'I 

NOAA Technical Memorandum NMFS 

MAY 1983 

RE-ESTIMATION OF THREE PARAMETERS ASSOCIATED 

WITH ANCHOVY EGG AND LARVAL ABUNDANCE: 

TEMPERATURE DEPENDENT INCUBATION TIME, 

YOLK-SAC GROWTH RATE AND EGG AND 

LARVAL RETENTION IN MESH NETS 

Nancy C. H. Lo 

NOAA-TM-NMFS-SWFC-3 1 

U.S. DEPARTMENT OF COMMERCE 

National Oceanic and Atmospheric Administration 

National Marine Fisheries Service 

Southwest Fisheries Center 
NOAA Technical Memorandum NMFS 

The National Oceanic and Atmospheric Administration (NOAA), organized in 1970, has evolved 

into an agency which establishes national policies an manages and conserves our oceanic, coastal, and 

atmospheric resources. An organizational element within NOAA, the Office of Fisheries is responsible for fisheries policy and the direction of the National Marine Fisheries Service (NMFS). 

In addition to its formal publications, the NMFS uses the NOAA Technical Memorandum series to 

issue informal scientific and technical publications when complete formal review and editorial processing are not appropriate or feasible. Documents within this series, however, reflect sound professional 

work and may be referenced in the formal scientific and technical literature. 
NOAA Technical Memorandum NMFS 

This TM series is used lor documentallon and timely communication 01 preliminary results. imterim reports. or 

Special purpose inlormation. and have not received complete formal review. editorial control. or detailed editlng 

MAY 1983 

RE-ESTIMATION OF THREE PARAMETERS ASSOCIATED 

WITH ANCHOVY EGG AND LARVAL ABUNDANCE: 

TEMPERATURE DEPENDENT INCUBATION TIME, 

YOLK-SAC GROWTH RATE AND EGG AND 

LARVAL RETENTION IN MESH NETS 

Nancy C. H. Lo 

National Marine Fisheries Service 

Southwest Fisheries Center 

8604 La Jolla Shores Drive 

La Jolla, California 92038 

NOAA-TM-NMFS-SWFC-3 1 

U.S. DEPARTMENT OF COMMERCE 

Malcolm Baldrige. Secretary 

National Oceanic and Atmospheric Administration 

John V. Byrne. Administrator 

National Marine Fisheries Service 

William G. Gordon. Assistant Administrator for Fisheries 
-1- 

ABSTRACT 

The estimates of three parameters required for northern anchovy 

(Engraulis mordax) abundance assessment were updated using new data from 1981 

and 1982. These three parameters are incubation time, yolk-sac larval growth, 

and retention of eggs and larvae in various mesh nets. 

The growth data of the yolk-sac anchovy larvae were updated by including 

a set of new data collected in 1981. This new data set consisted of larval 

length and age collected at three temperatures: 13.5, 15.0, and 16.5"C. The 

incubation time was related to the water temperature in a negative exponential 

form. 

larvae, in which the temperature-dependent growth rate has an exponential 

f orm. 

A Gompertz model was used to describe the growth of yolk-sac anchovy 

The results of a three-vertical-net experiment conducted in March 1982 

showed that 0.333 mm mesh was not extrusion-free. The retentions of 0.333 mm 

Nitex mesh relative to 0.150 mm and 0.075 mm meshes are 0.91 for eggs, 0.63 

for larvae - < 4.0 mm (preserved standard length), 0.95 for larvae = 4.5 mm, and 

1 for larvae > 4.5 mm. The retention of eggs and larvae for large meshes can 

be corrected accordi ngly . 
- 2- 

1. INTRODUCTION AND DATA SOURCES 

Quantitative assessment of egg and larval abundances from ichthyoplankton 

data depends on the use of appropriate correction factors or weights for 

various parameters, as it is impossible to have a bias-free sampler. These 

parameters were most recently estimated by Zweifel and Smith (1981) for the 

northern anchovy. 

negative binomial weighted model developed by Bissel (1972) (Zweifel and Smith 

1981; Hewitt 1982) with each observation weighted by its effective sampler 

size. Since the completion of their work, new and more complete data have 

become available at the Southwest Fisheries Center (SWFC) for three of these 

parameters--incubation time, growth in length of egg through yolk-sac stage 

larvae, and extrusion of eggs and larvae through the meshes of plankton nets. 

In order to correct for the biases, Zweifel applied a 

New data were collected from a laboratory experiment conducted in 1981 on 

temperature specific incubation rates and yolk-sac larva growth rates of 

northern anchovy. In addition, an experiment at sea was conducted in March 

1982 to determine retention of anchovy eggs and larvae in three identical net 

frames, each with a different mesh net. Data from older sources are combined 

with these data to provide new parameter estimates. 

To improve estimates of the relationship between temperature and both 

incubation time and yolk-sac larval growth and to establish criteria for 

developmental stages of yo1 k-sac anchovy, a 1 aboratory experiment was 

conducted at three temperatures (13.5, 15.0 and 16.5"C) in 1981 using eggs 

from a captive brood stock. These data were used along with those collected 
-3- 

by David Kramer and employed by Zweifel and Lasker (1976) and Zweifel and 

Hunter (MS) (at temperatures 14, 17 and 20°C) to develop a revised model for 

expressing the relationship between yolk-sac larval growth and temperature. 

Estimates of retention of anchovy eggs and larvae in small mesh nets were 

investigated during a week-long field experiment conducted in March 1982 in 

the Los Angeles Bight at a single station. 

tows were made using three 25 cm diameter frames each with a Nitex net of 

different mesh size (0.333, 0.150 and 0.075 mm) mounted on the same wire. 

These plankton nets are deployed to 70 m depth and retrieved vertically. They 

are referred to as CalVET nets (CalCOFI vertical nets, Hewitt in press). The 

anchovy eggs taken in each of the nets were sorted according to their 

developmental stages and the standard length of the anchovy larvae was 

measured. 

One hundred forty-two vertical net 

The retention of anchovy eggs and larvae in large mesh nets (0.55 and 

0.505 mm vs 0.333 mm) was reexamined. Data from 0.333 mm mesh CalVET tows and 

0.505 mm mesh Bongo tows (McGowan and Brown 1966) taken during January-April 

in 1979-81 along with those used by Lenarz (1972) were included in the 

analysis to redefine the retention of eggs and larvae in various mesh sizes of 

plankton nets. 

2. METHODS 

2.1 Temperature Dependent Incubation Time and 

Growth of Yo1 k-Sac Northern Anchovy 
- 4- 

In the 1981 laboratory experiment anchovy eggs were incubated at three 

nominal temperatures (13.5, 15 and 16.5"C) in 10 liter containers in 

temperature controlled water baths with 20 eggs taken per hour until hatching. 

After hatching, 20 yolk-sac larvae were taken every 4 hours and 10 of these 

were measured to determine mean standard live length. 

hatch and approximate time of last hatch were recorded. 

located at the surface while larvae are usually in the middle depths, both 

surface and middle depth temperatures were recorded. 

The time of the first 

Because eggs are 

At 16.5OCY larvae older than 4.14 days (3.78-3.96mm) were excluded 

because they began to starve and would bias the growth curve downward. 

temperatures used in the analysis were geometric mean surface temperature 

before hatching and middle depth temperature after hatching, measured every 4 

hours. 

live length of anchovy larvae were used along with Kramer's larval data set, 

reported in Zweifel and Lasker (1976), to fit a temperature dependent growth 

curve for yolk-sac anchovy larvae (Table 1). 

The 

The elapsed time from fertilization, and the measured mean standard 

2.2 Retention of Anchovy Eggs and Larvae 

in Various Mesh Nets 

In estimating the abundance of eggs and larvae, one of the sources of 

bias is their extrusion through the meshes of the net. Extrusion is measured 

by the ratio of catch retained in a large mesh net to that taken in a smaller 

mesh net. 

Retention of anchovy eggs and larvae in 0.333 mm Nitex mesh compared to 
-5- 

Table 1. Live length (mm) and age from fertilization (days) of yolk-sac 

larvae at various temperatures ("C). 

was computed from equation (3)). 

(The predicted length 

OBSERVED PREDICTED 

AGE LENGTH LENGTH SE 

(days) (mm) (mm) 

TEMP. DATA 

OC SOURCE 
- 6- 

smaller Nitex meshes (0.150 and 0.075 mm) was investigated with the previously 

mentioned 1982 field experiment. 

to port, center and starboard positions, and every 6 hours, two of the nets 

were switched according to a predetermined system to el imi nate possible bias 

due to net position. 

The three 25 cm nets were randomly assigned 

Retention of anchovy eggs and larvae in 0.505 mm Nitex mesh compared to 

0.333 mm Nitex mesh was estimated from the larvae taken during January-April 

in 1979-81 in the 0.505 mm mesh Bongo net and the 0.333 mm mesh CalVET net at 

stations where both nets were towed. Retention of eggs and larvae in 0.55 mm 

silk mesh (1 m diameter net) compared to that in 0.333 mm Nitex mesh (0.5 m 

diameter net) was discussed by Lenarz (1972). 

taken in a 0.505 mm Nitex mesh net were compared to those taken in a 0.333 mm 

Nitex mesh net (Smith MS) although most of the larvae were neither counted nor 

measured. 

In the same study the eggs 

3. RESULTS 

3.1 Incubation Time as a Function of Temperature 

The incubation time of eggs was first analyzed by Zweifel and Lasker 

(1976) and was found to be inversely related to the temperature, i.e., the 

higher the temperature, the shorter the incubation time. 

incubation time of anchovy eggs discussed in the Methods section and those 

used by Zweifel and Lasker (1976) were used to fit an exponential equation 

expressing the relation between incubation time and incubation temperature 

(Fig. 1) 

The new data on 
-7- 

0 

m 

0 

e * 

0 

M 

0 

cu 

Predicted 

0 Observed 

. 

a 

0 

8 

r( 

I I I I 1 1 I I I 

11 12 13 14 15 16 17 18 19 20 21 

0 

8 

r( 

Temperature 

Figure 1. 

temperature ( "C) . Incubation time (days) of anchovy eggs as a function of 
-8- 

where tI is the incubation time in days and temp is the temperature in "C 

(Fig. 1). Equation (1) can be used to estimate anchovy egg production by 

adjusting the standing stock of eggs for given average water temperature (Lo 

In prep.). 

3.2 Temperature Dependent Growth of Yolk-Sac Northern Anchovy Larvae 

After the onset of feeding, growth in sea caught anchovy larvae appears to 

be independent of water temperature within season (Methot and Kramer 1979; 

Methot 1981). 

and have assumed that only the egg and yolk-sac stages of anchovy growth are 

temperature dependent and growth over the rest of the larval period (4.1-27 

mm) is temperature independent or food dependent. 

growth of yolk-sac northern anchovy with the data of Zweifel and Hunter (MS) 

and estimated the relation between live length and age at 6 temperatures using 

the Gompertz growth equation (Laird 1969). 

Thus I have followed the procedure of Methot and Hewitt (1980) 

I combined the new data on 

where Lt is the live length (mm) at age t days from fertilization. 

L, is the asymptotic length (mm) at the age of first feeding, 

Lk is the live length (mm) at age tk 
- 9- 

tk is either the age at hatching, which is temperature dependent 

incubation time (tT) or age 0 (to) 

and ‘temp is the growth coefficient which is temperature dependent. 

Equation (2) was derived from the assumption of the exponential form of 

the age-dependent instantaneous growth rate. i.e., 

(2.1) 

where is the growth rate at age tko Substituting L, for 

LkeX/a and L&, for in eq (2.1) produces eq (2). The values of the 

coefficients for each of 6 temperatures (see Table 1 for data) are with tk = 

tI, the incubation time: 

L 

tempOC (SEI n 

(mm) 

13.47 4.166 

(0.117) 

14.00 4.21 

(0.29) 

15.03 4.328 

(0.208) 

16.23 4.287 

(0.467) 

17.00 4.546 

(0.108) 

20.00 4.152 

(0.040) 

3.11 

( 0.0 347 

2.27 

(0.33) 

2.86 

(0.078 ) 

2.84 

(0.0566) 

2.406 

(0.104) 

2.4 

(0 .O 734 

0.551 30 

0.78 7 

0.556 30 

0.9438 11 

1.1543 8 

1.71 10 

(0.090 1 

(0.38) 

(0.1555) 

(0.417) 

(0.026) 

(0.027) 

The coefficient dtemp is a function of temperature. 

fit to (dtemp, temp) giving the final version of the length-age relation for 

yolk-sac anchovy larvae less than 4.1 mm with tk = to and Lk = Lo 

An exponential curve was 
- 10- 

Equation (3) was simultaneously fitted to all the data collected at 6 

temperatures and resulted in the following estimated parameters (Table 1 and 

Fig. 2): 

Parameters Estimates (SE) 

LOO 4.25 mm 0.093 mm 

0.32 mm 0.17 mm LO 

A 0.11 0.02 

B 0.12 0.006 

3.3 Retention Coefficients for Anchovy Eggs and Larvae 

This section discusses the results of a series of simultaneous vertical 

tows of 0.333, 0.150 and 0.075mm mesh conducted in March 1982, the estimation 

of egg retention by nets of two large mesh sizes compared to smaller meshes, 

and the estimation of the retention of anchovy larvae as a function of 

preserved standard 1 ength. 

The following notations are used through the text for the retention rate 

calculation: 

- 

YiL: catch per unit volume of water filtered (0.05 m3/m 

depth) for mesh i and egg and larval length L. 

- 

RijL = YiL/Y.jL: the retention rate of mesh i compared to mesh j. 

h 

The sample statistics are denoted as jiL and R for YiL and R 

where 

0 for eggs 

larval length (mm) (preserved standard length), 

L= 
-11- 

Length (mm) 

2.0 2.5 3.0 3.5 4.0 4.5 5.0 

I I 1 1 I 1 

U 

0 

N 

0 

v 

0 

00 

0 

I 

P 

Figure 2. 

temperatures. 

Growth curves of yolk-sac stage of anchovy larvae at various 
-12- 

i and j = 1 for 0.075 and 0.150mm Nitex meshes, 

2 for 0.333mm Nitex mesh, 

3 

4 

for 0.505mm Nitex mesh Bongo 

for 0.505mm Nitex mesh 1 m ring net, 

and 5 for 0.55mm silk mesh 1 m ring net. 

RCFijL = l/RijL: retention correction factor, which was used as a 

multiplier to correct egg and larva counts. 

The basic procedure for computing retention of eggs and larvae of length 

L from mesh i (compared to mesh 1) for meshes .505 mm and .55 mm (i - > 3) is: 

and 

function of its preserved length (L) for a given mesh size i: 

2. The retention of larvae (Ril~) was also described as a 

The coefficients Ai and Bi are estimated in later sections. 
-13- 

3.3.1 Retention Coefficients of Eggs and Larvae in 0.333mm 

Mesh From the Simul taneous Three-Vertical-Net Tows 

In order to evaluate whether the three meshes (0.075, 0.150 and 0.333 mm) 

retain the same amount of eggs and larvae, statistical testing procedures were 

selected after careful examination of the data. All the egg and larva samples 

were first sorted and the larvae measured to the nearest 0.5 mm. 

sample contains counts of eggs and larvae of 2.0, 2.5, 3.0, ..., 6.5+ mm, a 

total of eleven groups. The last length group contains larvae equal or larger 

than 6.5 mm. 

deviation), the frequency distribution of counts in each group by mesh size 

(Fig. 31, and the correlation between groups within mesh size. 

Thus, each 

I examined the basic statistics (sample mean and standard 

The basic statistics indicated that within larva length group, the sample 

standard deviation (s) was proportional to its sample mean (;) among meshes, 

e.g., the ratio, s/j, was 1.11 to 1.15 for 2.0 mm, 0.83 to 0.97 for 2.5 mm 

etc. (Table 4). 

symmetric. 

skewed, with at most 0.40 of samples containing zero catch, whereas the 

distributions of larvae > 4.5 mm were highly skewed, with 0.69 to 0.97 of the 

samples containing zero catch and the maximum count being 8 (Table 2 and Fig. 

3). Because all the larvae distributions were skewed, the logarithmic 

transformation was applied to larva data, x = In (y+l), prior to the 

computation of correlation coefficients. 

between adjacent groups for eggs and larvae - < 4.0 mm. The correlation between 

adjacent groups seems stronger in meshes 0.075 and 0.150 mm than 0.333 mm. As 

a result, a multivariate analysis of variance (MANOVA) was chosen for eggs and 

For each mesh size, the distribution of egg counts was fairly 

The distribut ons of larva counts between 2.0 and 4.0 mm were 

Significant correlation exists 
-14- 

EGG AND LARVA COUNTS 

E Lr I I ---uuuuuWunnnm*unno LIOCWOW~QLJmmr)UOW~QUUm-,UOYP 

0000c.000000000000000000000- 

00000000000000000000000000~ 

00000000000000000000~0000-( 

____~I_________- ___"__ YI 

.............. ............. ........... .,I.**.. t. . .......... .AI.*. 

,.I.*. 

..... ..... ..... ..... ..... ..*.. .**.. 

..... ..*. .... 

a*.* .*. .t. 

.t .. 

Y 

s~xx8xx888888888xx~xx8~888~ OOOUDOGOODOOi~ODOUOOOOC.OOOO~ 

__._ ____ m ............... .......... ......... ......... ........ ....... ....... ....... 

...... ...... 

.... .* 

.. .. . * .t .. 

................. ............ ........... .......... .......... ....... .I*.*.. 

....... ....... ...... 

.... ..... I.. 

.... .I. 

1.1 .... ... 

................ ................ ........... .......... ........ ........ ...... .... .... .... .... 

... ... .. 

.................. ................. ................ ............. ............ ........... .......... 

*.I.. . .*e.. , . ....... ...... ...... ... 

P 

VI 

0 

3 

3 

d 

.. 

.. .. .. .. .. .. .. .. .. .. .. .* .* 

.. .. .. .. .. *. 

.. .I .. 

.......... ......... ........ ........ ....... 

*1..* .. ..... I.,.. 

..... .e*.. 

..... ..... ..I. ..*. .*.... 

I.. 

,., 

1.. 

.I. 

..I 

I.. .* 

.I 

L. .* 

........ 

..e.. ..... ..... ..... .... .*. ... 

................. ................ ............... .............. ............ ........... ........... ........... ......... ....... ..I ... ... *. 

3 

3 

P x 0 

3 

3 

3 

3 

Y 

~UUOUOUOmO~OUOUOUO~OmOmOmOOOOOOoOOOOOOOOOOOOoOoooooo~ 

OOOOUOOOOOOOOOOOOOOOOOOOOO~ 

........................... .................... ................. .............. .*.*..*. ........... .* *'*.I.** t *. ........ .*. *.. It, . ..... .... ... ... .. 

t. 

I. 

.. 

1. 

.*. f. *. 

............ ........ ....... I ./ , ...... .I 

.***.I ..*.*. ..*e . .e.. .... .e.. 

.... .... .... ..I. 

+*.I ..*. ..*I .... 

.. 

..................... ................... .............. .............. ............. ............. ........ ........... ....... ......... ........ ............... .................. P 

....... 0 

d 

........... ............ VI 

...... ...... ..... ..... ..... .e*. . ..... .... ..... ..... .... *.. ... ... .. 1 

............... 

.......... ............ 

.......... .......... ......... ....... ....... ....... . ....... * . . . ....... ...... 

..... ..... *.. . :* 

........ ....... ....... ...... ...... 

..... ..*.e 

..... .... ..... 

..I. 

.I*. 

.... .... ..*. .... .. I .. 'L 

.I 

I. 

.. *. *. *. 

f. 

OW ow

.. 

.** ... 

... ... .*. ... ..* ... ... ** 

.. .. .. .* 

I. 

.. *. 1. 

........ ........ ........ ...... .... .*. *. 

.I 

.. .. 

.. 

3 

3 

g 

3 

3 

__ 

ff .. .* 

3 

3 

3 

3 

Figure 3A. Frequen y distributions of anchovy eggs and larvae by leng-h 

groups (2-4 mm) for each of three mesh sizes (0.075, 0.150 and 0.333 mm) 

based upon three-vertical-net experiment, 1982. 

denoted by 'MI. Each dot represents one count. 

is the total frequency for that category. 

Sample means are 

The number at the end 
-15- 

LOG (egg and larva counts + 1) 

.* .*. 

............... .............. ............. ............ ........... ......... ....... ...... ...... . *.** * .... ... ... ... 

............. ............. ............ ........... ........... ........... ........... ........ ...... .I 

.... .... .... . *.. .. ** 

.. x 

3 

3 

........... ......... * . *I. 

. . . t. , I + .** 

.*.*I ...... , ..I * . +.. . I.. . I** , *** . t.. .... e.. .... .... * ..I t *.* 

: : : : ::' 

.. -. 

t. .. .. .. 

3:: 

W 

............. ............ ............ ............ ............ .......... ..... , .. 1 I .... . . *. 

.. 

. . . 1.. *** . * t. 

*.* . *** .... . . *. .... .... * ** .... 

I. 

*I 

..... ..... .... .... .... * 

.* 

v 

0 

3 

3 

.................. ............... ............... ............... .............. ............ .......... ......... ........ ....... *. . .* * .. 

................ ............... ............ ............ ........... ........... ........... ........... ......... ....... ...... ..... 

.. ..I 

.................. ............... ............... .............. .............. ........... .......... ......... ......... ....... ..... 

P 

A 

VI 

0 

3 

3 

3 

3 

0 DIMOULDmONLDmOULB~o,~)DmONP- oGooooooooooooooooooooooGoz 

OoOOOOOOOOoOO~OOOOOOoooooo~ 

........................... .............. ........... ........... ........... 

.......... 

........... Y 

........ VI ....... 

..... 

.... .... .... .... 

I. 

.. .. .. 

..... 3 ..... 3 

W 

............ 

............ 4 .......... 

.......... 

......... 

........ 

...... . *.. ... ... .. 

............ ? 

.......... VI 

.......... 0 

........ 3 ........ 3 

-_ ........ ................. .............. .............. .............. ...... ...... t * . ..* ..* ............. ............ ........... ............ ........... .......... ..... ..I. ........... 

......... ....... . tt t. 1. .......... .......... ......... ....... t . *** . *.** ..... .. .. ..*. .... ..... ..t t. I. . .I.* .... t. t. 

t.. 

*.. f t. . .... .. *.* *. .. .. **. 

.. . .** 

.I ** *. 

.I *. P :* g 0 

3 

3 

*. 

.. .* 

.I 

"0 

00 

E 0 

0 

3 

3 

Figure 3B. Frequency distributions of anchovy eggs and larvae by length 

groups (2-4 mm) for each of three mesh sizes (0.075, 0.150 and 0.333 mm) 

after log transformation based upon three-vertical-net experiment, 1982. 

Sample means are denoted by 'MI. 

number at the end is the total frequency for that category. 

Each dot represents one count. The 
-16- 

Table 2. 

for anchovy eggs and larvae by length group, the maximum catch for each 

of three mesh sizes and the chi-square values for larvae - > 4.5mm based 

upon three-vertical-net-experiment, 1982. 

Number of samples with zero catch from a total of 140' samples 

Number of samples 

with zero catch Maximum catch chi-square 

0.075mm 0.150mm 0.333mm 0.75mm 0.150mm 0.333mm d.f.=2 

Eggs 

2.0 mm 

2.5 

3.0 

3.5 

4.0 

4.5 

5.0 

5.5 

6 .O 

6.5+ 

0 

42 

16 

0 

7 

27 

103 

111 

131 

132 

117 

0 

38 

10 

0 

8 

24 

97 

107 

133 

130 

102 

0 

33 

9 

2 

18 

52 

97 8 

103 5 

136 2 

133 2 

118 2 

3 5 0.83 

3 5 1.27 

1 1 2.0 

1 1 0.6 

3 2 7.24* 

11.94 (d.f.=lO) 

'Two samples were discarded because they were spoiled. 

*Significant at 5% level. 

E 
-17- 

i. 

larvae < 4.5 mm and a chi-square test on the proportion of samples with zero 

catch among three meshes was chosen for larvae - > 4.5 mm to detect the 

retention difference of three meshes. 

For eggs and larvae - < 4.0 mm, a two-way (factor) MANOVA was conducted to 

test whether the mesh sizes of 0.075, 0.150 and 0.333 mm and the position of 

the three nets (starboard, center and port) had any significant effect on the 

catches. 

proportional to its sample mean within the length group, and the frequency 

distributions were skewed, a logarithmic transformation x =ln(y+l) was applied 

to larva data to equalize the variances and reduce the skewness of the data. 

The constant "1" was added to the original data for zero observations (Scheff; 

1958; Snedecor and Cochran 1969; Li 1965; Aitchison and Brown 1973). 

Comparison of the variances of transformed data showed that except for larvae 

of 2.0 mm, the variances within length groups among meshes were not 

significantly different. Moreover, the distributions of the transformed data 

were more symmetric than those of the original data (Fig. 3). 

from the two-way MANOVA indicated the net position made no significant 

difference in catch (p=0.83), while mesh size made a significant difference (p 

< O.OOl), as did the interaction of mesh size and net position (p < 0.001). 

Because the sample standard deviation of larva counts was 

The results 

Because the interaction of mesh size and net position was significant, a 

separate MANOVA was run for each of the three positions. It was found that 

the overall mean catches of eggs and larvae among meshes were significantly 

different at each position. The univariate tests show that the mean catch was 

significantly different for eggs and larvae < 4.5 mm with the exception of the 

mean catch of larvae of 2.0 mm and 2.5 mm on the starboard side which was not 

significantly different among meshes. The cause of the interaction is 
-18- 

unknown. 

Since the position of the net did not affect the catch, a one-way MANOVA 

was used to evaluate the difference among meshes. The mean catch of anchovy 

eggs and larvae taken in small mesh nets (0.075 and 0.150mm) was compared to 

that taken in 0.333mm mesh net, after the mean catch was compared between 

small meshes (0.075 and 0.150mm). 

0.075mm net was significantly different from that in the 0.150mm mesh net 

(p=0.04). However, the significant difference was mainly due to egg counts 

(catch in 0.150 mm was slightly higher than that in 0.075 mm mesh (p=0.03)) 

The mean catch of eggs and larvae in the 

whereas all the larvae catches seemed 

Therefore, the catches from these two 

compared with that of 0.333 mm mesh. 

to be the same between these two meshes. 

small meshes were combined to be 

. 

The mean catch in the 0.333 mm mesh net 

was different from both of the small mesh nets (0.075 or 0.150mm) (p < 0.001) 

(Table 3). 

mm mesh net presumably by extrusion through the meshes. 

Hence, eggs and larval anchovy <4.5 mm appear to be lost by 0.333 

To compare the retention of larvae - > 4.5 mm among 3 mesh sizes, a 2x3 

contigency table was first constructed for each of the 5 groups where the 

first attribute was mesh size (.075, 0.150 and 0.333 mm) and the second was 

catch (zero and non zero). All but the last length group had insignificant 

chi-square values. Because little correlation exists among the groups, the 

sum of the 5 chi-square values was used to test the overall retention 

difference among the mesh sizes. 

insignificant at 5% level (Table 2). 

larvae - > 4.5 mm from 0.333 mm mesh net. 

The chi-square value (11.94) was 

Thus there seems to be no extrusion of 
-19- 

Table 3. One-way analysis of variance of retention of anchovy eggs and 

larvae (< 4.0 mm, log transformation) in three meshes -- 

comparison between catches in 0.075 mm and 0.150 mm meshes, 

and comparison between catches in 0.333 mm and small meshes. 

Sum of Mean F 

Effect Variate squares d.f. squares (d.f.) P 

.075 mm vs. A1 l1 TSQ = 13.67 2.25 0.04 

.150 mm (6,397) 

Univariate Tests (1,402) 

eggs 3793.13 1 3793.13 5.01 0.03 

2.0 mm 1.68 1 1.68 1.44 0.23 

2.5 2.69 1 2.69 2.96 0.09 

3 .O 0.25 1 0.25 0.68 0.41 

3.5 0.33 1 0.33 0.44 0.51 

4.0 0.11 1 0.11 0.25 0.62 

,075 mm & 

.150 mm vs. 

.333 mm All' TSQ = 114.14 

Univariate tests 

eggs 4419.34 1 4419.34 

2.0 mm 2.93 1 2.93 

2.5 7.19 1 7.19 

3.0 18.89 1 18.89 

3.5 15.79 1 15.79 

4.0 11.71 1 15.79 

Error 

eggs 304141.94 40 2 756.57 

2.0 467.95 402 1.16 

2.5 364.70 40 2 0.91 

3.0 147.90 402 0.37 

3.5 303.01 402 0.75 

4.0 177.77 402 0.44 

18.79 0.0002 

(6,397) 

(1,402) 

5.84 0.02 

2.52 0.11 

7.93 0.005 

51.35 0.000 

20.95 0.000 

20.95 0.000 

lMul tivariate analysis. TSQ is Hotelling T2 statistic 

2p<o. 000 1 
-20- 

Anchovy eggs and larvae taken in the two small mesh nets (0.075 and 

0.150mm) were combined to produce the mean catch for eggs and larvae by length 

classes. 

data were used as the basis for estimating the retention of eggs and larvae in 

large mesh nets in the latter sections. The retention coefficients of eggs 

and larvae by 0.5 mm and 1 mm length classes in 0.333 mm Nitex mesh are in 

Table 4. Relative to small meshes, the 0.333 mesh retains 0.91 of anchovy 

eggs and 0.63 of anchovy larvae < 4.5 mm length. 

(No log transformation was used for computing catch ratios.) These 

3.3.2 Retention Coefficients for Various Mesh Nets and 

Life Stages of Northern Anchovy 

The retention of anchovy eggs and larvae was estimated for two mesh sizes 

(0.55mm silk and 0.505mm Nitex) on two frames (1 m ring net and Bongo net). 

To be consistent with the sampling scheme of the current egg production method 

(Stauffer and Picquelle 19801, the retention of eggs was reestimated for the 

first 4 months and CalCOFI central regions (regions 4, 7, 8, 9, and 11) 

(Huppert et. al. 1980). All egg catches in ring nets and Bongo nets were 

standardized to the sampling unit used for CalVET net catches (0.05m5/m 

depth). 

Because no larval catch data were available for the 0.505mm Nitex 1 m 

ring net, the larvae taken in Bongo and CalVET net tows were combined with 

the three-vertical-net experiment data to arrive at an estimate of larval 

retention in 0.505 mm Nitex mesh net. 
-21- 

Table 4. Sample mean catch of anchovy eggs and larvae in small meshes, 

and 0.333mm (y' ), and retention coefficients 

for eggs and eL arvae by 0.5 mm length grouping and 

1 mm length grouping based upon three-vertical 

net experiment 1982 (n=140). 

parentheses. 

Standard errors are in 

(1) 

eggs 

2. Omm 

2.5 

3.0 

3.5 

4.0 

4.5 

5.0 

5.5 

6 .O 

6.5+ 

(2) (3) 

Mean catch 

.? (SEI 

.075mm 

2.!j3 mm 

3.75 

4.75 

5.75 

6.5+ 

2.2S4 mm 

3.25 

4.25 

5.25 

6 .O 

6.5+ 

78.57 

(2.10 

5.66 

(0.55 

10.81 

(0.89 

13.86 

(0.72 

9.34 

(0.64 

2.87 

(0.23) 

0.46 

(0.09) 

0.26 

(0.05) 

0.08 

(0.03) 

0.06 

(0.02) 

0.18 

(0.04) 

. i 50mm 

86.12 

(2.40) 

7.54 

(0.73) 

12.33 

(0.89) 

14.85 

(0.72) 

8.61 

(0.62) 

2.50 

(0.20) 

0.43 

(0.06) 

0.30 

(0.05) 

0.05 

(0.02) 

0.07 

(0.02) 

0.32 

(0.05) 

(411 (5) 

Mean catch in Mean catch 

small meshes .0333mm 

Yl L 

82.34 

6.6 

11.57 

14.36 

8.97 

2.69 

0.44 

0.28 

0.06 

0.07 

0.25 

32.533 

11.66 

0.73 

0.13 

0.25 

18.174 

23.32 

3.13 

0.35 

0.07 

0.25 

~~L(SE) 

75.22 

(2.40) 

4.49 

(0.42) 

7.42 

(0.52) 

9.17 

(0.50) 

5.71 

(0.44) 

1.55 

(0.14) 

0.42 

(0.07) 

0.40 

(0.07) 

0.03 

(0.01) 

0.05 

(0.02) 

0.2 

(0.04) 

21.09 

7.26 

0.82 

0.08 

0.20 

11.91 

14.89 

1.97 

0.43 

0.05 

0.20 

211 

0.91 

(0.01) 

0.68 

(0.04) 

0.63 

(0.02) 

0.64 

(0.03) 

0.57 

(0.06) 

0.95 

(0.16) 

1.43 

(0.27) 

0.44 

(0.26) 

0.74 

(0.31) 

0.80 

(0.18) 

0.65 (0.02) 

0.62 (0.03) 

1.13 (0.14) 

0.60 (0.19) 

0.80 (0.18) 

0.66 (0.03) 

0.64 (0.02) 

0.63 (0.05) 

1.24 (0.22) 

0.74 (0.31) 

0.80 (0.18) 

'(4)=C(2)+(3) I/2 

2( 6 I=( 5 )/(4 1 

32.5 mm = 2.0 mm + 2.5 mm + 3.0 mm, 3.75 mm = 3.5 mm + 4.0 mm etc. 

42.25 mm = 2.0 mm + 2.5 mm, 3.25 mm = 3.0 mm + 3.5 mm etc. 
-22- 

3.3.2.1 Retention Coefficient for Eggs in 0.55mm Silk Mesh 

1 m Ring Nets (Rslo) and 0.505mm Nitex Mesh 1 m Ring Nets (R410) 

A n 

- 

A one-meter (1 m) ring net of 0.55mm silk mesh was the standard CalCOFI 

plankton net from 1951-1968. 

This 0.505mm Nitex mesh 1 m ring net was used until 1978 when the Bongo frame 

was introduced for ichthyoplankton surveys (Smith and Richardson 1977). 

(MS) estimated the retention of anchovy eggs in 0.55 and 0.505 mm mesh 1 m 

ring nets by comparing their catches to that of the 0.5 m diameter 0.333 mm 

mesh ring net. 

because of seasonal changes in egg size. 

0.505 mm mesh nets relative to that taken by the 0.333 mm mesh net (Smith MS) 

are shown bel ow: 

In 1969, the silk mesh was replaced by Nitex. 

Smith 

A seasonal difference in egg retention seems to exist probably 

The retention of eggs in 0.55 and 

Winter Spring Summer Fa1 1 Mean 

0.55mm R520 0.29 0.27 0.08 0.13 0.24 A 

A 

3.70 13.07 7.45 4.25 

A 

0.505mm R420 0.40 0.28 0.09 0.26 0.33 

A 

(1969) RCF420 2.47 3.53 11.72 3.89 3.00 

Analysis of the data of Jan-April from the 1966-68 mesh experiment (75 

paired tows with positive catches from either net or both nets (0.55 and 

0.333mm)) and the 1982 three-vertical-net experiment indicated that the 

retention of anchovy eggs in 0.55mm silk mesh compared to the 0.333mm Nitex 

mesh and small mesh (0.075 or 0.150mm Nitex mesh) was 0.3 (R520) and 0.27 

(R51o = 0.30x0.91) respectively. 

silk mesh net, the egg counts must be multiplied by the retention correction 

/c 

A 

In order to correct the egg counts in 0.55mm 

factor 3.62 (SE = 0.65) (Table 5). 
-23- 

Table 5. Sample mean catch of eggs in large meshes (7. ) and 0.333mm 

(-2~) retention coefficignts compared to bot! 0.333mm 

(#- i an9 small meshes (Ril ) and retention correction 

Standard errors are in 

parentheses. 

fac l f0 or (RCF) in January-Aprit. 

Mean Catch h /r A 

Mesh Size Year n Ri 20 R2 10 Ri 10 (i 1 

.55 mm 1966-68 15.65 51.53 75 .30 0.91 0.27 

silk 1 rn (1.93) (8.07) 

ring net 

.505 mm 1969 18.63 

Nitex 1 m (3.34 

ring net 

(4) 

(5) 

.505 mm 2.69 

51.60 

(9.41 

31.52 

82 .36 .91 .33 

116 .09 .91 .08 

Nitex Bongo (0.38) (5.32) 

net 

(3) 

1980 3.17 32.29 35 .10 .91 .09 

(0.87) (9.14) 

1981 2.48 31.19 81 .08 .91 .07 

(0.39) (6.56) 

P2F1 

(SEI 

3.62 

(0.65) 

3.04 

(0.49) 

12.76 

(2.56) 

11.19 

13.82 

/r A 

'RCF may not equal to l/Rilo due to rounding errors. 
-24- 

The analysis of the data of the first four months from the 1969 mesh 

experiment (82 paired tows with positive catches from either net or both nets 

(0.505mm and 0.333mm Nitex)) and the 1982 three-vertical-net experiment 

indicated that the retention of eggs in nets of 0.505mm Nitex mesh compared to 

0.333mm and small meshes was 0.36 (R420) and 0.33 (R410 = 0.36 x 0.91) 

respectively. 

egg counts must be multiplied by the retention correction factor 3.04 (SE = 

0.49) (Table 5). 

h A 

In order to correct the egg counts in 0.505 Nitex mesh net, the 

h 

3.3.2.2 Retention Coefficients for Eggs in 0.505mm Nitex Mesh Bongo Net (R3102_ 

The 1 m ring frame was replaced by the Bongo frame as the standard 

CalCOFI gear in 1978, because it reduced net avoidance by large larvae (Smith 

and Richardson 1977). The retention of eggs by the Bongo and ring frames with 

the same mesh size were believed to be equivalent but this appears not to be 

the case. 

To estimate the retention of eggs and larvae in the 0.505mm Nitex mesh 

Bongo net, data from Bongo and CalVET net tows consisting of 116 stations with 

positive catches from either net or both nets were used in the analysis. 

Bongo catches were standardized to the CalVET 0.05m3/m depth sample unit 

(Table 5). 

was 0.09. 

(R3lo) was 0.09x0.91 = 0.08 (Table 5). 

the 0.505mm Nitex mesh Bongo net, one has to multiply the catch by the 

All 

4 

The retention of eggs in 0.505mm mesh compared to 0.333mm (R320) 

The retention of eggs in the Bongo net compared to the small mesh 

In order to correct the egg catch in 

A 

retention correction factor 12.76 (SE = 2.56). In other words, the small mesh 

(0.075 or 0.150mm mesh) retains almost 13 times more eggs than the Bongo net 
-25- 

and 3 times more than the 0.505mm Nitex mesh 1 m ring net. 

the Bongo gear is about 1/4 as effective as the 1 m ring with the same net 

material. 

that the retention difference between Bongo and 1 m ring frame of 0.505mm mesh 

could be due to different egg sizes. 

It appears that 

Because data were collected in different years, one may speculate 

3.3.2.3 Retention Coefficients for Larvae in 0.55mm 

Silk Mesh 1 m Ring Nets (ffrjlL1 

As mentioned in an earlier section, prior to 1969, the standard CalCOFI 

net was the 0.55mm silk mesh 1 m ring net. 

1966-1968 mesh experiment, 26 tows were selected by Lenarz (1972) for his 

analysis of retention. 

19 tows are available for reexamination of the retent on of anchovy larvae by 

length class (Table 6). 

calculated according to the formula: 

From larval data collected in the 

Due to loss of the raw data sheets, only the data from 

The retention of larvae in 0 55mm mesh net was 

A 

where R21L is assumed to be 1 for L > 4.5hm because no significant difference 

was found between catches of 0.333mm mesh (JzL) and that of the small meshes 

(ilL) (Table 4). The seeming decrease of retention of larvae larger than 

4.5mm in the three-vertical-net experiment could be caused by avoidance of 

larvae or may be due to random error. The retention of larvae compared to 

h 

0.333 mesh net (R52L) is assumed to be 1 for L - > 6.5 mrn. 

The logistic equation that describes the relation between retention of 
-26- 

Table 6. Sample mean catch of larvae in 0.55mm silk mesh 1 m ring net (75L) and 0.333mm Nitex mesh 0.5m ring net (y2 ), and 

the1 r retention coefficients compared to both b.333mm mesh 

(R52L) and small meshes (R and R21~) based on data 

vertical-net experiment, 1982. 

from January-April 1966-19 $AL mesh experiment, and 1982 three- 

(1) (2) (3) (4) (5) (6)' (713 

(mm) (i5L) (ti*L) 

Preserved Mean catch Mean catch ,, A n 

length (L) in .55 mm in .333mm R5 2L R21L R5 1L r*511 

2.5 0.45 1.50 0.30 

3.75 0.42 0.72 0.58 

4.75 0.45 0.59 0.77 

5.75 0.34 0.39 0.87 

6.5t 0.80 0.80 0.99 

2.25 0.13 0.67 .20 

3.25 0.48 1.17 .41 

4.25 0.45 0.58 .77 

5.25 0.41 0.53 .77 

6.00 0.19 0.24 .79 

6.5t 0.80 0.80 .99 

n = 19 

0.65 .19 

0.62 .36 

(1.13)l .77 

(.60) .87 

(.80) .99 

.66 .13 

.64 .26 

.63 .48 

(1.23) .77 

(.73) .79 

(.80) .97 

.14 

.39 

.66 

.86 

1 .oo 

.ll 

.28 

.53 

.77 

.88 

1 .oo 

'( 

'(6) = (4) x (5) 

3(7) is computed from equation (5). 

) was substituted by 1 in computing (6). 
-27- 

h 

larvae (R51L) and preserved length (L), (Table 6 and Fig. 4) is: 

[1 + e4.53-l.09*L]-l for L < 6.5mm 

for L 2 6.5mm 

3.3.2.4 Retention Coefficients for Larvae in 

h 

0.505mm Nitex Mesh Bonqo Nets (R,,, ) 

(5) 

The Bongo net has been used to collect larvae during CalCOFI 

ichthyoplanktonic surveys since 1978. I used the 1979-1981 Bongo-CalVET data 

to estimate the retention of anchovy larvae in the 0.505mm Nitex mesh net. A 

total of 383 stations had samples from both Bongo and CalVET nets (147 from 

1979, 96 from 1980, and 140 from 1981). A weighted negative binomial was used 

to estimate average catch for each larval length class (Zweifel and Smith 

1981). The Bongo net catch was further standardized to the 0.05m3/m depth 

sampling unit (Table 7). 

small mesh net (R31L) was calculated according to the formula: 

The catch ratio of the 0.505mm mesh Bongo net to the 

A 

PI A n A 

R31~ = R32~ xR21~. The retention coefficient (R31~) and the corresponding 

preserved length (L) were fitted to a logistic model which estimates the 

retention of larvae of given preserved length (L) (Table 7 and Fig. 4): 

[l + e3.96s-o.9357L]-1 for L < 6.5mm 

for L 2 6.5mm 

4. CONCLUSION AND DISCUSSION 

(6) 

Both new temperature-dependent incubation time function (eq 1) and growth 

function for yolk-sac anchovy larvae (eq 3) are improvements over the past 
- 28- 

Table 7. Sample mean catch of larvae in .505mm Ni tex mesh Bongo net 

(72,) and 0.333mm Nitex mesh CalVET net (7 ) and theiz 

re ention coefficipts compared to both 0.$!33mm mesh (R32L) 

and small meshes (R and R ) based upon CalCOFI cruise 

data in Jan~ary-Apr?~~1979-1$#l, and three-vertical -net 

experiment, 1982. 

(1) (2) 

Preserved Mean catch 

1 ength in .505mm 

(mm) Bongo (j5L) 

1979 (n=147) 

2.50 

3.75 

4.75 

5.75 

1980 (n=96) 

2.25 

3.25 

4.25 

5.25 

6.25+ 

1981 (n=140) 

2.25 

3.25 

4.25 

5.25 

6.25+ 

1.02 

0.50 

0.40 

0.32 

0.36 

1.35 

0.87 

0.89 

0.68 

0.89 

2.24 

1.30 

1.03 

0.82 

(3) 

Mean catch 

in 0.333mm 

(92L) 

4.ai 

3.86 

1.02 

0.78 

1.36 

3.47 

0.64 

0.34 

0.23 

1.93 

5.59 

2.14 

0.71 

-- 

(4) 

R32L 

A 

0.21 

0.13 

0.39 

0.41 

0.26 

0.38 

1.36 

2.62 

-- 

0.46 

0.43 

0.61 

1.45 

-- 

(5) 

R21L 

A 

0.65 

0.62 

1.13 

(.60 

0.66 

0.64 

0.63 

(1.23 

-- 

0.66 

0.64 

0.63 

(1.23) 

-- 

'(6) = (4) x (5) 

2(7) is computed from equation (6) 

3( was substituted for computation 

(6) 

r311 

A 

0.14 

0.08 

0.44 

0.41 

0.17 

0.25 

0.86 

(2.62) 

-- 

.30 

0.27 

0.38 

(1.45) 

-- 

(7) 

r*311 

0.16 

0.39 

0.62 

0.80 

0.13 

0.28 

0.50 

0.72 

-- 

0.13 

0.28 

0.50 

0.72 

-- 
-29- 

8 

0 

0 

0 

e 

P 

A 

P 

Y 

I 

66 

Preserved Length (m) @) 

Figure 4. 

(R 

equation (6). 

Retention of anchovy larvae in 0.52 mm silk mesh 1 m ring net 

) and in 0.505 mm Nitex mesh Bongo net (R3 ) compared to small 

mes 51iL es. Solid line is from equation (5) and do kk ed line is from 
- 30- 

models (Zweifel and Lasker 1976; Zweifel and Hunter MS; and Methot and Hewitt 

1980) because they have much simpler forms and are based upon a larger data 

set, covering a wider temperature range. 

The analysis of catch data from the three-vertical-net experiment 

(simultaneous tows of 0.075, 0.150, and 0.333mm nets) indicated that eggs and 

larvae were extruded from 0.333mm mesh which was previously believed to be 

extrusion free. 

0.91 for eggs, 0.63 for larvae - < 4.0mm, 0.95 for larvae = 4.5mm, and 1.0 for 

larvae > 4.5mm. 

small meshes (average catches of 0.075 and 0.150mm mesh) together with that of 

large meshes (0.55 and 0.505mm) compared to 0.333mm gives a much less biased 

estimate of retention of eggs and larvae than those previously reported (Smith 

MS; Lenarz 1972; Zweifel and Smith 1981; Hewitt 1982). There seems to be 

little difference in retention of larvae between 0.55 mm silk mesh and 0.505 

mm Ni tex mesh. 

The retention of anchovy eggs and larvae in 0.333mm mesh are 

The retention rate of eggs and larvae in 0.333mm compared to 

The final estimates of anchovy egg retention in 0.55 mm silk, 0.505 mm 1 

m Nitex ring nets and 0.505mm Bongo nets are 0.27, 0.33, and 0.08, 

respectively. 

mesh nets but the reason for this difference is unknown; this effect should 

definitely be studied in future field experiments. 

extrusion through the 0.333mm mesh net alters the estimates of larval 

abundance, and consequently changes the shape of the larval mortality curve 

from one with a constant apparent instantaneous mortality rate to one with an 

age dependent instantaneous mortal i ty rate (Lo In Prep.). 

A large difference exists in retention between the two 0.505mm 

Correction for larval 
-31- 

ACKNOWLEDGEMENTS 

I thank H. Geoffrey Moser and Carol Kimbrell for conducting laboratory 

experiment of temperature-specific egg incubation and yolk-sac larval growth; 

William Flerx, Jack Metoyer and others for conducting the three-verticalexperiment; plankton laboratory staff for sorting and measuring eggs and 

1 arvae from the three-vertical-net-experiment; Barry Fi nzel and Cynthia Meyer 

for processing computer data; John Hunter, Roger Hewitt, Alec MacCall, Richard 

Methot and Paul Smith for providing editorial and technical reviews of the 

manuscript; and Mary Dewitt and Julie Shoemaker for typing the manuscript. 
-32- 

LITERATURE CITED 

Aitchison, J. and J.A.C. Brown. 1973. The lognormal distribution 

with special reference to its use in economics. Cambridge 

University Press. 176 p. 

Bissel, A.F. 1972. A negative binomial model with varying 

element sizes. Biometrika, 59: 435-441. 

Dixon, W.J., M.B. Brown, L. Engelman, J.W. Frane, M.A. Hill, R.I. 

Jennich and J .D. Toporek. 1981. BMDP statistical software. 

Department of biomathematics, University of California, Los Angeles, 

University of California Press, Berkeley, Los Angeles, London 

726pp. 

Hewitt, R.P. 1982. Spatial pattern and survival of anchovy larvae: 

implications of adult reproductive strategy. Ph .D. Thesis. Univ. 

of California, San Diego, 187p. 

. In press. Roll, heave and vertical ichthyoplankton tows. 

Ocean Sci. and Eng. 

Hewitt, R.P. and R.D. Methot. 1982. Distribution and mortality of 

northern anchovy in 1978 and 1979. CalCOFI Reports 23:226-245. 

Huppert, D.D., A.D. MacCall, G.D. Stauffer, K.P. Parker, J.A. McMillan 

and H.W. Frey. 1980. California's northern anchovy fishery-- 

Biological and economic basis for fishery management. NOAA-TMNMFS-SWFC- 1. 

Laird, A.K. 1969. The dynamics of growth. Res/Dev. 20(8):28-31. 

Lenarz , W. H. 1972. Mesh retention of larva of Sardinops Caerula 

and Engraulis mordax by plankton nets, U.S. Fish. Bull. Vol. 70(3): 

839-848. 

Li, J.C.R. 1965. Statistical inference I. Edwards Brothers, Inc. 

Ann Arbor, Michigan, 658p. 

Lo, Nancy, C.H. In prep. Egg production of the central stock of 

northern anchovy, 1951-1982. 

McGowan, J.A. and D.M. Brown. 1966. A new opening-closing paired 

zooplankton net. SI0 Ref. (Scripps Inst. Oceanogr.) (66-23). 

Methot, R.D. 1981. Growth rates and age distributions of larval and 

juvenile northern anchovy, Engraulis mordax, with inferences on 

larval survival. Ph.D. Thesis, Univ.ofCalifornia, San Diego, 

203p. 
- 33- 

Methot, R.D. and D. Kramer. 1979. Growth of northern anchovy, 

Engraulis mordax, larvae in the sea, U.S. Fish. Bull. Vol. 77(2): 

- 

Methot, R.D. and R.P. Hewitt. 1980. A generalized growth curve for 

young anchovy 1 arvae: derivation and tabu1 ar example. Southwest 

Fisheries Center Adm. Rept. LJ-80-17. 

Scheffg, H. 1959. The analysis of variance. John Wiley & Sons, Inc. 

New York, London, Sydney, 477p. 

Smith, P.E. 1972. The increase in spawning biomass of northern 

anchovy, Engraulis mordax, U.S. Fish. Bull. Vol. 70(3): 849-874. 

Smith, P.E., and S.L. Richardson. 1977. Standard techniques for 

pelagic fish egg and larva surveys. FA0 Fisheries Technical Paper 

No. 175. 

Smith, P.E. MS. Time series of the abundance of anchovy 

eggs in the California Current Region. 

Snedecor, G.W. and W.G. Cochran. 1956. Statistical methods applied 

to experiments in agriculture and biology. The Iowa state College 

Press, Ames, Iowa, 534p. 

Zweifel, J.R. and J .R. Hunter. MS. Temperature-specific equations 

for growth and development of anchovy, Engraulis mordax, during 

embryonic and 1 arval stages. 

Zweifel, J.R., and R. Lasker. 1976. Prehatch and posthatch growth 

of fishes - a general model, U.S. Fish. Bull., Vol 74(3): 609-621. 

Zweifel, J.R., and P.E. Smith. 1981. Estimates of abundance and 

mortality of larval anchovies (1951-751, Rapp. P.-v. Reun. Cons. 

int. Explor. mer., 178: 248-259. 
RECENT TECHNICAL MEMORANDUMS 

Copies of this and other NOMTechnical Memorandums are available from the National Technical 

Information Service, 5285 Port Royal Road, Springfield, VA 221 67 Paper copies vary in price Microfishe copies cost $3 50 Recent issues of NOAATechnical Memorandumsfrom the NMFS Southwest 

Fisheries Center are listed below 

NOM TM-NMFS SWFC 21 

22 

23 

24 

25 

i 

26 

27 

28 

29 

30 

"An annotated bibliography of the ecology of co-occurring tunas 

(Katsuwonus pelamis. Thunnus albacaresj and dolphins (Stenella 

attenuata, Stenella longirostris and Delphinus delphis in the 

eastern tropical Pacific" 

S. D. HAWES 

(November 1982) 

Structured flotsam as fish aggregating devices 

R. S. SHOMURA and W. M. MATSUMOTO 

(November 1982) 

Abundance estimation of dolphin stocks involved in the eastern 

tropical Pacific yellowfin tuna fishery determined from aerial and 

ship surveys to 1979. 

R. S. HOLT and J. E. POWERS 

(November 1982) 

Revised update and retrieval system for the CalCOFl oceanographic data file. 

L. EBER and N. WILEY 

(December 1982) 

A preliminary study of dolphin release procedures using model 

D. B. HOLTS and J. M. COE 

(December 1982) 

"Possible effects of sampling biases on reproduction rate estimates 

T. POLACHECK 

(January 1983) 

"Reports of porpoise experiment testing detection of on-track 

R. S. HOLT 

(February 1983) 

"Two computer programs to project populations with time-varyinq 

T. GERRODETTE. D. GOODMAN & J. BARLOW 

(February 1983) 

Report of eastern tropical Pacific research vessel marine mammal 

R. S. HOLT 

(March 1983) 

Estimating age of spotted and spinner dolphinsfStenella attenuata 

A. C. MYRICK, JR., A. A. HOHN, P. A. SLOAN, M. KIMURA 

(April 1983) 

purse seines. 

for porpoise in the eastern tropical Pacific." 

schools (pet dots), March 7-April 5, 1981 ." 

vital rates." 

survey, May 15-August 3, 1982. 

and Stenella longirostris) from teeth. 

and D. D. STANLEY