mean length..

64.5

1.1

57.0
1.1

4.9
1.0

20.5

1.3

IV

Catch/tow

Mean length __

51.3
1.2

5.8
1.2

30.3
1.5

V

Catch/tow ...
Mean length..

--

6.7
1.3

10.9
1.2

9.7
1.4

VI

Catch/tow . . .
Mean length..

•58.9
1.1

54.7
1.0

30.7
1.3

129.1
1.1

362.1
0.9

♦462.8
1.0

VII

Catch/tow

Mean length..

•50.5
1.4

116.9
1.2

10.0

1.6

49.6
1.7

87.5
1.3

*235.5
1.1

* Sampling limited to two days and 10 samples.
t Fork length in Inches.

catches of any given tow were indicative of a certain lime during the
tide. The first order interactions, year \ time and time x station, were
not significantly different at the 95 percenl level from the second order
interaction, so the three were combined to estimate sampling error
(Table 2).

TABLE 2

Analysis of Variance of 1954-1956 Tow Net Surveys

Variable Degrees of Freedom Sum of Squares Mean Square

Year 1' 4.252 2.126

Station 4 8.281 2.07*1

Time 14 0.949 0.068

Year x station . 8 2.485 0.311

Error __. 196 6.61s 0.034

Total 224 22.585

Three important results of this analysis are: (i) differences among
yearly catches are highly significant (F = 62.53 with FA)1 = 4.70) ; (ii)
differences among mean catches at the stations are highly significant
(F = 60.88 with F.01 = 3.85), clearly indicating an unequal distribu-
tion of bass in the area sampled; (iii) the year x station interaction is
significant (F = 9.15 with FM = 2.85), indicating significant annual
differences in geographical distribution.

To test the hypothesis that these stations sampled the population in
many miles of river due to fish being carried by the relatively fast-
moving water during minus ebb tides, the relationship between the
catches at Stations I, II, III, and V was examined. Float studies

7l! I \i.in IRN LA FISH \\l> GA M E

(Calif. Div. of Water Resources, L952 indicated thai water moves from
Station III to Station V in approximately 3 hours. Hence, early catches

at Station III should be similar to late catches a1 Station V. Such a
relationship was evident only in 1956 (Table 3). Catches at stations
1 and II also failed to show a relationship to those at Station TIT.

TABLE 3

Total Catches of Striped Bass at Stations III and V
During Comparable Periods of Sampling

Station III Station I

Tows 1-5 Tons /0-/.7

1954 — 230 67

1! 155 9 104

1956 91 81

7957-7 962 Surveys

Boat breakdowns prevented 1 day of sampling at each station in 1957
and 1 day at three stations in 1962. The 1959 results are aberrant
because the survey "was 2 weeks late. This occurred because young bass
reached a 1-inch mean length a month earlier than in any other year.

Annual catches were relatively low from 1957 through 195!) and
then increased sharply to a 10-year high in 1962 (Table 1).

Appreciable variations in catches on different days at the same sta-
tion have occurred during some years (Table 4).

TABLE 4

Variability in Catch of Striped Bass at
Station I During Annual Surveys

Mean catch per ton-

Year Scries I Series IT Series III

1957 - 33.6 14.2

1958 ___ 43.8 37.8 31.2

1959 ___ 14.0 17.0 8.2

1960 50.8 37.4 38.0

1961 __. 160.2 219.6 93.0

1962 350.2 205.2

Indices of Abundance

The only measure of abundance possible for all years is an index of
abundance at Stations I and II (Table 5. Annual survey A), since
these were the only stations sampled every year. Broader based indices
were calculated for 1957 through 1962 from catches at Stations I. II.
VI, and VII (Table 5. Annual survey B), ami for 1954 through 1956
from catches at Stations I through V (Table 5, Annual survey C) :
1960 is the base year used for the first two indices. The last index was
calculated using 1954 as a base and multiplying each annual abun-
dance index by 1.34 to put them on the same scale as the other indices.

The indices agree closely with each other. They show a decline in
abundance from a 1953-54 peak to a low in 1959. and then a sharp in-
crease through 1962. with abundance being greatest in 1961 and 1962.

JUVENILE STRIPED BASS ABUNDANi I 77

TABLE 5

Indices of Annual Abundance of Striped Bass Fry in the
Sacramento-San Joaquin Delta '

Yen,

Indea 1953 195J, 1955 1956 1957 1958 1959 1960 1961 1962

Annual survey A 2- 1.23 1.34 0.68 0.44 0.32 0.35 0.14 1.00 2.47 4.36

Annual survey B 8— 0.48 0.07 0.19 1.00 2.49 4.12

Annual survey C *— 1.34 0.54 0.54

Delta-wide survey A B_ 0.49 1.00 1.40 3.20

Delta-wide survey B «_ 0.38 1.00 1.04 2.60

Delta-wide survey C7_ 0.44 1.00 1.20 3.34

Delta-wide survey D 8_ 1.00 2.42

1 Underlining indicates best estimates ol relative abundance.

-.Sum of mean catches jjet tow at Stations I and II divided b} the I960 sum.

'Sum of mean catches per tow at Stations I. II, VI, and Vll divided by the 1960 sum.

'Sum lit' the mean catches per to« at Stations I. II. Ill, IV, and V. divided bj 1954 sum. and multiplied by

l.:!l to equate it tn cither indices.
5 Total number of bass collected at Stations l 30 during three surveys when more than 7u percent of all ba

were between 0.7 and 2.0 inches long, adjusted for annual differences in survey procedures, and divided

by I960 total.
" Similai to Delta-wide survej A except that catch at each station was multiplied bj the thousands of acre

feet id' watei present at the station and stations with "a" suffixes included in 1962 in addition to stations

1-30.

7 Similar to Delta-wide survey U except that catches during f surveys were included (Survej No. 1 ex-

cluded in 1961) and only 1.0-1.4 inch bass were included, except during first survey, when those larger
than that were included, and fourth survey, when th smaller than that were included.

8 Similar to Delta-wide survey B bul include- stations 31, 33, 34, and 35, and excludes stations 9, and 19 24.

Delta-wide Surveys
Length Composition of Catch

Four Delta-wide surveys were made annually in !!»•")!». 1960, and 1962,
and five were made in 1961 (Table ft). The 1960, 1961, 1962 catches

TABtE 6

Summary of Striped Bass Catches During Delta-wide Surveys *

First Second Third Fourth Fifth

Year xuntii survey survey survey survey

1959

Date 6 13 18 6 27-7/1 7/11-15 7/25-29

Total catch 556 824 640 272

Percentage 0.7-2.0

inches 91 72 70 66

Menu length f . 1.1 1.1 1.5 1.9
1960

Date __. 6 16-20 0/30-7/4 7 13-18 7/28-8/1

Total catch 1.737 1,329 758 2*0

Percentage 0.7-2.0

inches ^2 89 85 55

Menu length f - 0.8 1.1 1.5 2.1
1961

Date 6/5-9 6/19-23 7/4-10 7/17-21 7/31-8/3

Total catch 1.061 3,736 4.42s 1.152 335

Percentage 0.7-2.0

inches 55 81 82 91 04

Mean length f __. 0.7 0.8 1.0 1.4 1.9
1962

Date 6/26-29 7/8-12 7/23-27 8/6-10

Total catch 10,814 8,099 3,103 733

Percentage 0.7-2.0

inches 85 96 88 64

Mean length f 0.9 1.2 1.5 1.9

* Catches are not comparable in all years due to changes in survey procedures and stations described in text
t Fork length in inches.

78

CALIFORNIA i I -I I ami <;AMK

showed similar patterns, with mean Length increasing from 0.8 or 0.9
inches to about 2 inches over a period of four surveys. The hulk of the
catch was made during the firsl three of these surveys, when over 80
percenl of the bass were 0.7 to 2.0 indies long. In 1!>5!». hass were larger
during the first survey and the size range was greater, and only about
7(i percenl of the catch was in the 0.8 to 2.0-inch range, except during
the firsl period.

Length frequency distributions of the catches are not as similar as the
means (Figure 3 . Three modes progress 1h rough the fishery in 195!),
while there were two modes in I960 and 1961, and only one in 1962. The
modes probably indicate either periodicity in spawning or periodicity
in survival. The modes on successive surveys generally coincided during
1959 and 1960, and the modes a! 0.7 inches coincided in 1961.

en

UJ

O
>

<

in
in

<

CD

rr

1959 c .c

3,000

,1

1 i

W

I i
I i
1 i
I i

Second Survey

— — —Third Survey

Fourth Survey
Fifth Survey

2000

1 i
i i

■V

1 ,

/ •• 1

1 1 ' 1

1,000

/IP

; i \

1 !/ s

1 i/
'/

\>!.'\ \ ' ' l

.\J

V. x'--

01

rr

oj 2,000

20 30

FORK LENGTH IN INCHES

2 0 30

FORK LENGTH IN INCHES

1961

10 2 0 3 0

FORK LENGTH IN INCHES

45,000

40,000
0

J

E 35,000

O

> 30,000

t 25,000

x 20,000

o")

in

<

CD 15,000

</> 10,000
rr

UJ
CD

5 5,000

=>

1962

2 0 3 0

FORK LENGTH IN INCHES

FIGURE 3. Length frequencies of striped bass caught during Delta-wide surveys.

Geographical Distribution

Appreciable annual variations occurred in the geographical distribu-
tion of young bass (Table 7). Distribution was similar in 1959 and

JUVENILE STRIPED BASS ABUNDANCE 79

1961, with about 60 percent of the bass in the lower Delta and most of
the rest in the San Joaquin Delta. The 1960 distribution was similar,
but even more bass were in the lower Delta and fewer in the San
Joaquin Delta. The population was generally farther downstream in
1962.

TABLE 7

Relative Distribution of Young Striped Bass in the

Sacramento-San Joaquin Delta

Percentage of Total Catch *

Stations D~W~ I960 1961 1962 t

San Joaquin Delta

1, 2 and 3 16 7 VI 4

4, 5. 6, and 8 . 16 8 U 7

Lower Delta

7 and 30 _ 13 L6 13 21

9, 10, 11, and 12 % . - 41 25 32 18

13 and 29 _ 8 37 21 17

Suisun Bay Area

14, 15, and L6 4 4 5 11

26, 27, and 28 _ 2 2 3 19

17, 18, and 25 - 1 1 1 3

San Pablo Bay Area

20 and 23- Trace 0 0

♦Percentage of total catch weighted by water volume during the tlner Delta-wide Surveys with over 70 percent

of bass between 0.7 and 2.0 inches
t Stations with "a" suffixes tabulated with station of same number. Part of station 13 included in station 30a.
X station 9 not sampled in 1961 and 1962.

Indices of Abundance

Four indices of abundance were calculated from the Delta-wide sur-
veys (Table 5). Delta-wide survey indices A and B were based on
catches during the three surveys each year when over 70 percent of
the bass caught were 0.7 to 2.0 inches Long (Table 6). Both were ad-
justed by depth correction factors during 1959 and 1960, and for 1961
because only two diagonal tows were made at most stations that year.
The depth correction factors were calculated by grouping similar sta-
tions and dividing the sum of the average diagonal tow catches by the
sum of the surface tow catches (Table 8 . Index A was calculated by
dividing the total catch during the three surveys in each year by the
1960 total catch. Index B was calculated by weighing the catch at each
station by the appropriate water volume (Appendix A), summing the
weighted totals, and dividing each year's total by the 1960 total.

TABLE 8

Comparison of Diagonal Tows and Surface Tows During
the First Four 1961 Delta-wide Surveys

Total catch *

Stations Diagonal tons Surface tons t'ntio

14-2+3 467.5 430 1.1

4+5 + 6+8 504.r, 511 1.0

7+30 162 Ins 1.5

29 104.r, 165 0.6

11 185..-, 55 3.4

12 195..-, 18 10.9

13 165.5 67 2.5

15+16 135 (17 2.0

25+26+27 18.5 22 0.8

* Catches include only fish 0.7-2.0 inches long. Catches from diagonal tows were divided by two, since two
diagonal tows and only one surface tow were made at each station.

Ml ( M.II'OKMA FISH AND GAME

Delta-wide survey Index C estimates bass fry abundance ;is they
pass through the size interval 1.0 to 1.1 inches. Modal lengths (Figure
■ \ indicate this interval is approximately equal to bass growth during
a 2-week period. Tims, each group would be sampled only once. This
index was calculated by using the total catch of 1.0- to 1. 4-inch bass,
weighted by wain- volumes, during four surveys (Survey 1 excluded
in 1961 , in addition, the weighted catches of ba^s Larger than tins on
the firsl survey and smaller than tliis on the fourth survey were in-
cluded.

Delia-wide survey I) was calculated similarly to Index B, but Sta-
tions '.) and 19-24 were excluded and Stations 31, 33, 34, and 35 were
included.

All three indices show similar trends of increasing abundance during
1959 through 1962.

A weighted index comparable to Index B was calculated for each of
five size groups of bass (Table 9). Annual differences are smallest in
the largesl and smallest groups, and greatesl in the middle group.

TABLE 9

Index of Abundance of Various Sizes of Striped Bass

Length group lf>r,9 19(1/)* 1961 V.u; l

0.0-0.5 45 100 00 112

0.6-o.H 28 100 84 208

1.0-1.4 41 100 118 328

1.5-1.9 50 100 Hi!) 215

2.0+ 110 100 57 99
* Basf yeai

Growth Rates

Distances between modal lengths in subsequent surveys are prob-
ably accurate measures of growth for 2-week periods. The distances
between pronounced modes in tenths of inches are: 1959 — 0.5, 0.6,
0.7: 1960—0.4, 0.4. 0.6; 1961—0.4. 0.6; 1962— 0.8. 0.4 (Figure 3).

Exploratory Tow Net Sampling

Considerable exploratory tow netting was done between 1954 and
1958. Most sampling in areas covered later by the Delta-wide surveys
contributed nothing additional to our knowledge of young bass dis-
tribution. However, sampling in the Sacramento River above Rio Vista,
in San Pablo Bay, and in the Xapa River and adjacent sloughs con-
tributed substantially.

On August 7 and 8. 1!».")7. eight tow net samples were taken at
scattered locations from the south end of Steamboat Slough (Station
W i to the mouth of the Feather River. The only bass was collected
near Station X. At the same time, seine collections caught 13 bass at
Station W in two hauls. 18 at Station AA in three hauls, and 3 at
Station BB in one haul.

( »n .July 7. 1958, no bass were caught in five tow net samples between
Stations W and A A.

On July 17. 1957, one bass was caught in six tow net collections
in the Napa River between the mouth and Xapa.

JUVENILE STRIPED BASS ABUNDANCE 81

The Napa River was sampled on three occasions in 1958. On June
1!), 26 bass were caught in four samples between the mouth and Station
21. On June 26, 429 bass were caughl in eight samples in the river
and adjacent sloughs in the general area covered by Stations 20-23. On
July 22, 227 bass were caught in seven samples in this area and three
in the main river between Station 21 and Napa.

The only sampling in San Pablo Bay consisted of 12 tow net hauls
on Jnne 25, 1958 at scattered lucidities throughout the Bay. Only nine
bass were taken in the eastern pari of the Bay. In contrast, the re-
mainder of the catch was composed of Sacramento smell. Spirinchus
thaleickthys, 7: smelt. Hypomesus spp„, L10; anchovy, Engraulis mor-
dax, 1, 157; splittail, Pogonichthys macrolepidotus, 24; threespine
stickleback, Gasterosteus aculcdtus, -'5; unknown goby, 208.

Seine Surveys

Pall seine surveys collected young bass in appreciable numbers from

eastern San Pablo Bay to \ly>\ i the Sacramento River and Mossdale

on the San Joaquin River (Table 10).

TABLE 10

Catches of Young-of-the-Year Striped Bass Made in Fall Seine Collections

Y umber of young -of -the-y ear
striped bass i>< r seine haul

Station Location 1956 1957 1958 W59

A San Pablo Baj at .China Camp 0 0 0

B San Pablo Bay at Pt. San Pedro 0 0 0

C San Pablo Bay at Pt. Wilson 5 4 0

D San Pablo Bay al Rodeo L9 9 53 1

E Carquinez Strait at Por1 Costa 76 so 10 3

F Sacramento R. al Middle Grounds 53 L6 T 101

G San Joaquin H. a1 Antioch _ 300 20 L33 6

H Taylor Slough 5 1 2

I Sand Mound Slough at Piper Slough __ 50 3

J Fishermen's Cut 0 o 1

K Sau Joaquin R. at Medford Island- 550 82 129 172

L San Joaquin R. at Headreach Island <>on 22 37 10

M San Joaquin R. at Roberts Island 200 lL'S 82 436

X Salmon Slough at Doughty Cut 8 •". 14 3

() San Joaquin R. \ mi. below Mossdale s -

P San Joaquin R. 1 mi. above Mc>»sdale__ 86 1 2

Q San Joaquin R. 3 mi. above Mossdale 0

R San Joaquin R. 10 mi. above Mossdale 3

S Mokelumne R. at Highway 12__ 62 12 1 2

T South Fork Mokelumne R. above Hog Slough 1' 7 1 1

U Sacramento R. at Sherman Island__ 77 38 82 3

V Sacramento R. below Rio Vista__ 90 163 .'.1 10

W Steamboat Slough, south end 15 17 12 1

X Steamboat Slough, north end — 44 7 4

Y Sacramento R. at Ryde 25 13 23 5

Z Sacramento R. above Freeport 5 7 2 3

AA Sacramento R. at American R 5 0 1 +

BB Sacramento R. at Feather R 2 15 0

2—12488

82 I Mil ORNLA ll-ll AND GAME

Accuracy of Measurement of Local Abundance
Size Selectivity

Ratios of bass catches in Hi'' standard-mesh ael to those in the fino-
mesh net during two pairs of tows ;ii Station 14 and three pairs at
Station I indicated the standard net's efficiency increases sharply as
kiss size increases from 0.5 to 0.7 inches and reaches 100 percent at
approximately 0.8 inches (Table 11 i. This is supported by the fact
thai of \2 bass fry gilled in the standard bobbinet during 1958, the
percentages of 0.6-, 0.7-, and 0.8-inch fry were 12. 76, and 12. respec-
tively.

TABLE 11

Comparison of the Lengths of Striped Bass Fry

Caught in Standard Tow Net and Tow Net

with Small Mesh Cod End

Length *

Standard \ et

Small Cod End \ « /

Ra tio

0.2

0

63

0.00

0.3

4

151

0.03

0.4

14

102

0.14

0.5

36

198

0.18

0.6

175

326

0.54

(l.T

283

346

0.82

0.8

150

128

1.17

0.9

36

39

0.92

1.0

:>,

r>

-

1.1

0

5

1.2

l

(i

1

l

0

-

1.4

0

1

-

Fork length in inches.

Striped bass become less vulnerable to the net as they grow, pre-
sumably because of increased swimming ability. The Limit of vulner-
ability is about 3.5 inches, since virtually no larger ones were caught,
even though they occurred in the areas sampled. However, no satis-
factory method was found to measure accurately the decline in vulner-
ability. During the Delta-wide surveys, annual modal length varied
from 0.7 to 0.9 inches and the catch of larger fish generally declined
sharply (Figure 3). This resulted from a combination of mortality and
declining vulnerability, and no facts are available to measure the
contribution of each. However, the small catch of bass longer than
2 inches (11.4 percent of the catch in 1959, and half or less of this in
other years' suggested the net was quite inefficient for bass of this size.

Vertical Distribution

During 1960 and 1961, vertical distribution was sampled at nine
localities (Tables 12 and 13). In the western part of the Delta (Sta-
tions 7-30), bass were generally concentrated near the bottom, while
in the eastern part (Stations 1-5) they were more evenly distributed,
with greatest concentration frequently near the surface.

Bass showed a general tendency to raise off the bottom during flood
tides. This was more pronounced and general in the western localities.
This tendenc}^ was particularly pronounced and closely correlated with
tidal stage at Station 12 in both 1960 (Figure 4) and 1961.

JUVENILE STRIPED BASS ABUNDANCE s'l

TABLE 12
Vertical Distribution of Striped Bass During Ebb Tides

Mean catches per tows at various depths below surface f

Station

Date N;

limber of tows

5 feet

15 feet

25 feet

15

6/14/60

10

4.2

17.1 **

15.0

14a

7/25/60

10

2.1

8.3

14.1 **

12

6/15/61

7

1.6

15.7

20.5 **

12

7/23/60

10

1.4

16.9

65.1 **

12

7/27/61

7

0

18.5

70.8 **

12

8/ 2/60

5

8.2

12.0

!t4.0 **

30

6/27/00

10

16.."

32.5 **

24.0

7

6/16/61

7

0.4

23.5

28.3 **

7

7/13/61

7

2.6

34.5

L04.8**

n

6/14/61

7

38.8 **

25.2

9.0

5

7/12/61

7

19.8

32.1 **

29.1

1

6/24/60

10

29.5

33.5 **

13.9

1

7/21/60

10

13.3 **

7.0

3.2

3

0/13/61

7

38.4 **

21.2

7.::

3

7/11/61

7

21.8

81.6 **

23.5

t In this

and subsequent

tables, single asterisks

denote differences

significant at 95

percent levels and double

asterisks denote differences significant at 99

percent levels.

TABLE 13

Verti

cal Distribution of Striped Bass

During Flood Tides

Date X

}frnn cntehrs per t<

nr at various

depths beloic surface

Station

umber of tons

5 ii 1 1

15 feet

25 feet

16

7/20/61

7

1.0

0.7

7.8 **

1 la

7/25/60

r>

2.4

LO.O

11.4**

L2

6/15 61

7

0.9

21.8**

L2.9

12

7/23/60

5

2.8

14.4

34.5 **

12

7/27 61

7

0.6

11>

64.0**

11'

8/ 2/60

10

2.4

38.9 **

24.9

30

6/27; 60

5

9.2

23.0

32.0**

7

6/16/61

7

6.7

42.0

4.".4 **

7

7/13/61

7

10.0

27.8

68.0**

5

6/14/61

.")

27.5 **

15.4

2.8

5

7/12/61

7

23.5

U..2 **

24.1

1

6/24/60

5

28.8

L6.8

18.4

1

7 21/60

5

6.6 **

1.0

2.5

3

6/13/61

7

50.5 **

36.5

17.8

3

7/11/61

7

14.7
TABLE 14

23.1

28.2 **

Mean

Lengths of Stripe

d Bass Caught

at Different Depths

Mean lengths at various depths

Station

Date

15

0/14/60

14a

7/25/60

12

6/15/61

12

7/23/60

12

7/27/61

12

8/ 2/60

30

6/27/60

7

6/16/61

7

7/13/61

5

6/14/60

5

7/12/61

1

6/24/60

1

7/21/60

3

6/13/61

3

7/11/61

feet 15 feet 25 feet

0.8 • 0.8 0.7

1.8 1.7 1.7
0.6 0.7 0.6

1.9 1.5 1.6
1.9 1.6 1.8
2.4 2.1 2.0
1.0 1.1 1.1
0.7 0.7 0.8
1.2 1.1 1.1
0.7 0.8 0.7
1.0 1.0 1.0
0.9 1.0 1.0
1.4 1.4 1.5
0.7 0.7 0.7
0.9 0.9 0.9

M

C \l ll'dKMA PISH AND GAME

Mean length of bass and depth were nol correlated excepl a1 Sta-
tion 12, where fish near the surface were larger late in the season
Table 14).

150

en
if)

a

o

LU

w 50

CD

5
■D
Z

15 feet below woter surfoce
25 feet below woter surfoce

EBB TIDE

low flood tide

Slack

time in relation to tide

HIGH EBB TIDE
SLACK

FIGURE 4. Relationship between striped bass tow net catches at different depths and tidal stage.

Horizontal Distribution

Horizontal distribution was measured between 1957 and 1961 (Tables
15 and 16).

Huge concentrations of small bass were found along the shore in
the western Delta. As they grew, their distribution became more even,
and in several instances significantly more of the larger bass were
caught at mid-river.

Bass were more evenly distributed at Stations 1. 3, and 5, but sunn'
mid-river catches were significantly greater at Stations 3 and 5.

Variations Due to Tidal Stage

Evidence of significant vertical distribution variations related to
tide was presented earlier. A comparison of the ratios of bass caught
near shore to bass caught in mid-river during ebb tides with compar-
able ratios during flood tides (Table 17) indicates that differences
were not consistent, even though they were sometimes great.

JUVENILE STRIPED BASS ABUNDANCE 85

TABLE 15

Horizontal Di

stribution

of Striped

Bass During Ebb T id.

es

1/ 1 un catches ji

er tow

i?ass i

..7 inches

\ ii n. In r
of

Bass to O.K inchi -
Near Mid-

Bass 0.9-1
fear

. / inches
Mid-

or

mini

\ ear

Mid-

Stat ion

Date

loirs

shore

river

shore

river

shore

iic cr

16

6/28/57

7

401 **

1 15

34

26

0

0

16

6/20 58

8

68 *

12

20 **

5

• 1

0

L6

7/ 3 58

8

L57**

34

38 **

6

;;

+

16

8/ 1/58

8

24 *

6

19

71

2

■:,r, **

16

7/2() 61

7

0

(i

9

+

L8

0

L4a

7 22 59

8

0

0

• >

9

6

27 **

III

7/27 :.7

7

0

(i

(1

0

~i

8

30

7 26 57

7

0

(i

II

(i

1

ll

30

7/13 58

7

14

12

1

8

0

o

30

7 L6 58

8

23

L8

5

8

0

0

30

7/24 58

8

28*

10

20 **

6

4

2

12

6/1 r. til

6

282 **

L2

7**

1

ii

II

12

7 27 63

7

6

+

11

9

1

21 -

7

6 L6 01

."i

225 **

11

2.") **

t

o

+

7

7 L3 63

7

L0

7

8

:;»

1

■j" **

1

6 23 60

8

27

13

1 1

21

+

+

3

7/11/61

7

14

19

11

10

+

1

5

6/14 61

6

8

21*

• >

4

0

0

r>

7/12. 61

7

4

7*
TABLE 16

8

18**

1

•J

Horizontal Dis

tribution i

of Striped

Bass Durin

g Flood Tides

l/< n n catches i>

! r (omj

Bass 1

..; inches

\ ii in hi r

of

Bass to 0. v in' In &
Near Mid-

Bass 0.9-1

\ i Hi-

. / iin In -
J/id-

or

more

\ i a ,

Mid-

St n t'u in

Date

tmrs

shore

river

shore

river

short

river

16

6 20 58

1

3 i

15

23

7

0

n

16

7/ 3 58

•1

L27

29

41

8

n

0

16

7/20 61

6

0

(i

6

1

18

9

14a

7/22/59

4

0

0

5

3

L8

L3

30

7/13/5S

4

35

9

L5 *

4

0

0

30

7 16/58

4

14

19

9

9

0

0

12

6 1.V61

7

350 **

11

10 **

1

0

0

12

7 27/61

7

1 **

+

11

11

.">

25 •

7

t; it; (il

7

145**

25

18

0

II

0

1

6/23/60

4

18

5

32*

11

+

+

3

7/11/61

7

6

8

7

12*

+

1

5

6/14/61

7

• '

13**

1

3*

0

0

5

7/12/61

7

7

6

1

211 **

1

2

However, mid-river catches made on comparable tows before and fol-
lowing slack tide were greater on ebb tides more often than on flood
tides (Table 16). Most differences were not statistically significant, but
because of small samples the analysis of variance test was not very
sensitive in most cases. On the other hand, the equal division of sig-
nificantly larger catches between ebb and flood tides, and the lack of
consistent pronounced differences at any location suggest there was
no general difference in catches at different tidal stages.

86 < AL1F0RNIA FISH AND GAME

TABLE 17

Ratios of Striped Bass Catch Near Shore to Catch
in Mid-River During Ebb and Flood Tides

Bass 1 ■"> or wore
Bass to 0.8 Inches Bass 0.!> /./ inches inches

DaU Station Ebb Flood Ebb Flood Ebb Flood

6 20 58 16 5.6 2.3 in 3.0

7 3 58 16 1.6 1.1 6.3 5.1

7 22 .V.i 14;i 0.3 l.C 0.2 1.4

7/13 58 30 1.2 3.9 0.5 3.8

7 L6 58 30 L.3 0.7 0.6 l.o

6/15/61 12 23.5 31.8 7.0 LO.O

7 27 61 12 20.7 36.8 1.2 1.0 0.04 0.4

6/16/6] 7 20.5 5.8 6.3 3.0

6 23 150 1 2.1 3.6 0.7 2.9

7 11 i,i :: o.7 0.8 0.6 0.6
6/14/61 5 0.3 0.4 0.5 0.3
7/12/61 5 0.6 1.2 0.4 0.04

TABLE 18

Catches of Striped Bass During Ebb and Flood Tides

No. pairs Mean catch per tow

Station Date of toics

16 6/20/5S 4

16 6/27/57 6

16 7/ 3/58 4

16 7/20/61 7

14a 7/22/59 4

14a 7/25/60 5

VI 6/26/57

VI 7/24/57 6

12 6/15/61 7

12 7/23/60

12 7/27/61 7

12 8/ 2/60

31 1 6/27/60 5

30 7/ 3/58 4

30 7/16/5S 4

30 7 25/57 5

30 8/ 7/56 5

7 6/16/61 7

7 7/13/61 7

5 6/14/61 7

7/12/61 7

1 6/23/60 4

1 6/24/60 5

1 7/21/60 5

3 6/13/61 7

3 7/11/61 7

Relationship of Efficiency to Water Transparency

Trawl net efficiency is generally closely related to water transparency,
so tow net efficiency should be similarly related. Unfortunately, no
method has been found to measure this, since there is no way of ob-
taining an absolute measure of bass abundance in any area, or of hold-
ing abundance constant and observing the effect of varying water
transparency on catches.

Most areas inhabited by young bass are quite turbid, with turbidity
declining somewhat as summer progresses. For example, Secchi disk
readings at 27 stations between June 19 and 23, 1961 varied from 3

Ebb

Flood

15

22

174

151

52

39

+

9 **

35

23

30

24

195

215

16

13

38

36

65

52

89

109

115

77

75

64

15

13

19

28

8

4

11

13

52

94*

142

106

73**

46

81

93

28 **

16

56

64

13**

10

67

105**

127**

66

JUVENILE STRIPED BASS ABUNDANCE

87

to 17 inches and averaged 11.2 inches, while on July 31 to August 3
they varied from 7 to 31 inches and averaged 13.3 inches. Changes
were generally small and increases exceeded 5 inches at only five sta-
tions.

During the June 19-23 period, total catches gave no indication of re-
lationship to turbidity at stations with Secchi disk readings less than
13 inches (Figure 5). Where readings were over 13 inches, low catches
probably reflected scarcity rather than decreased net efficiency, since
five of these stations were at the area's western periphery, and the
two stations closest to these had readings of 3 and 11 and catches of
3 and 4. Catches were uniformly low from July 31-August 3, so they
could not be related to turbidity.

614

100
NUMBER OF BASS

FIGURE 5. Relationship between striped bass tow net catches and water transparency during

June 19-23, 1961 Delta-wide survey.

DISCUSSION
Evaluation of Indices
Accuracy of Measuremenis of Local Abundance

The tow net 's size selectivity limited the size range of bass caught
efficiently. The lower limit of the size range is clearly defined as 0.7-0.8
inches. The upper limit is not clearly defined, but apparently bass
over 2.0 inches are sampled inefficiently.

Vertical distribution measurements showed that previous sampling
results in Old River, which indicated 70 to 92 percent of all bass were

CALIFORNIA FISH \M> GAME

in the top 10 feel of water (U.S. Dept. of [nterior, 1957), are nol
aniversally applicable. However, those results were qualitatively similar
to ours al Stal inns 1-5.

The varying vertical distribution of young bass is a potential source
of bias, !)iu it can be overcome by sampling all depths equally. The fact
thai diagonal tow catches in the Delta-wide surveys were as much as
10 times the surface tow catches (Table 8) illustrates this bias' poten-
t ial importance.

The uneven horizontal distribution presents a more serious problem
than does vertical distribution, since it is impractical to eliminate this
bias by sampling all portions of the cross-sectional area equally. It
causes estimates of abundance to be biased downwards in the areas
where concentrations occur near shore. However, this Idas' importance
is minimized, since it occurs when the bass are relatively small, since
it docs not occur in all areas, and since the shallow shelf next to shore
constitutes only 2 to 4 percenl of the river's cross-sectional area. I
estimated the error it causes by assuming bass abundances in waters less
than and more than 10 feet deep were uniformly equal to concentra-
tions indicated by shore and mid-river samples. The average underesti-
mate was about 15 percent for bass 0.7 inches and larger on the 4 days
when the greatest concentrations were near shore at Stations 7, 12, and
16. The range of the underestimates was 6 to 37 percent.

There do not appear to be any biases associated with tidal stage.

The importance of differences in water transparency is not fully
known. However, general high turbidity throughout the area, the lack
of correlation between catch and turbidity, and the occasional good
catches at Stations 10. 18, and 2b, where turbidity was lower, suggest
it was not serious in the area covered by the Delta-wide surveys.

Thus, while several factors bias catches, 1 believe tow net samples
give reasonably accurate measures of local abundance of 0.7- to 2.0-
inch bass, so long as all water depths are sampled equally.

Relationship of Water Movement to Young Bass Movement

The basic premise in planning the annual surveys was an hypothesis
that b;iss abundance in a few areas would reflect abundance over a
wide area, because water moving past any locality during a large ebb
tide would carry b;iss from a considerable distance upstream past that
locality. This hypothesis was based on measurements showing water
moved as much as 13 miles during large ebb tides (Calif. Div. of Water
Resources, 1952). While it is evident that water flow greatly affects the
movement and distribution of young striped bass, several sources of
information indicate this hypothesis should be modified.

The large concentrations of young bass found along shorelines and
near the bottom in some areas clearly demonstrate that bass have con-
siderable control over their movement at an early age. While these
bass are too small to maintain their position in mid-water during pe-
riods of maximum tidal movement, they apparently seek favorable areas
during periods of low water velocity, so their movement cannot be
assumed to be directly correlated to water flow.

Diurnal catch fluctuations at the Tracy Fish Collection Facility also
indicate that young bass have considerable control over their movement.
Louver screens there collect fish from water entering the Delta Mendota

JUVENILE STRIPED BASS ABUNDANCE 89

Canal. Catches of striped bass are typically much greater at night than
(hiring the day (Bates et al., I960, Figure 15), indicating bass tend to
maintain their position during the day and move voluntarily at night.

More recent information indicates water generally moves much less
than 13 miles during a tide. For- example, a float we placed in the San
Joaquin River at the mouth of False River at the beginning of an ebb
tide on -Inly 29, 1957 moved a little over 7 miles downstream, and a float
we placed in the Sacramento River at Three-Mile Slough about an hour
after the start of an ebb tide on July 30, 1957, moved •">! miles down-
stream. The tidal variations at the Golden Gate on these dates were
-)-6.1 to — 0.5 and +5.5 to — 0.1. The Department of Water Resources
estimated the maximum tidal movements from the Sacramento River at
Stations 13a and 10. and from the San Joaquin River at Station (i on
August 20, 1959 were 8, 6, and 7 miles, respectively (Carl Warner,
Letter). On that day. tidal variation at the Golden (late was • 5.7 to
— j— 0.1. These water movements were at mid-river; movements near the
channel's periphery are appreciably less.

Hence, it is not surprising that catches at annual survey stations did
not reflect catches at stations farther upstream.

Temporal Distribution of Young Bass

The annual surveys can be biased by differences in temporal distri-
bution even though they are made at approximately the same time in
relation to bass size at Antioch. One cause of this is that survey time
could vary as much as a week in relation to bass size at Antioch since
minus tides occur only every other week. The rapid changes in bass
abundance, indicated by differences in daily catches during the 1957-
1962 annual surveys and by the differences between successive Delta-
wide surveys, indicate this bias is important.

Bias also occurs because successful spawning is noi distributed
through the season in a similar manner each year. In years such as
1962, when the distribution was unimodal. a single survey during the
peak of abundance would sample the population more efficiently than
in years such as 1959, when there were several modes.

The Delta-wide surveys minimized this bias by taking several samples
each season. Some differences between Delta-wide and annual survey
results are partially due to this bias and show its importance. For ex-
ample, the annual survey indicated the difference in abundance between
1959 and 19(52 was about 20 times, while the Delta-wide survey indi-
cated only a sixfold difference.

Geographical Distribution of Young Bass

Annual surveys would measure abundance accurately only if geo-
graphical distribution remained the same each year. When analysis of
the 1954-1956 surveys showed that geographical distribution varied, the
survey stations were changed to try to sample the most densely popu-
lated areas to minimize the bias. The surveys and exploratory sampling
indicated this could best be done by retaining Stations I and II and
selecting additional stations in Spoonbill Slough and Montezuma
Slough, where large numbers of bass had been caught regularly. How-
ever, the magnitude of geographical distribution variations shown by
the Delta- wide surveys (Table 7) indicates that no group of four or five
stations can give an accurate indication of annual abundance.

'Mi CALIFORNIA PISH A.ND GAME

The Delta-wide survey stations used during 1962 did no1 cover 1 1 1 « ■
whole area inhabited by young bass. Young bass probably occurred in
the unsampled portions of the southeastern San Joaquin Delta in con-
centrations aboul equal to their abundance in the adjacenl sampled
areas I Erkkila et al., 1950; Calhoun, 1953). However, the water volume
there forms only a small fraction of the total volume in the Delta.

The exploratory tow ael sampling and the fall seining indicated few
young hass occur in the Sacramento River above Station 10. This sub-
stantiated earlier findings (Calhoun and Woodhull, 1948), so this omis-
sion was probably not important.

The omission of the western part of Carquinez Strait, San Pablo Bay,
and the Xapa River may have seriously biased the survey results. Ap-
preciable bass concentrations certainly occurred in the Napa River in
1958, but this may have been a fairly unusual occurrence, since virtu-
ally no bass were caught there in 1957, 1959, l!)(i(), or 1961. This and
the fact that the water volume at the four Napa River stations included
in the 1959 and 1960 surveys amounted to less than three percent of the
water volume of the area now surveyed indicates omission of these
stations probably causes little bias.

Some young bass are present in Carquinez Strait and San Pablo Bay,
and the water is relatively clear there, so low net efficiency might cause
poor catches. However, the small bass catches there in 1958, when many
bass were caught in the Napa River and when many other fish were
caught in San Pablo Bay, tends to refute this. We have observed, schools
of bass in sheltered places along the shore in this area, which may indi-
cate they seek sheltered areas in clear water and are thus unavailable to
the tow net. The water volume here is great, so the presence of a few
bass could significantly bias the survey. However, I believe the bias is
small, since this is certainly the periphery of the bass' range.

Comparison of Annual and Delta-wide Surveys

The three annual survey indices show similar trends, although some
appreciable differences in magnitude occur, with Index A having great-
est variability. This was to be expected, since it is based on more limited
sampling, and it indicates that Indices B and C are superior.

While all Delta-wide survey indices had similar trends, there are
appreciable differences in magnitude among indices. The differences in
magnitude between Indices A and B reflect annual geographical differ-
ences in distribution and the unequal volumes of water at various sta-
tions. For example, the difference between 1960 and 1961 is due pri-
marily to the fact that 28 percent of the I960 catch was made at
stations with water volumes over 60,000 acre-feet, while 42 percent of
the 1961 catch was made at these stations. These variations indicate
that weighing by volume is necessary, and that Index A is unsatis-
factory.

Theoretically, Index C should be superior to Index B, since biases
due to temporal variations in annual distribution would be less. The
size range 1.0 to 1.4 inches has additional advantages in that the net
had close to maximum efficiency in this range and few bass were either
larger during the first survey or smaller during the last survey.

However, survey C was not as good as survey B, because the catches
in the limited size range were affected more by chance variation than
was the total catch. This is exemplified by differences in the relative

JUVENILE STRIPED BASS ABUNDANCE 91

abundance within different size groups (Table 9). Annual variations in
growth and mortality rates would also tend to make Index B more
accurate. Therefore, Index B is superior for 1959-1962 and Index D
should be used in the future, since its stations cover the Delta better.

For the 1959-1962 period, both the Delta-wide and annual survey
indices exhibit similar trends. However, differences in magnitude ex-
ceeded 100 percent primarily because of the annual survey's greater
biases, but also because of its greater sampling variability, associated
with its more limited nature. Therefore, Delta-wide surveys are prefer-
able, not only because of their greater accuracy, but also because they
provide additional information on geographical distribution.

The best estimate of relative abundance during the 10-year period
c;iii be made by combining "Annual Survey" Index A for 1953-1956,
■'Annual Survey" Index P> for 1957 and 195s. and Delta-wide survey
Index B for 1959-1962 (Table 5).

Comparison of Surveys and Catches at Tracy Fish Collection Facility

Fish in the water entering the Delta Mendota ('anal are screened out
by louvers at the Tracy Fish Collection Facility (Bates et al., 1960).
Striped bass catches there should be proportional to the abundance of
Ikiss in the sloughs south of the San Joaquin River, Delta-wide survey
stations 1, 2. and 3 sampled part of this area and catches there were
similar to the relative annual catches at Tracy (Table 19). This sup-
ports the accuracy of the Delta-wide surveys.

TABLE 19

Comparison of Relative Annual Abundance of Striped Bass at Stations 1, 2, and 3
with June and July Catches at Tracy Fish Collection Facility

Weighted catch at Ratio to 1959 Tracy'1 Ration to

Year Stations 1, 2, S abundanct catch 1959 catch

1959__ 13.r>!H l.oo 8,860 1.00

1960__ ir(.s47 1.17 10,246 1.16

1961___ L's.:?33 2.08 15,166 1.71

1962___ 26,426 1.94 14,032 1.58

1 To nearest thousand bass.

Causes of Uneven Local Distribution

The causes tor the variability in vertical distribution are not obvious.
The concentration of fish near the bottom in the western Delta was
probably related to the lower water velocities there, since bass have
been shown to seek areas of lowered velocity (Kerr, 1953). The upwards
movement during flood tide in the western Delta may also have been
related to velocities, since velocities are less during flood tides than ebb
tides. However, the fact that bass generally remain near the bottom
during low slack tide, come up during peak flood tide flows, and then go
back down as high slack tide approaches (Figure 4) indicates it is not a
simple reaction to velocity.

The differences between the eastern and western Delta are even more
difficult to explain. A possible explanation is eastern Delta waters gen-
erally carry a heavy load of finely divided plant detritus. This is most
dense near the bottom and could either cause bass to avoid this area or
cause inaccurate sampling results by clogging the net. However, this
hypothesis was discounted by the distribution at Station 7, where there
also was a heavy load of plant detritus, and by the lack of any sub-

92 I ILIFORNl \ PISH \\"l> GAM]

stantial change al eastern Delta stations during slack title when virtu-
ally all plant detritus settles to the bottom.

Another possible explanation is thai water velocities are generally
greater in the western Delta. Bowever, again this cannot be a simple
reaction to velocity, since there was no common distribution when veloc-
ity approaches zero al slack t ide.

A reasonable hypothesis for the cause of differences in horizontal
distribution between the eastern and western areas is thai western
areas had shallow shelves with growths of sedges {Scirpus sp.) extend-
ing into the water, while at eastern stations the hanks dropped abruptly
to 20 or more feet. The shallow areas near shore would attract fish.
siner water velocities would be lower, especially where the sedge growths
extended into the water.

Causes of Abundance and Distribution Variations

A primary purpose of this work was to relate the abundance and
distribution estimates with observations of physical and biological envi-
ronmental changes, to try to identify conditions controlling spawning
success. Physical factors such as salinity (Bishai, 1961), and water cur-
rents | Bishai, 1960) have been directly or indirectly related to the
survival of pelagic fish eggs and larvae, and light is deleterious to
trout eggs (Leitritz, 1959).

A relationship between water temperature and egg and larval bass
survival would not be surprising, since striped bass spawning is closely
related to water temperatures. Peak spawning usually occurs at temp-
eratures between 60° and 67 F. ( Raney, 1952), and spawning fre-
quently ceases during periods of decreasing water temperatures in the
Sacramento-San Joaquin River system 'Calhoun. Woodhul] and John-
son. 19.1D; Chadwick, 1958; Albrecht, unpublished data).

Air temperature is the only environmental factor previously shown
to be related to striped bass abundance. The mean February to May air
temperature in Washington, D. C. had a —0.354 correlation with the
commercial catch of adult striped bass 2 years later along the Atlantic
Coasl from 1884-1937 (Merriman, 1941). This correlation is significant
at the one percent level. Presumably, air temperature was related to
egg or larval survival indirectly through other environmental factors,
Mich as water temperature.

Correlation coefficients for the relationships between young bass
abundance and water temperature, water temperature fluctuations,
runoff, salinity, and light (sky cover- (Table 20) were not signifi-
cantly different from 0. However, significant relationships may still
exist, since correlation coefficients are quite variable for small samples
(Snedecor, 1956). Estimates of bass abundance are not precise, and the
most desirable environmental measurements are not available in all cases.
Moreover, while one factor may affect egg and larval survival, overall
survival is probably controlled by a combination of factors, so a high
correlation between one factor and voting fish abundance is unlikely
(Ricker, 1958).

Spawning stock size is a biological factor which might determine
abundance of young. While no marked relationship generally exists be-
tween the size of an adult stock and the number of recruits (Beverton
and Holt. 1957). Radovieh (1962) has shown that the Pacific sardine

JUVENILE STRIPED BASS ABUNDANCE 93

TABLE 20

Relationship Between Abundance of Young Striped Bass
and Various Environmental Factors

II uter Water

Abutnlii>i<-r of tempera- temperature Sky

Year young bass ture1 fluctuations2 liunoff3 Salinity' cover6

1953 1.23 61.1 11 659 22 L58

1954 1.34 (!4.2 11 640 348 107

1955 0.68 61.8 15 320 112 92

L956 0.44 62.4 10 866 8 127

L957 0.48 r,:;.r, \:, 503 84 165

1958 0.67 63.9 7 1,749 4 in I

1959 - 0.38 65.3 12 224 326 95

1960 . __ 1.00 63.9 18 301 192 134

1961 1.04 259 248 L30

1902 2.00 76 131

Correlation

coefficient —.24 .04 .09 .13 +.17

1 Mean April-May water tempei itui t Coi I ta P.G & E. Steam Plant, Antiocb.

-Sum of decreases in mean temperatures between successive days from the day that the mean temperature first

reaches 60° F. to the end of .May at the Conti i Costa Steam Plant.
8Tota] in' i ured Bon to the Delta during April, May. and June in ten thousands of acre feet. From Calif.

Dept. of Water Resources Water Supervision and Watei Flow Bulletins.
' Average salinity in parts of chlorides per 100,000 parts of water during June and July at Collinsville on
imento River. Measurements taken l. ftei iiii:li high tide .it 1-daj intervals. From Calif. Dept.

of Wat. -I Resources Watei Supervision and Watei Flow Bulletins.
5 Sum of daily sunrise-sunset sky cover in lOths during May at Sacramento Airport. From records of U.S.

Dept. of Commerce, Weather Bureau.

(Sardinops caeruleus) population fits a model describing the relation-
ship of stock size and environmenl to production of young.
Available Long-term indices of adull bass abundance are based on

catch statistics of limited accuracy ( Chadwick, 1962 i, and none of these
provides a suitable measure of spawing stock. The besl available index
of bass spawning stock is angler success in the Delta during the springs
of 1959 through 1962 i Albrecht and ( Jhadwick, m.s. i. The mean catches
per hour there during These springs were 0.1 1 s. 0.085, 0.074. and 0.050.
These have a definite negative relationship with the index of abundance
of young for these years, but The significance of this cannot be judged
from so few measurements.

The distribution of young bass might also be affected by environ-
mental conditions. Water flow and salinity are the environmental condi-
tions most likely to affect distribution, since bass eggs and larvae are
pelagic and since bass seek fresh water for spawning (Raney, 1952).
In the Sacramento-San Joaquin Delta, the effects of water inflow and
salinity cannot be differentiated, since they are mutually controlled. For
correlation purposes, relative distribution of young bass was measured
by both the percentage of the annual survey total catch made at Sta-
tions 1. II, and VI for the years 1957-19(32 and the proportion of the
total bass catch taken above the confluence of the Sacramento and San
Joaquin rivers during the two extensive 1951 surveys (Calhoun, 1953)
and during the 1959-1962 Delta-wide surveys. The correlation coeffi-
cients between distribution and runoff and salinity are quite high
(Table 21). The correlations with our annual survey distribution are
significant at the 10 percent level and 1 percent level, respectively.
While evidence based on so few years is not conclusive, it strongly indi-
cates that young bass are farther upstream during years of high sa-
linity and low runoff than in years of low salinity and high runoff.
This could reflect either the distance adults migrate upstream to spawn

94 CALIFORNIA PISH AND GAME

TABLE 21

Relationship Between Distribution of Young Bass and Salinity
at Collinsville and Runoff to Delta

Proportion of bass catch abo\ < Proportion of A nnual

confluena of Sacramento and Survey total catch caught
Year San Joaquin finis at stations I. II, and VI

1951 81

1957 68

1958 49

1959 94 84

1960 94 85

1961 91 90

1962 <iT 83

Correlation with salinity* +.74 +.76

Correlation with runoff f — .78 ■'•>'■'<

Si. Table 20 fur salinity measurements. 1951 salinity v
See Table -11 for runoff measurements. 1951 runoff = 502.

or how far eggs and larvae are carried downstream by water currents.
Facts necessary to determine the relative role of each are not available.

Relation of Recruitment to Abundance of Young

The second purpose of this study was to determine if recruitment to
the fishery is related to abundance of young-of-the-year bass. This has
never been measured for any striped bass population. However, good
fishing on the Atlantic Coast has been related to dominant year-classes,
which have been recognized in their third year by rough quantitative
observations (Merriman, 1941). Dominant year-classes have not been
recognized in California's striped bass population.

Striped bass enter the fishery as 8-year-olds. Good measurements of
annual recruitment are not available. At present, the best measure is
the angler catch per hour for 3-year-old bass in the Delta during April
and May of 1959 through 1962* (Albrecht and Chadwick, m.s.). This
essentially measures the relative abundance of males, since 3-year-old
females are immature and do not migrate to the Delta (Chadwick, un-
published data). The respective catches per hour were 0.034, 0.033,
0.016, and 0.016. These would be recruitment indices for the 1956-1959
year-classes. Except for 1958, they parallel the abundance of young in-
dicated by our annual surveys.

While annual recruitment cannot be measured from the total angler
catch, the total catch does reflect trends in recruitment. The fall party
boat fishery in Carquinez Strait-.San Pablo Bay gives the best available
measure of overall bass abundance (Chadwick, 1962), and has the
added advantage of being largely composed of bass at the end of their
third and fourth growing seasons.

The catches per hour there were 0.24, 0.35, 0.23, 0.24, 0.20 for 1957
through 1961. If recruitment is related to the abundance of young bass,
these catches per hour should reflect trends indicated by spawning
success surveys three or four years earlier and, except for 1957, they
do. While these data suggest a direct relationship between bass recruit-
ment and abundance of young during their first summer, the data are
so limited I consider this to be a tentative hypothesis.

JUVENILE STRIPED BASS ABUNDANCE 95

Growth and Survival

The 2-week growth increments of 0.3 to 0.7 inches are smaller than
comparable growth increments of 0.5 to 1.1 inches reported in the
Patuxent River (Mansueti, 1058). As a result, Patuxent River bass
average over 2 inches long in early July, while bass in the Delta aver-
age 1.0 to 1.5 inches long then, despite the fact that peak spawning
occurs during May in both places.

Growth increments were greatest in 1959 and smallest in 1962, sug-
gesting that growth may be negatively correlated with abundance.

The relationship between bass size and net efficiency precludes accu-
rate survival estimates from tow net catches. However, the coincidence
of modes in our 1959 and 1960 Delta-wide surveys indicates biweekly
cycles in spawning time or survival, since survey- were taken at 2-week
intervals. Tidal stage is the only environmental factor having an obvi-
ous 2-week cycle, so survival or -pawning intensity may be related to
tidal stage.

The decreasing annual variations in abundance indices ;is bass size
increased from 1-inch to over 2 inches (Tabic 9) could be caused by
density dependent mortality. However, the small annual variations
among 0.3- to 0.5-inch bass would not be expected if this were true.
Hence, the small animal variations were probably chance similarities
among the small catches within the largesl and smallesl size groups.

ACKNOWLEDGMENTS

Thanks are expressed to the many members of the Department of
Pish and Game who contributed to the success of this program. These
include George McCammon, John Skinner, and Arnold Albrecht, who
supervised the 1953, 1954-1956, and 1962 surveys, respectively. John
Robinson, Robert Toth. and William Heubach also assisted in carrying
out parts of the field work. All of these and Frederick Meyer assisted
in tabulating and analyzing the data. Vincent Catania made all of the
nets, contributed many ideas, and captained the boat at all times.
Donald Fry, Jr., contributed the basic ideas for the method of fishing
the three nets to measure vertical distribution.

I thank the California Department of Water Resources for calculat-
ing water volumes, and the Pacific Gas and Electric Company for
providing the water temperature measurements.

SUMMARY

We sampled young-of-the-year striped bass to measure their relative
abundance throughout their range in the Sacramento-San Joaquin
River system. We did this to obtain a measure of annual abundance
which could be used to determine: (i) if spawning success and recruit-
ment are correlated, and (ii) which environmental factors control
spawning success.

Sampling was done with a fixed frame tow net, which earlier studies
had shown was efficient for sampling young bass. The sampling in-
cluded: (i) various experiments to determine if the tow netting accu-
rately measured abundance in the immediate area of sampling; (ii)
annual surveys consisting of one series of samples at a few stations
to try to develop an annual index of abundance; (iii) Delta-wide sur-

9<i I \i.ii'(ii;\[.\ PISH AND QA ME

veys consisting of repeated sampling al many stations throughout the
bass' range to develop an index of abundance suitable for determining
ii' our annual surveys accurately measured abundance; and (iv) limited
exploratory tow netting and seining to determine the range of young-
of-1 he-year bass.

Experiments to determine if tow netting accurately measured Local
abundance showed that it did measure the abundance of 0.7- to 2.0-inch
bass reasonably accurately, at least within our Delta-wide survey area.
Accuracy requires sampling all depths equally because the vertical
distribution of bass is not uniform and is also variable. Variations in
horizontal distribution biased sampling of smaller bass in some areas,
but this bias appeared to be relatively insignificant. The effects of water
transparency were not thoroughly evaluated, but the available evidence
indicates it was noi a serious problem in the survey area.

The uneven distribution is largely unexplained, bu1 behavioral char-
acteristics partially related to tidal stage and water velocity are impor-
tant. These behavioral characteristics indicate that even very young
bass have considerable control over their distribution and movement.

Our annual and Delta-wide surveys showed important annual geo-
graphical and temporal differences in bass distribution, although the
Delta-wide surveys showed that most of the population was in the
Sacramento and San Joaquin rivers within a few miles of their con-
tinence. Marked changes in abundance at given localities occurred
within 2 days, and overall abundance in the Delta changed signifi-
cantly within 2 weeks.

Biases associated with these differences were the primary cause of
substantial errors in our annual survey abundance estimates. These
errors tended to magnify annual variations. Delta-wide surveys pro-
vided more accurate measures of annual abundance, although they
were also somewhat biased, because tow netting and seining showed
thev did not cover the entire nurserv area, and there were biases in
the accuracy of local measurements.

Our annual surveys indicated that young bass declined in abundance
from a 1953-54 peak to a 1959 low and then increased to a 10-year high
in 1962. The Delta-wide surveys showed a similar 1959-1962 trend.

Xo relationships were detected between young bass abundance and
water temperature, water temperature fluctuations, runoff, salinity,
light, or spawning stock size. However, the available data are inade-
quate for a definitive evaluation. The data do show their distribution
probably has a relationship to salinity and water runoff to the Delta,
with bass being farther upstream in years of greater salinity intrusion
and lower runoff.

The results also suggest a direct relationship between abundance of
young-of-the-year bass during the summer, and year-class recruitment.
They also indicate that growth of young bass is slower here than in the
Patuxenl River, and is negatively related to abundance.

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1956. Statistical methods. Ames, Iowa State College Press, p. 163.
I'.S. Departmenl of the Interior

L957. Fish Protection al the Tracy Pumping Plant, Central Valley Project, Cali
fornia, !>(> pp.

Winsor, C. P., and G. L. Clarke
1!»40. A statistical study of variation in the catch of plankton nets. Jour. Mar.
Res., vol. ■'>, no. 1. pp. l-.'54.

JUVENILE STRIPED BASS ABUNDANCE 99

APPENDIX A

Water Volumes ' of Delta Segments Represented by
Delta-wide Survey Stations

1959-61

1962

1959-61

1962

ut inn

volume

volume

Station

volume

volume

1

23

19

213

2

15

20

14

3

15

21

5

4

11

22

1

5

21

23

3

6

40

24

113

7

56

25

13

8

22

26

40

9

5

27

81

60

1(1

32

•-'7a

49

11

52

35

28

in

1 l.-i

27

29

!l

12

63

53

30

02

7>-2

13

90

43

.-sou

26

L3a

31

:;i

11

14

4

32

5

15

15

33

8

16

20

:;i

10

17

44

35

•>•>

18

M

70

1 Volumes in thousands of acre feet at mean half-tide with an estimated reliability uf ± 15 percent. Estimates
made by Delta Branch, California Department ol w itei Ri urce

SOME OBSERVATIONS ON FACTORS ASSOCIATED

WITH SURVIVAL OF STRIPED BASS

EGGS AND LARVAE'

ARNOLD B. ALBRECHT

Inland Fisheries Branch

California Department of Fish and Game

INTRODUCTION

Striped bass, line, -us saxatilis I Walbaum), are the primary gamefish
inhabiting the Sacramento-San Joaquin Delta. They have flourished
there since being introduced Prom New Jersey in 1879.

The population is now threatened by habitat changes which will re-
sult from a planned water development project. Although the specific
plan for this project has not been selected yet, it will certainly alter
current, salinity, and temperature conditions in a major portion of the
present striped bass spawning grounds. Knowledge of the possible
effects of these changes on striped bass reproduction is needed to insure
adequate consideration for this species in the final project design. This
paper reports the results of laboratory experiments conducted during
l!Mi2 and 1963 to determine these effects.

In conjunction with these experiments, measurements were made of
the diameter, specific gravity, and vertical distribution of developing
striped bass eggs. This information could be useful in designing screen-
ing apparatus to protect the developing semi-buoyant eggs from water
diversion pumps.

This work will also aid in evaluating the feasibility of introducing
striped bass into reservoirs, since lack of successful reproduction is
believed to be the cause of failure in attempts to establish striped bass
populations in freshwater impoundments.

There have been no previous laboratory studies of the factors which
may affect striped bass egg and larval survival, but many field observa-
tions have yielded pertinent facts.

Actual observation of spawning (Woodhull, 1947; Morgan and Ger-
lach, 1950), and the collection of recentlv-spawned, developing eggs
(Pearson, 1938; Woodhull, 1!>47; Calhoun' and Woodhull, 1948; Cal-
houn et a!., 1950; Tresselt, 1952; and Rathjen and Miller, 1957) have
shown that striped bass spawn in fresh water in a moderate to swift
current. Mansueti (1958a) infers that suspension of the semi-buoyant
striped bass egg by water current is necessary for its survival. Consid-
ering the failure of striped bass to reproduce in freshwater impound-
ments, this is a logical assumption, but it apparently has not been sub-
stantiated by experiments or direct field observations.

1 Submitted for publication November 1963. This work was performed as part of
Dingell-Johnson Project California F-9-R ; "A Study of Sturgeon and Striped
Bass," supported by Federal Aid to Fish Restoration funds.

( 100 )

STRIPED BASS EGG AXD LARVAL SURVIVAL 101

Spawning has never been observed in brackish or salt water. Tresselt
(1952) collected developing eggs at salinities up to 2,000 ppm, and we
in California have captured newly-hatched bass in brackish waters fre-
quently, but they could have easily drifted into these areas from fresh
water. Concerning brackish water spawning, Mansueti (1958a) states.
"The production of eggs in brackish waters, of greater density than the
eggs, would probably insure floatation, and hence survival, especially in
quiet waters." This would also apply to eggs produced in fresh water
and carried into brackish water. No previous studies have been made
to determine the maximum salinity thai will allow egg and larval
survival.

Water temperature is the principal factor controlling the time of
striped bass spawning (Calhoun et al., 1950; Erkkila et al., 1050;
Rathjen and Miller, 1957; and Chadwick, 1958). The minimal tem-
perature at which spawning occurs in most areas is about 58°F. Peak
activity occurs a1 60-65°F. and declines rapidly thereafter. At these
temperatures, 2 days or less are required for hatching.

Striped bass eggs have been incubated successfully at temperatures
ranging from 58 F. (Bigelow and Welsh. 1925) to 72 F. (Merriman,
1!I41).L> However, no previous attempl has been made to determine
temperature tolerance limits, or the effed of temperature fluctuation
on c^^ survival.

Numerous diameter measurements of developing striped bass eggs
been made on the Atlantic Coasl (Pearson, 1938; Merriman, 1!»41 ;
Mansueti, 1958a; and Mansueti and Hollis, 1963 . Generally, means of
approximately 3.5 nun were observed, with a range of 2.4 to 3.95 mm.
Smaller eggs (1.32-1.53 mm) were collected from the Blackwater,
Transquaking, and Manokin rivers (Mansueti and llullis. 1963). In
California, Wuodhull (1947) reported a mean diameter of 3.3 mm for
a preserved sample of eggs from the San Joaquin Kiver.

The specific gravity of the striped bass egg has not been measured
previously. Pearson (1938) and .Mansueti (1958a) both state that the
striped bass egg "'is slightly heavier than fresh water." suggesting a
specific gravity slightly greater than 1.0.

Observations on the depth at which striped bass eggs move in the
water are conflicting. Sin-face and bottom samples, in which there were
large numbers of eggs, taken from two stations on the Mattaponi River,
Virginia, indicate a greater egg concentration on the surface (Tresselt,
1952). In the Hudson River, New York. Rathjen and Miller (1957
found a subsurface net (18 to 20 feel < was more efficient (1.42
eggs hour) than a surface net (0.44 eggs hour) or bottom trawl (0.61
eggs/hour). Hatton (1942) and Woodhull '1!»47'. concerning limited
collections in the Sacramento-San Joaquin Delta, report egg concen-
trations near the bottom.

METHODS

Developing striped bass eggs were collected from the Sacramento and
San Joaquin rivers by large-mesh plankton nets (23 meshes/inch) set
in the current from an anchored skiff. These nets were 20 inches in
diameter, with a cone approximately 4 feet long. A quart Mason jar
was attached at the apes of each net.

2 See Mansueti. 1958a, Table 3, page 10, for a summary of published hatching times
of striped bass eggs.

102 CALIFORNIA PISH AND GAME

Collected eggs were placed in 5,000 ml round-bottom flasks and
incubated under the desired physical conditions. Approximately LOO
eggs were placed in each hatching Mask. The period from time of collec-
tion to the start of the incubation tests varied from 1 to 4 hours.

Tests of the effed of egg suspension were made in fresh water agi-
tated with air to suspend eggs either over a gravel substrate or with no
substrate. 'These were compared with tests in which eggs were allowed
to rest on a gravel substrate. In all other tests, eggs were kept suspended
by air agitation in water of desired temperature and salinity without
any substrate. One observation was made on egg tolerance to sunlight
by exposing 100 developing eggs in a 2,500 ml open-top jar to brighl
sunshine for 5 hours, and retaining a similar shaded control.

Only one attempt was made to keep larval bass alive beyond the
absorption of their yolk sac. These fish were \'^\ daily rations of brine
shrimp.

All eggs for the laboratory rearing experiments were collected in
the temperature range of 63 to 68°F. Acclimatization to the desired
temperature was gradual, usually over a period of approximately 30
minutes. Temperature was controlled by placing the hatching flasks
in water baths, supplied either with tap water or water recirculated
from a Harshaw temperature control unit. The initial 1962 hatching
experiments were conducted in the Delta Field Base near Antioch.
Diurnal temperature fluctuations in the building resulted in tempera-
ture changes of about 10°F. in the water bath. Some 1962 and all 1963
experiments were conducted in the Sacramento Field Station where a
temperature control unit was available and temperature fluctuations
could be kept under 2°F.

Saline solutions consisted of brackish San Francisco Bay water mixed
with fresh American River water. Eggs were transferred directly into
the desired saline solution without any acclimatization.

Chloride analyses of the San Francisco Bay water were made by
the chemical laboratory of the California Department of Water Re-
sources using the Mohr method. Water samples for oxygen determina-
tions were siphoned from the center of the hatching flasks at the time
of the first larva count, and analyzed by the Rideal-Stewart modinca-
t ion of the Winkler Method.

Eggs and larvae were measured using an ocular micrometer in a
dissecting microscope.

Egg specific gravity was measured by placing individual eggs in a
series of saline solutions of known densities and observing if they
floated, remained suspended, or sank. Saline solutions of various den-
sities were prepared using 99.8 percent pure NaCl and distilled water.
After the approximate egg specific gravity was determined, a series of
NaCl solutions ranging in density from 1.00030 to 1.00065, with inter-
vals of approximately 0.00005, were prepared for the measurements
reported here. Individual eggs were assigned the specific gravity value
of the solution they were most equal to in density. New solutions were
usually prepared for each sample of eggs. Eggs were transferred from
one solution to the next on the tip of an eye dropper, using care to
avoid contamination of each solution. Eggs with a damaged chorion
were not used.

STRIPED BASS EGG AND LARVAL SURVIVAL

103

FIGURE 1. Top view, .striped bass eggs less than 12 hours

William E. Schafer, June 1963.

old at 64 F. Phofograph by

FIGURE 2. Top view, striped bass eggs approximately 36 hours old at 64° F. Phofograph by

William E. Schafer, June J 963.

104

CALIFORNIA PISH \Nl> GAME

FIGURE 3. Striped bass larvae shortly after hatching. Photograph by William E. Schafer,

June 1963.

Measurements of egg diameter and specific gravity were made in
quarter stages of onx development, based upon a hatching time of
48 hours at 62°F. Drawings from Mansueti (1958a) aided in aging
the collected eggs.

The vertical distribution of developing bass eggs was studied by
fishing three plankton nets simultaneously at different depths and com-
paring catches. Subsurface nets were fished slightly longer than the
surface net, but the number of eggs collected per minute of sampling
was determined for each ne1 and employed in calculating egg density
at various depths. Ne1 sets ranged from 10 to 20 minutes in duration.
"Water velocity was recorded with an Ott current meter.

RESULTS

Suspension of Developing Eggs

In all laboratory experiments, eggs kepi suspended by air bubble
agitation of the water hatched better than those allowed to rest on a
substrate (Table 1). Eggs suspended in flasks without any substrate
had a mean hatch of 81 percent, and eggs suspended over a gravel
substrate had an average hatch of 61 percent. The lower hatch in the
latter case may have been due to difficulties encountered in keeping
eggs suspended over the gravel substrate. In comparison, no eggs al-

STRIPED BASS EGG AND LARVAL SURVIVAL 105

lowed to rest on a gravel substrate without aeration hatched, and only
an average of 8 percent of the eggs resting on a gravel substrate with
aeration at the surface hatched.

TABLE l

Survival of Striped Bass Eggs Suspended by Aeration Over No Substrate (NS),

Suspended by Aeration Over a Gravel Substrate (SG), Resting on a

Gravel Substrate, Aeration at Surface (RG), and Resting on

a Gravel Substrate, No Aeration (NA)

Time

Live

Date

Wa 1

1). 0.

\ o. of

interval

larvae

started

Condition

temp. F.°

ppm

> ggs

(hours)*

< /<. rceni i

5 6 62

NS

62-7-!

7.7
8.4

L00
L00

50

92
93

.-

U

8.3

50

"

58

RG

it

7'.'
8.0

100
L00

..

3

8

ti

ti

8.0

50

H

0

\.\

tt

7.0

Km

*;

0

• •

a

6.4

100

..

0

..

..

7.1

.-,(1

it

0

5/6/63

SG

62-64

8.8

100

71'

38

RG

••

7.:.

1(10

"

0

5/9/63

SG

62-64

9.1

88

72

93

RG

•■

8.8

88

..

10

5/14/63

SG

62 64

8.8

Km

71'

:,1

RG

..

9.0

Km

••

27

* In this and following tables, hours refer to the time period from the start of the test to the larva count.

The average oxygen contenl of the flasks in which air was introduced
ai the surface was only 0.3 ppm Lower than in those flasks with the
air introduced near the bottom. Water samples for these measurements
were siphoned from the center of the hatching flasks, so micro-oxygen
deficiencies could have existed in the immediate perimeter of each egg.
Also, fine debris settled on the chorion of eggs riol in suspension, and
could have interfered with the respiration of the developing embryo.

Egg and Larval Salinity Tolerance

Laboratory experiments indicated striped bass eggs can withstand
a modei-ate increase in salinity, and that survival of the resulting
larvae is best in water of slight salinity (Table 2).

In 1962, hatches of 63, 89, and (|4 percent were obtained in water
of high salinity (chlorides 14.101) ppm ; however, the resulting larvae
reared in this water suffered an almost complete mortality within 48
hours after hatching. Hatches in fresh water controls ranged from
87 to 93 percent, and 5 days after hatching 75 percent still survived.

The second year's results were similar but larval survival was more
variable. High hatches wen- achieved at salinities up to 9,480 ppm of
chlorides. Survival was consistently high in water of low salinity
( chlorides H20-948 ppm), and relatively good in fresh water and water
of moderate salinity (chlorides 4,595-4,740 ppm). Survival in water
of higher salinity (chlorides 9,190-9,480 ppm) was good in one of three
flasks; however, many of these fish were deformed.

Standard lengths and yolk absorption were similar for larvae devel-
oping at the various salinities (Table 3). The yolk sac was over 50
percent absorbed at 6 days, and growth in body length ceased.

106

CALIFORNIA I-IMI AND GAME

TABLE 2
Survival of Striped Bass Eggs and Larvae at Various Salinities

( Ihlorides

Water

I). 0.

Nun ilici

Percentage of larvae surviving (hours)

|

I late started

ppm

temp. 1

ppm

of eggs

K) 64

88

160

5 1 t 62

7'.

58-65

8.4

120

87

7 OSS

a

120

90

1 1,100

a

7. 1

120

94

•'. -'1 62

Fresh

00-73

7.9

133

93

Fresh

"

7.8

99

88

88*

82

71

14.100

"

7.0

133

03

14.100

6.9

133

89

26*

2

1

Fresh

02-04

8.5

100

72

144

216

264

5/6/63

97

83

54

37

Fresh

"

9.7

100

70

65

41

30

920

••

7.7

100

100

95

94

94

920

a

8.8

100

96

78

71

67

l 595

"

8.5

100

91

69

47

42

4.595

it

8.5

100

100

59

47

42

9,190

"

8.1

100

96

10

9,190

it

8.2

100

98

70

42

34

5/17/63

Fresh

04

100

93

24

2

948

u

100

95

68

46

4.740

"

100

92

45

18

9,480

100

90

56

14

Surviving larvae combined.

TABLE 3

Mean Standard Length (s.l.) and Mean Yolk Mass Length (y.l.) in mm of Striped
Bass Larvae Reared in Water of Various Salinities at 64° F.

72 hours

1 1 hours

216 hours

264 hours

Chlorides ppm

Larvae

s.l.

y.l.

Larvae

s.l.

y.l.

Larvae

s.l.

Larvae

s.l.

Freshwater

920

13

10

9

5.0
4.6
4.8

l.l
1.0
1.0

6
5
5

8

5 . !)
6.0
5.9
5.6

. 5
.6
.0
.6

5
4
5
5*

5.7
6.0
5.8

5.4

11
12
12
17**

0.0
5.8

4,595,

6.1

9,190.

5.6

* 3 deformed bass.
** 3 deformed ha^s.

The tolerance of larval bass to sudden salinity increases was investi-
gated also (Table 4). Three-day-old larvae from eggs hatched in fresh
water were transferred to saline solutions of 948 and 4.740 ppm of
chlorides. < hie freshwater control was retained. At the age of approxi-
mately 6 clays, the larvae in all three solutions were fed brine shrimp
daily. Survival was better in saline solutions over a 3-week period;
however, brine shrimp survived better in the salt water also, so the
more continuous food supply could have enhanced bass survival. Can-

STRIPED BASS EGG AND LARVAL SURVIVAL

107

nibalism was noted at the age of about 2 weeks and it became more
prevalent as the bass grew.

TABLE 4

Survival of Striped Bass Larvae when Transferred (T)
from Fresh Water to Saline Water

Live
Date Vo.of eggs Temp, larvae T,5/28 Lire /f"'"e (Days) **

started per jar F°. (72 hrs.) (96 hrs.) 1 6 23

5/24/63 100 65 !>7 NoT 83 31 9

5/24/63 loo 05 99 948 ppm * 90 41 23

5/24/63 LOO 65 88 4,740 ppm * 86 39 19

* Chlorides.
** Days after transfer from fresh water.

Egg and Larval Temperature Tolerance

The previously described l!Mi2 egg suspension and salinity tolerance
experiments indicated 10 F. temperature fluctuations between 58 and
73°F. do not prevent hatching, since an average of s"> percent of the
eggs in five fresh water tests hatched (Tables 1 and 2).

Other laboratory experiments indicated eggs and larvae can survive
at various constant temperatures ranging from 55 to 75°F. (Table 5).
Only 2 of 53 eggs held at 52 F. hatched. At 55 l-\. a mean hatch of 88
percent was obtained in three flasks, while at 62-64°F., a mean hatch
of 85 percent was obtained in six tests. The highest mean hatch. !>7
percent, came from three flasks held at 67-69 F. At 75 F.. survival at
72 hours was 67 percent, while at 80 F. it was only 7 percent.

TABLE 5

Survival of Striped Bass Eggs and Larvae
at Various Water Temperatures

fhite Water D.O. So. of Live larvae (percent)

started temp. F°. ppm eggs '/O hours 1 Y'f hours

5/29/62 52 53 4

5/29/62 _ . 67-69 .",:{ 98 83

5/20/62 _ 74-78 53 66 45

.'J hours 90 hours

6/7/62 . 67-(i!t 108 97 86

6/7/62 " los '.it; 74

6/7/62 70-76 108 93 76

6/7/62 " 108 81 57

72 hours 144 hours

5/6/63 62-64 8.7 100 81 71

5/6/63 " 8.5 100 97 83

5/6/63 " 8.7 100 76 65

5/6/63 80 7.5 100 3

5/6/63 : " 7.5 100 17

5/6/63 " 7.2 100 2

5/14/63 62-64 8.8 100 85 51

5/14/63 75 7.6 100 7<i 11

5/15/63 62-64 8.7 91 78 20

5/15/63 75 8.1 91 71 4

5/17/63 62-64 8.7 100 93 24

5/17/63 75 7.6 100 55 1

6/10/63 55 100 90 60

6/10/63 " - 100 90 30

6/10/63 " 100 83 54

Larval mortality occurred sooner at the higher temperatures. This
was probably due to faster yolk absorption, and because no provision

108

CALIFORNIA PISH VND GAME

was made for other nourishment. Yolk absorption ;it 72 hours in the
larvae reared ;it 75 V. was nearly comparable to yolk absorption in
larvae reared a1 62-64 V. at 144 hours (Tables 3 and 6). Hence, sur-
vival tnighl be similar a1 these two temperatures if adequate food was
available.

TABLE 6

Mean Standard Length and Mean Yolk Length (in mm) of

Striped Bass Larvae Reared in Fresh Water of

Various Temperatures at 72 Hours

Date Water TMrvae Standard Yolk

started temp. F. examined length length

6/10/63 r>r> 5 I.I 1.3

:> 17/63 . 64 4 4.7 1.0

5/17/63 . 7.1 4 5.0 .8

5/18/63 . _ 64 l i.e. .!>

5/18/63 . _ 7."> 5 -I.:; .7

5/9/63 . . 64 13 5.0 1.2

5/9/63 . _ 80 13 4.!) .5

Egg Tolerance to Sunlight

One observation was made on the effect of sunlight on egg survival.
Ninety-three of 100 eggs in an open-top 2,500 ml jar, exposed to 5 hours
of bright sunshine, hatched. A control, not exposed to the sunlight, had
a 78 percent hatch.

Egg Diameter and Specific Gravity

The diameter and specific gravity of eggs in seven collections were
measured (Table 7). Eggs in five collections from the lower San Joa-
quin River ranged from 3.3 to 4.6 mm in diameter, with means of 3.8
to 4.0 mm. Eggs in two collections from the Sacramento River near
Sacramento ranged from 2.5 to 3.8 mm in diameter, with means of 3.2
and 3.3 mm. Egg specific gravity measurements ranged from 1.0003 to
1. 00065, 3 with means of approximately 1.0005.

TABLE 7

Diameter and Specific Gravity Measurements of Striped Bass Eggs
Collected in the Sacramento and San Joaquin Rivers

Locality

Num-
ber
of
eggs

Diameter (mm)

Specific gravity

Date

Range

Mean

Range

Mean

April 17, 1962

San Joaquin River

84
25
20
83
50
64
25

3.4-4.3
3.3-4.6
3.8-4.2
3.3-4.4
2.7-3.8
2.5-3.6
3.3-4.1

3.8
3.9
4.0
3.9
3.3
3.2
3.8

1.00033*- 1.00053
1.00042 -1.00065
1.00033 -1.00065
1.00046 -1.00062+**
1.00042 -1.00062+***
1.00033 -1.00053

April 23, 1962

1.00045

April 25, 1962

May 7, 1962

June 12, 1962

San Joaquin River

San Joaquin River

Sacramento River __

1.00050
1.00051
1.00055

June 13, 1962
Mav 13, 1963

Sacramento River

San Joaquin River

1.00054
1.00043

* tine egg, 4.6 mm in diameter, had a specific gravity of approximately 1.00006.

** Four eggs sank slowly in a NaCl solution of 1.00062. They were assigned a value of 1.00065 for calculation
lit' the specific gravity mean.
*** Two eggs sank slowly in a NaCl solution of 1.00062. They were assigned a value of 1.00065.

3 The most dense saline solution used for measuring the Sacramento River collections
had a specific gravity of 1.00062. Six eggs sank slowly in this solution and were
assigned a specific gravity value of 1.00065 for calculating the mean.

STRIPED BASS EGG AND LARVAL SURVIVAL

109

No differences in egg size or specific gravity were noted among quar-
ter stages of egg development. The May 7, 1962 collection provided the
best comparison of these measurements (Table 8).

There was an inverse correlation between diameter and specific
gravity in the eggs collected from the Sacramento River on June 12
and 13, 1962 (Table 9). This suggests that larger eggs are more
buoyant.

table 8

Diameter and Specific Gravity Measurements of 83 Striped Bass Eggs
Collected May 7, 1962 from the San Joaquin River Near Antioch

\ umber
of eggs

Diameter (mm)

Specific gravity

Egg age (hours)

Range

Mean

Range

Mean

0-12

20
21
22
20

3 . 6 -4 . 1

3.7 l.l
3.3 1.3
3.6 1.2

3.9
4.0
3.9
3.9

1.00033-1.00065
1.00037-1.00059
1.00037-1.00065
1.00037-1.00065

1.00051

12-24

1 . 00047

24-36

1.0Q051

36-48

1 . 00053

Totals

83

3.3 It

3.9

1.00033-1.00065

1.00051

TABLE 9

Mean Specific Gravity by Egg Diameter of 114 Striped
Bass Eggs Collected June 12 and 13, 1962, from
the Sacramento River, Sacramento
Egg diameter Mean

( mm ) \ umber of eggs specific gravity

2.5 — 3 1.000G4

2.6 (i

2.7 1 1.00065

2.8 . 3 1.00063

2.9 . -2 1.00064

3.0 . 10 1.00057

3.1 . 11 1.00054

3.2 L6 1.000.14

3.3 . 24 1.00054

3.4 . 16 1.00053

3.5 __ .15 1.00050

3.6 . !i 1.00050

3.7 :t L.00050

3.8 ___ 1 1.00050

Vertical Distribution of Developing Eggs

All observations of the vertical distribution of developing striped
bass eggs were made in the San Joaquin River above the Antioch
Bridge. Only those sets in which 20 or more eggs were collected are
reported here.

Considerable numbers of eggs were observed at all collecting depths
at various tidal velocities (Table 10). At surface velocities of 0.6 to
0.9 feet-per-second, eggs were generally collected in larger numbers
near the bottom, while at higher velocities distribution was more
variable.

1 ID CALIFORNIA FISH AND GAME

TABLE 10

Vertical Distribution of Developing Striped Bass Eggs at Various Tidal
Velocities in the San Joaquin River Near Antioch, 1962

8urfact Vo.of Percentage of ioinl ~by net

velocity eggs per Surface Mid-water Bottom

Date Tide ft./sec. S nets 0-5' 10-15' 15-25'

5/8__ __flood .6 34 24 18 ~>1

5/29_. flood .9 81 25 .".7 38

5/29 ..flood .9 35 28 29 44

4/15_. flood .9 29 81 11 7

:. 8 ebb .9 20 0 26 74

ebb 1.1 10,661 66 27 7

5/29— flood 1.5 24 39 49 12

5/29 flood L.6 36 0 83 18

5/29- flood 1.7 25 22 54 25

4/24 ebb 1.8 185 .".7 59

5 _'9___ __flood L.9 77 32 6 62

4/24_. ebb 2.0 1,022 38 44 17

5/29 flood 2.1 .",7 87 48 15

5/8 ebb 2.3 552 73 19 8

5/8 ebb 2.7 1,456 56 23 22

5/8 ebb 2.9 2,065 59 25 16

5/8__. ebb 2.9 415 65 31 4

In four consecutive large collections, made at velocities exceeding
2.3 feet-per-second. eggs were more concentrated near the surface.
However, in another large collection made at a velocity of 1.1 feet-per-
second eggs were also concentrated near the surface. This suggests that
large egg collections may indicate recent spawning at or near the sur-
face, and that these eggs may not have had time to disperse.

DISCUSSION

The laboratory hatching and rearing experiments had some major
limitations. Plankton netting provided a relatively small number of
eggs and many of these were in an advanced stage of development.
Thus, they were exposed to the desired physical incubating conditions
for only a brief period before hatching. Also, most tests were short in
duration because of a high larval mortality. This morality has been
reported previously in a rearing experiment (Mansueti, 1958b) and
also has been experienced at the Weldon striped bass hatchery (Raney,
1952 '. Despite These limitations, some definite conclusions can be drawn
from this st iidy's results.

The results indicate egg suspension by water movement is important
for egg survival, and the currenl velocity required to insure e<><r suspen-
sion in fresh water is apparently about 1 foot-per-second. Since striped
bass e^<rs normally take 2 days to hatch, about 30 miles of water Aoav-
ing at 1 foot-per-second would be required to suspend eggs throughout
development. However, it is possible that striped bass eggs do not need
to be kept suspended continuously during incubation, and that partial
or periodic intervals of suspension might suffice.

since striped bass seek temperatures of 58° to 65°F. for spawning,
and eggs and larvae can survive in constant or fluctuating water tem-
peratures between 55 and 75°F.. temperature does not appear to be a
factor limiting egg and larval survival. However, Mansueti ('1958b)
believes starvation is the principal cause of larval mortality. Thus, at

STRIPED BASS EGG AND LARVAL SURVIVAL 111

higher water temperatures the availability of natural food would be-
come more important to Larval survival.

While no one has observed striped bass spawning in brackish or salt
water, their eggs have been observed in slightly saline water. This
study's results indicated that eggs and larvae can survive at all salin-
ities likely to be encountered under natural conditions. They also in-
dicated that low salinity enhances larval survival. The importance of
this needs more evaluation.

The one observation made on tolerance of eggs to sunlight indicated
water clarity does not adversely affect egg survival.

Since suspension of the developing egg appears to be necessary for
its survival, the factors concerned with egg buoyancy need to be con-
sidered. Egg diameter and specific gravity measurements indicated
larger eggs tend to have a slightly lower specific gravity. Thus, they
would be more buoyant and probably survive better. Previous studies.
reviewed earlier, and our egg collections made in the Sacramento and
San Joaquin rivers indicate considerable differences in egg sizes from
different areas. The sizes of striped bass eggs collected from the Sacra-
mento River at Sacramento (2.5 to 3.8 mm > correspond closely with the
general sizes of bass eggs on the Atlantic ( 'oast, while bass eggs collected
from the lower San Joaquin River were considerably larger than any
reported previously. However, since only two egg collections were made
in the Sacramento River, it is not known if these eggs are consistently
smaller than those produced in the San Joaquin River.

Mansueti I 1!C>ni. recognized e<_vj size variation on the Atlantic Coast
and listed three possible cause-: i arrested expansion of the chorion
caused by high osmotic pressure from a sharp salinity gradient; (ii)
fish size; (iii) actual differences in size of eggs produced by bass from
different areas. His data do not support ihis latter thesis.

The increase in osmotic pressure, caused by a salinity gradient, does
not explain the size difference between eggs in the Sacramento and San
Joaquin rivers, since there is no sharp gradient. In fact, egg size is the
reverse of what would be expected from this theory since salinity is
lower in the Sacramento River.

If egg size is related to fish size, and if larger cues survive better,
conservation of large bass might be desirable, providing recruitment is
correlated with egg survival. However, it should be noted that there is
some evidence of intermittent spawning in older female bass (Lewis.
1962).

If egg size and buoyancy are related to physical factors in the envi-
ronment, certain specific areas are probably more valuable than other
areas for striped bass production and special effort should be made to
preserve them. However, the effects of slight salinity differences, and
the importance of natural food availability need more evaluation to de-
termine if such critical areas for larval survival exist.

ACKNOWLEDGMENTS

I am indebted to Harold K. Chadwick for his guidance and criticisms,
and to William Heubach, Richard Fenner, and Vincent Catania for
their assistance in collecting eggs and conducting laboratory experi-
ments.

1 12 CALIFORNIA FISB A.ND GAME

SUMMARY

Developing striped bass eggs were collected by Large mesh plankton
nets Prom the Sacramento and San Joaquin rivers, and incubated under
various water movement, salinity, and temperature conditions to study
the effects of these factors on egg and larval survival. Suspension of
developing eggs by water movement enhances egg survival; low salinity
(920-948 ppm chlorides) enhances egg and larval survival, and moder-
ate salinity I 1,595 1,740 ppm chlorides) is not detrimental; and. eggs
can survive in either constanl or fluctuating water temperatures rang-
ing from 55 id 75 V. A relatively small supply of eggs, many in an
advanced stage of development when colleeted. and a high natural
larval mortality, limited the preciseness of these results.

Egg diameter and specific gravity measurements were made also.
Eggs collected in the lower San Joaquin River during May averaged
3.8-4.0 mm in diameter, while eggs eollected from the upper Sacra-
mento River in June averaged 3.2-3.3 mm. The average specific gravity
of striped bass eggs was approximately 1.0005, with a range of 1.0003
to 1.00065. Egg specific gravity was related to egg size, with larger
eggs having a slightly lower specific gravity. Egg diameter and spe-
cific gravity were not related to egg age.

( ibsen at inns of | he vertical distribution of developing eggs indicated
c™'s are generally concentrated uearer the bottom at velocities less than
1 foot-per-second. Egg distribution at greater velocities is probably
quite random.

Of the factors investigated, egg suspension was the most important
to egg survival. Since egg buoyancy is related to egg size, a knowledge
of the factors affecting egg size is needed.

Salinity and temperature fluctuations, within the range likely to be
encountered, were not detrimental to egg survival, but larval survival
was enhanced by low salinities, and larval mortality was greater at
higher temperatures. Further work on the role of slight salinity differ-
ences and natural food availability is ueeded to evaluate the signifi-
cance of these results.

REFERENCES

Bigelow, Henry B. and William W. Welsh

L925. Fishes of the Gulf of .Maine. Bull. U.S. Bur. Fish. (1924), vol. 4o. ,,t. 1.
pp. 251-256.
Calhoun, A. J. and C. A. Woodhull

L948. Progress report on studies of striped bass reproduction in relation to the
Central Valley Project. Calif. Fish and Game, vol. 34, no. 4, pp. 171-188.
Calhoun, A. .7.. C. A. Woodhull, and W. C. Johnson

L950. Striped bass reproduction in the Sacramento River System in 1948. Calif.
Pish and Came. vol. 36, no. 2. pp. 1 .">."">- 1 4. ~.
< Jhadwick, Harold K.

L958. A Study Of the planktonic fish eggs and larvae of the Sacramento-San
Joaquin Delta with special reference to the striped bass I Roccus saxatilis).
Calif Dept. Fish and Came, Inland Fish. Br., Adm. Kept. 58-5, 24 pp.

Erkkila, Leo F., James \V. Moffett, Oliver B. Cope, Bernard B. Smith, and Reed S.
.Wilson
1950. Sacramento-San Joaquin Delta fishery resources: Effect of Tracy pumping
plant and Delta cross channel, U.S. Fish Wildl. Serv., Spec. Sci. Rept. :
Fish. do. 56, 109 pp.

STRIPED BASS EGG AND LARVAL SURVIVAL 113

Hatton, S. Ross

1942. Striped bass spawning areas in California. Calif. Fish and (lame. vol. 28.
mi. 1. p. 65.

I ewis, Robert M.

1062. Sexual maturity as determined from ovum diameters in striped bass from
North Carolina. Trans. Am. Fish. Soc, vol. ill. no. :J». pp. 279-282.

Mansueti, Romeo

1958a. Eggs, larvae and young of the striped bass. Roccus saxatilis. Md. Dept.

Res. and Educ. Contrib. no. 112, 35 pp.
1958b. New publication describes how young striped bass or ■'rock'" were reared
successfully in laboratory. Maryland Tidewater News, vol. 14. no. (i. p. 2.">.

.Mansueti. Romeo J. and Edgar II. Hollis

1963. Striped bass in Maryland tidewater, I'. of Md. Nat. Res. Institute. Educ.
Ser. no. 61 . -!•'> pp.
Merriman. Daniel

1941. Studies on the striped bass (Roccus saxatilis) of the Atlantic ('oast. U.S.
Fish Wildl. Serv., Fish. Bull. ::."». 77 pp.
Morgan, Alfred R. and Arthur R. Gerlach

1950. Striped bass studies on Coos Bay, Oregon, in 1949 and 1950. Oregon Fish
Comm., Contrib. no. 14. ."•!! pp.
Pearson. John < '.

1938. The life history of the striped ha>s. or rockfish, Roccus saxatilis (Wal-
baumi. Bui. F.S. Bur. Fish., vol. 49, no. 28, pp. 825-851.
Raney, Edward ('.

1952. The life history of striped bass. Bingham Ocean. Coll. Bull., vol. 14. art. 1.
pp. 5-97.
Kathjen. Warren F. and Lewis C. Miller

1957. Aspects of the early life historj of the striped bass (Roccus saxatilis) in
the Hudson River. Jour. N.Y. Fish and (lame vol. 4, no. 1. pp. 4:>-C><>.
Tresselt, F. F.

L952. Spawning grounds of the striped bas^ or rock. Roccus saxatilis (Walbaum)
in Virginia. Bingham Ocean. Coll. Bull., vol. 14. art. 1. pp. 98-110.
Woodhull, C. A.

1!>47. Spawning habits of the striped bass (Roeeu* saxatilis) in California
waters. Calif. Fish and Game, vol. ■">•">. no. 2, pp. 97-102.

PARTYBOAT LOGS SHOW HOW SKINDIVERS
FARED DURING I960, 1961, AND 19621

WILLIAM F. WOOD

Marine Resources Operations
California Department of Fish and Game

Skindivers, particularly in southern California, are chartering an
increasing number of fishing boats each year in an effort to find first-
rate diving. California law (California Department of Fish and Game,
1961a) requires the operators of fishing (diving) charters to keep daily
records of the fish caught from their boats. This paper summarizes all
diving catch records received from 1960 through 1962 except a few un-
readable, incomplete, or improbable logs.

Greater charter-diving effort in southern California, as compared to
central and northern California, is apparently fostered by physical fac-
tors. The ocean is warmer, ranging to 70° F. or more, and usually is
quieter. To reach many of the better diving areas, a boat is required,
whereas good diving from shore is abundantly available along central
California coast. Water clarity may also be a plus factor in the south.

Unlike hook-and-line fishermen, skindivers are not limited to what-
ever action is provided when the fish takes the hook. Many divers spend
all or part of their underwater time taking photographs, shell collect-
ing, exploring, searching for treasure, and in pure "fish watching."
These activities should be considered when catch and effort are dis-
cussed ; however, at present we have no way to measure them.

During 1960-1962, the Department of Fish and Game received 527
useful catch records for diving charters. 14 from central and 513 from
southern California.

TABLE 1

Marine Species, Catch and Effort, in the San Francisco Bay
and Monterey Areas, 1960-1962

Xumber reported
Common name 1960 1961 1962 Total

Abalone* 128 20 12 160

Rockfish * __ 15 37 71 123

Lingcod 22 17 40 79

Cabezon lit 12 31

Perch* 11 11

Kelp bass 2 2

Total 184 86 136 406

Number of trips - 5 2 7 14

Number of divers 32 29 96 157

Number of diver-hours 138 127 348 613

Catch/diver 5.8 3.0 1.4 2.6

Catch/diver-hour 1.3 0.68 0.39 0.66

* Probably ninie than one kind.

1 Submitted for publication November 1963.

r 11.1 i

SKINDIVER CATCH STATISTICS

115

Central California charter boat operators reported 157 divers caught

406 fish of six kinds (Table 1). There were probably more than one
species each of rockfish, perch, and abalone. The most frequented area
was the Farallon Islands, but divers working Monterey Peninsula had
greater success (Table 2).

Southern California boat operators reported 8,893 divers caught

21.137 fish, mollusks, and crustaceans of 21 kinds (Table 3). Few

TABLE 2

Marine Species, Catch and Effort by Diving Area,
Central California, 1960-1962

< ' a Irl, by urea

Monterey Monterey

Common name Farallon Is. Peninsula />'<"/ Total

Abalone* L05 55 L60

Rockfish* 108 l."i 123

Lingcod 44 ::."". 79

Cabezon 17 14 No Catch 31

Perch * 11 11

Kelp bass __. 2 2

Total -J7 1 132 MM;

Number of trips 8 5 1 II

Number of divers 114 23 20 1.V7

Number of diver-hours 126 &\ 100 613

Catch/diver _^_ 2. I .",.7

Catch/diver-hour 0.64 1.5

* Probably more than one kind.

TABLE 3
Marine Species Taken by Charter-divers off Southern California, 1960-1962

Number reported

Common name 1960 1961 1962 Total

Abalone* 2,044 3,374 7,0l't; 12,444

Kelp bass . 715 v,u 1,169 2,736

Spiny lobster 150 »>2s 1,446 2,224

California sheephead 453 »•«',< 1 1,004 2,117

Rockfish * 238 92 48 378

Perch* 144 164 66 374

Opaleye . 95 88 89 272

Pacific bonito 47 35 23 105

Sculpin 38 21 28 87

California halibut ___ 11 4 31 46

White seabass 1. 20 19 4 43

Flatfish * 17 11 14 42

California vellowtail 17 18 2 37

Cabezon 1 3 31 35

California barracuda ___ 13 9 10 32

Rock scallop 21 10 31

Lingcod 9 4 18 31

Halfmoon 11 7 18

Giant sea bass 5 4 9

Miscellaneous * 5 7 64 76

Total 4,022 6,021 11,094 21,137

Number of trips 71 160 282 513

Number of divers 1.239 2,604 5,050 8,893

Number of diver-hours 5,722 11,597 23,841.25 41,160.25

Catch/diver 3.25 2.3 2.2 2.4

Catch/diver-hour 0.70 0.52 0.47 0.51

116

< AMI MKN'IA Klsli \\1> GA Ml

white seabass, yellowtail, barracuda, bonito, and giaul sea bass were
taken; however, individual fish were often Large. The average reported
weight of 43 white seabass was 32 pounds, with one individual weighing
66 pounds. Gianl sea bass averaged 200 pounds, while one leviathan
weighing 400 pounds was reported. The miscellaneous group (Table 3
includes three Pacific angel sharks, three California morays, two horn
sharks, two California swell sharks, two white croakers, and 64 un-
named fish.

Mos1 of the divers favored Santa Catalina Esland, bu1 the catch-per-
diver-day there was the lowesl of all the known areas (Table 4). Novice
divers frequently pick this area as a training ground.

TABLE 4

Marine Species, Catch and Effort by Diving Area,
Southern California, 1960-1962

Catch by area

Santa Santa Santa 8an

Catalina <'ruz. Inacapa Barbara Clentente Palos

('/minion name Is. Is. Is. Is. Is. Verdes

Abalone* 7,027 2.s96 2.141 185 190 5

Kelp bass 343 1,451 866 36 40

Spiny lobster . 735 784 324 291 fi4 26

California sheephead .._ 617 701 568 151 80

Rockfish * 4 242 130 2

Perch* 7 iss 179

Opaleye 153 119

Pacific bonito 7 63 35

Sculpin 25 39 20 3

California halibut 28 16 2

White seabass 3 22 18

Flatfish* 1 17 24

California yellowtail 3 21 13

Cabezon 32 1 1 1

California barracuda __ "p 18 9

Rock scallop <> 5 20

Lingcod 7 15 9

Halfmoon 18

Giant sea bass 7 2

Miscellaneous* 24 50 2

Total 8,892 6,683 4,462 u<;s 378 54

Number of trips 3 00 104 84 8 14

Number of divers _ 5,069 1,878 1.465 278 176 27

Number of diver-hours 23,971.2.". 8,644 6,531.5 1,219.5 669 125

Catch/diver 1.75 3.6 3.0 2.4 2.1 2.0

Catch/diver-hour ___. 0.37 0.77 0.68 0.55 0.57 0.43

* Probably more than one kind.

Santa Cruz, Anaeapa. Santa Barbara, and San Clemente Islands
and the Palos Verdes Peninsula were also popular diving locations.
The best all-around diving area in southern California was Santa
Cruz Island, where only 21 percent of the divers bairued 23 percent
of the abalones, 53 percent of the kelp bass, 35 percent of the spiny
lobsters, and 33 percent of the sheephead.

Logs submitted by the skippers of southern California diving-charter
boats in 1D58 and ID.")!) showed that 1.72") divers bagged 3.3 fish, mol-
lusks, and crustaceans per-diving-day (Young, 1961). During 1960-
1962, divers averaged 2.4 animals per-diving-day (Table 3). The seven

SKINDIVEK CATCH STATISTICS

11

Common and
Cha

Common name

Was, giant sea
Bass, kelp

Barracuda, < lalifornia
Bonito, Pacific
( 'abezon

< !roaker, white
Flatfish*
Halfmoon
Halibut, < 5alifornia
Lingcod

Moraj . California

Sculpin

Seabass, white

Shark. California swell

Shark, horn

Shirk. Pacific angel

Sheephead, ( !alifornia

Rockfish*

Perch*

< >|ialc.\ e
rellowtail, California

Abalone *
Scallop, rock

TABLE 5

Scientific Names of Marine Species Taken by
rter-divers in California, 1960-1962

Scientific name
Fishes

Ktereolepis gigas
Paralaorax clathratus
ttphyraena argentea
Sarda chiliensis
Scorpaenichthys marmoratus
Genyorn m us lineatus
species of bothids and pleuronectids
Medialuna californiensis
Paralichthys californicus
Ophiodon elongatus
(I inn nothorax mordant
Scorpaena guttata
Cynoscion nooilis
i i phaloscyllium titer
Heterodontus francisci
Sq an 1 in " ail i font ha
Pimelometopon pulchru m

Si hils/mh 8 Spp.

species of embiotocids
Girella nigricans
S'< i loin dorsalis

Mollusks

Haliotis spp.
Hinnites multirugosus

Crustaceans

/'mi iilirns interruptus

Lobster, spiny

* Probably more than one kind.

most frequently taken species were t tie same in both periods. Hook-
ami-line fishermen averaged approximately six fish-per-day, 1960-1962,
according to the logs from skippers in the California partyboat fleet
California Department of Pish and Game, 1961b. 1962, and 1963).

ACKNOWLEDGMENTS

I would Like to thank Earl E. Bbert, Jack W. Schott, and Charles 11.
'urner for advice, and am deeply indebted to John L. Baxter and
'arke II. Young for help in writing and editing the manuscript.

REFERENCES

'"alifornia Department of Fish and Game

1961a. Fish and Game Code. 42nd ed.. Sacramento State Print. Off., 284 pp.

1061 h. Report of the California party boat fleet, 1960. Terminal Island. Calif.

State Fish. Lab., 2 p.
1962. Report of the California partv boat fleet, 1961. Terminal Island. Calif.

State Fish. Lab., 2 p.
L963. Report of the California partv boat fleet. 1962. Terminal Island. Calif.

State Fish. Lab., 2 p.
Young, Parke H.

1961. Party boat lops show how skindivers fared during 1958 and 1959. Calif.

Fish and Game. vol. 47. no. 3, pp. 303-305.

RECENT OCCURRENCES OF INTERGENERIC HYBRID

FLOUNDERS, INOPSETTA ISCHYRA (JORDAN AND

GILBERT), FROM CALIFORNIA AND OREGON1

PAUL H. REED

Marine Resources Operations
California Department of Fish and Game

Intergenerie hybridization occurs between several species of pleuro-
tiectids. Norman (1934) mentioned six examples within the family and
llubbs and Kuronuma (1942) reported another. Inopsetta ischyra
(Jordan and Gilbert), the only hybrid flounder known to occur
off the coast of western North America, has been rarely taken in Cali-
fornia waters, although reported as common off Washington. Recently,
two of these hybrid flounders were brought to my attention. I received
a female specimen, 390 mm sl, from Dick Young, master of the trawler
City of Eureka, on February 2, 1962 (Figure 1). It was caught about
14 miles north of the California-' >regon border at Mack Arch, Oregon
in 150 to 360 fathoms of water and was placed in the California Acad-
emy of Sciences collection (CAS 23174). The second specimen, placed
in the same collection (CAS 12651) by the University of California,
was a male, 149 mm sl, collected at Drakes Bay by a Mr. Arnheim
prior to 1945. It represents the second authenticated California occur-
rence, although Eureka and San Francisco fishermen have occasionally
reported catching hybrid flounders.

Jordan and Gilbert (1880) originally described Inopsetta ischyra as
a distinct species (Parophrys ischyrus) from four specimens collected
at Seattle. Washington. Jordan and Gilbert (1882) suggested the name
Pleuronectes ischyrus, and Jordan (1887) proposed the name Inopsetta
ischyra which persists today. Villadolid (1927) maintained specific
status in his description of three additional specimens from the Puget
Sound area. Norman (1934) was first to suspect that Inopsetta was a
hybrid and recorded Lepidopsetta bilineata and Platichthys stellatus as
probable parents. Schultz and Delacy (1936) accepted the same species
as possible parents, but later Schultz and Smith (1936) compared 11
hybrids from Puget Sound with all possible parent species and con-
vincingly presented Parophrys vetulus and Platichthys stellatus as
probable parents. Aron (1958 substantiated the hybrid nature of
Inopsetta by establishing abnormalities in gonads and gonadal
products.

Herald (1941) documented the first California occurrence of Inop-
setta, It was caught off San Fancisco and established the southern range
limit. Clemens and Wilby (1961). apparently unaware of this occur-
rence, reported the range from Washington to the Bering Sea.

1 Submitted for publication July 191

(118)

HYBRID FLOUNDER OCCURRENCES

119

FIGURE 1. Hybrid flounder Inopseffa ischyra (Jordan and Gilbert), CAS 23174,
southern Oregon in February 1962. Photograph by the author, May 1963.

taken off

To establish the hybrid nature of the Drakes Bay and Alack Arch
specimens, I compared them with Hi individuals of each parenl species

caught off Humboldt County. California (Table 1 I. Values intermedi-
ate between the parenl averages were calculated to facilitate compari-
sons. Counts and measurements were made in accordance with Hubbs
and Lazier (U'loMi unless otherwise indicated.

Comparison of the hybrids with the parent species reveals the typical
intermediacy of meristic and morphometric data characteristic of hy-
brid flatfish. Most of these data for both hybrids closely approach or
equal the intermediate condition. The principal caudal ray count and
the snout length of the Drakes Bay hybrid fall outside the extremes
of the parent ranges. As the ranges are narrow and overlap, these
normal variations should be expected. Hybrid data presented in Table 1
agree closely with those reported by Schultz and Smith (1936) for 11
Tnopsetta ischyra from Puget Sound.

Scales on both hybrids bore marginal etenii. The scale surfaces of
the Mack Arch specimen were partially covered with spinous projec-
tions resembling the tubercles of Platichthys stellatus. Scale spination
was pronounced on the eyed side. Spines were most abundant anteriorly
on both sides. No spinous projections were found on scale surfaces of
the Drakes Bay specimen.

The body on the eyed side of the Mack Arch hybrid was olive-brown
mottled with black. Dorsal and anal fins were yellow-brown with dusky
blotches at regular intervals near their bases. The blind side was a
typical creamy-white. Paint dusky blotches were present on the blind
side of the dorsal and anal fins. Coloration of the Drakes Bay hybrid
had been obliterated bv extended storage in formalin.

120

CALIFORNIA I'lsll AND GAME

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HYBRID FLOUNDER OCCURRENCES 121

Herald (1941) reported a ventral lateral line branch on the blind
side of the first California Inopsetta but believed it was an anomalous
condition. Neither hybrid treated in this study possessed such a branch.

All specimens of Parophrys vetulus and Inopsetta ischyra were
dextral. Dextrality was 30 percent for the 10 Humboldt County Plat-
ichthys stellatus (normally, over 40 percent are dextral).

ACKNOWLEDGMENTS

1 wish to extend thanks to YV. I. Follett of the California Academy
of Sciences for his assistance in this study. To Dick Young, master
of the City of Eureka, and his crew. 1 also express thanks for con-
tributing the Mack Arch Inopsetta.

LITERATURE CITED
A ion, William

1958. Cytological and histological studies <>n the hybrid of Platichthys stellatus
X Parophrys vetulus with notes on its backcross to /'. vetulus. Copeia,
no. 2, pp. 105 111.

Clemens, W. A. and G. V. Wilby

1961. Fishes of the Pacific coast of Canada. Fish. Res. Bd. Canada, Bull. 68
i second edit ion l . pp. 196-197.

Berald, Karl S.

1941. First record of the hybrid flounder, Inopsetta ischyra, from California.
Calif. Fish and Came. vol. 27, no. 2, pp. 44-46.
Huhbs, Carl L. and KatSUZO Kuroimma

l'.ill'. Analysis of hybridization in nature between two genera of flounders in
Japan. Papers Mich. Acad. Sci., Arts and Letters, vol. 27, pp. 267-306.
Hubbs, Carl L. and Karl F. Lagler

1958. Pishes of the Greal Fakes region. Cranbrook fust. Sci.. Bull. no. 26 (re-
vised edition i . pp. 19-26.
Jordan. David Starr

1887. A catalogue of the fishes known to inhabit the waters of North America,
north of the tropic of cancer, with notes on species discovered in 1883
and 1884. F.S. Com. Fish.. Rept. for 1885, p. 136.
Jordan, David Starr and Charles IF Gilbert

1880. Description of two new species of flounders I Parophrys ischyrus and Hip-
poglossoides elassodon) from Puget's Sound. F.S. Nat. Mus. Proc, vol.
3, pp. 276-280.
1882. Synopsis of the fishes of North America. F.S. Nat. .Mus.. Bull. no. 16,
pp. 832-833.
Norman, J. R.

1934. A systematic monograph of the flatfishes ( Heterosomata ) . Brit. Mus. Nat.
Hist., vol. 1, 459 p.

Schultz, Leonard P. and Allan C. Delacy

1936. Fishes of the American Northwest. A catalogue of the fishes of Wash,
and Ore. with distributional records and a bibliography. Jour. Pan-Pac.
Res. Inst., in Mid-Pac. Mag., vol. 11, no. 1, pp. 63-78.
Schultz, Leonard P. and Richard T. Smith

1936. Is Inopsetta ischyra (Jordan and Gilbert), from Puget Sound, Washing-
ton, a hybrid flatfish? Copeia, no. 4, pp. 199-203.
Villadolid, Deogracias V.

1927. The rediscovery of Inopsetta ischyra, a rare species of flounder. Annals
Carnegie Mus., vol. 17, pp. 395-397.

NORTHWARD MOVEMENT OF THE
CALIFORNIA SEA OTTER'

ROBERT T. ORR

California Academy of Sciences

and

THOMAS C. POULTER

Stanford Research Institute

Since California sea otters (Enhydra lutris nereis) were rediscov-
ered in 1938 off Bixby Creek, Monterey County, these animals have
extended their range southward at leasl to Poinl Conception and prob-
ably to the Channe] Islands. Northward movement, however, has been
slight, with the species now regularly occurring in Carmel Bay and
around parts of the .Moninvv Peninsula. Boolootian (1961) has care-
fully summarized the recently authenticated California occurrences and
quite justifiably questioned several sight records reported north of the
Monterey region.

Since May 1961, we have been visiting Ano Nuevo Island, San
Mateo County. 40 miles north of the Monterey Peninsula, in connec-
tion with studies on the pinnipeds of that area (Orr and Poulter, 1962).
These visits have been weekly, if not more often, during the summer
and generally bi-weekly, weather permitting, during the remainder of
ill" year. On nearly each occasion the area around Ano Nuevo Point,
as well as the surrounding kelp beds, have been scanned for sea otters.

Until the summer of 1963 this species was not observed in the area.
On July 11, Alex Ermacoff, Stanford Research Institute, was on the
island and saw two sea otters in a cove on the seaward side. Unaware
of this discovery we observed two otters in the same cove on the follow-
ing day. One animal swam around a point and out of view shortly after
the two were sighted at 11 :30 a.m. but the other remained until we left
in mid-afternoon. On a number of subsequent visits during July and
the first half of August, a sea otter was seen in the same cove. It could
be observed from a blind as close as 75 feet, and was thought to be
the same individual.

On Augusl 23, there was no otter in this cove, but one wras seen off
the northwest end of the island in a small bay formed by a series of
exposed reefs. None was seen on August 30 although the area around
the island, as well as Ano Nuevo Point and part of Ano Nuevo Bay,
was examined carefully. Bowever, these animals could easily be over-
looked among the numerous sea lions, harbor seals, and kelp floats.

Because the pinniped population in this region reaches its peak a1
the end of August, as a result of an influx of California sea lions
(Zalophus californianus), we thought this might have caused the otters

1 Submitted for publication November 1963.

i 122 >

NORTHWARD SEA OTTER MOVEMENTS

123

FIGURE. 1. The usual position of a resting sea otter, floating on its back with front and hind

legs raised. Note the flipper-like appearance of the hind limbs. Ario Nuevo Island, San Mateo

County, California. Photo by Thomas C. Poulter, August 8, J 963.

id move in Less densely populated kelp beds nearby, possibly between
Ano Nuevo Point and Pigeon Point. < >n September 6, however, an otter
was seen again off the northwest end of the island.

The relationship between sea otters and sea lions was of considerable
interest to us. The otter seen in the cove on July 12 usually dove when
a Steller sea lion (Eumetopias jiibata) came within 4 or 5 feet of it.
When not diving for food, eating, scratching, or otherwise engaged,
it floated on its back, anchored by a piece of kelp (Macrocystis), often
within a few feet of a reel' with an active breeding Steller sea lion
rookery. No animosity was exhibited by any of the female or non-
established male Steller sea lions that often swam close to the otter.
They did, however, evince curiosity.

Subsequently, the sea otter permitted both Steller and California sea
lions to come close and even contact it with their muzzles. On August
23, individuals of both species were observed at the northwest end of
the island touching their noses to the sea otter while it floated on its
back seemingly unperturbed.

On September 6, however, the presence of numerous Steller pups,
as well as a number of cows, seemed to disturb a sea otter seen between
1 pm and 1 :30 pm. The pups at this season of year spend a consider-
able part of their time playing in the coves and surge channels. They
even attempt to play with the adult females as well as California sea
lions that may venture within their range of activity. Their reaction
to the otter Avas essentially the same as to another pup. The otter,
however, doA'e frequently to escape their attention and surfaced at a
different locality each time. Gradually it moved seaward toward one
of the outlying rocks about 200 yards west of the north end of the
island where there were no voung sea lions to annoy it.

124

( \l.ll HKM.l I ISM AMi <; \\u:

FIGURE 2. A sea otter and a Steller sea lion viewing each other at very close range. Ano
Nuevo Island, San Mateo County, California. Photo by Thomas C. Povlter, August 8, 1963.

It seems pertinent here to mention another older record north of
Monterey. On December 28, 1940, a dead sea otter was brought to the
California Academy of Sciences. San Francisco, by a representative of
the California Department of Fish and Game. This animal had been
found the previous day on the beach at Twin Lakes, Santa Cruz
County, by Mrs. William R. Pera and Mrs. Clyde Smith of Santa
Cruz. It was a female, 1136 mm tl, weighing 41f pounds. Several
external and internal injuries were noted, but their cause was not
known. In view of later information about great white sharks (Car-
charodon carcharias) attacking sea otters (Orr, 1959), it may have been
a victim of one of these fish. The condition of the reproductive tract
indicated it had recently given birth to a young.

LITERATURE CITED
Boolootian, Richard A.

1961. The distribution of the California sea otter. Calif. Fish and Game, vol.
47. no. 3, pp. 287--". 12.

Orr, Robert T.

L959. Sharks as enemies of sea otters. Jour. Mamm., vol. 40, no. 4, p. 617.
Orr, Robert T., and Poulter, Thomas C.

1962. Ano Nuevo marine biological park. Pacific Discovery, vol. 15, no. 1, pp.
13-19.

NOTE

GRASS ROCKFISH, SEBASTODES RASTRELUGER (JORDAN AND
GILBERT), FROM THE YAQUINA BAY AREA, OREGON

Grass roekfish have been reported as ranging from Playa Maria Bay,
Baja California, to Eureka, California (Phillips, 1957). Four speci-
mens captured in the Yaquina Bay vicinity extend their known range
northward some 270 miles.

On May 27. 1962, during a spearfishing "species contest" (Van
Arsdel, 1968) the senior author found a 43 cm >i. grass roekfish weigh-
ing 6 pounds 11 ounces perched on the grave] rim of a current-scoured
depression at the end of a spur of the Y/aquina Bay south jetty. The
fish faced a strong tidal cm-rent and presented a sculpin-like appear-
ance in a striking pose with the spines erect and pectoral fins fanned
ou1 perpendicular to the body. Recognized as unusual for this area, it
was presented to the junior author for identification and is now pre-
served in the collection of the Department of Fish and Game Manage-
ment, Oregon State University as OS 1300.

On June 9, 1963, a second specimen. 27 cm sl (OS 1301 . was ob-
tained from Mr. Steve Ryan during a spearfishing meel in the same
area. The waters off Y/aquina Head yielded a third individual. 30 cm
si. (OS 1802), from a depth of 25 feet, below the vegetation zone.
August 4, 1963. Mr. Bill Herder speared the fourth on August 27.
1968. This specimen (OS 1304) is 15 cm SL; its 53-em total length
(21 inches makes it one of the longesl recorded. Steve Ryan and
other divers in the area claim to have taken grass roekfish several times
from the kelp beds in the Yaquina vicinity where they apparently are
not rare.

Measurements and meristic data from the first three specimens com-
pared with Phillips's i L957 values show only minor deviations which
probably represent geographical variation.

REFERENCES
Phillips, Julius B.

1!>."7. A review of the rockfishes of California. <';ilit". Depr. Fish and Game, F'ish
Bull. 104. 158 p.
Van Arsdel. Wm. C, III.

1963. Spearfishing for science. Skindiver, vol. 12. no. 5, pp. 84-35.

William C. Van Arsdel, III and Carl E. Bond, Oregon State Univer-
sity, Corvallis, Oregon, November 1963.

I 125 )

BOOK REVIEWS

Freshwater Fishes of the World

By Gunther Sterba (translated and revised by Denys \V. Tucker) The Viking
Press, New York. 1963; ^7s pp., numerous black and white plus color illus-
trations ; $17.50.

Freshtvater Fishes of the World is the second major German work on aquarium
Bshes to be translated into English. The hook was "Printed in East Germany.
U.S.S.R. occupied." As indicated by the title, this is not a book of tropical aqua-
rium tishes. Fishes from almost every habitat, geographical area and temperature
rani;c arc discussed, and many have never been described in an aquarium handbook.

Professor Gunther Sterba. Director of the Zoological Institute, Leipzig Univer-
sity, has made a major contribution to Aquatic Biology with this volume. It deals
with the identification, care, and biology of over 1,300 species, and contains 1,193
illustrations consisting of 102 color photographs, 42.'! black and white photos, and
668 line drawings. The quality of the photos ranges from good to excellent. Unfor-
tunately, the caliber of the line drawings is not up to the quality expected in a
volume of this type.

My main criticism of this book lies with the relation of the figures to the text.
The photos and drawings do not follow the order in which the species are pre-
sented in the text. In order to find a figure referred to in the text, one must con-
stantly turn pages. Conversely, it is extremely difficult to locate the text that ap-
plies to a particular figure without reference to the index. It is hoped that the
next edition will have a more logical placement of the figures. The common names of
many species, particularly those of North America, are omitted.

Professor Sterba writes in a concise style which enables him to transmit a wTealth
of information in a minimum of space. He starts with general information on the
biology of a family, including breeding habits and suitability for the aquarium.
Then, the specific biology of individual species is discussed.

The beginning aquarist may find the descriptions of the biology of individual
species somewhat on the sketchy side. The amateur will have to look elsewhere
for help regarding aquarium plants, fish diseases, water quality, filtration, and the
other myriad problems which plague the home aquarium.

Much credit for this volume must be given to Denys W. Tucker, of Great Britain,
who was able to translate and update this massive volume in only 5 months. The
efforts of Professor Sterba and Mr. Tucker have resulted in a book which will prove
to be of great value to the professional fisheries worker as well as the serious
aquarist. — Michael L. Johnson, California Department of Fish and Game.

The Complete Illustrated Guide to Casting

By Joe Brooks, Doubleday and Company, Inc., NeAV York, 1963 ; 192 pp., illus-
trated; $4.95.

For the fisherman who wants to learn how, reading '"The complete illustrated
guide to casting'' is a must.

The author has enlisted the aid of foremost experts in fresh and saltwater fishing
to come up with over 200 photographs profusely illustrating the casting techniques
he describes. The photographs were taken under actual fishing conditions especially
for the book. Almost without exception the text and numbered picture appear on
the same page. They are so skillfully coordinated that the reader is never lost
searching for the picture that illustrates the text.

The book is easily readable and the author, a recognized authority on fishing, has
drawn on a lifetime of experience to describe and illustrate how experts handle
different kinds of fishing gear. The categories covered include fly casting, plug cast-
ing, spinning, and surf casting. Experienced fishermen as well as beginners should
welcome this comprehensive volume for its coverage of both the basic and advanced
information on casting. — George D. Seymour, California Department of Fish and
Game.

(126)

BOOK REVIEWS 127

The Valley: Meadow, Grove, and Stream

By Lorus J. and Margery Milne, Harper & Row. Publ., New York, 1963; xiii |
17S pp., illustrated ; $4.50.

Verj few people, other than naturalists, seem to sense fully the pulse and throb
of life as it exists in any natural area in which they live. Authors Lorus and Mar-
gery .Milne have, through keen observations and descriptive writing, interpreted the
daily natural life of both plants and animals in a small river valley in rural Xew
England.

The valley's cycle of life, its inter-relationships and adjustments of organisms to
their environment, is dramatically portrayed. Similar descriptions should be recorded
of other common regional environments throughout the world. (I would like to see
a similar treatment given to some western valley with its plant and animal associa-
tions.) It is an interesting hook for those who enjoj an informative and philosophic
account of nature. Perhaps its greatest contribution may be to encourage others to
make similar detailed observations of local flora and fauna. — Willis A. Evans, Cali-
fornia Department oj Fish and Game.

Fur and Fury

By ('. B. Colby, Duell, Sloan and Pearce, New York. L963 ; 127 pp., 16 half-
tones ; $3.50.

Without the dust cover, one might wonder just what kind of a I k he has chosen

to browse. The title indicates anything from science-fiction to a pulp western. How-
ever, the dust cover ami the title page divulge the secrel thai the pages will intro-
duce the reader to. "Natures most talented family" the weasels or Mustelidae.
From the well known skunks and the playful otters to the comical-looking badger
and the treacherous wolverine the life historj and habits of each member of the
family are discussed. After a short introduction explains the title and describes more
tangible family characteristics, 15 species are treated in 14 chapters. Why the
hooded and hognose skunks were combined in a single chapter while the striped and
spotted skunks each rated a separate chapter is not explained. There are 16 excel-
lent photographic illustrations of the mustelids, only one by the author, and the
footprint of each animal is sketched near the photo for the henetit of amateur
trackers.

The author's background is widely varied Hi- education was in art hut his career
began as an editor of aviation magazines, for slightly over a decade he has heen
writing stories on a varietj of subjects, many devoted to the outdoors and slanted
toward the \ outhful audience

Mr. Colby has collected a greal deal of factual information about the '•weasel-"
and has presented a mosl interesting storj upon the lL'7 pages between the covers
of Fur din] Fury.— William />. Craig, California Department of Fish and (hum.

100 Desert Wildflowers

By Xatt \. Dodge, Southwestern Monuments Association, Globe, Ariz., 1963; 32
p., 100 color photos ; $1.50 (paperbound).

This small book presents 100 color photographs of some of the more common
desert flowers (including cacti I of Arizona. Xew Mexico. California, Texas, Nevada,
and northern Mexico. Good color photographs are seldom found in the available
identification manuals, making this book particularly valuable when used with defini-
tive keys.

Common and botanical names accompany each photograph along with a brief de-
scription of the usual habitat and notes on field lore. Hints for flower photographers
appear on the inside of the front cover. Suggestions for additional reading follow
the text. — Parke H. Young, California Department of Fish and <!mne.
Advances in Marine Biology— Volume J

Edited by F. S. Russell, Academic Press, Inc.. London, 1963 ; xiii -f 410 p.,
illustrated ; $13.50.

This is the first volume of a new series which will condense into concise articles
recent developments in marine biological research. These reports bring together
articles, many known only to professional researchers in the given field, widely
scattered throughout the growing number of scientific publications. The editor has
covered a variety of subjects in Volume 1, each prepared by one or more experts.

"Rearing of Bivalve Mollusks" describes the special equipment and techniques
developed for spawning and rearing bivalves through early stages to metamorphosis.
It discusses foods, growth, diseases, and breeding of several species under labora-

128 I \I.Muk\iA PISH AND GAME

torj conditions. Primarj emphasis is on Crassostrea virginica and ifercenaria
Venus) mercenarin bul 15 other species of clams, mussels, scallops, and ship-
worms are covered, including photographs of larvae grown in the laboratory. Anyone
involved with rearing larval forms will certainly be interested in the techniques
discussed.

"The Rreeding of the North Atlantic Freshwater-eels" analyzes the differing
opinions on the breeding of Inguilla anguilla.

"Some Aspects of Photoreception and Vision in Fishes" compiles recent work
on extra-ocular lighl reception, and ecological and behavioral studies. The section
on ecology and behavior summarizes lighl in relation to migration, vertical move-
ments, si i ling, -i ii*I responses to lights and light intensity.

"The Biology of Coral Reefs" summarizes work on coral reef and atoll biology.
The paper has been divided into appropriate sub-headings, describing corals, and
their reef-building activities, and the productivity associated with the resultant
structure.

"The Behavior and Physiology of Herring and other Clupeids" is a rather com-
plete treatise on the physiology and behavior of Clupea harengus, in particular,
and other clupeids in general. Papers on fishing mortality and its estimation, and
fecundity as a means of distinguishing races and for estimating stock size have
not been included.

Each paper has been conveniently broken up into sub-sections for easy location
of specific topics. An extensive bibliography follows every article. This series will
become a valuable reference source and should he available in marine laboratories
and libraries. The price may seem rather high to the individual, but considering
the amount of research and effort condensed into this book, it is a bargain.

An annual volume is planned and in the preface Dr. Russell requests suggestions
for future volumes.- — E. .1. Best, California Department of Fish and Came.

The Origins of Angling and a new printing of "The Treatise of Fishing with an Angle"

By John McDonald assisted by Sherman Kuhn and Dwight Webster and the
editors of Sports Illustrated. Doubleday & Co., Inc.. New York, 1963; xiii 4-
L'T.'l p., black and white plus color illustrations, $10.

The Treatise of Fishing with an Angle was written in manuscript form about
1425, several centuries before Walton's more notorious work. It started the long
sequence of "how to do it" fishing books.

In his introduction. John McDonald says. "The principal justification for this
book is that The Treatise of Fishing with an Angle, the first writing on modern
sport fishing, has long been out of print." It is hard to disagree with his statement
that no better essay on fishing has been written, and that it should always be in
print.

I found the extensive background material about the Treati.se. and the supple-
mentary historical discussions in the first part of the book unusually interesting.
It gave many insights into the nature of angling and of people's attitudes toward
it at its incept imi as the sport we know. The author has a knack for making
scholarly material readable. In this respect, he did a particularly good job in
explaining how the cult of chivalry influenced angling traditions in many significant
ways.

It was disappointing to learn that the engaging nun. Dame Juliana Berners.
almost certainly did not write the Treatise, particularly after enjoying so much
Beatrice Cook's anecdote about her in Truth is Stranger Than Fishin. The per-
sistence of this myth down the centuries is an interesting story in itself.

The Treatise introduced the first modern trout flies, discussing twelve established
patterns. McDonald discusses them in detail, and the whole history of trout flies
at some length. He gives his concept of the twelve patterns, which are described
but not illustrated in the 'Treatise. There are four color plates of these flies tied
from the written descriptions in the Treatise.

The second pari of the book includes facsimilies of an incomplete manuscript
copy of the Treatise written by a scribe about 1450, and of the first edition in the
second Book of St. Albans, printed in 1946. Transcripts of the two documents in
modern script parallel them on facing pages.

This handsome volume will please the angler with a historical or philosophical
bent. — Alex Calhoun. California Department of Fish and Game.

printed in California office of state printing
12488-800 12-63 5,300

Notice is hereby given that the Fish and Game Commission
shall meet on April 3, 1964, at 10 A.M., in the State Employment
Building, 722 Capitol Mall, Sacramento, California, to receive
recommendations from its own officers and employees, from the
department and other public agencies, from organizations of
private citizens, and from any interested person as to what, if
any, orders should be made relating to birds or mammals, or
any species or "variety thereof, in accordance with Section 206
of the Fish and Game Code.

Notice is hereby given, pursuant to Section 206 of the Fish
and Game Code, that the Fish and Game Commission shall meet
at 10 A.M. on April 24, 1964, in room 358, City Council Cham-
ber, 1600 Pacific Center, San Diego, California, to announce
publicly the regulations it proposes to make relating to birds or
mammals, or any species or variety thereof for the 1964 hunt-
ing season.

Notice is hereby given that the Fish and Game Commission
shall meet on May 29, 1964, at 10 A.M. in room 1138, New
State Building, 107 South Broadway, Los Angeles, California,
to hear and consider any objections to its determinations or
proposed orders in relation to birds and mammals for the 1964
hunting season, such determinations resulting from hearing held
on April 24, 1964. This notice is published in accordance with
the provisions of Section 206 of the Fish and Game Code.

FISH AND GAME COMMISSION

Monica O'Brien

Secretary to the Commission

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