53

493d

“6161 ‘ease AVAJNS je}0) ay) UI PUe

| AON 4 100 1 das
L

seaseqns sno} ul UONONpPOJd H6e eyey Janis Aep payewiysy ‘E aNBI4

ton toner 4 Nar 1 AWW tudv

\ aww

1. 1 i

SUNVILY SiaGiW

ro0e

g 8 8

8
By
(g.01 X) AV Had GSNMWdS SOD3

oorr

0091

og!

“0002


19

wire was paid out to sample to a maximum depth of 200 m, or to within 5 m of
the bottom at depths less than 205 m. Surface temperatues were measured with
a stem thermometer. Temperatures to the bottom were recorded by expendable
bathythermograph probes.

All fish eggs and larvae were removed from the samples; eggs of selected
species (including yellowtail flounder) were identified and separated according
to developmental stage. Three stages were used: fertilization to blastopore
closure; blastopore closure to tail free; and tail free to hatching. Eggs
were staged so that we could determine the mortality rate experienced by
yellowtail flounder eggs in 1977, and so that we could use early-stage eggs
only (to minimize any mortality-induced bias) for the total egg production
calculations. “The mortality rate was calculated by regressing the loge (total
season's abundance of each of the three stages) on the weighted mean age of
these stages; since, if the mortality rate is fairly constant, the population
will decline exponentially (Figure 5). The resulting mortality rate (16.156%
per day) was then used to adjust the numbers of early-stage eggs sampled/10m2/day
to become the numbers of eggs spawned/10m2/day. This procedure required knowledge
of each stage's duration at various incubation temperatures, which were determined
at NEFC's Narragansett Laboratory by G. Laurence (pers. comm.). Incubation
temperatures associated with yellowtail flounder eggs from plankton samples were
determined as the mean of the surface and bottom temperatures at each station.

The number of early-stage eggs at each station was standardized by allowing
for the water volume filtered by the net and the maximum depth sampled, and
expressed as the number of early stage eggs sampled/10m2, Then, using the
known incubation rate at the temperature encountered on station, and adjusting
for mortality I calculated, for each station, the number of eggs spawned/10m2/day:

Eo = ex (at )*

where Eo is the number of eggs spawned/10m2/day, at age zero,
ex is the number of eggs sampled/l0m2/day, at age x days,
x , jis the age, in days, determined by temperature, and
m is the daily mortality rate (m = -0.16156).

From Figure 6 it can be seen that the sampled distribution of the number of

eggs spawned/10m2/day is highly skewed; inclusion of the zero values would have
produced an even greater skewness. However, the observed distribution of the
non-zero values was found to be well approximated by a lognormal distribution.

A distribution with a non-zero probability of zero values and whose conditional
distribution of non-zero values is lognormal is called a A-distribution
(Aitchison 1955). The minimum variance unbiased estimator of the arithmetic mean

(k) is given by:
k= [np zn] + Lexp (y)] + [6ny(s2 + 2)]-

where nis the sample size




62

Os2'sessl Ova Ll6 950° L9€ B2G° EBL zSE°2ZL O96'LOL 9L‘16 622 '0 £25" L9E 9° LLL L 0861
€bS 092 8° Z6LL @

Ov9‘826°E OOZES H9G*L = BZL“ GBL p98°26E 6065192 + BSz°BIZ ZEP*96L 8820 OL9°4S2L = bh GEZE L 646L
v00 "bee 0° 8S @

O2B°282°S Ol LH9SZ = P9GTSO'L 282°BZG —- BBL*ZSE OBPE62 =IbL*P9Z E9E'0 090°2202 =v L2e9 U 8Z6L
229 v6 0°8éL é

099°926°b OfeEor'2 2£€°S86 999°26b bbb‘Sze EOLELZ ELESIVZ £820 sso°¢Sbe §=— bb bS9 L LL6L

Ove'vSl'h OLi*220°2 898° OES vevSlb 966922 L6L‘0E2 LIL*LOZ 80E"0 v80°PSel 9 LbSb U 9/61

0v6 ‘OLS OLb* S52 B8L*Z0L 60° LS £90° bE 98E°82 = L¥S*S2 402°0 OEL SSL L°82S L SL6L

082‘ 60L 068° tS 956‘ 12 826 ‘OL BLlets 660‘9 68b‘S lee"0 SEL ED vest l bl6L

S0°0 Ol0 S2"0 0S°0 SL°0 06°0 00" L Z xX $0 Mol/X  Aaaung ura,

TWATAMNS 993 AOA PIS

*“spuazqey adej 02

“quaLotggaod AZLLeZMOW LeAAe_ SL _Z pue MOY sad yo}eO Ue>W SLX “O86L-P/6L
yueg safsoag wors Su0y IL4jaW UL ‘*ds SazApoumy ‘aoueL pues yo SazeWLZSa y90}s BuLuMeds *Z a[qeL



73

where the specific rate coefficient is

As recommended by Thornton and Lessem (1978) Ky is specified as 0.98 which
results in the best fit of data. t, = 9°C for haddock, the optimum
temperature for growth. Growth rates at temperatures greater than 9°C were
assumed to be near the optimum growth rate (i.e. K,>0.98 and <1.0) because
information on haddock growth is insufficient to establish the growth rate-
temperature relationship at temperatures above 9°C.

Mortality

The estimation of mortality from catch curves assumes: 1) that all
individuals in a sample are from one source that has been producing at a
constant rate over the time needed to reach the greatest age or length
observed, and 2) that mortality is constant over the entire age or length
range of the sample. Fishes, in general, do not spawn at a constant rate but
rather exhibit an annual spawning peak with spawning intensity decreasing over
time before and after the peak. The spawning curve can usually be
approximated by a normal distribution. This description is particularly
appropriate for temperate and boreal species (Cushing 1975, Wyatt 1980) and
certainly describes haddock spawning on Georges Bank (Marak and Livingstone
1970). Assuming a normal curve, spawning mortality will be overestimated from
catch curves calculated during the ascending limb of the curve and
underestimated on the descending limb. Hewitt and Methot (1982) have shown,
through simulation studies, that when larval numbers are accumulated from
systematic monthly catch curves that mortality estimation biases tend to
cancel out and the calculated mortality from the combined monthly samples
estimates the expected larval mortality if mortality is constant.

The assumption of constant mortality over the ages or lengths observed
was not verified but rather that the calculated mortalities from accumulated
samples for the entire spawning season represent an average value for all
lengths or ages in the samples. The yearly catch curves appear to
substantiate this because the decrease in numbers at age are not erratic but
are reasonably smooth over the entire age range.

The instantaneous "mortality" coefficients (Z) were calculated from age-
frequency curves for each year. Lengths were corrected for shrinkage and
abundances were corrected for retention (see above) before construction of the
frequency curves. The slope of the exponential relationship of abundance on
age was used to estimate Z as

N = a EXP(Z t)
where N = number of larvae at age t in days.

The exponential decrease in the age frequency of field-sampled larvae,
here defined as Z, has two distinct components. One component measures the


Atlantic Mackerel and Spawning Population Estimates

Table 1. _Ichthyoplankton survey dates (1977) and coverage.

No. of
Survey Cruise samples Sampling dates Strata

1 GO-77-41 102 5 Mar-6 Apr 345
DL-77.03 69 19 Mar-8 Apr 12

2 DL-77-04(pt. 1) 93 13-22 Apr 1,23

3 AL-77-02 105 14 Apr-13 May 3,4,5,6,7.8
DL-77-04(pt. 2) 37 24-29 Apr 2

4 DL-77-05(pt. 1) 90 4-13 May 12,3

5 NO-77-02 15 24 May-5 Jun 4(part),7
DL-77-07(pt. 1) 33 12-16 Jun A(part),6
DL-77-05 (pt. 2) 7 18-27 May 23

6 DL-77-07(pt. 2) 94 21-30 Jun 1,23

7 YU-77-02 143 31 Jub30 Aug Upart),2(part),3,4,5,7.8
DL-77-09 15 30 Juk3 Aug \(part).2(part)

NOTE: AL = “Albatross 1V", DL = “Delaware II", GO = “Goerlitz”, NO = “Nogliki", YU = "Yubileiny”.

to adjust the numbers of early-stage eggs sampled /m? /
day to the numbers of eggs spawned /m* /day. This
procedure required knowledge of the duration of each
stage at various incubation temperatures; this has been
reported by Worley (1933).

The number of early stage eggs at each station was
standardized by correcting for the volume filtered and
the maximum depth sampled, and expressed as the
number of early stage eggs/m’. Then, using the incu-
bation rate at the surface temperature encountered on
the station, and adjusting for mortality we calculated,
for each station, the number of eggs spawned / m’/day.

From Figure 2 it can be seen that, even with the zero
values omitted, the distribution of the number of eggs
spawned/m’/day is highly skewed. There is a large
proportion of zeros and low values inherent in data of
this kind. Inclusion of the zeros produces greater
skewness than that shown and addsa certain arbitrari-
ness to the analysis. The proportion of zeros is deter-
mined to a great extent by the initial choice of the area
to be surveyed. If the precise spawning areas were
known, then the distribution of sampling could be
tailored to those areas and the number of zeros would
be minimal. However, the spawning areas are not
known beforehand; furthermore such surveys are gen-
erally not designed to sample only one species or con-
fined to sampling ichthyoplankton. Hence most sur-
veys cover a region, part of which is not suitable for
spawning by a particular species or where spawning
just does not occur. The proportion of zeros in these
data was thus used to estimate the percentage of the
area surveyed where spawning occurred. The observed
distribution of the non-zero values (Fig. 2) was found

to be well approximated by a log-normal distribution.
A distribution that has a non-zero probability of zero
values and whose conditional distribution of non-zero
values is log-normal is called a A-distribution (Aitchi-
son, 1955). The minimum variance unbiased estimator
of the arithmetic mean (k) is given by:

s?
ket
= Lexp (0) v0, ($ )

where n is the sample size,

n is the number of non-zero values,
Mm is the number of zero values,

y is the sample mean of log. (eggs spawned
/m /day) for non-zero values,

s is the sample variance of the log values,
and

wn, is given by an infinite series and can be
found in Aitchison and Brown (1957).

For larger values of the population variance s*, k isa
much more efficient estimator than the sample mean
of the untransformed data (Pennington, 1979 ms).
Furthermore, for large values of s' and/or small values
of n; the factor wn, should be used rather than using

the usual approximations

vo( ron (-

either of which give, as we found in this situation,
highly biased estimators. For our analysis Yn, was


68

INTRODUCTION

The study of the abundance of fish eggs and larvae to estimate the size
of the parental stock that produced them has had a long and often erratic
history. In 1895 the Nordsee-Expedition attempted to assess the North Sea
fish stocks from plankton egg surveys but not until Sette (1943), working on
Atlantic mackerel, Scomber scombrus, in the northwest Atlantic, was an
estimate of spawning stock derived from the distribution and abundance of
ichthyoplankton. During the next 20 years, as sampling methods and
opportunities improved, numerous stock assessments from plankton surveys were
made, notably Saville (1956) and Simpson (1959) in the North Sea and Sette and
Ahtstrom (1948) in the eastern Pacific. Today, 10+ year data sets useful for
stock assessments from early life history stages exist only in the northeast
Atlantic and eastern Pacific. Such data sets provide a fisheries independent
estimate of spawning stock or at least an index of changes in the parental
stock over time.

The impetus for this study resulted from the effects of management of the
Georges Bank haddock stock and their impact on the traditional use of the
commercial catch-at-age information to derive stock estimates using virtual
population analysis (VPA). According to Clark et al. (1982), VPA estimates
for 1974-1977 were in some doubt due to the lack of directed fishing effort
data as a result of incidental catch regulations. Estimates of stock size in
recent years (Overholtz et al. 1983) were derived using estimates of total
mortality from research vessel trawl survey catch-at-age data to estimate a
terminal F for VPA. A fisheries independent estimate of spawning stock sizes
for the 1977-1982 time span was deemed useful for comparison with recent VPA
stock estimates.

The MARMAP program is miltinational and designed to measure changes in
both physical and biological components of the continental shelf ecosystem
from Cape Hatteras, North Carolina to Nova Scotia (Sherman 1980). A minimum
of six surveys a year provide information about nutrients, primary production,
zooplankton, ichthyoplankton and water column temperature and salinity. The
MARMAP program provides an opportunity to derive fisheries-independent
estimates of spawning biomass from both fish egg and larvae catches.

MATERIALS AND METHODS

Survey Area_and Sampling Intensity

MARMAP surveys are conducted in continental shelf and slope waters from
Cape Hatteras, North Carolina to Nova Scotia, Canada in depths from about
10-1200 m (Fig. 1). From February 1977 to June 1982, 36 surveys were
completed and haddock larvae were captured on 19 surveys (Table 1). A
standard survey includes approximately 180 stations at fixed locations
(Fig. 1). Nonstandard sampling locations were made during all or part of some
surveys, particularly in 1977, to supplement incomplete areal and/or temporal
coverage of standard survey stations. Station locations were selected from a
stratified random sampling pattern used on Northeast Fisheries Center resource
surveys (Grosslein 1969}. Sampling intensity was maintained at approximately
one station per 1200 km*.


Table 2. Yellowtal flounder 299 production estinate

26

Eogs Spawned

E9gs_ Spawned
Represented by

sta. in Subarea Sampling this Effort in
- Error Area Per Day Midpoint oays ‘this Subarea
Subarea Survey 9m j 2 e ofk®— (kme]— (x 10-8) Date Represented = {x 10-12)
1 1 150 18880 9 24 var 21.47 0
t 2 7 o 18560 ° V4 Apr 21,09 o
1 a7 4 18560 0 5 May 3443 0
1 5 179 16566 0 22 Jun 49.28 0
1 7 wy? o 16560 oO VW aug 50.52 oO
2 1 5a 1s 2.47529 1.79708 7 1429 2.22 67288 49.4090 29 Mar 20,58 1.0168
2 2 $8 222.9783 2.01189 16.3336 «5.5099 67288 = 109.3084 19 Aor 1a!20 Vsete
2 3 37 2 2.56954 2.37808 19.2872 7, $061 67288 130.1831 26 Apr 10.26 13363
2 2 56 24 2doast 220831 T1384 4472567288 74,9478 § tay 13.18 09674
2 5 89 222199876 Zggsta 1615960 «6.7946 «= 7Za8 112.3403 23 may 23.54 218446
2 6 59 0 67288 Qo 25 Jun 41.95 oO
2 ? 38 °O 67288 o 18 dug 50.47 0
3 i) 18 3 0.37156 0.93012 0.3226 0.2214 Varah 0.4559 7 Mar 39.87 0.0180
i 2 cl] 3 3.43819 0.69344 14,5323 9.0516 113th 20.5356 22 Apr 13,04 0.2678
3 3 3 5 Fated «212710 30.4383 291823614131 71.2701 15 apr 23142 115691
3 3 7 8 $ 22099 «2.67768 123.048) az 9708 TaI3 173.8792 M1 ay 16 60 2.8873
5 3 3 $0689 1.2e7KH 72 3491571399413] 3875 26 Yay 24.19 213388
3 8 3 tne na 2.883 7.9588 14131 213092 38 Gun 30 38 5.188
3 ; > 00 1131 0 18 dug 47.28 0
+ i) 70 1S 2.31562 2.55894 5.5399 3.4207 ga7og 56.2027 2h Mar 39.72 2.2252
a 2 $$ 24 49082 2.33162 19.8971 8.3088 aa73a 167.0197 30 tor ai 8.3150
4 Sal 503880 29818 70.2165 «et asad a7 585 3909 3 dun 49.98 29.7608
2 7 5 32.7938) 0.52486 «0.5786 0.3776 84708 23066 3 dug 54.08 0.2143
5 1 1s 1 nea. na. 0.1229 0.1229 19137 0.2351 Aor 26.08 9.0061
3 3 12 z 3.06265 9.68158 16.2830 16.0688 19337 31 1608 27 Agr 85.57 2.0832
3 7 19 0 19137 o 10 dug 105.08 fy
6 wy 2 1.42497 1.32494 0.5908 0.4980 29837 1.7628 6 May 38.43 0.0677
6 5 175100359 zlooess = 4a68S 2.9389 2987 13/3220 14 Jun 38.43 0.5120
7 3 S oO 9299 oO 12 May 23.00 0
7 3 9 4 1.56137 0.65554 2.6784 1 4214 9299 2.4906 a Jun 43.87 0.1093
; 7 2 ¥a6779-V37082 = 21208 = 2.0879 8239 211438 8 tug 6a 74 0.1517
8 3 7 9 9734 0 9 May 91.82 °
a 7 300 974 a 3 aug 9182 8

The estimated total egg production is

For my * 1, the mean is estimated by

56.8616 x 1012 eggs (std

error = 10,3592 x 1012)

and its variance by (2)2, wnere x 1s the single non-zero value: both are unbiased est inators


97

For the data at hand, since the nonzero values from an individual
cruise were distributed lognormally, the production rate for each subarea
and cruise was calculated using equation (1). Alternate cruises were then
used to calculate two estimates of total production for each subarea (or
a combination of subareas if production was low). The average of the two
values (equation (4) with 2 = 2) estimates egg production in each subarea
with an estimated variance given by equation (5). The final estimate of
total production for the entire region is the sum of the subarea estimates
of production and its variance is the sum of their estimated variances.

One reason for calculating subarea estimates is to increase the number

of degrees of freedom for the estimate of the total variance. But since

the variances of the production estimates for the subareas were considerably
different, Satterthwaite's formula (Cochran, 1977, p. 96) was used to
estimate the effective number of degrees of freedom.

It was also desired to obtain a rough indication of the proportion
of the total variance due respectively to spatial and temporal effects for
. the surveys. Equation (2) was used to estimate the spatial component of
variance, which along with the estimate of the total variance, was used in
conjunction with equation (3) to obtain an estimate of the variability due
to time for the present survey design.

Finally, estimates of spawning stock size based on total egg production
were calculated as described in Berrien et al. (1981), Berrien (1981), and
Berrien (1983). It is assumed that the variability of the estimates were
due mainly to the variability of the egg production estimates and hence the
variance of the spawning stock size estimates reflect solely the variability

of the egg data.


ABUNDANCE (NO. x 107!)

33

50 74

4 10)

yre 4.002777 -0.176214 x

40 -0.9842
30 54
274
10 7
0 T T T Tt T ee

0 1.0 2.0 3.0 4.0 5.0

AGE (DAYS)

Figure 5, Regression of stage-abundance on the weighted mean age: used

to calculate season-long mortality rate for Limanda ferruginea
eggs, 1977; y is egg abundance at age (x=no. of days), ris the
regression coefficient.


53

RESULTS

Sand lance larvae were captured at 737 stations which accounted for over
61% of the stations occupied during the surveys used in this study. Back-
calculated numbers at hatching under 10 m@ ranged up to 77,000 with the
highest densities occurring on Georges Bank and from Nantucket Shoals to
Long Island, New York (Sherman et al. 1981). Mean catch per tow was lowest
in 1974 at 153.4 larvae per 10 m2, and highest in 1977 at 6544.4 larvae per
tow.

The estimated mortality rates ranged from 0.207 to 0.363 which gives a
decrease of 19% to 30% per mm of growth and daily mortality between 6% and
10% for the length interval 5-27 mn.

Spawning stock estimates based on egg survival between 1.0 and 0.05
increased 50-fold between 1974 and 1978, then decreased to approximately
one-third of the 1973 level in 1980 (Table 2). Incubation time for Ammodytes
sp. eggs is unusually long, greater than 30 days (G. Laurence pers. comm.),
indicating egg mortalities could be high. If daily mortality is 5% for just
30 days, then survival is only 22% to hatching and at 45 days survival is 10%.

DISCUSSION

Standard techniques for assessing stock size of pelagic species using
fisheries data, e.g. fishing effort and fishing mortality, are being seriously
questioned (Saville and Schnack 1981). For those species without a directed
fishery or where managers have prohibited fishing there will, of course, be
no fisheries related data available to assessment biologists to apply to
fisheries models. In such cases, research vessel trawl surveys are often
used to provide catch-per-tow data as a measure of catch-per-unit effort
when fishing effort of the commercial fleet is inadequate or unavailable.

Sand lance do not support a fishery in the northwest Atlantic nor are
research vessel catches adequate for stock assessment due to net avoidance
and the burrowing habits of sand lance (Livingstone 1962; Meyer et al. 1979).
However, trawl survey indices (stratified mean catch-per-tow) do indicate
higher abundance of sand lance in recent years though large annual fluctuations
of the index have occurred (Grosslein et al. 1980). For sand lance and many
other species, macroscale egg and larval surveys provide a fisheries independent
method of assessing spawning stock size as well as monitoring major biotic
changes in the marine ecosystem.

The dramatic 50-fold increase in the sand lance spawning stock biomass,
following the precipitous decline in Atlantic herring and Atlantic mackerel
stocks, indicates a significant change in the species composition of the
pelagic finfish community. Clark and Brown (1977) estimated a 6-7 million
ton. decline in mackerel and herring stocks from 1968 to 1975. Average biomass
on Georges Bank declined 42% and production of fish and squid (Kcal/Km2) de-
clined by 26% from 1964 to 1975 (Grosslein et al. 1980). Assuming the basic
productivity of the shelf has not changed, then a surplus of fooa energy was
available during the mid-1970's. Sand lance biomass increased 30-fold from
1974 to 1976 indicating a shift in energy flow within the pelagic component
of the ecosystem. Sand lance population levels increased after the herring


SUBAREA €

SUBAREA S

SUBAREA 4

Mar 5 - Apr 8
N=I71

Eggs spawned/10 m2/day

“Ne None
\ 0 AN
N-100 SY
101 1000 WY 36°
SUBAREA 1

| .

I a

| ’, ¥

| a §

I 36° . we . 78 & 7a!

Figure 1. Left; total survey area and subarea boundaries for seven ichthyo-
plankton surveys, 1977. Right; distribution of yellowtail flounder
eggs during the first survey, 1977.


61

Table 1. Summary of surveys used to estimate sand lance,
Ammodytes sp., spawning stock, No = total stations
sampled, N; = stations with sand lance larvae.

Year Survey Dates Ng Ny
1974 ALB 74-02 Feb 11-22 58 4]
ALB 74-04 Mar 13-Apr 2 19 W

ATW 74-02 Apr 2-22 22 =)

TOTAL 99 61

1975 ALB 75-02 Feb 12-28 73 44
CWL 75-02 Mar 5-11 7 im

ALB 75-03. Mar 3-17 2 «16

TOTAL 116 7

1976 ALB 76-01 Feb 10-25 103 96
DEL 76-05 Mar 3-23 7 48

TOTAL 178 144

1977 GOR 77-01 Mar 3-Apr 7 88 47
DEL 77-03 Mar 19-Apr 8 68 55

DEL 77-05 May 17-27 87 21

NOG 77-02 May 22-Jun 6 57 7

DEL 77-07 dun 6-30 318

TOTAL 331 138

1978 DEL 78-02 Feb 14-Mar 17 102 84
ARG 78-04 Apr 13-Nay 20 948.

TOTAL 221 132

1979 DEL 79-03 Feb 25-Mar 14 101 85
DEL 79-04 Apr 11-29 34 24

TOTAL 735 = 109
1980 ALB 80-02 Feb 27-Apr 5 122 82



98

RESULTS

Tables I and II summarize the statistics used to estimate the egg
production for each subarea at the times represented by the: individual _
surveys. Also given are estimates. of the standard-error.of the estimated .
rate of production (c) resulting from the spatial variability at the times
sampled. The daily egg production curves for each subarea and for the .
entire region are shown in Figures 2-4.

Table III contains estimates of total seasonal egg production for
each species based on treating the series as two alternating systematic
samples. In parentheses, under the production estimates, are the estimates.
of production derived by treating the series as a single systematic.sample.
Also in Table III are estimates of the components of the sampling variance
due to temporal and spatial effects for the surveys as conducted. Column
6 gives the estimated standard error of the total seasonal egg production
estimates and in column 7 are its effective number of degrees of freedom.

In Table IV are estimates of spawning stock size for each species
based on the egg production estimates. Confidence intervals for these
estimates (80% for mackerel and silver hake, 70% for yellowtail) are also
presented. Again, it should be noted that the confidence intervals only

take into account the variability of the egg estimates.

DISCUSSION AND CONCLUSIONS

In practice the dates at which plankton survey cruises are conducted
are spread throughout a season rather than chosen randomly with respect to
time. Therefore, the surveys are effectively systematic in time. For
natural populations, systematic sampling can be much more efficient than :

random sampling, particularly so for populations which vary continuously


39

oblique tows were made by adjusting the vessel speed to maintain a 45° wire
angle throughout the haul and paying out enough wire to sample to within 5m
of the bottan, or to a maximun sampling depth of 200 m. Usually the vessel
speed was around 1.5 kt (2.8 km/hr) but varied fron about 1.0 to 2.0 kts. See
Jossi et al. (1975) for a detailed description of sampling procedures.

All fish eggs and larvae were removed from samples. The egas of selected
species, including silver hake, were identified, then further separated into
developmental stages. Eags were staged to detennine mortality rate. Two egg
stages were used for silver hake: just spawned to tail free, and tail free to
hatch. Using early-stage data for census calculations minimizes any hias
which might be introduced by an inaccurate mortality rate. The instantaneous
daily mortality rate (Z) was derived using the expression:

N
N= Kr (Guiland 1969)

which becomes:

. dn No-In Ny

z t

where: Z is the instantaneous daily mortality rate,
Ny is the number of eggs at the beginning of time interval t, and
Ne is the number of eags at the end of t.

In this case the values N, and Ny were the season-long abundances of eggs in
the two above-mentioned stages and t was the difference between their weighted
mean ages. The resulting instantaneous mortality rate (Z = .6344) was used to
adjust the numbers gf early-stage eggs sanpled/10n“/day to becone the numbers
of eggs spawned/10m‘/dav. This procedure required knowledge of each stage's
incubation time at various temperatures. Only limited information on this
exists for silver hake, but that which is available indicates a very similar
incubation rate as for its congener the Pacific hake, Merluccius productus.
Incubation time versus tenperature for Pacific hake has heen reported (Zwei ful
and Lasker 1976); and since the two species apnear to be similar in this
relationship, incubation time versus tenperature for Pacific hake was used for
silver hake. Surface water temperature associated with each silver hake eqg
collection was used as incubation tenperature.

The number of egqs sampled at each station was standardized by allowing
for the volume of water filtered by the net,and the maximum depth sampled, and
expressed as the number of eggs sampled/10m°. Then using the incubation rate
at the tenpgrature on station and adjusting for mortality, the number of eggs
spawned/10n‘/day was calculated, using the equation from Gulland (1969) noted
above, where:

Ng is the number of eggs spawned/10 m@/day at age zero,
Nz is the number of eags sannled/10 m2/day with mean age t, and

Z is the instantaneous daily mortality rate (Z = .6344).


81

Table 2.--The A-mean catch-per-tow of haddock larvae on Georges Bank by day
and night and the ratio of night caught to day caught by length

interval.
Day Caught Night Caught
d-mean A-mean

Length Number of catch/tow Number of catch/tow Ratio
(mm) stations (0) stations (N) N/D
2 1 0.069 1 0.087 1,26
3 7 1.258 9 1.355 1.08
4 36 3.072 21 2.153 0.70
5 22 2.043 15 1.642 0,80
6 al 1.891 1 1.966 1.04
7 21 1.494 10 1.797 1,20
8 v7 1,060 13 2.083 1,97
9 WV 1,222 8 0.972 0.80
10 15 0,704 10 0.915 1.30
il 10 0,502 5 0.463 0.92
12 3 0.112 5 0.437 3.90
13 5 0,192 1 0.069 0.36
14 1 0.012 1 0.070 5.83
15 6 0.271 - - -
16 2 0,045 - - -
17 - - - - -
18 - - 2 0.142 -



This paper contains results of five recently completed stock assessments
based on eygs or larvae collected on MARMAP surveys. In direct comparison
with fishery-dependent assessments, three of the five population estimates,
those for Atlantic mackerel, Scomber scombrus; silver hake, Merluccius.
bilinearis; and haddock, Melanogrammus aeglefinus, were found to be in close
ayreement. In the case of yellowtail flounder, Limanda ferruyinea, a VPA was
not available for tne year in question because fisheries data were inadequate
for the analysis. A VPA is not possible for sand lance, Ammodytes sp.,

because, with the exception of a limited bait fishery, thi all

small foraye
species is not fished commercially nor is it caught efficiently on NEFC
research trawl surveys. Thus the MARMAP ichthyoplankton surveys provide the
only available means for estimatiny spawning stock size.

The manuscript by Pennington and Berrien analyzes the precision of
spawning stock size estimates based on eyy surveys. It is shown that egy
surveys provide estimates of stock abundance which are sufficiently accurate
to detect major population trends. We are now conductiny computer simulations
based on actual survey frequencies to determine the variability associated
with methods using larvae for back calculations. These simulations will
concentrate on: 1) effects of survey timing and frequency relative to larva
production curves; 2) variability of larva mortality estimates; 3) effects of
within-survey variances in catches; 4) effects of chanyiny water temperature
on the within-season yrowth rates of larvae; and >») effects of non-randoia
distribution of larvae by size or age within the survey area.

When using survey collections of eyys to derive estimates of spawning
stock biomass we beyin by separatiny the eygs of a species into two or three
developmental stgyes. Catches of these staged eyys are adjusted to become the
numbers per 10 m° of sea surface area. Egys in each staye are aged according
to temperature-dependent incubation rates. Numbers at age are integrated and
expanded over space and time so as to derive total season-lony survey-wide
estmates of abundance at each stage. Egy mortality rates are calculated from
the exponential decrease in numbers at aye. Usiny these mortality rates
described by the data, numbers of egys spawned are back-calculated from each
occurrence of early-staye eygs. These numbers of eygs spawned are expanded
over time and area and integrated with similar values from all surveys to
calculate an estimate of total eyg production for the spawniny season within
the total survey area. Total egy production is then used to calculate a
Spawning population estimate by the formula:

=~
N= FR

total number of mature fish in the stock,

total annual egy production of the population,
fecundity, the number of eggs produced per female, and
= the proportion of mature females in the population.

where:

N
P
F
R

Catches of larvae can also be used to calculate spawning stock biomass.
First each larva is ayed by applying temperature-dependent yrowth equations or


LIST OF TABLES

ATLANTIC MACKEREL, Scomber scombrus, EGG PRODUCTION AND SPAWNING POPULATION
ESTIMATES FOR 1977 IN THE GULF OF MAINE, GEORGES BANK, AND MIDDLE ATLANTIC
BIGHT

Table 1. Ichthyoplankton survey dates (1977) and coveraye.

Table 2. Atlantic mackerel egg production estimate.

Table 3. Calculations for Atlantic mackerel spawning population estimate.

YELLOWTAIL FLOUNDER, Limanda ferruginea, ESTIMATES OF EGG ABUNDANCE

AND POPULATION SIZE DURING SPRING 1977 IN GULF OF MAINE, GEORGES BANK,

SOUTHERN NEW ENGLAND AND MIDDLE ATLANTIC BIGHT WATERS

Table 1. Ichthyoplankton survey dates (1977) and coverage.

Table 2. Yellowtail flounder egg production estimate.

Table 3. Calculations for yellowtail flounder population estimate.

Table 4. Yellowtail flounder population and catch statistics.

SILVER HAKE, Merluccius bilinearis, EGG CENSUS AND ADULT POPULATION ESTIMATE

FOR 1979 IN WATERS OFF EASTERN UNITED STATES

Table 1. Silver hake egg production by subarea, 1979; N = no. samples in
subarea; Ny = no, samples containing silver hake eggs and K = mean

density of eggs spawned per 10 m° per day.

Table 2. Silver hake population estimate, Gulf of Maine, 1979; numbers in
parentheses are estimated.

Table 3. Silver hake population estimate, Georges Bank, 1979; numbers in
parentheses are estimated.

Table 4. Silver hake population estimate, southern New England, 1979; numbers
in parentheses are estimated.

Table 5. Silver hake population estimate, Middle Atlantic, 1979; numbers in
parentheses are estimated.

Table 6. Spawning population estimates for three subareas, 1979; numbers in
parentheses are comparable values from VPA estimates (Almeida-).

‘Preceding page blan| «|




67

AN ASSESSMENT OF THE GEORGES BANK HADDOCK STOCK BASED ON LARVAE
COLLECTED ON MARMAP PLANKTON SURVEYS, 1977-1982

by

Wallace Morse

U. S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Sandy Hook Laboratory

Highlands, New Jersey 07732

MARMAP Contribution No. MED/NEFC 84-09

| Pre page blank |


76

all years except 1979. The length frequency for 1979 showed a modal length at
25 mm indicating its unsuitability for. mortality estimation. Mortalty for
1979 was estimated as the-average mortality of years 1977-1982, minus 1979.

Daily percent mortality ranged from 9.0 (Z = 0.0933) in 1980 to 12.2
(Z = 0.13062) in 1982 (Table 3). The 1982 larval catches were quite small
relative to the other years examined and show the magnitude of interannual
variability of catches and indicate a possible problem when this variability
is not accounted for or is unknown.

Larval Abundance and Spawning Stock Biomass

The A-mean catch-per-tow of larvae at hatching was calculated for each
subarea by survey (Table 4). The southern Gulf of Maine (SGOM) contributed
only small numbers of larvae during 1977 and 1978. and no larvae from 1979-
1982, SGOM accounted for 1.4% of all larvae. Georges Bank (GB) subarea
contained 86.1% of the larvae and catches there were dominant during all but
four surveys. The northern Middle Atlantic Bight (NMA8) subarea contributed
12.5% of the larvae captured with significant numbers caught during 1977, 1979
and 1980.

Total larval production by subarea, survey and year are given in
Table 5. These represent expansions of A-mean catch-per-tow by the surfgce
area of each subarea. Production ingpeased from approximately 3.6 x 10
larvae in-1977 to a peak of 9.3 x 10° in 1979. A 49% decrease occurred from
1979 to 1981 and a precipitous decrease was found in 1982 to only 5.5% of. the
1981 level.

Spawning stock biomass estimates shown in Table 5 are a function of
larval production and thus follow the same trends. Peak biomass at 127,522 t
occurred in 1979 and the lowest estimate was in 1982 of 3,590 t. Other years
were between 49 and 94 thousand t.

DISCUSSION

The techniques of using ichthyoplankton for spawning stock biomass
estimation have been well documented, e.g. Smith and Richardson (1977) and
Zweifel and Smith (1981), although surprisingly few data sets exist which meet
even the minimum technical requirements necessary to derive meaningful
estimates. The ichthyoplankton. sampling of the MARMAP program has provided a
unique opportunity to use a 6-year data set in the northwest Atlantic to
estimate the spawning biomass of numerous species.

This study of haddock larvae on Georges Bank attempts to address what
Zweifel and Smith (1981) call the “effective sampler size" by accounting for
some of the most serious biases encountered in larval sampling. These biases
include. standardization of net catches to the number of larvae under 10 m* of
surface area, net avoidance, extrusion through the net meshes, temperature-
dependent growth and annual changes in larval mortality.

A comparison of spawning stock biomass from larval data and-VPA and. -
research vessel-catch-per-tow (kg) (Overholtz et al. 1983) shows similar
trends for all three values (Table 6). The greatest magnitude of change
occurred in the biomass estimates from larval data when 1982 is included.


NOAA Technical Memorandum NMFS-F/NEC- 30

This TM series is used for documentation and timely communication of
preliminary results, interim reports, or special purpose information; and
has not received complete formal review, editorial control, or detailed
editing.

> So
*oraenror

Recent Estimates
of Adult Spawning Stock Biomass
Off the Northeastern United States
from MARMAP Ichthyoplankton Surveys

Peter Berrien’, Wallace Morse’, and Michael Pennington?

‘Sandy Hook Lab., National Marine Fisheries Serv., Highlands, NJ 07732
2Woods Hole Lab., National Marine Fisheries Serv., Woods Hole, MA 02543

(|. RepRouceo By,
US, Department of Commerce
| Navona Feennical

[ Springheld, Viginia 22161

J

U.S. DEPARTMENT OF COMMERCE

Malcolm Baldridge, Secretary

National Oceanic and Atmospheric Administration
John V. Byrne, Administrator

National Marine Fisheries Service
William-G. Gordon, Assistant Administrator for Fisheries

Northeast Fisheries Center

Woods Hole, Massachusetts

July 1984


102

REFERENCES |

Aitchison, J. and Brown, J.A.C.: 1957, ‘The Lognormal Distribution",

Cambridge University Press, Cambridge, U.K.

Berrien, P.L.: 1981, ‘Yellowtail flounder, Limanda ferruginea, estimates .
of egg abundance and population size during spring 1977 in-the Gulf
of Maine, Georges Bank, Southern New England and Middle Atlantic
Bight waters’. ICES C.M. 1981/G:65, 18 pp. (mimeo).

Berrien, P.L.: 1983, 'Silver hake, Merluccius bilinearis, egg census and
adult population estimate for 1979 in waters off eastern United States.

ICES C.M. 1983/G:46, 14 pp. (mimeo) .

Berrien;.P.L., Naplin, N.A. and. Pennington, M.: 1981, ‘Atlantic-mackerel,
Scomber scombrus, egg production and spawning population estimates for
1977 in the Gulf of Maine, Georges Bank, and Middle Atlantic Bight'.. -
Rapp. P.-v. Réun. Cons. Int. Explor. Mer, 178, 279-288.

Cochran, W.G.: 1977, ‘Sampling Techniques’, third edition, John Wiley

and Sons, New York.

Jones, R.: 1956, 'The analysis of trawl haul statistics with particular
reference to the estimation of survival rates'. Rapp. P.-v. Réun.
Cons. Int. Explor. Mer, 140, 30-39.




103

Jossi, J.W., Marak, R.R. and Petersen, H., Jr.: 1975, ‘MARMAP Survey I
manual. At-sea data collection and laboratory procedures’. MARMAP

Program Office, NMFS, NOAA, Wash., D.C.

Lockwood, J.d., Nichols, J.H. and Dawson, W.A.: 1981, 'The estimation of
a mackerel (Scomber scombrus L.) spawning stock size by a plankton

survey. J. Plankton Res. 3, 217-233.

Pennington, M.: 1983, ‘Efficient estimators of abundance, for fish and

plankton surveys'. Biometrics.39, 281-286.

Rao, C.R.: 1973, ‘Linear Statistical Inferences and Its Applications’,

third edition, John Wiley and Sons, New York.

Saville, A.: 1956, ‘Eggs and larvae of haddock (Gadus aeglefinus) at

‘Faroe’. Mar. Res. Scot., No. 4.

Saville, A.: 1964, ‘Estimation of the abundance of a fish stock from

egg and larvae surveys'. Rapp. P.-v. Réun. Cons. Int. Explor. Mer,

155, 164-170.

Simpson, A.C.: 1959, 'The spawning of the plaice (Pleuronectes platessa)
in the North Sea'. Fishery Invest., London, Ser. 2, 22(7), 111 p.



24

Lockwood, S. J., J. H. Nichols and W. A. Dawson. 1981. The estimation
of a mackerel (Scomber scombrus L.) spawning stock size by plankton
survey. J. Plankton Res. 3(2): 217-233.

Murphy, G. I. 1966. Population biology of the Pacific sardine (Sardinops
caerulea). Proc. Calif. Acad. Sci., Ser. 4, 34: 1-84.

Pennington, M. 1980 ms. Efficient estimatorsof abundance for fish and
plankton surveys.

Royce, W. F., R. J. Buller, and E. D. eines) 1959. Decline of the
yellowtail flounder (Limanda ferruginea) off New England. Fish. Bull.
Fish. Wild]. Serv., 59(146): 169-267.

Saville, A. 1964. Estimation of the abundance of a fish stock from egg
and larvae surveys. Rapp. P.-v. Réun. CIEM, 155: 164-170.

Sette, 0. E. 1943. Biology of the Atlantic mackerel (Scomber scombrus) of
North America. Part I: Early life history, including the growth, drift
and mortality of the egg and larval populations. Fish. Bull. Fish
Wildl. Serv., 50(38): 149-237.

Sherman, K. 1980. MARMAP, a fisheries ecosystem study in the NW Atlantic:
Fluctuations in ichthyoplankton-zooplankton components and their
potential for impact on the system. pp. 9-37. In: F. P. Diemer,

F. J. Vernberg and D. Z. Mirkes (eds.). Advanced concepts in ocean
measurements for marine biology. Belle W. Baruch Institute for Marine
Biology and Coastal Research. University of South Carolina Press.

Smith, P. £. and S. L. Richardson. 1977. Standard techniques for pelagic
fish egg and larva surveys. FAO Fish. Tech. Pap. No. 175: 100 p.

Smith, W. G., J. D. Sibunka, and A. Wells. 1975. Seasonal distributions
of larval flatfishes (Pleuronectiformes) on the continental shelf between
Cape Cod, Massachusetts and Cape Lookout, North Carolina, 1965-66.
NOAA Tech. Rep. NMFS SSRF-691: 68 p


83

Table 4,--The A-mean catch-per-tow of haddock larvae at hatching by subarea
and survey, 1977-1982.

SUBAREA
NMAB GB SGOM
Std. Std. Std.
Survey A-mean error 4-mean error A-mean error
17-2 6.75 ° = 4,41 5.98 3.72 - -
77-3 3.26 2.61 523.12 372.58 - -
77-4 124,12 43,94 87.66 35.54 45.57 42.63
78-1 - - 9.81 7.23 - -
78-2 - - 1018.39 700,81 - -
78-3 . 2.34 15.71 42.32 29.84 10,98 43,90
79-1 2.70 17,08 - - - -
79-2 - - 65.40 26.18 - -
79-3 309.21 204.56 1720.76 952.70 - -
80-1 8.95 60.03 173.39 95.62 - -
80-2 202.45 145.28 1018.55 613,12 - -
80-3 23.58 7.02 115.00 55.69 - -
80-4 - - 2.70 13.22 - -
81-1 2.62 17.18 27.56 12.82 - -
81-2 - - 563.52 334.73 -
81-3 28.94 15.14 551.15 230.81 - -
82-2 - 38.41 30.32 -

82-3 10.13 6.11 9.96 5.46 -



78

REFERENCES boon. *
Ahistrom, E. 1954, Distribution and abundance of egg and larvae populations,
of the Pacific sardine. U.S. Fish Bull., 93: 83-140, og

Aitchison, J. 1955. On the distribution of a positive random variable having
a discrete probability mass at the origin. J. Am. Statist. Assoc., 50:. -
272, 901. : re

Blaxter, J. H. S.. 1971. Feeding and condition of Clyde herring larvae.
Rapp. P.-v. Reun. Cons. Int. Explor. Mer, 160: 128-136.

Clark, S. H., We. J. Overholtz and R. C. Hennemuth. 1982. Review and
assessment of the Georges Bank and Gulf of Maine haddock fishery.
J. Northw. Atl. Fish. Sci., 3: 1-27. .

Clutter, R. I. and M. Anraku. 1968. Avoidance of samplers. In.
D. J. Tranter (ed.). Zooplankton Sampling. UNESCO Monogr. on Oceangr.
Methodol., 2: 57-76,

Cushing, D. H. 1975. Marine Ecology and Fisheries. Cambridge, Univ. Press.

Farris, D. 1961, Abundance and distribution of eggs and larvae and survival
of larvae of jack mackerel (Trachurus symmetricus). U.S. Fish. Bull., 61:
247-279.

Grosslein, M. D. 1969. Groundfish survey program of BCF Woods Hole. Comm.
Fish. Rev., 31: 22-35,

Grosslein, M. D. 1971. Some observations on accuracy of abundance indices
derived from research vessel surveys. Int. Comm. Northw. Atl. Fish.,
Redbook 1971 (III): 249-266.

Hewitt, R. P. and R. D. Mothot, dr. 1982. Distribution and mortality of .
Northern Anchovy larvae in 1978 and 1979. CalCOFI Report, 23: 226-245,

Hodder, V. M. 1963. Fecundity of Grand Bank haddock. J. Fish. Res, Bd.
Canada, 20(6): 1465-1487, .

Laurence, G. C. 1978, Comparative growth, respiration and delayed feeding
abilities of larval cod (Gadus morhua) and haddock (Melanogrammus
aeglinefus) as influenced by temperature during laboratory studies. Mar.
Biol., : 1-7. °

Laurence, G. C. 1979, Larval length-weight relations for seven species of
northwest Atlantic fishes reared in the laboratory. U.S. Fish. Bull., 76:
890-895.

Lenarz, W. H. 1972. Mesh retention of larvae of Sardinops caerulea and
Engraulis mordax by plankton nets. U.S. Fish. Bull., 70: 839-848,

Lenarz, W. H. 1973. Dependence of catch rates on size of fish larvae. Rapp.
P,-v. Reun. Cons. Int. Explor. Mer, 164: 270-275.




48

Table 4. Silver hake population estimate, southern New England, 1979; numbers in parentheses are estimated.

% Theoretical % Total

Length Reference 7% females egg production males  populatign Spawners,
(on) catch ferale mature Fecundity by ref. catch mature estimate both sexes
1.0

2

3 0.547 (50.0) (0) (0) 24158174

4 4.075 (50.0) (0) (0) 179971772

5 8.145 (50.0) (0) (0) 359722719

6 7.101 (50.0) (0) (0) 313614614

7 4.461 (50.0) (0) (0) 197019404

3 1.178 (50.0) (0) (0) $2026196

9 0.189 (50.0) (0) (0) 8347157

10 0.097 (50.0) (0) (0) 4283991

i 0.010 (50.0) (0) (0) 441649

12 0.039 (50.0) (0) (0) 1722429

13

4 0.021 (50.0) (0) (0) 927462

15 0.011 (50.0) (0) (0) 485813

16 0.134 (50.0) (0) (0) 5918090

7 0.291 (50.0) (0) (0) 12851972

18 0.294 50.5 (0) (0) 12984466

19 0.201 47.8 (1.8) 47579 82.301 (7.1) 8877135 405336
20 0.251 48.0 10.5 54703 692,592 10.2 11085378 1146685
al 0.279 SLL 14.2 62466 1265.106 14,5 12321994 1767792
22 0.388 53.4 22.8 70892 3349549 14.8 17135963 3268308
23 0.422 51.4 19.9 80003 3452.633 19.2 18637568 3645458
24 0.563 50.7 27.7 99822 7106 .172 29.2 24864812 7071316
25 0.476 51.8 32.5 100370 050.873 33.3 21022470 6913281
26 0.395 46.3 43.3 111669 8835.340 48.0 17445117 7994361
a7 0.407 44.4 54.6 123742 12211,948 63.1 17975095 10663752
28 0.494 42.3 62.5 136608 17828 522 80.1 21817437 15852654
29 0.625 39.7 69.4 150290 25879.750 87.7 27603032 22202472
30 0.908 32.5 73.5 164807 35768 389 90.4 WIOTSRS 34047983
3 1.001 35.3 80.8 180182 51472.770 93.8 44209017 39438157
32 1.376 39.2 89.6 196433 94862.478 93.9 60770836 56040246
33 1.085 42.8 96.0 213582 95238.128 94.2 47918864 45508823
34 0.991 47.7 (99.0) 231648 108383 .888 94.1 43767368 42207854
35 0.746 55.8 (100.0) 250652 104263.612 97.5 32946980 32582586
36 0.653 66.0 (100.0) 270613 116664 .133 98.5 28839648 28692653
v7 0.550 7h.4 (100.0) 291551 114492.078 93.3 24290669 23825211
38 0.306 77.8 (100.0) 313486 74592.614 93.3 13514445 13313069
39 0.326 85.5 (100.0) 336436 93730.935 (93.3) 14397742 14257482
40 0.248 90.7 (100.0) 360421 81089.535 = (100.0) 10952883 10952883
41 0.198 92.7 (100.0) 385459 70718.929 (100.0) 8744641 8744641
42 0.177 97.3 (100.0) 411571 70859.315 (100.0) 7817179 7817179
43 0.180 100.0 (100.0) 438774 78979.320 7949673 7949673
44 0.155 100.0 (100.0) 467087 72398.485 6845552 6845552
45 0.103 100.0 (100.0) 496529 51142.487 4548980 4548980
46 0.040 100.0 (100.0) 527118 21084720 1766594 1766594
a7 0.040 100.0 (100.0) §58872 22354880 1766594 1766594
48 0.043 100.0 (100.0) 591810 25447 .830 1899089 1899089
49 0.007 100.0 (100.0) 625950 4381-650 309154 309154
50 0.022 100.0 (100.0) 661310 14548 .820 971627 971627
51 0.011 100.0 (100.0) 697907 7676.977 485813 485813
52 0.011 100.0 (100.0) 735759 8093.349 485813 485813
53

$4

55 0.055 100.0 (100.0) 857024 47136 .320 2429067 2429067
56

57 0.022 100.0 (100.0) 944465 20778.230 971627 971627
58

59 0.011 100.0 (100.0) 1037347 11410.817 485813 485813
60

61 0.011 100.0 (100.0) 1135805 12493 .855 485813 485813

Totals = 1782935073 469761390

“Dashed line within "Total population estimate’ column indicates size at age 2.8 yr, see discussion.


90

ABSTRACT

Methods are given to measure the effects of spatial and temporal
differences in fish egg production on the precision of estimates of
total seasonal egg production derived from ichythyoplankton surveys.
The techniques are applied to the results of large scale plankton sur-
veys conducted in 1977 and 1979 off the northeastern United States.
For the three species analyzed (Atlantic mackerel, Scomber scombrus;
silver hake, Meriuccius bilinearis; and yellowtail flounder, Limanda
ferruginea), the surveys produced estimates of total egg production
having an average coefficient of variation equal to 31%. Estimates
of spawning stock size based on the egg production estimates compared

favorably with other independent assessments of stock size.


69

For analysis of haddock data, the survey area was stratified into three
subareas: -northern Middle Atlantic Bight (NMAB), Georges Bank (GB) and
southwestern Gulf of Maine (SGOM) (Fig. 1). These strata were selected based
upon hydrography, topography, and spatial and temporal density gradients of
haddock larvae abundance. Haddock larvae captured on western edge of the
-Scotian Shelf were not included in this analysis.

Ichthyoplankton Sampling and Analysis

Ichthyoplankton was sampled with 6l-cm bongo net frames fitted with
505- and 333-y mesh nets. A double oblique tow was made at each station to a
depth of 5 m above the bottom or to a maximum tow depth of 200 m. Vessel
speed varied between 1 and 2 kts to maintain a constant 45° tow-wire angle.
Calibrated flow meters suspended within the mouth of each net and a
bathykymograph were used on each tow to determine water volume filtered and
maximum tow-depth, respectively. Details of the net configuration are given
by Posgay and Marak (1980) and field sampling methods by Smith and Richardson
(1977).

Samples were preserved in a 5% formalin and seawater solution. Fish eggs
and larvae from the 505-y mesh net were sorted and larvae were identified,
enumerated and measured to the nearest 0.1 mm SL. For taxa which were
abundant in a tow, approximately 50-100 specimens were measured to obtain a
representative length frequency. For this study all lengths of haddock larvae
were rounded to the nearest mm. The total abundance of each taxon at a
station was standardized as the number of larvae under 10 m* of surface area
to the maximum tow depth (Smith and Richardson 1977).

The analysis of ichthyoplankton survey data usually includes the
calculation of mean catch-per-tow. The data set often contains stations where
the species of interest is absent and the frequency of abundances at positive
stations is non-normally distributed, usually negative binomially or
lognormally distributed. Such data are described by the A-distribution
(Aitchison 1955). Therefore, the analysis of haddock data was made using
the A-distribution to determine the mean catch-per-tow and its standard error
(Pennington 1983).

Net-Mesh Retention

The bongo net sampler provides suitable samples for analysis of retention
rates of larvae at the lower end of the larval length frequency curve. Nets
of mesh size 505- and 333-y are arrayed simultaneously at all standard MARMAP
stations. Many of the variables affecting larval catches, e.g. time of day,
tow speed, tow depth, etc., are constant for the two nets at a station thus
permitting direct comparison of the retention rates of the two nets.

Catches at 18 stations on Georges Bank where larval haddock were abundant
were sorted from both nets and compared. Initial comparison of the length
frequencies and total number of larvae caught indicated the 333-y net retained
a higher proportion of smal] (<6.0 mm) larvae and that total catch was greater
(1860 vs 1090 larvae). Approximately 97% of the difference in total catch is
accounted for in lengths 3.0-6.0 mm, therefore lengths greater than 6.0 mm
were considered fully retained by the 505-y mesh net.


= J
ar |

40"
68 68)
‘.
lomerers 38”)
om
Apr 13 = 23 70
N=93

Eggs spawned/10 m2/dey

fags spawned/10 m2/dey
None

10 NN | . . 119 NN
H-100 NYY oe NAO NOS
101-1000 WY 26" Pe \ an 101-1000 (WC 36"

72 S, : 7 72"
-— S\ i
g 7 oe 7

Distribution of yellowtail flounder eggs during the second and
third ichthyoplankton surveys, 1977.

200m,

Figure 2.


42

silver hake spawning on Georges Bank, based on egg samples in 1959-62 (Sauskan
and Serebryakov 1968), and abundances of larvae in 1971 (Colton and Byron
1977) and 1979 (Silverman 1982) indicate considerable variation .in the
relative importance of western versus eastern Georges Bank silver, hake
spawning between years. Patterns of egg densities described for western and
central Georges Bank during summer 1979 show the highest spawning levels on
central rather than on western Georges Bank (Fig. 1). And although Silverman
(1982) illustrated somewhat greater concentrations of larvae on southwestern
rather than on eastern Georges Bank during October, he also noted advective
circulation which would tend to move larvae from spawning areas farther

east. Lack of sampling in the western Gulf of Maine in July, and in Middle
Atlantic waters in April and November-December may have biased the estimate
downward. Overall I feel the estimate of egg production is conservative,
slightly lower than it probably would have been if we had covered all the area
every time.

Spawning population estimates derived from these egg production numbers
were consistently greater than the estimates from VPA as reported by Almeida
and Anderson (1981) (Table 6). Moreover, as noted above, had we been able to
fully sample all areas on all surveys the discrepancies would probably be even
greater than those noted here.

Silver hake catches have undergone sharp declines in recent years due to
reductions in biomass and, since the implementation of extended jurisdiction
in 1977, restrictions placed on the foreign fishery. Consequently, population
estimates from VPA for the most recent years must be considered tentative due
to the VPA's tendency to underestimate population sizes in a fishery with
declining catches (Almeida pers. comm.)*.

One reason for the disparate population estimates may lie in the use of
different size (age) at maturity information. Almeida and Anderson (1981) and
Anonymous (1982) used a spawner age definition of age 2+ for all years
calculated. This assumes that no one-year-olds are spawners and all two-year-
olds and older are spawners. However, the size at maturation can vary between
years. The length at 50% mature for female silver hake was observed to vary
by as much as 3.7 op between adjacent years during the period 1977 to 1980 (W.
Morse unpubl. data)‘. The use of the “age 2+" definition, in conjunction with
growth relationships described by Almeida (1978) would exclude many fish which
I calculate as spawners in 1979 based on the percent mature-at-length. Had I
used the criterion of age 2.8+ year to define spawners (as would apply to
autumn data rather than age 2.0+ year) then my calculated estimates of
spawners would be closer to the VPA estimates (1.155 x 10” spawners with a
biomass of 342.4 x 10° MT).

Another possible source of bias in my population estimate could be in the
use of Mari and Ramos' (1979) fecundity data. If their determination of total
fecundity was based, even partially, on gonad samples taken after the
beginning of spawning, then the fecundity estimates would be biased
downward. This appears to be a possibility in their study, since they note
that gonad samples were taken off Nova Scotia during July and August.
Resulting population estimates on my part would be biased upwards.


4930

66h--18E-ZOL--n86T 239140 ONTANTYA INBWNNBADD “S “A

“6LGL ‘eave AdAJNS Je}0} OU} UL pue Seaseqns sno} UI UONONPOd 66a eyeYy Jens Aep payewnNsy ‘py aunbi4

| AON 4190 4 d3S ton Ar .Nar LAV dv \ uv
1 1 1

1ll

8

(g01 X) AVG Had CANMVds S093

§

+ OObL

roogt

“0002


47

Table 3. Silver hake population estimate, Georges Bank, 1979; numbers in parentheses are estimated.

% Theoretical % Total

Length Reference 3 fenales egg production maies  populatign Spawners,
(on) catch fenale mature Fecundity by ref. catch mature estimate both sexes
1.0

2 0.189 (0) (0) 22996214

3 3.586 (0) (0) 436319691

4 5.537 (0) (0) 673703884

5 4.167 (0) (0) §07011755

6 2.673 (0) (0) 325232162

7 1,389 (0) (0) 169003918

8 0.882 (9) (0) 107315663

9 0.730 (0) (0) 88821354

19 0.388 (0) (0) 47209158

lL 0.166 (0) (0) 20197732

12 0.012 (0) (0) 1460077

13 0.008 (0) (0) 973385

14 0.004 (0) {0) 486692

15 0.004 (0) (0) 486692

16 0.004 (0) (0) 436692

v7 0.011 (0) (0) 1338404

18 0.032 (0) (0) 3893539

19 0.038 (1.8) 47579 15.309 (7.1) 4623577 213003
20 0.059 10.5 $4703 178.796 10.2 7178712 743591
al 0.089 14,2 62466 348.856 14.5 10828905 1555835
22 0.205 22.8 70892 1693 .526 14.8 24942983 4711430
23 0.270 19.9 80003 2182.809 19.2 32851734 6424308
24 0.359 27.7 89822 4395.520 29.2 43680638 12432318
25 0.435 32.5 100370 6650.763 33.3 52927793 17426497
26 0.645 43.3 111669 14380 546 48.0 78479141 35969211
27 0.474 54.6 123742 15890. 768 63.1 57673043 33959214
28 0.438 62.5 126608 16087 .948 0.1 53292812 - 38652467
29 0.274 69.4 150290 11302.815 97.7 33338426 26824881
30 0.457 73.5 164807 21938315 90.4 55604601 46542458
31 0.316 80.8 1g0182 17923.747 93.8 38448696 34117527
32 0,442 89.6 196433 31529 .808 93.9 53779505 49561691
33 0.358 96.0 213582 32004084 94.2 43558965 41374396
4 0.307 (99.0) 231648 37722879 94.1 37353638 36130463
35 0.305 (100.0) 280652 46997 ,799 97.5 37110292 36728612
36 0.240 (100.0) 270613 43280.761 98.5 29201541 29055416
37 0.263 (100.0) 291551 5039. 406 93.3 32000022 31394985
38 0.124 (100.0) 313486 31995 .760 93.3. 15087463 14908642
39 0.107 (100.0) 336436 32168.395 (93.3) 13019020 12926210
40 0.091 (100.0) 360421 31132.157 (100.0) 11072251 11072251
41 9.069 (100.0) 385459 25836.006 (100.0) 8395443 8395443
42 9.039 (100.0) 411571 16051.269 (100.0) 4745250 4745250
43 0.043 (100.0) 438774 18867.282 (100.0) 5231943 5231943
44 0.034 (100.0) 467087 15086.910 (100.0) 4136885 4136885
45 0.035 (100.0) 496529 16509.589 (100.0) 4258558 4258558
46 0.038 (100.9) 527118 19028.960 (100.0) 4623577 4623577
a7 0,025 (100.0) 558872 13273.210 (109.0) 3041827 3041827
48 0.021 (100.0) 591810 11806.610 (100.0) 2555135 2556135
4g 9.020 (100.0) 625950 11893.050 (100.0) 2433462 2433462
50 0.010 (100.0) 661310 6613. 100 1216731 1216731
51 0.022 (100.0) 697907 15353.954 2676808 2676808
52 0.913 (100.0) 735759 9564 .867 1581750 1581750
53 0.015 (100.0) 774886 11623.260 1825096 1825096
54 0.010 (100.0) 815300 8153.000 1216731 1216731
55 9.010 (100.0) 857024 570.240 1216731 1216731
56

37 0,003 (100.0) 944465 2833.395 365019 365019
58 0,010 (100.0) 990218 9902.180 1216731 1216731
59 0.004 (100.0) 1037347 4149 388 486692 486692
60 O.01L (100.0) 1085870 11944570 1338404 1338404
61 9.004 (100.0) 1135805 4543.220 486692 486692
62

63 0.006 (100.0) 1239975 7.439.850 730039 730039

Totals = 3226770275 576504911

“Dashed line within "Total population estimate” colunn indicates size at age 2.8 yr, see discussion.


43

FOOTNOTES
Ip, Almeida, unpubl. data, pers. comm., NMFS, Woods Hole, Massachusetts.

ey. Morse, unpubl. data, pers. comm., NMFS, Sandy Hook Laboratory, Highlands,
New Jersey.

REFERENCES CITED

Aitchison, J. 1955. On the distribution of a positive random variable having
a discrete probability mass at the origin. J. Am. Statist. Assoc., 50:
272, 901.

- Almeida, F. P. 1978. Determination of the von Bertalanffy growth equation
for the southern New England-Middle Atlantic, Georges Bank and Gulf of
Maine stocks of silver hake. NMFS, NEFC, Woods Hole Lab., Lab. Ref. No.
78-13.

Almeida, F. P. and E. D. Anderson. 1981. Status of the silver hake resource
off the northeast coast of the United States - 1981. NMFS, NEFC, Woods
Hole Lab., Lab. Ref. No. 81-36.

Anderson, E. D. 1974. Comments on the delineation of red and silver hake
stocks in ICNAF Subarea 5 and Statistical Area 6. Int. Comm. Northwest
Atl. Fish., Redbook, 8 p.

Anderson, E. D., F. E. Lux and F. P. Almeida. 1980. The silver hake stocks
and fishery off the northeastern United States. Mar. Fish. Rev., Jan.
1980: 12-20.

Anonymous. 1982. Silver hake. pp. 24-30. in Status of the fishery
resources off the northeastern United States in 1981. NOAA Tech. Memo.
NMFS-F/NEC-12.

Bigelow, H. B. and W. C. Schroeder. 1953. Fishes of the Gulf of Maine.
U. S. Fish and Wildl. Serv., Fish. Bull. 53: 577 p.

Clark, S. H. and B. E. Brown. 1977. Changes in biomass of finfishes and
squids from the Gulf of Maine to Cape Hatteras, 1963-74, as determined
from research vessel survey data. Fish. Bull., U. S. 75(1): 1-21.

Colton, J. B. and R. R. Byron. 1977. Gulf of Maine-Georges Bank
ichthyoplankton collected on ICNAF larval herring surveys September
1971-February 1975. NOAA Tech. Rept. NMFS SSRF-717. 35 p.

Conover, J. T., R. L. Fritz and M. Vieira. 1961. A morphometric study of
silver hake. U. S. Fish Wildl. Serv., Spec. Sci. Rep. Fish. 368: 13 p.

Guiland, J. A. 1969. Manual of methods for fish stock assessment. Part 1.
Fish population analysis. FAO Man. Fish. Sci. 4: 1-154.

Inada, T. 1981. Studies on the merlucciid fishes. 8ull. Far Seas Fish. Res.
Lab. 18: 172 p.


72

describe net-treatment shrinkage for northern anchovy, Engraulis moradx, from
4 to about 35 mm Tong, at which time ossification is complete. Her formula
was adopted for a mean net-treatment time of 10 min and adjusted to lengths
between 4 mm, the approximate length at hatching, to 15 mm when ossification
is essentially complete. Thus shrinkage was maximum at 4 mm and decreased
exponentially to near zero at 15 mm. The equation describing the relationship
of preserved and net-treated larval length (P,) to live length (L,) was:

L_ = 1.78369 p, 9-88979

L

where lengths are mm x 10,

Temperature-Dependent Larval Growth

Changes in larval growth rate, both between samples during a cruise and
between seasons or years, affect the time (days) a larva spends within a given
length interval. The greater the change in larval growth due to temperature,
the more serious will be the bias upon estimates of larval production and
mortality (Saville 1956, Zweifel and Smith 1981). Therefore, the age of each
larva was determined using growth rates and length-weight relationships given
by Laurence (1978, 1979). :

The growth rate of larval haddock was assumed to be curvilinear in
relation to temperature where the maximum rate occurs at an optimum
temperature and decreases as the temperature varies above or below the
optimum. Thornton and Lessem (1978) developed an algorithm for modifying
growth rates relative to environmental temperature which uses as input the
temperature (t) and growth rate multiplier (Ke) at t. Information presented
by Laurence (1978) showed optimum growth occurred at 9°C under laboratory
conditions and 4°C was near the Tower threshold temperature. By converting
growth per week in weight to growth in mm per day from length-weight relations
(Laurence 1979), the average growth rate per day at 4°C was 0.81% and at 9°C
it was 2.96%. Thus the age of larvae can be calculated as:

In(r*)
ie}

Age (days) q
where 1, is observed length, L, is length at hatching (4.0 mm) and

q = K, 0.02964, The value 6.02964 is the optimum instantaneous growth
effictent at 9°C for haddock larvae. The growth rate miltiplier (Ky) is
determined from the growth rate multiplier at ty (4°C) which equals 0.274 ©
(0.81/2.96), the observed temperature (t) and ry, the specific rate
coefficient by the formula

Ky EXPLry (tt) )]

KO =
t THK, {EXP ry (t-t7) -1


82

Table 3.--Summary of regression analysis of haddock larvae on Georges Bank
for estimating mortality (Z).

Age

y , , (days) Regression constants se 2
ear interva a 2 r
1977 14 1-53 2054.54 -0,10206 +0,0391 291
1978 13 1-49 1708.975 -0,11389 +0.0440 78
1979 - - - -0.10814" - -

1980 ll 9-49 3285 .560 -0.09386 40.0346 82
1981 13 1-49 1836 .550 -0.10029 +0.0401 094
1982 6 17-37 245.672 -0.13062 +0.0266 68

*average Z for 1977-1982


37

This paper not to be cited without prior reference to the author

International Council for the ICES C.M. 1983/G:46
Exploration of the Sea Denersal Fish Committee

SILVER HAKE, Merluccius bilinearis, EGG CENSUS AND ADULT
POPULATION ESTIMATE FOR 1979 IN WATERS OFF EASTERN UNITED STATES

Peter Berrien

U. S. Department of Conmerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Sandy Hook Laboratory
Highlands, New Jersey 07732 USA

ABSTRACT

Seasonal eaq production of silver hake, Merluccius bilinearis, is
calculated fron broadscale ichthyoplankton surveys off eastern United States
in 1979 and used to derive bionass estimates of the adult population.

Spawning occurred fran late March to mid-December, reachina a peak in the
first half of July; it occurred fron North Carolina to the Gulf of Maine and
western Scotian Shelf and was most abundant on Georges Bank gnd in southern
New England waters. The sum of eggs spawned (208.7049 x 10*° eggs) is related
to the theoretical egg production of a reference catch of adults to potain
estimates of all spawnerg and of the total "catchable” poputatiog.
estimate of 1.54755 x 10% spawners, with a bianass of 364.4 x 10
is calculated.

netic tons,

INTRODUCTION

Silver hake, Merluccius bilinearis, is an econanically important species
which occurs in she f waters of eastern North America. It is found as far
north as southern and eastern Gulf of St. Lawrence, southern Newfoundland and
Grand Banks, and as far south as South Carolina. It is most abundant fron
Nova Scotia to New York (Nichols and Breder 1927; Bigelow and Schroeder 1953;
Inada 1981).

Previous studies have indicated that the population consists of separate
stocks (Conover et al. 1961; Konstantinw and Noskoy 1969; Nichy 1969;
Anderson 1974; Almeida 1978). As a result of these studies, population
estimates and management measures for silver hake have been reported for’ three
areas which are roughly in accordance with ICNAF (International Conmission for
the Northwest Atlantic Fisheries) and NAFO (Northwest Atlantic Fisheries
Organization) divisions and subdivisions: 1) Gulf of Maine, 2) Georges Bank,
and 3) southern New England-Middle Atlantic stocks (Anderson et al. 1980).

The fishery for silver hake was almost exclusively that of the United
States until 1962 when fleets fron European countries, notably the USSR, began

Preceding g page blank |


107

"WW ‘ALO SpooM ‘9439N ‘S4WN SUOLSLALG QUaUSSassy 92.4N SY

“LeAaL Z0L
¥*

“LeA21 £08,
SiqeLLeay ON ax(g01X66°2 “ golxse") gol X 8E°T Aapunols | be3MOL LBA
gol X LL 4» (g0TX96°T gQlXvt'T) gol * SST ByxeY AALLS
gol X 96° xf gOlX2t'2 “gotxte’) ll * 02°T Lavayoeu otquelyy
(SiSApeue y40Yo9) an [easazuy aouaptyuo , (shaauns 66a) saLoads
4274S 4907S: Butumeds tao ; : 49035 Butumeds

40 97 PUL S9 30 97 RULZSZ

@ZLS 4903S Bulumeds jo sazewiysy “AL atqey



TABLE OF CONTENTS

LIST OF TABLES... .cceseeeeeee Peet eeeeeeene teens eee ee 2
LIST OF FIGURES cc cece cece cere ese e een teen eeteeceteeeresetereeees Ti
INTRODUCTION. ....0e see eeeeee Perera ree eee eee eee eee eee eee eee eee eee ree es

ATLANTIC MACKEREL, Scomber scombrus, EGG PRODUCTIUN AND
SPAWNING POPULATION ESTIMATES FOR 1977 IN THE GULF OF MAINE,
GEURGES BANK, ANU MIDDLE ATLANTIC BIGHT... ..ccecccecveceecerceeeeveeee 7

YELLOWTAIL FLOUNDER, Limanda ferruginea, ESTIMATES UF EGG

ABUNDANCE ANU PUPULATION SIZE DURING SPRING 1977 IN GULF OF

MAINE, GEURGES BANK, SOUTHERN NEW ENGLAND AND MIDDLE ATLANTIC

BIGHT WATERS... eceeeneeeeeene Pere ere eee eee eee eee eee eee ee ee eee ser?

SILVER HAKE, Merluccius bilinearis, EGG CENSUS AND ADULT
POPULATIUN ESTIMATE FOR 1979 IN WATERS OFF EASTERN UNITED STATES..... 37

SPAWNING STOCK BIOMASS ESTIMATES UF SAND LANCE, Anmodytes sp.,
OFF NORTHEASTERN UNITED STATES DETERMINED FRUM MARMAP PLANKTON
SURVEYS, 1974-1980... ccc ceeseccencnsere cen enreseetecncsseeeeteereces 2090

AN ASSESSMENT OF THE GEURGES BANK HADDUCK STUCK BASED ON LARVAE
COLLECTED ON MARMAP PLANKTON SURVEYS, 1977-19820........- see eeeeeceee 67
MEASURING THE PRECISION UF ESTIMATES OF TOTAL EGG PRODUCTION

BASED UN PLANKTON SURVEYS. ..ceseeeeeee sec eeeeceee rereeeerrre es oe BY

Preceding page blank

een


199

as a consequence, the estimate of seasonal egg production for yellowtail
is the least precise of the three.

One way to assess the accuracy of egg surveys is to. compare the
estimates.of spawning stock size based on the surveys with other available
estimates. Table IV contains estimates of spawning stock size derived
both from the egg surveys and from cohort analysis. For Atlantic mackerel

9

the spawning stock estimates based on the egg survey (1.20 x 10° fish) com-

pared favorably with cohort analysis (.96 x 10° fish). The estimate for

silver hake: from cohort analysis (.77 x 10° fish), though considerably

lower than the estimate’ based on the egg survey (1.55 x 109

fish), is just
within the 95% confidence interval for the egg survey estimate. Due to
silver hake catches having sharply declined in recent years, the estimate
based on cohort analysis is considered tentative since cohort analysis
tends to underestimate population sizes in a fishery with declining catches
(Berrien, 1983). The estimate for yellowtail (1.38 x 108 fish) based on
the egg survey appears to be quite reasonable, although no cohort analysis
is available (Berrien, 1981).

There are other possible sources of uncertainty in egg abundance
estimates which have not been addressed here. Errors could result from
insufficient coverage of spawning area and season due either to inadequate
survey design or vessel operations and the vagaries of weather. For in-
stance, an apparently important spawning area of silver hake in the western
Gulf of Maine was not adequately sampled in the summer resulting .in egg--
estimates that are probably low. Another possible, but less worrisome

source of bias in egg census work, could arise through choice of a water


60

Sherman, K. . 1980. MARMAP, a fisheries ecosystem study in: the northwest
Atlantic: Fluctuations in ichthyoplankton-zooplankton components
and their potential for impact on the system. pp. 9-37. In:

F. P. Diemer, F. J. Vernberg, and D. Z. Mirkes (eds.). Advanced
Concepts in Ocean Measurements for Marine Biology. Belle’ W. Baruch

Institute for Marine Biology and Coastal Research. Univ. S. CarolinaTM
Press.

Sherman, K., C. Jones, L. Sullivan, W. Smith, P. Berrien and L. Ejsymont.

1981. Congruent shifts in sand eel abundance in western and eastern
North Atlantic ecosystems. Nature 291(5815): 486-489.

Westin, D. T., K. J. Abernethy, L. £. Meller and B. A. Rogers. 1979.

Some aspects of biology of the American sand lance, Ammodytes
americanus. Trans. Am. Fish. Soc. 108(3): 328-331.

MARMAP CONTRIBUTION NO. MED/NEFC 82-52


46

Table 2. Silver hake population estimate, Gulf of Maine, 1979; numbers in oarentheses are estimated.

& Theoretical 7 Total
Length Reference 3 females egg production males populatipn  Spawners,
(an) catch fenale ature Fecundity by ref. catch mature estimate both sexes
1.0
2
3
4 0.039 (50.0) (0) (0) 831957
5 0.047 (50.0) (0) (0) 1002615
6 0.102 (50.0) (0) (0) 2175888
7 O.111 (50.0) (0) (0) 2367878
8 0.082 (50.0) (0) (0) 1749243
9 0.091 (50.0) (0) (0) 1941233
10 0.124 (50.0) (0) (0) 2645197
i 0.034 (50.0) (0) (0) 725296
12 0.006 (50.0) (0) (0) 127993
13 0.046 (50.0) (0) (0) 981283
14 0.096 (50.0) (0) (0) 2047894
15 0.235 38.6 (0) §013075
16 0.394 51.1 (0) (0) 8404900
7 _ 0.783 $0.4 (0) (0) 16703138
18 1.270 39.5 (0) (0) 27091935
19 2.062 48.5 (1.8) 47579 855.776 (7.1) 43987063 1993327
20 3.652 49.1 10.5 $4703 10291.028 10.2 77905312 8061003
al 4.541 45.9 14.2 62466 18496 .324 14.5 96869667 13912654
22 5.878 45.5 22.8 70892 43200285 14.8 125390862 23119066
23 6.691 19.9 80003 48074604 19.2 142733966 27855832
24 6.368 27.7 89822 74815 .490 29.2 135843656 38704167
25 4.761 32.5 100370 75447.174 33.3 101562758 33425685
26 3.802 43.3 111669 87065.145 48.0 81105147 37125135
27 2.390 54.6 123742 78283.509 63.1 50984035 30069976
28 1.344 62.5 136608 56767.181 80.1 BEETS 20468825
29 1.064 69.4 150290 55688.028 87.7 22697495 17821406
30 0.837 73.5 164807 49751.309 90.4 17855078 14660300
31 0.598 80.8 180182 42799217 93.8 12756675 , 11150508
32 0.646 89.6 196433 56860.652 93.9 13780622 12643662
3 0.770 96.0 213582 81023.921 94.2 16425819 15624857
34 0.889 (99.0) 231648 101999 023 94.1 18964355 18310363
35 0.777 (100.0) 250652 103961.075 97.5 16575145 16381961
36 0.688 (100.0) 270613 114129.409 98.5 14676576 14591378
37 0.518 (100.0) 291551 106380.896 93.3 11050096 10831247
338 0.385 (100.0) 313486 93403 .624 93.3 8212909 8088495
39 0.367 (100.0) 336436 105667.348 (93.3) 7828929 7783291
40 0.195 (100.0) 360421 65235.841 (100.0) 4159785 4159785
41 9.138 (100.0) 385459 51422.004 (100.0) 2943848 2943848
42 9.102 (100.0) 411571 40582.300 (100.0) 2175888 2175888
43 0.035 (100.0) 438774 15152.841 (100.0) 746628 746628
44 9.034 (100.0) 467087 15880958 725296 725296
45 9.019 (100.0) 496529 9434.05) 405312 405312
46 0.021 (100.0) 527118 11069.478 447977 447977
a7 0.013 (100.0) 558872 7265336 277319 277319
48 0.013 (100.0) 591810 7693530 277319 277319
49 9.003 (100.0) 625950 1877.850 63997 63997
50 0.005 (100.0) 661310 3306 .550 106661 106661
51
52
53 0.010 100.0 (100.0) 774884 7748840 213322 213322
54 0.015 100.0 (100.0) 815300 12229.500 319983 319983
55 0.003 100.0 (100.0) 857024 2571 .072 63997 63997
56
$7 0.003 100.0 (100.0) 944465 2833395 63997 63997
58 0.010 100.0 (100.0) 990218 9902.180 213322 213322
59
60 0.003 100.0 (100.0) 1085870 3257 .610 63997 63997
61
62
63 0.007 100.0 (100.0) 1239975 8679 .825 149326 149326
64
65 0.003 100.0 (100.0) 1349991 4049973 63997 63997
66 9.007 109.0 (100.0) 1407233 9850.631 149326 149326
67
68 0.003 100.0 (100.0) 1526268 4578 .804 63997 63997
Totals = 1333381504 396288428

*Dashed line within "Total population estimate" column indicates size at age 2.8 yr, see discussion.


9

The rate (1,) of production for a subarea at time t (taken to be

the midpoint of sample collection) is then estimated by

where A is the area of the subarea, and its variance by

var(T,) = Aevar(c).

To calculate an estimate of total seasonal egg production (T), the

production rates are integrated over time or
~taT
k t,

where ayee- +a, are constants which depend on the spacing of the cruises

and tyres ty are the times represented by each individual survey cruise.
A sequence of plankton surveys is in effect most often a systematic

survey taken over time. For a sequence of k surveys conducted, for example

at monthly intervals, let T, denote the estimate of total egg

pe toreeeoty
production based on the k surveys. Then the variance of Th t is

v toreees k

given by (Rao, 1973, p. 97):


20

ny is the number of non-zero values

y is the sample mean of loge (eggs spawned/10m2/day) for
non-zero values

s2 is the sample variance of the log values, and

Gn, is given by an infinite series and can be found in Aitchison
and Brown (1957).

For our analysis, Gny was calculated by a program written for this purpose.
The variance of k, given by Pennington (ms. 1980), is estimated by:

ny
n

-1 n,-2
1
[én Gas +s2)]

which is a more efficient estimator of var(k) than that used by Berrien et al. , in
press). Confidence intervals can be generated by assuming k (or a weighted

sum of the k's when estimating totals) is approximately normally distributed

with standard error equal to ¥(var k). The retransformed mean density (k)

was raised to the number of eggs spawned in each subarea per day, then multiplied
by the number of days represented by each effort in each subarea. The subarea
estimates were summed over time, resulting in the total number of yellowtail
flounder eggs spawned in 1977 in the area surveyed.

2 \45
[on (S972 - 2h

var(k) = a sexp(2y)-

n

The number of days represented by an effort (part of a cruise) within
a subarea was determined by first calculating the midpoint of time of sampling
within each subarea, each time it was surveyed. Then, for each midpoint, half
the days between the preceding midpoint and half between the following midpoint
were summed to produce the number of days represented by that particular effort
jin that subarea.

The estimate of total egg production for the season, in conjunction with
the spring 1977 groundfish trawl survey length-frequency distribution of the mean
catch per tow, was used to estimate the population size of mature yellowtail
flounder. The trawl survey results were used, rather than commercial fishery
data, so as to be sure that all potential spawners were represented. A theoretical
number of eggs spawned by the mature females in the trawl survey catch was
calculated. This theoretical egg production by the catch was divided into the
total season's egg production (based on the plankton survey) to derive a factor
by which the trawl survey catch could be multiplied to give an estimate of the
entire "catchable" (including spawning) population.

RESULTS

Seven distribution charts show the densities of eggs spawned per day during
the series of surveys (Figures 1-4). Judging from the egg occurrences during
the first survey and their incubation rates at prevailing temperatures, spawning
began at least as early as during the last week of February (27th) in southern
New England waters, by the first week of March (3rd) on western Georges Bank,


16

P. L. Berrien, N. A. Naplin, and M. R. Pennington

Dividing the estimated total eggs spawned (3.032 x
10'*) by those spawned by the commercial catch gives a
factor (12.0986), which when doubled (to adjust for
the sex ratio), and multiplied by the number of mature
females caught, produces the estimated population of
spawners (1.2247 x 10° fish). This spawning popula-
tion estimate, which applies roughly to ICNAF areas 5
and 6, Nova Scotia to Cape Hatteras, is 88.8% of the
spawning stock estimate (1.3786 x 10° fish) given by
Anderson and Overholtz (1978) for ICNAF areas 3 to
6, Newfoundland to Cape Hatteras.

DISCUSSION

In order to obtain an accurate estimate of the total
egg production of a species during a spawning season
it is necessary to plan survey cruises which sample
throughout the entire spawning season and area; and
one should sample often enough to be able to describe
changes in spawning intensity during the season.
Shortcomings in the sampling scheme, especially those
concerning seasonal and areal coverage, can easily
introduce bias into the egg production estimate which
would be hard, or impossible, to detect.

In this study, the distribution charts and production
curve show that the spawning season was adequately
covered in time. However, the areal coverage was
apparently not so complete. We may have missed
some areas of low egg density offshore, beyond the
survey area. We believe this to be a minor fault, as
spawning appeared to be much more intense in the
inner, or shoreward portion of the continental shelf
water than offshore. We may have missed some eggs
by not sampling close enough to shore from Block
Island Sound to the western Gulf of Maine, an area of
approximately 1600 km’. Allowing for this bias by
assuming similar egg densities to those found in the
adjacent areas surveyed would increase the egg pro-
duction and spawning population estimates by 0.54%,
giving values of 3.0485 x 10°* eggs produced by 1.2313
x 10° mature fish. Our cruise frequency varied with
stratum. We sampled more often in southern strata
(5-7 times) than in the north (2-4 times). This clearly
influences the precision of the estimates, but we are
uncertain about both the magnitude and direction of
any bias so introduced.

The resulting coefficient of variation (c.v. = 0.37)
indicates a relatively low level of precision in the egg
production estimate, despite the rather extensive

effort reported here. The effectiveness of the technique
is better when you consider, that the level of effort (7
surveys within 251 000 km’) was not directed solely
toward mackerel egg sampling, but also toward yel-
lowtail flounder (Limanda ferruginea), whose spawn-
ing does not necessarily coincide in space or time with
that of mackerel. If we were to sample, at a similar
level of effort, only for mackerel eggs on future sur-
veys, we could certainly improve the precision. By
using the knowledge gained on this series of surveys,
and by restratifying over time and area, we could
probably decrease the coefficient of variation. The
probability of conducting a single-species oriented ser-
ies of cruises, however is remote, leading to the conclu-
sion that the precision level presented here is probably
typical of such ichthyoplankton surveys. However,
even witha multispecies approach, some improvement
in precision of mackerel egg production estimates
might result from changing the area stratification to
reflect the inshore vs. offshore egg density difference
noted here. Such restratification would not be detri-
mental to the precision of estimates for other species.

REFERENCES

Aitchison, J. 1955. On the distribution of a positive random variable
having a discrete probability mass at the origin. J. Am. Statist.
Assoc., 50: 272, 901.

Aitchison, J., and Brown, J. A. C. 1957, The log-normal distribu-
tion. Cambridge Univ. Press, London.

Anderson, E. D., and Overholtz, W. J. 1978. Status of the North-
west Atlantic mackerel stock — 1978. U. S. Dept. Comm..
NMFS, NEFC, Woods Hole Laboratory, Lab. Ref. No. 78-49.

Berrien, P. L., and Anderson, E. D. 1976. Scomber scombrus
spawning stock estimates in ICNAF Subarea $ and Statistical
Area 6, based on egg catches during 1966, 1975 and 1976. ICNAF
Res, Doc. 76/X11/140.

Jossi, J. W., Marak, R. R., and Petersen, H., Jr. 1975. MARMAP
Survey I manual. At-sea data collection and laboratory proce-
dures. MARMAP Program Office, NMFS, NOAA, Wash... D.C.

Morse, W. 1978. Fecundity and spawning of Atlantic mackerel
(Scomber scombrus) in the Northwest Atlantic. ICES C.M. 1978
H: 64

Pennington, M. 1979 MS. Use of logarithmic transformation tor
analyzing biological data

Sette, 0. E, 1943. Biolgoy of the Atlantic mackerel (Nconther scom=
brus) of North America, Part 1: Farly life history. ineluding the
growth, drift and mortality of the egg and larval populations
U. S. Fish Wild. Serv.. Fish, Bull. S0(38); 149-237,

Worley, L., G. 1933. Development of the ege of the mackerel at
different constant temperatures. J. Gen. Physiol, 16(8): 841-887



99

(Cochran, 1977, p. 221). Egg production for the three species analyzed
appears to be fairly continuous over time. That is, though the estimated
error of the individual production rates (c) for each subarea is re-
latively large, the rates (see Tables I and II) do not vary erratically
over time, but for most subareas, rise to a peak and then decline.

There are various ways to estimate the variance of the results from
a single systematic sample after making some assumptions (Cochran, 1977,
p. 223). Where practical, unbiased estimates of the sampling variance
can be made by dividing the effort into two (or more) systematic samples
with random starts. Though the MARMAP surveys were not designed as two
independent series of surveys, logistics and the large area covered pro-
duced alternate surveys with starts approximately random in each subarea.
A disadvantage of the method used to estimate the total variance is that
it may overestimate the true value, especially if the complete survey,
being systematic in time, has been effective in reducing the variance.

The relative sizes of the variance components (Table III), though
imprecise as reflected by the negative estimate of the time component
for silver hake, indicate the sources of variability for the surveys as
conducted. For example, the proportion of the total variation due to
time was highest for yellowtail flounder and lowest for silver hake. This
results from the fact that one cruise in a subarea accounted for 52% of
the yellowtail egg production (Table I) as compared with 22% from a single
cruise for silver hake (Table II). The high concentration of egg pro-
duction in a short time period for yellowtail is the reason that the

estimate of the total variance has only 1 effective degree of freedom,


28

Table 4. Yellowtail flounder population and catch statistics.

v.p.A.b Summer Traw] Survey
Fishery@ Population mean no. per tow

Landings Estimate Southern Georges
Year (m.t. x 107-3) (no. x 10-6) New England Bank
1960 19.4 199.7 ND ND
1961 25.1 284.6 ND ND
1962 31.5 292.7 ND ND
1963 49.2 203.1 28.2 18.4
1964 53.0 205.7 24.5 | 11.2
1977 16.9 ND 9.0 2.0

aclark et al. (1981)
DBrown and Hennemuth (1971)


“LL6L ‘ease ABAINS GVWHVW ou) UII UONONPOJd B6a josayoeW oNUeNY Ayep payewns3, *Z-aun6i4

+ AVA | udv
n

109

rooo!

+000e

FOooe

+O000r

- 000s

0009

(g-01%) AVO Yad GSNMYdS SDD3


52

pue *yaXts

“6161 *SAanans wor YUE LMOAYIY! gVNYVH

yquanas

“U1JUs 947 GuLunp $669 ayey Jaa[ts yo uolIngizisig “2 aunbLy

W colt
XX ott
200

40p/,1 01/poumods #653

1Ol=N
0% 994 SI non

ee

eo . - .

Py

om 3 fu ot [e 3 Fc et
U2 BK

2 §

NS] fe
QS 001-101
XY Ft
NX ort

uN,

mw [9c

4op/_u O1/pavmod 5863

St=N

KS coot- 101 Looe om
SS wrt ae

NX ore

+ evn

40p/, 1 o1/paumods +663

Srl=N
z 495 - 41 Boy



106

*(3%@7 aas) Aaauns 34,ewWazShs ajuys e se sAaduns Guy3ea43 UO paseq saqewy]Sz
.

(lS). . 7 :
oT 2 8s . vis Lol Lov Aapuno[y L}RIMOL [aA
(602) ‘
a4 02 £02 982 9c61 ooo aqeY ABALES
. (£00) :
rar eel G2e 1v061 bl6b £9001 favayoew 34QuUe IVY
(21-01) (24-01%)
“yp yo UORQINPOsg [eIOL 663 yo uo) 2nposy (yz-01%) (y2-01%) azeds 07 (,2-01%) auy7 03
AoqUNy BA49905)3 JO 40449 pavpurys Lupoy puqwmyy sy uvj ref Zen 1¥7O, anp uojyyejau, ‘aNp UO}ZRpAVA supaads

“SOHISPTETS peqepoussy pue uopZINporg 667 jeuOSeas [eI01 Jo SazeW,7Sz

“HED ataey


70

The relationship of length and proportion retained by the 505-y net
relative to 333-y net was calculated by applying the linear model of Lenarz
(1972) such that C; = a + bL; where C; equals the relative ‘numbers (percent of
total number caught) at length i caught by the 505-y mesh net divided by the
relative numbers caught by the 333-y mesh net and Lj equals length in mm. The
relationship for lengths 3.0-6.0 mm equals Cy 1.059 + 0.0452 L;. The
length where C; equals 1 (4.6 mm) indicates the Jehger at equal retention by
both nets, therefore C; at 5.0 mm was assigned a 1 and the regression
recalculated. Thus for lengths 3.0, 4.0 and 5.0-mm, C; equalled 0.272,: 0.800
and 1,00, respectively and the linear equation equalled Cy = -0.765 + a. 0364
Ly. The correction factor for extrusion through the 505-y mesh net is then

Ni

Nit °T

where Ni, is corrected catch at length i and N. is number caught at
length 1. Corrections were made for lengths ch, 8 mm which equals the length
at which C; approaches 1.

Net_Avoidance *

The ability of fish larvae to actively avoid capture through sensory
detection of an approaching net may result in a serious underestimation of
total abundance. When visual detection by larvae of an oncoming net is the
primary sensory cue then the difference between day- and night-caught larvae
should give a measure of avoidance. Clutter and Anraku (1968) reviewed the
problem of avoidance and concluded that due to high sampling variability it
may be difficult to specify avoidance effects upon catches within useful
confidence limits. However, various attempts have been made to account for ‘at
least some of the avoidance problem by investigating day-night differences in
larval catches (Ahistrom 1954, Farris 1961, Lenarz 1973). Lenarz studied four
species and developed an exponential equation to relate catch rates to larval
length and time of day. He found night catches exceeded day catches and the
ratio of night to day increased with increasing length of the larvae. This is
expected if vision and swimming ability improved as larvae grow.

I investigated the day-night differences in catches of larval haddock
from eight surveys of the Georges Bank subarea during the months April-June in
1977-1981. Daytime hours were from 1 hr after sunrise to 1 hr before sunset
and night was designated as the time between 1 hr after sunset to 1 hr before
sunrise. During these surveys, 142 day-stations and 83 night-stations were
sampled. The difference in the number of day and night stations reflects the
latitudinal difference in daylight and nighttime hours during the. spring
months on Georges Bank. The expected ratio of day:night equals 1.63:1 which
for exact proportioning of sampling effort day- -stations would number 139 and
night-stations would number 86.

‘Before comparing the day catches to night catches, effort must..be
standardized both spatially and temporally. Preliminary attempts to adjust
effort by survey was confounded by the inclusion of stations where the. .
probability of catching haddock larvae was zero. This confounding occurs
because a zero tow will affect the day-night comparison when the probability
of catching haddock larvae is not zero and thus avoidance is the determining


22

spawned (56.862 x 1012) by those theoretically spawned by the reference

catch gives a factor (37.967) which when multiplied by either the reference
catch, the number of females, or the number of mature females in the reference
catch produces an estimate of that population (Table 3). By these methods

total population estimates of mature females (49.349 x 106), all females (100.707
x 106) and all fish (200.881 x 106) were calculated. A total male population

of 100.174 x 106 fish was determined by subtraction, resulting in an overall

sex ratio of 49.87% male to 50.13% female.

DISCUSSION

The estimates in Table 3 include fish as small as 6 cm in length. There-
fore, to compare these results with virtual population assessments (VPA) based
on commercial catch statistics, it is necessary to eliminate smaller fish not
yet recruited to the fishery. By subtracting those less than 27 cm, which is
the mean length of age 2 yellowtail flounder, approximately the size at which
50% recruitment occurs (Brown and Hennemuth 1971), an estimate of 138.1 x 106
fish is provided. Population estimates from 1960-1964 as well as commercial
landings and trawl survey catch-per tow statistics have been used to compare
my results with earlier estimates (Table 4). From these data it is clear that
landings and catch-per-tow values were considerably lower in 1977 than in the
early 1960's indicating a smaller population in 1977 than earlier. Had a similar
VPA estimate based on commercial fishery data been available’ for the 1977 yellow-
tail flounder population, it would undoubtedly have been less than 237 x 106 fish
reported by Brown and Hennemuth (1971) as the average population in southern
New England and Georges Bank waters for 1960-1964. Therefore my value of 138.1 x
106 fish (which is 58.2% of 237.2 x 106) which applied to waters between Nova
Scotia and Cape Hatteras, seems quite reasonable.

Due to insufficient data I could not determine the percent-mature-at-
length for male yellowtail flounder. Therefore I could not calculate an
estimate of the total spawning population, rather only that for spawning females,
as well as for all yellowtail flounder capable of being caught in the otter traw]
during the spring groundfish survey. Estimates reported here can be converted
from length frequencies to age frequencies with the appropriate length-age key.




an estimate of average larva growth rate which converts lenyths to ayes. The
aye frequency is then used to estimate larva “mortality” from the exponential
rate of decrease in abundance with increasiny aye. The “mortality” rate is
applied to the aye frequency to back-~calculate the number of larvae hatched
during the entire spawniny season. An estimate of egg inortality and the total
number of larvae at hatching yields a total estimate of egg production. The
final steps are then identical to those presented above for spawniny
population estimates usiny eggs.

REFERENCES CITED

AHLSTROM, E. H.
1968. An evaluation of the fishery resources available to the California
fishermen. pp. 65-80 In D. Gilbert (ed.). The future of the fishing
industry of the United States. Univ. Wash. Publ. Fisn., New Ser. 4

COUMBS, S. H.
1979. An estimate of the size of the spawniny stock of blue whiting
(Micromesistius poutassou) based on egy and larval data. ICES, C.M.
1979/H:41. 2U p. (mimeo).

CRUSSLAND, J.
1980. Tne number of snapper, Chrysophrys auratus (Forster), in the
Hauraki Gulf, New Zealand, based on egy surveys in 1974-75 and 197b-
76. Fish. Res. Div. New Zealand Ministry Ayric, and Fish., Fish. Res.
Bull. No. 22: 1-38.

CUSHING, D. H.
lyo7. The number of pilchards in the Channel. Ministry Ayric., Fish.
Food, Fish. Invest., Ser. 2, Vol. 21, No. »: 1-17.

deCIECHUMSKI, J. Dz. and D. A. CAPEZZANI.
1973, Studies on the evaluation of the spawning stocks of the Aryentinean
anchovy, Enyraulis anchoita, on the basis of eyy surveys. Rapp. P.-
v. Reun. Cons. int. Explor. Mer, 164: 293-301.

HARDWICK, J. E.
1973. Biomass estimates of spawning herriny, Clupea pallasi, herring eyys
and associated veyetation in Tomales Bay. Calif. Fish and Game 59(1):
33-61.

HOUDE, E. D.
1977a, Abundance and potential yield of the round herring, Etrumeus,
teres, and aspects of its early life history in the eastern Gulf of
Mexico. Fish. Bull., 75(1): 61-89.
HUUDE, E. D.
19776. Abundance and potential yield of the Atlantic thread herring,
Opisthonema oylinum, and aspects of its early life history in the

eastern Gulf of Mexico. Fish. Bull., /5(3): 493-512.


7]

factor producing a zero tow. It is clear then that zero tows may occur
because of: 1) avoidance; 2) the tow was made beyond the areal limits of
larval occurrence; or 3) larvae are not at the station because the sample was
taken outside the spawning time.

When I analyzed relative abundance (percent abundance), the difference in
day-night catches was again misleading because, on a relative scale (%), the
total abundance is ignored. Day catches might be 10 times the night catches
but when making relative comparisons this important difference is lost in the
analysis. It is also evident that large differences in percent abundance at a
few length increments between the day and night catches, usually the smallest
lengths of the compared length frequencies, will determine the relationship of
percentage of al] subsequent lengths. This relationship is evident in the
length frequencies (%) of Lenarz (1973). His catch curves for northern
anchovy by day and night show approximately 80% of the day catches occur in
the first two length intervals and only about 45% for the night catches. This
leaves 20% and 55% to be apportioned throughout the remaining length
intervals, thus producing the characteristic length-percent curves where night
catches exceed day catches in the larger size intervals.

Since both night and day catches of haddock larvae appeared to conform to
the A-distribution, I calculated the a-mean catch-per-tow for each mm length
interval for day and night catches to determine if avoidance could be detected
in the length frequencies. This approach eliminates the problems introduced
when using a relative scale and zero tows are included in the calculated
A-mean.

Shrinkage

The application of laboratory reared growth parameters to field collected
larvae requires intercalibration to acount for morphological differences due
to preservation and net treatment (Theilacker 1980). The factors of interest
here are larval length (SL) and the determination of differences between the
measured length of haddock larvae following collection and preservation from
surveys and the lengths of live, laboratory reared larvae at the same
development stage.

Preservation shrinkage was determined by measuring 25 (4.4-12.7 mm SL)
larvae immediately after capture, one day after preservation in 5% buffered
formalin solution and again seven days after capture. Mean shrinkage after
one day was 3.9% (S = 2.7) and after seven days total shrinkage was 4.2%

(S = 3.1). From these data it is clear that over 90% of the preservation
shrinkage occurred after one day. The maximum shrinkage between days one and
seven was only 1.9%. Mean shrinkage for length <7.9 mm was 5.0% and for
lengths >8.0 mm the mean was 1.9%. This is expected because shrinkage is
probably related to the degree of ossification (Theilacker 1980) and the ratio
of length after preservation to live length should reach an asymptote of one
when ossification is complete.

Both the mechanical damage during net collecting and death upon larval
length were documented by Blaxter (1971) and Theilacker (1980). Estimates of
shrinkage from these factors ranged from 19% for larvae 6 mm or less to
between 3% and 8% (depending upon the length of time in the net) for larvae
26 mm or greater. Theilacker (1980) developed an exponential formula to


77

However, as 1 mentioned earlier, the 1982 data appears anomolous is not
adequate for biomass estimates. Omitting the 1982 larval estimate, there was
a 2.6 fold change in spawning stock biomass with a minimum value in 1977 and
the peak in 1979. VPA estimates peaked in 1978 and then decreased steadily to
a minimum in 1982. The stratified mean catch-per-tow peaked in 1979, as the
Tarval estimates did, and the minimum value occurred in 1982, The catch-per-
tow showed the greatest variability with a 6.4 fold decrease from 1979 to
1982, All three values indicate a significant decrease in haddock spawning
stock biomass from a peak in either 1978 or 1979 to minimum biomass in 1982.

It is tempting to use a statistical comparison of the three data sets in
Table 6 but each estimate contains its own variability and uncertainties which
makes comparisons, such as correlation analysis, inappropriate. To illustrate
this point, Grosslein (1971) has shown that the research vessel surveys will
not detect a change in haddock abundance if the change is less than a factor
of 2. This corresponds to a confidence interval of the mean catch-per-tow on
the linear scale of 450%. The standard error of the d-mean catch-per-tow of
the larval data is often greater than 50% of the mean (Table 6) which again
illustrates the degree of sampling error inherent in the larval data.
Overholtz et al. (1983) do not give the variance component for their VPA
biomass estimates but, given the effects of misreporting of haddock landings
in recent years and the sensitivity of VPA to terminal F values, it seems
reasonable to assume the VPA estimates contain significant uncertainties.

Although this study has attempted to derive an “effective sampler size"
for haddock larvae, much work still needs to be done to reduce uncertainties
and increase the reliability of spawning stock estimates from larval
surveys. The two most important, and most difficult to define, variables used
in this study are larval mortality and temperature-dependent growth.
Mortalities estimated from age-frequencies pooled from a number of surveys
during a spawning season seems adequate if spawning intensity over time is
approximated by a normal curve and samples are collected frequently (monthly?)
throughout the spawning season (Hewitt and Methot 1982). However, the
interdependence of the growth rate, temperature and food supply and their
effects on the derived age-frequency curves need further study. Thus the next
steps needed to improve our estimates of spawning stock biomass include larval
growth studies, in situ, and vertical distribution studies to define the
larval fish habitat in relation to water temperature.



Figure 3. Estimated daily yellowtail flounder eyy production within the
MARMAP survey area, 1977.

Figure 4, Estimated daily silver hake egy production in four subareas and in
the total survey area, 1979.


105

v0 ot G2 S ay lz 90 L 9
£2 Le ol or 6b €s 6ny bt S
ae oT bbe L 0s 0s une €2 be (9z€8S)
s°9 Lot £°0€ 91 6p Le ken 9 £ opauenay
0 ) 0 0 z se adv 11 2 3 LPPIW
0 0 0 0 8b 22 94 92 t
10 “0 ot £ Lz a AON LT L
1's 9 6°81 €2 ab Sb 390 €1 9
SL Cur 2°0€ ic et 0s boy 61 $ (90665)
U6e S69 TOL 6I fp 6y we ¢ v puei6u3 aN
9°SI 6°92 peg 4 vb Ip AoW ET € usayy nos
2'0 90 Ur 0) $2 se ady ot 2
0 0 0 0 ov 02 4M b 1
0) 2'0 270 1 62 sz 32g 21 L- .
0'0 2°0 2'0 I 62 vs 320 22 9
8'9 vt ale el 61 2g Bny 92 S (6ogt)
yop 0° 80I 6" bez ol 6I 6b ine 6 v yueg 's36.1099
T°2€ S°OET 9°80 9 74 2s Aen 61 €
o'0 vo 0 I ze st 4PM BZ 2
0 0 0 0 S$ 6 4eW OT I
0 0 0 0 sb rat AON 12 t
v0 20 z°0 T ae lb 390 $2 9
v 62 162 6° bS a 6 SS ny 92 S
£9 Sor ver € U 8b te 9 ’ (92086)
bo 90 UT v 0s 6E Acw 12 € aupey 30 sing
0 ) 0 0 6E of ady 12 2
0 0 0 0 6 12 40H OT T
aye
(21-01x) Aaaang £q 240 a w u paquasauday quyodp iy asym (guy easy)
easeqns ut paumeds sh6z 40443 prepueys seg Guy dues Aaaans eaueqns

GL61 405 Sa} Pup ySz UOLZINPOAY 663 ayeY AaALIS “}T OLGeL


75

incubation was 17 days and a total egg survival of 26.8%. Saville (1953),
working on haddock eggs at Faroe, found egg mortalities were about 10% per day
for the 1950-1953 spawning seasons. Given an average incubation of 14 days,
total egg survival at Faroe (22.9%) is remarkably close to that found during
1979 in the Georges Bank-Gulf of Maine area. For this study, egg mortality
was assumed to be 10% per day and an average incubation time of 14 days. Thus
larval abundances were converted to egg abundances by calculating the number
of eggs at each station by applying the assumed egg mortality rate.

The A-mean eggs per 10 m* were then expanded for each survey using the subarea
surface area to give total egg abundance. Subarea and survey totals were
summed to give the total eggs spawned in each year.

Relative fecundity (eggs per gram of female) was estimated to be 640 from
haddock length-weight relationships (Hodder 1963) and length-fecundity
relationships of haddock on Georges Bank (Morse et al. unpublished data). Sex
ratio of the spawning stock was approximately 1:1 (Morse unpublished data) and
was assumed to be 1:1 for this analysis.

RESULTS
Net Avoidance

A total of 10,966 haddock larvae was captured during both day and night
tows; 7,174 during daylight hours and 3,792 at night. Table 2 gives
the A-mean catch-per-tow by millimeter length intervals for day and night
samples as well as the ratio of night to day d-means. Two conclusions are
obvious from the table: 1) for larval lengths greater than 12 mm and less
than 3 mm, the sample size is inadequate for day-night comparisons and 2) the
ratio of night to day A-means is quite variable - ranging from 0.70 at 4 mm to
3.90 at 12 mm.

If the assumption that visual detection of the approaching net by larvae
is a significant factor contributing to net avoidance then the ratio of night
to day catches should increase above 1.0 as larval swimming ability
increases. The trend in ratios in Table 2 does not support the above
hypothesis. In fact, ratios less than 1.0 occur at 4-, 5-, 9- and 11-mm
lengths and the only consistent trend of increasing ratios occur between 4- to
8-mm lengths. For lengths greater than 8 mm the ratio fluctuates between 0,80
and 3.90 and this length interval would be expected to show consistently high
ratios if visual detection and avoidance were a significant factor affecting
the catches. Thus, differential net avoidance could not be detected by
examining the difference in day and night catches. :

Mortality

Age frequencies were developed for each year using the methods described
above. Catches were corrected for extrusion loss through the 505 um mesh net
and preserved lengths were adjusted for shrinkage. The age of each larva was
then determined using the surface temperature at the place of capture as the
reference temperature to adjust for temperature-dependent growth. Age
frequencies for each station were then combined for each year to give the
total age frequency (Figure 2). Numbers at age were grouped into 4-day
intervals and exponential regressions were calculated for each year. The
slope of the regression line was used as an estimate of larval mortality for


101

column temperature which does not accurately reflect conditions ex-
perienced by an egg sample in question. The application of an inaccu-
rate mortality rate to egg catches would bias resulting production
levels. However, this effect is minimized by the use of the youngest
stage eggs to derive the final egg census estimates. Beyond egg
production estimates, errors in any of the following parameters on
adults could bias the resulting population estimates: the length-
frequency distribution, male-female ratio, percent mature at size,
and fecundity at size.

For the species considered, the egg surveys provide estimates of
sufficient accuracy for detecting large changes in the spawning popu-
lations. It should be stressed though, that the data are only from
one year for each species. But if the shape of the production curves
proves to be similar for other years, then the use of egg surveys to
estimate fish abundance would appear to offer a feasible method of
monitoring major fluctuations in spawning stocks. It provides a means
of estimating the absolute abundance for species for which no fishery
exists, and probably is cost effective in cases where fishery statistics

are inadequate to provide an accurate cohort analysis.


86

VIRGINIA .
“ay

Het
NORTH 2
ICAROLINAL;
= “3 ;
by je
SS cae f ¢
var‘thhs!

>. _7e° oo

/ : 364
° ° 50 100 150 200
KILOMETERS

74a 72° 70° 68° 66°

Figure 1. Standard MARMAP sampling locations and boundaries of subareas used

for analysis of haddock larvae.




50

Table 6. Spawning population estimates for three subareas, 1979; nuabers in
parentheses are comparable values fran VPA estimates (Almeida~)

Wtd. mean Weight of
length per Weight spawning

Population spawner per spawner populati og

(no. x 107°) (en) (kg) (MT x 107%)
Gulf of Maine 396.288 28.5 0.163 64.5
(120.1) (31.7)
Georges Bank 576.505 32.8 0.249 143.8
(302.9) (69.6)
So. New England- 574.754 33.7 0.272 156.1
Middle Atlantic (345.5) (92.7)
Total survey area 1547 .547 32.0 0.231 364.4

(768.5) (194.3)



12

P.L. Bernen. NA. Naplin, and M. R. Pennington

se “Qe ae x

Noe
an
Q
4
|
Elem
68.
38]
70.
MAY 4-13 JUNE 12 -JUNE 16 (NORTH)
90 STATIONS MAY 24-JUNE 5 (CENTRAL)
EGGS SPAWNED/M?/DAY MAY 18-MAY 27(SOUTH)
2-CRUISE_ BOUNDARY ~ ~~
[E. None y 185 STATIONS ‘
Olor-s0 EGGS SPAWNED Mm". DAY
Ei-100 none
HB i01-1000 76" Clor10 a6
HB 1001-5000 Chii-100
. 72 BB 101-1000
i 001-5000
Hl 500 :-10000 H
ee ‘ ‘
we we ae ay . 1

Figure 4. Distribution of Atlantic mackerel eggs during the fourth and filth ichthyoplankton surveys, 1977


4

Calculations of egg production estimates for subareas and the total area
were summarized (Table 1). Resulting values plotted over time for the total
area indicate that spawning intensity increased steadily and rapidly from late
March to July, reached a peak in the second week of July, then similarly
declined so as to end early in December (Fig. 3). The time lag of over one
Month between peaks in spawning, in Georges Bank and southern New England
waters on one hand, and in the Guif of Maine on the other, may represent a
seasonal progression in spawning intensity between the areas. However, this
lag may have reflected our low level of sampling in the Gulf of Maine in July,
especially in the western and southwestern portions where spawning has been
reported as significant (Bigelow and Schroeder 1953). MARIMAP collections of
larval silver hake during the last week of August 1979 (Silverman 1982)
indicate that western Gulf of Maine was an important spawning area during late
July and/or early August.

Despite being the smallest of the four subareas, comprising only 16.2% of
the total survey area, Georges Bank produced the most silver hake eggs. Over
the whole season 85.4 x 10°° eggs, or 40.9% of the total, were spawned
there. Peak spawning occurred during the second week of July when the mean
density was 224.9 eggs spawned/10m‘/day. One locality on Georges Bank
produced the two highgst spawning densities sampled; the values of 6617 and
1860 eggs spawned/10m“/day were sampled on 23 May and 13 July respectively
(Fig. 1). Southern New England waters ranked second in egg production,
contributing 33.8% of the total while the Gulf of Maine and Middle Atlantic
waters produced 17.4 and 7.9% respectiygly - Total production, for the eqyire
season was calculated as 208.7049 x 10°* eggs (std. error = 45.6339 x 10**,
coef. var. = 0.2187).

Calculations used in estimating population sizes of catchable and mature
silver hake are summarized in Tables 2 to 5. Length frequencies of fish in
the reference catches were assumed proportional to those of the population.
The reference catch is the subarea mean catch per tow from the fall 1979
bottom trawl survey (Almeida unpubl. data)~. Theoretical numbers of eggs
which could have been spawned by the reference catches were calculated for
each subarea using percent-female-at-Jeng th (Almeida unpubl. data)*+, percent-
mature-at-length (Morse unpubl. data)©, both from the 1979 fall bottom trawl
survey, and fecundity-at-length (Mari and Ramos 1979). Dividing the estimates
of total eggs spawned, by those theoretically spawned by the reference
catches, produced factors which when multiplied by the reference catches
produced population estimates for each subarea. A total spawning population
of 1.54755 x 10” fish results from summing all_,subarea estimates. This is
equivalent to a spawning biomass of 364.4 x 109 WT (Table 6).

DISCUSSION

The following conditions should be met in order for a series of plankton
surveys to produce an accurate egg census: the entire spawning area should be
sampled, the entire spawning season should be sampled, and sampling should be
frequent enough to be able to describe spawning intensity over time (Saville
1964). The latter two conditions were met during 1979 for silver hake off the
United States east coast. However, there were instances of incomplete areal
coverage. Lack of sampling on eastern Georges Bank during surveys in July and
August-September was not felt to be a major problem, assuming that the portion
we did sample was representative of the area missed. Previous reports of


Table 1, Silver hake egg production by subarea,

45

hake eggs and k = mean density of eags spawned per 10m

1979; N= no. samples in subarea; ‘y = no. sanples containing silver
per day.

Eggs spawned in Days Eggs spawned in
Std. error subareagday repr. by subarea, indicated
Subarea Sampling dates NW k (k) (x107?) survey by survey (xl07/2)
Gulf of Me. 10-14 Mar 9 i) i) - to) 21.025 0
8 Apr-7 May 39 0 0 - ° 36.190 0
(98026 im?) 19-29 May 50 4 1.0633 0.6183 10.4228 39.045 0.4070
9-12 July ll 3 13.3779 10.5182 131.1381 48.365 6.3425
25 Aug-2 Sep 39 lg, 54.9474 29.1356 §38.6273 54.620 29.4198
20-28 Oct 38 1 0.1889 0.1889 1.8521 46.775 0.0866
15 Nov-14 Dec 45 io) 0 - oo) 16.640 0
Gulf of Maine total = 36.2559
Geo. Bank 10-14 Mar 5 oO, a - oO 9.000 QO
1-22 Apr 32 1 0.1492 0.1492 0.6238 35.320 0.0220
(41809 km?) 19-24 May 27 6 148.6222 130.5056 621.3746 51.690 32.1189
9-13 Jul 19 14 224.8977 107.9549 940.2747 49.300 46.3555
24 Aug-2 Sep 19 13, 31.1972 11.3595 130.4323 52.475 6.8444
20-25 Oct 29 , 0.1875 0.1875 0.7840 54.025 0.0424
17 Nov-17 Dec 29 L 0.1848 0.1848 0.7727 25.480 0.0197
Georges 3ank total = 85.4029
So. N. Eng. 2-11 Mar 40 ie) 0 - 0 20.225 tC)
11-20 Aor 25 4 1.0637 0.5724 §.3722 24.825 9.2219
(59906 km?) 12-21 May 4a 24 63.4199 26.8508 379.9231 41.170 15.6414
4-10 Jul 43 19 130.0935 69.5369 779.3379 48.865 38.0823
17-24 Aug 38 ran 38.2218 14.2961 228.9716 50.090 11.4692
10-21 Oct. 42 2 18.8596 6.0945 112.9805 45.085 5.0937
19 Nov-20 Dec 27 3 0.9946 0.6619 5.9582 17.290 9.1030
Southern New England total = 70.6116
Mid. Atlantic 25 Feb-3 Mar 48 a) 0 - 0 22.235 0
13 Apr 2 0 Q - 0 34.605 Q
(58326 km2) 6-12 May 4g 16 30.6774 14.7907 178.9288 36.605 6.5497
17 Jun-4 Jul 50 7 24.4127 17.6317 142.3894 50.240 7.1536
11-18 Aug 4g 10 7.6297 3.7004 44,5013 $2,645 2.3428
4-11 Oct 48 5 2.4995 1.8963 14.5785 26.640 0.3884
Nov-Dec 9 - - - - - :

Middle Atlantic

Entire survey area

total = 16.4345

total =208.7049

“When My = 1 the value given under K is %, (exyeN), and std. error (k) is



74

death rate of larvae caused by numerous factors including predation,
starvation, genetic malformities, disease, etc. This represents the
traditional definition of Z and is assumed to be exponential for the purposes
of this study. The other component of Z is net avoidance by larvae which can
be assumed to increase as larvae grow. The relationship of net avoidance to
larval length is probably a power function which increases until 100%
avoidance at some length. This seems reasonable because plankton nets are
designed to capture only the very youngest life stages of fish and: length
frequencies of net samples are not continuous. The contribution by each of
these two components to the calculated instantaneous "mortality" coefficient
cannot be determined from the bongo net samples. An example of avoidance is
given by Murphy and Clutter (1972) who found the catches of anchovy
(Stolephorus purpureus ) larvae over 5.5 mm in length with a purse seine were
at Teast an order of magnitude greater than with towed plankton nets.
However, if it is assumed that rate of increase in net avoidance with larval
length is constant and that the smallest larvae cannot avoid capture or be
extruded, then Z can be used for backcalculating spawning stock size without
introducing a systematic bias.

Spawning Stock Biomass Estimates

The relationship of spawning stock biomass to ichthyoplankton is usually”
expressed as

_ it
ans

where B = spawning stock biomass, I = ichthyoplankton abundance and R; is the
production of I per unit weight of the spawning stock. I.is determined from
survey data and growth or incubation rates of larvae or eggs, respectively.
Ry usually represents egg production per unit weight of mature females from
fecundity studies adjusted for the ratio of females to males in the spawning
stock. Thus by determining the total abundance of eggs produced during the
entire spawning season and the production of eggs per gram of spawning stock
will give an estimate of total grams of spawning stock.

The use of larval abundance, i.e. the number of larvae at hatching, and
an estimate of egg mortality will yield a total egg abundance estimate. In
this study, estimates of growth and mortality were applied to shrinkage and
extrusion adjusted larval abundances to determine the number of larvae at
hatching at each station. Since larval haddock remain vulnerable to sampling
for as long as 53 days (see Table 3) and surveys were less than 53 days ‘apart
jn an area, then newly hatched larvae in a survey could be captured again in
the succeeding survey. This double sampling will overestimate spawning stock
biomass and must be eliminated before the estimates are made. To accomplish
this, the mean sampling date of tows containing haddock larvae in each of the
three subareas by survey was determined and any larvae hatched on or before
this date in subsequent surveys in the same subareas were dropped from the
biomass analysis.

An investigation of cod, Gadus morhua, and haddock eggs collected in
April and early May 1979 on Georges Bank and in the Gulf of Maine revealed an
average daily egg mortality of 7.5% (P. Berrien, personal communication).

Mean surface water temperature in the survey area was 4.6°C which indicates


Rapp. P.-v, Réun. Cons. int. Explor. Mer, 178: 279-288. 1981

ATLANTIC MACKEREL, SCOMBER SCOMBRUS, EGG PRODUCTION AND SPAWNING
POPULATION ESTIMATES FOR 1977 IN THE GULF OF MAINE, GEORGES BANK, AND MIDDLE
ATLANTIC BIGHT

P. L. BERRIEN and N. A. NAPLIN
U. S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Sandy Hook Laboratory
Highlands, New Jersey 07732, USA

and

M. R. PENNINGTON
U, S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Woods Hole Laboratory
Woods Hole, Massachusetts 02543, USA

The total seasonal egg production of Atlantic mackerel was used to estimate the spawning population for 1977.
Seven ichthyoplankton surveys were made from 5 March to 30 August. The survey area was divided into eight
strata, for each of which the total number of eggs spawned during the season was calculated. The sum of eggs
produced in all strata (3.032 x 10'* eggs) was related to the theoretical egg production of the commercial catch to
obtain an estimate of the number of spawning females. Assuming a | : | sex ratio, the spawning population estimate
was 1.2247 x 10" fish. This estimate, which applies roughly to ICNAF areas 5 and 6, amounts to 88.8% of, and thus
compares favorably with, the population estimate of 1.3786 x 10° fish derived from cohort analysis of commercial
catches and research trawl sampling in ICNAF areas 3 to 6, Newfoundland to Cape Hatteras (Anderson and

Overholtz, 1978).

INTRODUCTION

The present report provides a population size esti-
mate of Atlantic mackerel (Scomber scombrus), based
on egg abundance data. Catch-based estimates were
compared favorably with this fisheries independent
assessment of population size using ichthyoplankton
data.

A previous attempt to estimate the egg production
and corresponding spawning population of mackerel
has been made in the western North Atlantic. Sette
(1943) presented a classic study on eggs and larvae of
the 1932 year-class, including abundance and mortal-
ity estimates for eggs and larvae, growth rate of larvae,
observations on dispersion and the subsequent fate of
that year-class, and a spawning population size esti-
mate, Berrien and Anderson (1976) reported on egg
production and the number of spawners in the New

‘Preceding page blank |

York Bight in May 1975. This population estimate was
not satisfactory because of the restricted nature of the
survey. The estimate was based on one cruise within
the Bight and depended on assumptions regarding
spawning behavior that could not be definitely sub-
stantiated. Anderson and Overholtz (1978) have re-
ported on the 1977 population size of mackerel, using
cohort analysis of trawl catches.

METHODS

The total ichthyoplankton survey included the Gulf
of Maine, part of the Nova Scotian continental shelf,
Georges Bank, and continental shelf waters southward
to Cape Hatteras, North Carolina (Fig. !). Because
sampling locations were based on the sampling design
of the spring 1977 NMFS trawl survey, the extreme
offshore and inshore boundaries of that survey were


49

Table 5. Silver hake population estimate, Middle Atlantic, 1979; numbers in parentheses are estimated.

a Theoretical t Total

Length Reference fanales egg production males  populatign Spawners,
(on) catch female mature Fecundity by ref. catch mature estimate both sexes
1.0

2

3 0.194 © (50.0) (0) (0) 23737965

4 1.443 (80.0) (0) (0) 176566406

5 1.717 (80.0) (0) (0) 210093222

6 1.818 (50.0) (0) (0) 222451647

7 0.225 © (50.0) (0) (0) 27531144

8 0.070 (50.0) (0) (0) 9565245,

3 9.002 (50.0) (0) (0) 244721

10

ul

12

B 0.007 (50.0) (0) (0) 956524

4 0.007 (50.0) (0) (0) 856524

15 0.002 (50:0) (9) (0) 244721

16 0.027 (50.0) (0) (0) 3303737

Vv 0.027 (50.0) (0) (0) 3303737

18 9.020 $0.5 (0) (0) 2447213

19 0.022 47.8 (1.8) 47579 9.008 (7.1) 2691938 122916
20 0.022 48.0 10.5 54703 60.705 10.2 2691134 278487
a 0.018 S11 14.2 62466, 68.016 14.5 1835410 263320
22 0.032 53.8 22.8 70892 276.252 14.8 3915541 746803
23 Q.01l 51.4 19.9 80003 89.998 19.2 1345967 263268
24 Q.119 50.7 27.7 20822 1502.015 29.2 14560916 4140986
25 0.036 «= «51.8 32.5 100370 608.890 33.3 4404983 1448588
26 0.029 46.3 43.3 111669 648.670 48.0 3548859 1626109
7 0.087 4g. 54.6 123742 —-2610.416 63.1 10645376 6315385
28 0.015 42.3 62.5 136608 $41,352 80.1 1835410 1333617
29 0.031 © 39.7 69.4 150290 1283.636 87.7 3793180 3051040
30 0.033 (32.5 73.5 164807 -1299.952 90.4 WOT 3428348
31 0.004 35.3 80.8 180182 205.685 93.8 499443 436624
32 O.110 39.2 89.6 196433 7583.43 93.9 13459671 12411928
33 0.103 42.8 96-0 213582 © -9041.039 94.2 12603146 = 11969281
34 0.080 47.7. «= (99.0) 231648 = 5468410 94.1 6118032 5900035
35 0.079 $5.8 (100.0) 250652. —11041.321 97.5 9666491 9559579
36 0.029 66.0 (100.0) 270613. «$181. 102 98.5 3549859 3530372
37 0.100 71.4 = (100.0) 291551 20816. 741 93.3 12236064. 12001597
38 0.075 77.8 += (100.0) 313486 = 18282.504 93.3 9177048 9040303
39 0.005 85.5 (100.0) 3364361437591 (93.3) 611803 605843
40 0.065 90.7» (100.0) «360421 ~—«-21253.306 (100.0) = 7953442 7953482
41 0.070 92.7 (100.0) 385489 -25001.842 (100.0) _ 8565245 565245

Totals = 319938661 104993082

“Dashed line within "Total population estimate" colunn indicates size at age 2.8 yr, see discussion.


vi

SPAWNING STUCK BIUMASS ESTIMATES UF SAND LANCE, Ammodytes sp., OFF
NORTHEASTERN UNITED STATES DETERMINED FROM MARMAP PLANKTUN SURVEYS, 1974-1980

Table 1. Surmary of surveys used to estinate sand lance, Anmodytes sp.,
Spawning stock, Ng = total stations sampled, Ny = stations with sand
lance larvae.

Table 2. Spawniny stock estimates of sand lance, Ammodytes sp., in metric
tons from Georges Bank to Cape Hatteras 1974-80. & is mean catch
per tow and z is larval mortality coefficient.

AN ASSESSMENT UF THE GEURGES BANK HADDUCK STOCK BASED UN LARVAE COLLECTED UN
MARMAP PLANKTUN SURVEYS, 1977-1982

Table 1. Summary of survey dates, total number of stations sampled and
stations at which haddock larvae were captured by subarea.
NMAB = northern Middle Atlantic Biyht; GB = Georyes Bank;
SGOM = southern Gulf of Maine.

Table 2. The A-mean catch-per-tow of haddock larvae on Georyes Bank by day
and night and the ratio of niyht cauyht to day cauyht by Tenyth
interval.

Table 3. Sunmary of reyression analysis of haddock larvae on Georyes Bank for
estimating mortality (z).

Table 4. The A-mean catch-per-tow of haddock larvae at hatching by subarea
and survey, 1977-ly82.

Table 5. Total abundance of haddock larvae (x 1u?) by subarea, survey and
yearly total and spawning stock biomass estimates by survey and
year.

Table 6. Spawniny stock biomass estimates and stratified mean catch-per-tow
of the Georyes Bank haddock stock.

MEASURING THE PRECISIUN OF ESTIMATES UF TOTAL EGG PRUDUCTIUN BASED ON PLANKTON

SURVEYS

Table 1. Atlantic mackerel and yellowtail flounder eyg production estimates
for 1977.

Table 2. Silver hake eyg production estimates for 1979,

Table 3. Estimates of total seasonal egy production and associated
statistics,

Table 4, Estimates of spawniny stock size based on eyg surveys and a cohort
analysis.




21

by the second week of March (11th) in the New York Bight, and by the third

week of March (19th) on eastern Georges Bank. These results differ only slightly
from previous reports. The onset of spawning has been reported as: mid-March
near Gloucester, Massachusetts (Bigelow and Welsh 1925); during March in the
Mid-Atlantic Bight (Smith et al. 1975); and by early April at the latest in
southern New England waters (Royce et al. 1959). Bottom temperatures associated
with eggs taken on our first survey in 1977 ranged from 1.6 to 6.2°C with a

mean of 4.5°C (std. dev., 1.0°C). This is somewhat cooler than the implied
minimum spawning temperatures of 5 to 7°C given by Royce et al. (1959).

As revealed by the results of these surveys, the general area of spawning
changed little over the season, occurring principally over extreme eastern and
western Georges Bank, and over the shoreward half of continental shelf waters
west and south of Nantucket Shoals and south of Long Island, New York, with
lesser but consistent spawning in adjacent areas extending from the Nova Scotia
continental shelf southward to off New Jersey. We apparently sampled only the
eastern edge of the spawning area in the western Gulf of Maine referred to by
Bigelow and Schroeder (1953).

Table 2 summarizes the results from calculations used in deriving egg
production estimates for individual subareas as well as for the entire survey
area and season. Figure 7 portrays the spawning intensity over time for the
entire survey area and subareas. Subarea 3, part of southern New England waters,
contained the highest mean spawning density (123 eggs/l0m@/day during the fourth
survey). However, due to the difference in area measurement the greatest
contributor (with 595 x 109 eggs per day) to the overall daily egg production
was Subarea 4, including Georges Bank and parts of southern New England and
Gulf of Maine waters. The greatest individual station spawning density was
1042 eggs/10m2/day on eastern Georges Bank during survey 5. Peaks in spawning
intensity can be seen to occur earlier in Subareas 2 and 3, during the last week
of April and first two weeks of May, than in Subarea 4 where it occurred around
the first week of June in 1977.

Over the course of the entire spawning season Subarea 4 contributed the
greatest amount of spawning (67.9% of all eggs produced). In decreasing order
-Of abundance the other subareas contributed lesser amounts: Subarea 3, 13.7%;
Subarea 2, 13.3%; Subarea 5, 3.6%; and Subareas 6 and 7, 1.0 and 0.5% respectively.
The relatively minor abundances from Subareas 6 and 7 were not included
individually on Figure 6 because their portrayal would have confused the graph.
The total yellowtail flounder egg production for 1977 was estimated as 56.862
x 1012 eggs (std. error = 10.359 x 1012 eggs, coef. var. = 0.182).

Calculations used in estimating population sizes of adult, or “catchable"
yellowtail flounder, are summarized in Table 3. Length frequencies of fish in
the reference catch were assumed proportional to those of the population. Using
the percent-female-at-length (S. Clark, pers. comm.), percent-mature-at-length
(Royce et al. 1959), and fecundity-at-length (Howell and Kesler 1977), I
calculated the theoretical number of eggs which could be spawned by females in
the reference catch (1.4977 x 10!2 eggs). Dividing the estimated total eggs


$8 § § 4 3

Haeauency

240-

64

1974

1 ¥=1616.08€xp(~0.221x)

120.803

Thee

so-a9

100109 KO-9 200-209 260-289 300-09

AENGTH UMTERVAL ‘nmi

1975

Y=7569.83Exp(-0.207X)

620.987

s0-49

raot03

MWo-89 20-9 OMe moms

LENGTH INTERVAL, Immi

Figure 2.

FREQUENCY

FREQUENCY

so00- 1976
000% po Y=6 1764.3 1Exp(-0.302X)
FERS, .954
000+
30004
2000"

180-189 200-709 280-289 30.0-209

00109
LENGTH INTERVAL mens

1977

“Y= 158984,84Exp(-0.309X)
150.973

10,0004

$0-49 toons 0-9 200-209 20-29 som9

ANTH INTERVAL, [mm

Length frequencies and fitted regressions for sand lance,

Ammodytes sp., 1974-1977.


57

or length specific mortality becomes a factor at about 28 mm. Z was estimated
from the exponential regression coefficient of the decline in catch with :
increasing length in the interval 5-27 mm (Figures 2 and 3).

Larval production curves were determined for each survey by backcalculating
over time the number of larvae hatched. The lengths at each station between
5 and 27 mm were converted to ages (days old) by the relationship:

Age (days) = Le-bo (3)
G

where Ly is length at capture, Ly is length at hatching (5 mm) and G is growth
rate in mm per day. Estimates’ oF larval growth rates ranged from 11.6 mm per
month by Norcross et al. (1961) off Chesapeake Bay to 5.9 mm per month for
larvae on the Scotian Shelf (Scott 1972). An “average” growth rate (G) of
0.33 mm per day was used for larvae throughout the survey area for the entire
spawning season. Thus by applying equations 2 and 3 to the standardized
length frequencies of each station, daily larval production was estimated and
a curve was fitted to the data by eye to define the shape of the larval pro-
duction curve for each survey. For each year when surveys were made in the
same area at different times, a size overlap often occurred in the production
curves, Those fish contributing to the overlap in the second or later survey
in a given year were eliminated from the total larval abundance estimates
because those larvae were present in the first survey and would be counted
twice. Larval production curves were usually incomplete due to the timing
of the surveys or insufficient coverage during the entire spawning season.

In such cases, I estimated the beginning and/or end of hatching and completed
the production curve by fitting the remainder of the curve by eye. The per-
centage of area estimated in this way was used to correct the total larval
abundance.

Larval production, measured as the number of newly hatched larvae (5 mm)
represented in the catches, was determined for each station as the sum of Ny
for each length interval between 5-27 mm. Thus in equation 2, L equals observed
length minus 5. Total larval production for the entire survey area was deter-
mined by multiplying the mean larval production per 10 m2 times the total survey
area (160,041 km2). Statistical methods used are given in Aitchison (1955)
and Pennington (1982).

Total larval production was converted to spawning stock biomass in metric
tons by the relationship:

ssa(t) = GP-es-l.pr-l. 10-6

where LP is larval production, F is relative fecundity, ES is egg survival

and PF is the proportion of females in the spawning stock. Relative fecundity
was estimated from data presented by Westin et al. (1979) was 973 eggs per gram
of female and the sex ratio was assumed to be 1:1.


P. L. Berrien, N. A.

14

Naplin, and M. R. Pennington

Table 2, Atlantic mackerel egg production estimate.

Eggs spawned,

Eggs spawned represented by
Sid in stratum — Sampling this effort in
error Area. per day_—s midpoint «== ‘Days this stratum
Stratum Cruise nom tw 5 s x ofk’ km’) (No_x 10") date __ represented (No. x 10")
1 DL-77.3 is 0 15 16 $60 0 23 Mar 21.628 0
1 DL-77-4(pt. 1) 17-3 14 =1.784076 1.060294 0.0427 0.0386 16 560 (0.0007 14 Apr 21.1875 0.0150
1 DL-77-5(p. 1) 17017 16 560 0 5 May 34.5 0
1 DL-77-7%(p,.2) 17-0017 16 560 0 22 Jun 49.25 0
1 g¥u.77-2
LA
DEI) 7 007 16 $60 0 U1 Aug 50.25 0
2 DL-173 S40 84 67 288 0 29 Mar 20.5 0
2 DL-77-4(pt. 1) 68 44-24 -0.040103 3.553738 3.3292 1.6044 67 288 0.2240 19 Apr 14.1875 3.1782
2 DL-77-4(pt. 2) 57 420 IS 1.709243 6.402071 76.2885 61,3461 67 288 $.1333 26 Apr 10.25 52,6163
2 DL-77-5¢pt. 1) 66 34-32 -2:149910 4.928335 42.0080 30.1872 67 288 2.8266 9 May 12.9375 36.5696
2 DL-77-5(pt. 2) 69 35 34 -2,590489 4.041763 43.7950 26.3836 67 288 2.9469 22 May 23.5625 69.4358
2 DL-77-7(pt. 2) 69-7 62~—-(1,.636568 1.680508 1.0140 0.7700 67.288 = 0.087025 Jun 42.1875 2.8783
2 fYU-77-2
D Sot 580 58 67 288 0 15 Aug 50.5 0
3. GO-77-1 18 0 18 14131 0 6 Mar 39.625 0
3 AL-17-2 8 0 8 14131 0 15 Apr 23.5 o
3 DL-7-4(p. 1) 8 0 8 14131 0 22 Apr 7.475 0
3 DL-77-5 (ptt) 7 7 0 (1.217970 1.098071 $2838 = 2.6046 14 131 00747 UL May 22.25 1.6613
3 DL-77-S(pt.2) Bo 6 -2—«-2.418879 7.586451 90.7456 224.1528 14 131 1.2823 26 May 24.375 31,2567
3 DL-77-%p.2) 8 2 6 2.489205 3.077634 7.8254 $.9276 14 131 0.1063 29 Jun 40.8125 4.3400
3 YU-77-2 9 2 7 0.277717 120492803863 0.4493 14 131 0.0055 15 Aug 47.28 0.2579
4 GO-77-1 7m 0 70 84-794 0 21 Mar 39.625 0
4 AL-17-2 S401 $3 na 0.0110 0110 84794 0.0009 29 Apr 37,8125 0.0353
4 §NO-77-2
Bere pf 81 67 14 0.927658 5.008552 22.6866 11.7406 84794 1.9237 4 Jun 50.0 96 1850
4 YU-77-2 So S38 na. 0.0074 0.0074 84 794 0.0006 7 Aug 64.0 0.0402
5 GO-77-1 40 14 19137 0 Apr 26.125 0
S$ AL-77-2 2 0 2 19137 0 27 Apr 65.625 0
5 YU-77-2 a) 19.137 0 10 Aug 108.125 0
6 AL-17-2 9 0 19 29837 0 6 May 38.625 0
6 DL-77-7(pt.1) 18 2 16 1.223048 0.099645 0.0335 ——0,0236 29 837 0.0010 14 Jun 38.625 0.0386
7 AL-77-2 5s 0 5 9 299 0 12 May 23.0 t)
7 NO-77-2 9 7 2 1799080 2.630087 11.5437 11.6128 9299 0.1073 4 Jun 43.8125 47030
7 YU-77-2 7 0 °7 9.299 0 8 Aug 64.625 0
8 AL-77-2 7 07 9734 0 9 May 91.75 0
8 YU-77-2 30003 9734 0 8 Aug 91.75 0
The estimated total egg production is 3.032 x 10'* eggs (std. error = 1.1267 x 10'*).
*For ny = 1, the mean is estimated by %, and its variance by x where x is the single non-zero value; both are unbiased estimators.
NOTE: AL = “Albatross IV", DL = “Delaware I”, GO = “Goerlitz", NO ubileiny”

the season, around the beginning of June, then
decreased to a negligible amount during that month.

In all, stratum 2 accounted for the greatest amount
of spawning in the whole survey (54.3% of all eggs
produced). Other areas contributed, in decreasing
abundance, stratum 4 — 31.7%, stratum 3 — 12.4%,
stratum 7 — 1.6%, — and strata 6 and 1 — together
less than 0.02%. The total mackerel egg production for
the season was estimated as 3.032 x 10°" eggs (std. error
= 1.1267 x 10'* eggs).

Egg production over time, in the whole survey area,

is shown in Figure 6. The bimodality of the cumulative
production curve implies discrete peak spawnings in
stratum 2 and in strata 3 and 4. This may be a reflec-
tion of two major spawnings, perhaps caused by two
waves of spawners entering the area (such as two age
groups or two groups which had over-wintered in
different localities); or the bimodality may have
resulted from the sampling scheme and cruise sche-
dule. We may have missed many eggs in early or
mid-May in southern New England waters not sam-
pled, such as Massachusetts Bay; Nantucket Shoals;


3

4a"
fe
sg,
#
2
2 40
eat
rn
somaters 38"
-)
May 4-13 70" May 18 = Jun 16
N=90 N= 185
Eggs spawned /10 m2/day Fags spawned/10 m@/day
None None .
Ilo NS 1-10 AX
1-100 SOO N10 OY
101-1000 (WW 36 ror-1000 (ag
1001 -10,000 WANN
72 72)
€ ia SS e
7 \
g w ae y a w

Figure 3.

Distribution of yellowtail flounder eggs during the fourth and
fifth ichthyoplankton surveys, 1977.


5]

Saluepunog Paseqns

“shaaans (je 03 Aydde 9321 uo umoys

“6161 *SKanans uoryue_doAyry! dyAeivW YIANOY
pue ‘p4ryy ‘puodas ay7 Gulanp s6h6a ayey Aanqts Jo UoLInqL.asig

“| aanb4y

"399039

NYE,

a » vm ” 4 7 96
3 :
g- g C |
3 ; S ;
‘Sec
ik vee . Nee wh
QW 00001-1001
ge |.9e 000) Lae au,
SW ort
OUNWILY
ot NA ort yiaaiw
2U0N avon + von .
-op/ 1 o1/paumods $663 09/0 Ol/poumods 185 409/214 O1/poumods 5663
@i=N 0£1=N Se-N
£ oN
eb ine = 24 er oe 62-9 how ‘ox Chon ay
a _ 9
ae “remore

_ ONVIONS
MIN “OS

we

ve



7

This paper not to be cited without prior reference to the author

International Council for Demersal Fish Committee
the Exploration of the Sea C.M. 1981/G:65

YELLOWTAIL FLOUNDER, LIMANDA FERRUGINEA, ESTIMATES OF EGG ABUNDANCE
AND POPULATION SIZE DURING SPRING 1977 IN GULF OF MAINE,
GEORGES BANK, SOUTHERN NEW ENGLAND AND MIDDLE ATLANTIC BIGHT WATERS

by
Peter Berrien

U. S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Sandy Hook Laboratory
Highlands, New Jersey 07732 USA

ABSTRACT

The total season's egg production of yellowtail flounder was used to
estimate the total population and female spawning population for 1977. Seven
MARMAP (Marine Resources Monitoring, Assessment and Prediction) ichthyoplankton
surveys were made from March 5 to August 30. Based on sampling effort the survey
area was divided into eight subareas, for each of which a total number of eggs
spawned during the season was calculated. The sum of eggs spawned in all subareas
(56.8616 x 1012 eggs) was related to the theoretical egg production of a reference
catch of adults to obtain estimates of the female spawning population and the
total population. An estimate of 138.1 x 106 fish, age 2 and greater, of both
sexes was calculated.

INTRODUCTION

Yellowtail flounder (Limanda ferruginea) is a desirable food fish which
historically has sustained significant fishery catches on Georges Bank and
in southern New England waters. Landings reached a peak in the late 1960's
due to large increases in fishing effort, including that from a considerable
influx of foreign ships. There were subsequent drastic reductions in populations
and catches during the early 1970's in southern New England and mid-1970's on
Georges Bank (Clark et al. 1981).

MARMAP plankton surveys have been conducted since autumn 1976 to present,
generally six per year, at various seasons in Gulf of Maine, Georges Bank,
southern New England, and Middle Atlantic Bight waters out to the edge of the
continental shelf (Sherman 1980). Given a favorable cruise sequence, i.e.,
closely spaced in time, one objective of these surveys is to estimate the total
season-long abundance of eggs spawned by certain fish species of interest.

From this egg abundance estimate, in conjunction with knowledge of such biological
features as sex ratio, fecundity, percent mature at length, length frequency
structure of a representative catch of adults, and incubation rates of eggs at


84

Table 5.--Total abundance of haddock larvae (x 109) by subarea, survey and
yearly total and spawning stock biomass estimates by survey and

year.
Larval Sp. stock
Subarea abundagce biomass

Survey WAS GB SGOM (x 107) (t)
77-2 40.45 24,99 - 65.44 893.92
77-3 19,52 2187.10 - 2206.62 30142.50
77-4 743,53 366.50 182.28 1292.31 17653.00
TOTALS 3564.37 WCET. AZ
78-1 - 41.03 - 41.03 560.48
78-2 - 4257.78 - 4257.78 58161 .42
78-3 14.02 176.92 43.92 234,86 3208.20
TOTALS “4533.67 S1930.10
79-1 16,17 - - 16,17 220.88
79-2 - 273.43 - 273.43 3735.06
79-3 1852.33 7194.32 - 9046.65 123577.54
TOTALS 9336.25 T27533.48
80-1 53.62 724.94 - 778.56 10635.16
80-2 1212.78 4258.47 - 5471.25 74737 46
80-3 141,27 480.81 - 622.08 8497.63
80-4 - 11.29 - 11.29 154,22
TOTALS 6883.18 94027,31
81-1 15.76 115.24 - 131,00 1789.46
81-2 - 2356.03 - 2356.03 32183.45
81-3 173.38 2137.05. - 2310.43 31560.55
TOTALS 4797.46 65533.46
82-2 - 160.57 - 160.57 2193.39
82-3 60.68 41.64 102.32 1397.69

TOTALS 262.89 3590.08



38

fishing on Georges Bank. Catches increased markedly until the mid-1970's .
when, due to declining populations and ensuing restrictions on fishing, they
decreased rapidly (Clark and Brown 1977, Almeida and Anderson 1981). In the
Gulf of Maine the population of age 2+ silver hake, estimated from Virtual
Population Analysis (VPA) at 145 to 152 x 10° metric tons,(MT) in the early
1960's, decreased to a low of approximately 15 to 30 x 10° NT, in the early
1970's, then subsequently increased to between 25 and 40 x 103 MT in the late
1970's. On Georges Bank the decline was even greater, from about 550 to 600 x
10° MT in the early 1960's to a low of 20 to 30 x 10° MT during 1978 to

1981. Similarly silver hake jr southern New England-Middle Atlantic area
declined from 320 to 370 x 10% MT in the mid-1960's to between 60 and 80 x 10%
MT in 1978 to 1981 (Almeida and Anderson 1981).

Additional population estimates useful for comparative purposes can be
made based on plankton samples. These estimates, which are independent of
fishery statistics, are derived from total egg production numbers as
determined by plankton surveys, along with ancillary biological information
such as representative length-frequency distributions and fecundity, sex ratio
and maturation by size, taken on research trawl surveys. Population estimates
of adults, based on ichthyoplankton survey results, are now possible for
species off northeastern United States because of the inception of National
Marine Fisheries Service, MARMAP (Marine Resource Monitoring, Assessment and
Prediction) cruises in 1976. Within the framework of this program bi-monthly
surveys are conducted to sample ichthyoplankton, zooplankton and phytoplankton
and measure nutrients, primary production, chlorophyl1, salinity and
temperature (Sherman 1980). These surveys constitute the field work needed in
order to measure seasonal and annual variability in the structure, function
and rates of change in biological and environmental components of the shelf
ecosystem, with principal emphasis on fish population levels. The purpose of
this paper is to report on a silver hake egg census and corresponding adult
population estimate from MARMAP surveys in 1979.

PROCEDURES

The total MARMAP area includes the Gulf of Maine, the western part of the
Scotian Shelf, Geogges Bank and shelf waters southward to Cape Hatteras, an
area of 258,067 km*. During February to December 1979 seven surveys each
covered all or part of the area.

The total area is divided into four subareas, based on oceanographic and
‘biological considerations, these are: Gulf of Maine, Georges Bank, southern
New England and Middle Atlantic (see Fig. 1). Data are summarized according
to this subdivision, then for the purpose of comparison with adult catch
statistics and research trawl surveys, the southern New England and-Middle
Atlantic subareas, are combined in the adult population estimate. This
conforms to areas designated by the Resource Assessment Division of the
Northeast Fisheries Center for research trawl] surveys, but only approximately
with the same three nominal areas designated for management purposes. (Anderson
et al. 1980) which follow ICNAF subarea delineations.

Plankton was sampled with 6l-cm bongo nets fitted with 0.505 and 0.333-mm
mesh nets. The 0.505-mm side was used for ichthyoplankton collections. A
flowmeter in the net mouth determined water volume filtered and a
bathykymograph recorded tow profile and maximum depth sampled. Smooth, double


79

Marak, R. R. and R. Livingstone, Ur. 1970. Spawning dates of Georges Bank
haddock. ICNAF Res. Bull., 7: 56-58,

Murphy, G. I. and R. I. Clutter. 1972. Sampling anchovy larvae with a
plankton purse seine. U.S. Fish. Bull., 70: 789-798,

Overholtz, W. J., S. H. Clark and D. White. 1983. A review of the status of
the Georges Bank and Gulf of Maine haddock stocks for 1983, Woods Hole
Lab. Ref. Doc. 83-23, NOAA, NMFS. 33 p.

Pennington, M. 1983. Efficient estimators of abundance, for fish and
plankton surveys. Biometrics, 39: 281-286.

Posgay, J. A. and R. R. Marak. 1980. The MARMAP bongo zooplankton
samplers. J. Northw. Atl. Fish. Sci., 1: 91-99,

Saville, A. 1956. Eggs and larvae of haddock (Gadus aeglefinus L.) at
Faroe. Mar. Res. Scot., 1956, No. 4: 1-27.

Sette, 0. E. 1943. Biology of the Atlantic mackerel (Scomber scombrus) of
North America. Part I: Early life histroy, including the growth, drift
and mortality of the egg and larval populations. U.S. Fish. Bull., 50:
149-237,

Sette, 0. E. and E. H. Ahistrom. 1948. Estimations of abundance of the eggs
of Pacific pilchard (Sardinops caerulea) off southern California during
1940 and 1941. J. Mar. Res., 7: 511 p.

Sherman, K. 1980. MARMAP, a fisheries ecosystem study in the NW Atlantic:
Fluctuations in ichthyoplankton-zooplankton components and their potential
for impact on the system. pp. 9-37. In F. P. Diemer, F. J. Vernberg and
D. Z. Mirkes (eds.). Advanced Concepts in Ocean Measurements for Marine
Biology. Belle W. Baruch Institute for Marine Biology and Coastal
Research. Univ. South Carolina Press.

Simpson, E. H. 1959. The spawning of the plaice in the North Sea. Fish.
Invest., Lond., Ser. 2, 22: 7p.

Smith, P. E. and S. Richardson. 1977. Standard techniques for pelagic fish”
eggs and larval surveys. FAO Fish. Tech. Pap. 175. 100 p.

Theilacker, G. H. 1980. Changes in body measurements of larval northern
anchovy, Engarulus mordax, and other fishes due to handling and
preservation. U.S. Fish Bull., 78: 685-692.

Thornton, K. W. and A. S. Lessem. 1978. A temperature algorithm for
modifying biological rates. Trans. Am. Fish. Soc., 107: 284-287.

Wyatt, T. 1980. The growth season in the sea. J. Plank. Res., 2: 81-96,
Zweifel, J. R. and P. E. Smith. 1981. Estimates of abundance and mortality

of larval anchovies (1951-75): application of a new method. Rapp. P.-v.
Reun. Cons. Int. Explor. Mer, 178: 248-259,


56

Prior to the increase in sand lance, both Atlantic herring, Clupea
narengus, and Atlantic mackerel, Scomber scombrus, stocks decreased to
extremely low levels between 1964-1975. Northeast Fisheries Center
scientists are currently attempting to determine the consequences of this
structural change in the shelf ecosystem. As part of this effort, I have
derived estimates of the annual spawning stock biomass of sand lance using
fishery independent data. Because the taxonomy of sand lance in the north-
west Atlantic remains confused, the larvae were classified as Ammodytes sp.
and considered a single taxon.

METHODS

Ammodytes sp. larvae were collected during 18 surveys conducted by the
National Marine Fisheries Service of the continental shelf waters between
Nova Scotia and North Carolina from 1974-1980 (Table 1). This analysis is
based on information from these subareas: Georges Bank, southern New England
and Middle Atlantic (Figure 1). The Gulf of Maine subarea was not included
because catches of sand lance larvae were either nonexistent or relatively
insignificant.

Standard MARMAP I double-oblique tows were made at each station (Jossi
et al. 1975). Paired 60-cm bongo net frames, fitted with 0.505 and 0.333-mm
mesh nets, were towed at approximately 1.5 knots. Net catches were preserved
aboard ship in a 5% formalin solution. The ichthyoplankton in each 0.505-mm
sample were sorted, identified, enumerated and larvae were measured to +0.1. mm
at the Morski Instytut Rybacki, Szczecin, Poland. For analysis, lengths were
combined to whole millimeters, e.g. lengths between 8.0-8.9 mm were combined
into 8 mm. The number of larvae per mm interval at each station was standard-
ized to the number under 10 mé surface area to the depth of tow. This was
calculated using the volume of water filtered and maximum tow depth by the
equation:

Spy = 10 (nr2)-1(c-7)-1(D) (Ly) Q)

where S;, is number of larvae at length x under 10 m@, r is the radius. of
the bongo net mouth opening in meters, C is the calibration factor for the
flow meter in meters per revolution, T is flow meter revolutions, D is
maximum tow depth and L is number of larvae at length x. Total larval abun-
dance at a station is the sum of all S,x.

The instantaneous mortality rate (Z) was defined as:

N
a = Exp(-ZL) (2)
x

where Ny is the number of larvae at hatching and N, is the number of larvae
surviving to length L. Length at hatching was asstimed to be 5 mm and the
maximum length considered fully vulnerable to the sampling was 27 mm, the
approximate length at which metamorphosis begins (Cameron 1958; Macer 1965).
The 27 mm length was chosen because the standardized length frequencies .
become erratic at lengths greater than 28 mm. This indicates net avoidance


80

Table 1.--Summary of survey dates, total number of stations sampled and
stations at which haddock larvae were captured by subarea. ~
NMAB = northern Middle Atlantic Bight; GB = Georges Bank; SGOM =
southern Gulf. of Maine. so

Number of stations

Number of stations with haddock
by subarea by subarea
Survey Dates B SGOM NMAB GB SGOM
77-2 4 Mar-23 Apr 57 32 16 5 3 0
77-3 14 Apr-13 May 26 30 21 2 15 )
77-4 20 May-16 Jun 63 43 20 28 13 3
78-1 16 Feb-17 Mar 47 42 18 0 6 0
78-2 25 Apr-23 May 46 36 18 0 14 0
78-3 29 Jun-16 Jun 45 16 16 1 2 1
79-1 2 Mar-14 Mar 40 5 9 1 0 0
79-2 1 Apr- 7 May 44 33 22 0 16 0
79-3 12 May-29 May 44 30 21 8 14 0
80-1 20 Feb- 4 Apr 45 29 25 1 10 0
80-2 23 Apr-12 May 45 29 24 5 16 0
80-3 29 May-29 Jun 43 23 20 ll 8 0
80-4 8 Jul- 9 Aug 44 24 23 0 1 0
81-1 18 Feb-21 Mar 43 30 23 1 6 0
81-2 7 Apr-12 May 45 30 11 0 13 0
81-3 21 May-14 Jun 43 29 24 4 14 0
81-4 1 Jul-19 Jul 35 26 0 1 0 0
82-2 25 Mar- 7 May 42 26 22 0 4 0
82-3 18 May-11 Jun 39 35 14 3 5 0



25

Table 1. Ichthyoplankton survey dates (1977) and coverage.
No. of
Survey Cruise Samples Sampling Dates Subareas
1 G0-77-01 102 5 Mar-6 Apr 3,4,5
DE-77-03 69 19 Mar-8 Apr 1,2
2 DE-77-04 (pt. 1) 93 13-23 Apr 1,2,3
3 AL-77-02 105 14 Apr-13 May 3,4,5,657,8
DE-77-04 (pt. 2) 57 24-29 Apr 2
4 DE-77-05 (pt. 1) 90 4-13 May 1,2,3
5 DE-77-05 (pt. 2) 77 18-27 May 2,3
NO-77-02 76 24 May-5 Jun 4(pt.),7
DE-77-07 (pt. 1) 32 12-16 Jun 4(pt.),6
6 DE-77-07 (pt. 2) 94 21-30 Jun 1,2,3
7 YU-77-02 144 31 Jul-30 Aug 1(pt.),2(pt.),3,4,5,7,8
DE-77-09 15 30 Jul- 3 Aug = V(pt.),2(pt



INTRUDUCT LUN,
a

Panes
Major factors controlling year class success of coastal fish populations
act during the early life stayes of development: To further our understanding
of recruitment processes in the early life stages and to improve our potential
for forecastiny future yields to the fisheries, NEFC_ scientists initiated in
1977 an intensive field program known as MARMAP.. 73 An integral part of MARMAP
involves mesoscale ichthyoplankton surveys which are conducted at bimonthly
intervals to collect bioloyical and environmental information in continental
shelt waters between Cape Hatteras, orth Carolina and Cape Sable, Nova
Scotia; .an area of nearly 26U,UU0 ki ph

f

¢

~ These surveys provide an alternative to virtual population analysis (VPA)y
for estimating adult spawning biomass of commercially exploited species.,
Because ichthyoplankton-based population assessments do not utilize fishery
catch statistics, i.e. they are fishery independent, they provide the sole
source of information for deriving biomass estimates of species for which
there are no conmercial landing records.<<This yives an added dimension to the
importance of eyy and larva surveys as they‘can be used effectively to monitor
population levels of underutilized resources., Population estimates based on
repeated broadscale surveys Of eygs and/or larvae have been applied widely and
include the following species: Atlantic mackerel, Scomber scombrus (Sette
1943, Iversen 1977, Lockwood et al, 1981, Walsh et al. 1983, Iversen and
Eltink 1983); pilchard, Sardina pilchardus (Cushiny 1957); herring, Clupea
harenyus (Parrish and Saville 1962, Hardwick 1973); haddock, Melano. Ss
aeylefinus (Saville 1964); Argentine anchovy, Engraulis anchoita (deCiechomski
and Capezzani 1973); horse mackerel, Trachurus trachurus (Macer 1974); plaice,
Pleuronectes platessa (Houghton and Harding 1976); round herring, Etrumeus
teres (Houde I977a); Atlantic thread herriny, Opisthonema oylinum (Houde
13776); scaled sardine, Harenygula jaguana (Houde 1977c); blue whiting,

Micromesistius poutassou (Coombs 1979); snapper, Chrysophrys auratus
(Crossland 198U); and northern anchovy, Engraulis mordax (AhIstroin 1968, Smith
1972, Parker 198U, Stauffer 198U, Picyuelle and Hewitt 1983). These studies
were conducted in areas around the world includiny the Gulf of Mexico, the
North Sea, the eastern and western Atlantic Ocean, in the north, east,
southeast and southwest Pacific Ucean and assessed both demersal and pelayic

species.

Off northeastern United States fish eyys and larvae are collected at 177
stations by towing fine-meshed nets throuyh the water column from surface to
bottom or to a maximum depth of 2U0 m to monitor spatial and temporal
variability in the distribution, abundance, production and survival of fish
eygs and larvae. Measurements of other key components of the marine ecosystem
include: nutrients, phytoplankton, zooplankton, sea birds, marine mammals,
water temperature, salinity and dissolved oxyyen. In order to use plankton
surveys for assessment purposes, certain conditions must be met. Surveys
should sample the entire area of spawniny and the entire season must be
sampled frequently enough to permit an estimation of the eyy production rate
over time. These criteria are generally met by the MARMAP program,


40

Although frequency distributions of the numbers of eggs spawned/ 10m2/ day
were found to be highly skewed, In-transformation of non-zero densities
produced normal distributions. A data set which has a proportion of zero
values and which has a lognormal distribution is referrable to the
A-distribution, as described by Aitchison (1955). Mean densities and
associated variances were calculated using equations applicable to the
A-distribution (Pennington 1983, in press). Re-transformed mean densities
were raised to the number of eggs spawned in each subarea per day, then
multiplied by the number of days represented by each survey in each subarea.
The subarea estimates were summed over time to calculate the total number of
silver hake eggs spawned in 1979 in the entire area surveyed.

The number of days represented by a survey within a subarea was
determined by first calculating the midpoint in time of spawning (as
represented by early-stage collections) within each subarea, each time it was
surveyed. Then, for each midpoint, half the days between the preceding and
the following midpoints were summed and assumed to be the number of days
represented by that particular effort in that subarea. When no early-stage
collections were obtained within a subarea, the sampling mid-point was used.

The estimate of total eggs produced for the season, in conjunction with
the fall 1979 groundfish trawl survey length-frequency distribution of mean
catch per tow, was used to estimate the population size of mature silver hake
within each subarea. A theoretical number of eggs which could have been
spawned by the mature females in the trawl survey catch was calculated. This
theoretical egg production was divided into the total season's egg production,
based on the plankton survey, to derive a factor by which the trawl survey
catch was multiplied. This produced an estimate of the entire catchable
population, including spawners.

RESULTS

Silver hake eggs were taken during six of the seven plankton surveys
conducted in 1979. They did not occur on the first survey which was made on
3 February to 14 March. Judging from collection dates, ages of eggs at
collection and incubation rates, I found that eggs were first spawned on the
southern edge of Georges Bank as early as 30 March, and in inshore as well as
offshore southern New England waters as early as 14 April (Fig. 1). Spawning
rapidly increased during lay and June in area and intensity, spreading
throughout Georges Bank, southern New England and Middle Atlantic waters.
Eggs were most concentrated offshore in May, then in mid-shelf waters during
dune and July (Fig. 1). The peak in spawning intensity occurred during the
first half of July (Fig. 3). Unfortunately our survey at that time failed to
sample most of the Gulf of Maine (Fig. 1) where silver hake spawn during the
summer (Bigelow and Schroeder 1953). Spawning remained widespread throughout
August although at a lesser intensity than during the previous survey
(Fig. 2). By the time of the October survey spawning had virtually ceased in
the Gulf of Maine, was significantly reduced in area and intensity in Middle
Atlantic and Georges Bank waters and had decreased in intensity off southern
New England (Fig. 2). By November and December, spawning was so reduced as to
be almost terminated, although eggs were scattered in offshore waters of
southern New England and Georges Bank in the first two weeks of Gecember.
Whether or not spawning continued at this time offshore in the Middle Atlantic
waters was not determined.


aw


FREQUENCY

34

20 lo
| a q suRveY 1
i0 9 Nys34

i)
0 100 200
10
5 SURVEY 2
Ny=25
» ° 3 45 6?
30
: 15
20 10
5 SURVEY 3
W262
0 0 1
x T0123 45 67
otilnflet om om 5 fl 9
0 100 200 300 400
20 10
L 5 SURVEY 4
10 Ny=29
TT. ss 6D
wlll ne op 9 a
0 190 200 300 490
30
1] 15
20 10
5 SURVEY 5
y=84
10 0 OM
10 123 4 5 6 7
LOG, 1X), X #0
0 Odlmoa 1 pn a 5
0 100 200 300 400 500 600 700 800 900 1000 = 1100

X= NO, EGGS SPAWNED/1Om2/DAY, X # 0

Figure 6. Frequency distributions of non-transformed and loge-transformed
values of eggs spawned/10m2/day.


13

Atlantic Mackerel and Spawning Population Estimates

JUNE 21-JUNE 30
94 STATIONS

EGGS SPAWNED/M7/DAY

CJ none i

Do1-10

11-100

BB 100-1000 36"

JULY 30- AUGUST 30
158 STATIONS
EGGS SPAWNED/M’/DAY
CG) none
Oort0
EB11-100

ag

38"

36

Distribution of Atlantic mackerel eggs during the sixth and seventh ichthyoplankton surveys, 1977.



P. L. Berrien, N. A. Naplin, and M, R. Pennington

6s Q
\- Ke)
wee STRATUM E a
N te ‘STRATUM 6
oo
SS 4 ‘STRATUM 5 66"
. st
a ( x
N S
‘STRATUM 4
a ao
sw
a2"
TRAN
y
3a}
70° |
rR 2
“a
\
we
a ny
sreaTun 1
- he
ban .
Figure 1, Total area and stratum boundaries for seven ichthyo-

plankton surveys, 1977.

used for the plankton survey; that is the offshore boun-
dary was the 200-fm (365-m) contour, the inshore
boundary south and west of Nantucket was the shore-
line, and north and east of Nantucket it followed the
division between the inshore trawl survey strata (not
sampled) and the offshore strata. The total area
defined was about 251 000 km’.

Seven distinct ichthyoplankton surveys covered all,
or part of, the total area. Of these, six are shown on
distribution charts (Fig. 3-5); the first survey (cruises
GO-77-1 and DE-77-3), made from 5 March to 8
April, apparently before mackerel were spawning did
not reveal any eggs. Table | summarizes the sampling
dates and areas surveyed. Strata referred to in the
tables and figures were made necessary by the varying
effort, i.e., the number of cruises, within the eight
strata shown. This varying effort resulted from vessel
scheduling and, in some cases, from restrictions on
European vessel operations in U. S. and Canadian
waters, Plankton was sampled with 61-cm bongo
frames fitted with 0.505-and 0.333-mesh nets. The
0.505-mm mesh net was used for ichthyoplankton
analysis. A flowmeter was suspended within the
mouth of each sampler for volume-filtered determina-
tion, and a bathykymograph was attached next to the
sampler to monitor the tow profile and maximum
depth attained. A 45-kg ball suspended beneath the
bongo depressed the sampler during the tow.

A double-oblique plankton haul was made at each
station according to standard MARMAP I proce-
dures (Jossi et al., 1975). The vessel speed was adjusted
to maintain a 45° wire angle throughout the haul, and
sufficient wire was payed out to sample toa maximum
depth of 200 m, or to within 5 m of the bottom at
depths less than 205 m. Plankion samples were pre-
served ina 5% formalin and seawater solution. Surface
temperatures were measured with a stem thermom-
eter.

All fish eggs and larvae were removed from the
samples; eggs of selected species (including mackerel)
were identified and sub-divided according to develop-
mental stage. Three stages were used: fertilization to
blastopore closure, blastopore closure to tail free, and
tail free to hatching. Eggs were staged so that we could
use early stage eggs only (to minimize any mortality-
induced bias) for the total egg production calculations,
and to determine the mortality rate experienced by
mackerel eggs in 1977. The mortality rate was caleu-
lated by regressing the log. (total season's abundance
of each of the three stages) on the weighted mean age
of these stages; since, if the mortality rate is fairly
constant, the population will decline exponentially.
The resulting mortality rate (Z = 0.8840) was then used *

*Please note; the correct value for Z is 0.1233.


vii

LIST UF FIGURES

scombrus, EG PRODUCTION AND SPAWNING POPULATION

LF UF MAINE, GEURGES BANK, AND MIVULE ATLANTIC

ATLANTIC MACLEREL, Scor
ESTIMATES FurR 1977 IN
BIGHT

Figure 1. Total area and stratum boundaries for seven ichthyoplankton
surveys, 1977.

Figure 2. Frequency distributions gt non-transformed and loy,-transfornied
values of eyys spawned/m*/day.

Figure 3. Distribution of Atlantic mackerel eyys duriny the second and third
ichthyoplankton surveys, 1977.

Figure 4. Distribution of Atlantic mackerel eyys duriny the fourth and fifth
ichthyoplankton surveys, 1977.

Figure 5. Distribution of Atlantic mackerel eyys during the sixth and seventh
ichthyoplankton surveys, 1977,

Figure 6. Estimated daily eyy production in four strata and in the total
survey area; strata 1 and 6 are not shown, their contributions are
insignificant.

YELLOWTAIL FLOUNDER, Limanda ferruyinea, ESTIMATES OF EGG ABUNDANCE
AND POPULATION SIZE DURING SPRING 1977 IN GULF UF MAINE, GEORGES BANK,
SOUTHERN NEW ENGLAND ANU MIDDLE ATLANTIC BIGHT WATERS

Figure 1. Left; total survey area and subarea boundaries for seven
icnthyoplankton surveys, 1977. Riyht; distribution of yellowtial
flounder egys duriny the first survey, 1977,

Figure 2. Distribution of yellowtail flounder eyys duriny the second and
third ichthyoplankton surveys, 1977.

Figure 3. Distribtion of yellowtail flounder eyys during the fourth and fifth
ichthyoplankton surveys, 1977,

Figure 4. Distribution of yellowtail flounder egys duriny the sixth and
seventh ichthyoplankton surveys, 19/7.

Figure 5. Reyression of staye-abundance on the weiyhted mean aye; used to
calculate season-long mortality rate for Limanda ferruginea eggs,
1977; y is eyy abundance at age (x = no. of days), r is the
regression coefficient.

Fiyure 6. Freyuency distribution of gon-transforiied and loy,-transformed
values of egys spawned/1Um“/day,


104

0 0 0 0 0 0 0 0 € 26 Bay 6 2 (vt26)
0 0 0 0 0 0 0 0 L 26 few 6 T a
z:0 v2. z “lo S09 o ¢ 59 Bye oc
to > vt b ue 2 et L.> 6 7 uy 2 (6626)
oO 0 0: 0 : 0 an) oS 4 eH 21 if
$°0 oF ee sty 6S an 00 00 z a ‘et une pr 2 (e862)
Vo ; $0 90 2 * 0) 0 o- 6 BE Aen 9 1 9
‘ ae ‘ O° 0: - 0: Of Sor adyor€
oz. V9 E92 0 ' 9, 0) oat 99 ady (22 (ceTer)
0:0 10 V0 ot : t) ¢ 0 0 er. 292 ady T T
£0 oo) go 6 070 | 0°0 oo 1 $s 9 Bny 8 v
8°62 gz 20 . OS 2°96 6°6 “ez: i (18 0s une» £ (v6cve)
£'9 68 Let yz 00: 00 oo ot 65 8€ Aen OE Zz ’
ze ve 99° «ST oO. 0 ) 0 oz 0b aH IZ OT
0 0 0 £0 | £°0 vo - 2 6 ly bny stk
v0 ve ve oo. : ey 25 95 2 8 ty unp 629
82 rs ttae ele Tee = 6069 8 4 Aen 92S (ieten)
62 . oes = Orezd S ut v2 es © L a AW IT ob t
£0 6 Sl oe 0 0 0 0 8 £1 ady 22 €
ut B62 eS 9 0 0 0 0 8 £2 ady gt 2
00 z0 06 f'0 OE 0 0 0 0 gt ov eH L 1
0 0 0 ) 0 ) 8S 1S Bny SI L
0 0 o 0 62 90 or o£ 69 2b a)
rd a"9 “9 2 9769 Ul2 Bey se 69 rd Ae e2  §
ot sb Ur 92 9°98 e222 O'th e989 el eH 6 ’ (88229)
eT SL C6l 82 9°25 1 ae) aed ot ady oz, € 2
oT s"9 eT ez ae vl fe . bb 89 vt ady 6 Z
or ae eg st 0 0 0 0) we 62 oT
0 0 0 0 0 0 0 0 ut 0s 6ny IT S
0 0 0 0 0 0 0 0 au. 6p une 22}
0 0 0 0 0 0 0 0 vat “SE Aen S € (ogs9t)
0 0 0 0 On) 0'0 oo O€ au. 12 sdy ot Z I
‘0 0 0 60 0 0 ) 0 st 22 4H OT
5 a . 3 . 27°90
(21-01x) Aarang Aq yo 404g 0 aw (21-01%) farang fq 0 sous 0 w u— payuasarday quyodpyy —aspnuy — (24 PV)
easeqns uy paumeds s663 psaepuezs Raueqns uy paumeds s663 | puepueqs sheg Buypdwes = Aaaans Raueqns

UIONNOTS TVLMOTTSA

VANFAIWA ITN LY

“£L6T 40g $9} RWYISZ UO}JONPOrg 653 sapuno,y {}eyMOL {aA PUe [a4ayxIeH IFIUBLIY “T AL9eL


+ SOUTHERN \. J
NEW ENGLAND

kitometers: 38
—
° 60

0

36"

2

36 74

Figure 1. Station locations and analytical
subareas of standard MARMAP
surveys.


18

various temperatures, we can calculate the population size of adults. This
approach was utilized for Atlantic mackerel, Scomber scombrus, on the same
data base used here (Berrien et al. , in press).

The egg survey approach to population assessments is used to augment
the conventional assessment techniques (by research trawl survey or by analysis
of commercial fishery data) and thereby add support to these conventional and
more timely methods. Although plankton sampling gear operates in a relatively
predictable fashion, patchiness of eggs adds to the variance estimates around
abundance values; but this is a factor to be reckoned with in virtually all
biological sampling.

Additional discussion of the theory and techniques for egg survey work
can be found in papers by Saville (1964), and Smith and Richardson (1977)
Previous population estimates based directly on plankton survey data have been
made on pilchard, Sardina pilchardus (Cushing 1957), Pacific sardine, Sardinops
caerulea (Murphy 1966), (ewe anchovy, Engraulis mordax (Ahlstrom 1968), round
herring, Etrumeus teres (Houde 1977a), thread herring, Opisthonema oglinum
(Houde 1977b), and Atlantic mackerel, Scomber scombrus (Sette 1943, Lockwood et al,
1981, and Berrien et al. , in press).

PROCEDURES

The total ichthyoplankton survey area included the Gulf of Maine, part of
the Nova Scotian continental shelf, Georges Bank, and continental shelf waters
southward to Cape Hatteras, North Carolina (Figure 1). Because sampling locations
were based on the sampling design of the spring 1977 NMFS trawl survey, the
extreme offshore and inshore boundaries for that effort were used for the plankton
survey. That is, the offshore boundary was the 200-fm (365-m) contour; the
inshore boundary south and westward of Nantucket was the shoreline; and north
and eastward of Nantucket it followed the division between the inshore traw]
survey strata (not sampled) and the offshore strata. The total area defined is
about 251,000 km@. Seven ichthyoplankton surveys from March to August covered
all or part of the total area. These are portrayed on distribution charts
(Figures 1 to 4).

Table 1 summarizes the sampling dates and areas surveyed. Subareas referred
to in tables and figures were made necessary by the varying effort (i.e., the
number of cruises) within the eight subareas shown. This varying effort resulted
from vessel scheduling and operations and, in some cases, from restrictions on
European vessel operations in U. S. and Canadian waters

Plankton was sampled with 61-cm bongos fitted with 0.505- and 0.333-mm
mesh nets. The 0.505-mm mesh net was used for ichthyoplankton analysis. A
flow meter was suspended within the mouth of each sampler for volume-filtered
determination, and a bathykymograph was attached next to the sampler to monitor
the tow profile and maximum depth attained. A 45-kg ball suspended beneath
the bongo depressed the sampler during the tow.

A double-oblique plankton haul was made at each station according to
standard MARMAP I procedures (Jossi et al. 1975). i.e., the vessel speed was
adjusted so as to maintain a 45° wire angle throughout the haul, and sufficient


HUUUE, E. D.
1977c, Abundance and potential yield of the scaled sardine, Harengula
jayuana, and aspects of its early life history in the eastern Gulf of
Mexico. Fish. Bull., 75(3): 613-628.

HOUGHTON, R. G. and D. HARDING.
1976. The plaice of the Enylish Channel: spawning and migration. J. du
Cons. int. Explor. Mer, 36: 229-239.

IVERSEN, S. A.
1977. Spawning, egg production and stock size of mackerel (Scomber
scombrus L.) in the North Sea 1968-1975, ICES, C.M. 1977/H:17. 18 p.
(mimeo).

IVERSEN, S. A. and A. ELTINK.

1983. Spawning, eyg production and stock size of North Sea mackerel in
1982. ICES, C.M. 1983/H:46. 12 p. (mimeo).

LOCKWOOD, S. J., J. H. NICHOLS and W. A. DAWSON.
1981. The estimation of a mackerel (Scomber scombrus L.) spawning stock
size by plankton survey. J. Plank. Res., 3(2): 217-233,

MACER, C. T.
1974, The reproductive bioloyy of the horse mackerel Trachurus trachurus
(L.) in the North Sea and English Channel. J. Fish. Biol., 6: 415-438,

PARKER, K.

lygu. A direct method for estimating northern anchovy, Engraulis mordax
spawning biomass. Fish. Bull., 78(2): 541-544, , °

PARRISH, B. B. and A. SAVILLE.
1962, The estimation of fishing mortality rate for bank spawners, from
larval abundance data. ICES, C.M. 1960, Doc. No. 40. (mimeo).

PICQUELLE, S. J. and R. P. HEWITT.
1983, The northern anchovy spawning biomass for the 1982-83 California
fishing season. CalCOFI Rep., Vol. 24: 16-28,

SAVILLE, A.
1964, Estimation of the abundance of a fish stock from egy and larval
surveys. Rapp. P.-v. Reun. Cons. int. Explor. Mer, 155: 164-170.

SETTE, U. E.
1943. Bioloyy of the Atlantic mackerel (Scomber scombrus) of North
America. Part I: Early life history, including growth, drift, and

mortality of the eyg and larval populations. U.S. Fish Wildl. Serv.,
Fish. Bull., 50(38): 149-237.


23

REFERENCES CITED

Ahlstrom, E. H. 1968. An evaluation of the fishery resources available to
the California fishermen. In D. Gilbert (ed.), The future of the fishing
industry of the United States, pp. 65-80. Univ. Wash. Publ. Fish.,

New Series 4.

Aitchison, J. 1955. On the distribution of a positive random variable
having a discrete probability mass at the origin. J. Amer. Statis. Assoc.,
50: 272, 901.

Aitchison, J. and-J. A. C. Brown. 1957. The Lognormal Distribution. Cambridge
Univ. Press, London.

Berrien, P. L., N. A. Naplin, and M. R. Pennington. (In press). Atlantic
mackerel, Scomber scombrus, -egg production and spawning population estimates
for 1977 in the Gulf of Maine, Georges Bank, and Middle Atlantic Bight.

In R. Lasker and K. Sherman (eds.), The early life history of fish, II.
Rapp. P.-v. Reun. Cons. int. Explor. Mer., Vol. 178.

Bigelow, H. B. and W. C. Schroeder. 1953. Fishes of the Gulf of Maine.
Fish. Bull. Fish Wild]. Serv., 53(74): 577 p.

Bigelow, H. B. and W. W. Welsh. 1925. Fishes of the Gulf of Maine. Bull.
U. S. Bur. Fish., 40: 567 p.

Brown, B. E. and R. C. Hennemuth. 1971. Assessment of the yellowtail flounder
fishery in subarea 5. ICNAF Res. Doc. 71/14: 51 p.

Clark, S. H., L. O'Brien, and R. K. Mayo. 1981. Yellowtail flounder stock
status - 1981. NMFS, Woods Hole Lab., Ref. Doc. No. 81-10.

Cushing, D. H. 1957. The number of pilchards in the Channel. Fish. Invest.,
London, Ser. 2, 21(5): 27 p.

Houde, E. D. 1977a. Abundance and potential yield of the round herring,
Etrumeus teres, and aspects of its early life history in the eastern
Gulf of Mexico. Fish. Bull., U. S. 75(1): 61-89.

Houde, E. D. 1977b. Abundance and potential yield of the thread herring,

Opisthonema oglinum, and aspects of its early life history in the eastern
Gulf of Mexico. Fish. Bull., U. S. 75(3): 493-512.

Howell, W. H. and D. H. Kesler. 1977. Fecundity of the southern New England
stock of yellowtail flounder, Limanda ferruginea. Fish. Bull., U. S.
75(4): 877-880. —,

Jossi, J. W., R. R. Marak, and H. Petersen, Jr. 1975. MARMAP Survey I manual.
At-sea data collection and laboratory procedures. MARMAP Program Office,
NMFS, NOAA, Wash., D. C.


92

METHODS
The Data

Data analyzed in this paper were collected during MARMAP (Marine
Resources Monitoring, Assessment and Prediction) ichthyoplankton surveys
in 1977 (mackerel and yellowtail) and 1979 (silver hake). The MARMAP
surveys cover much (258,000 km?) of the continental shelf off the north-
east coast of North America from-Cape Hatteras, North Carolina to Nova
Scotia. Subareas for 1977 (Figure 1) were based on the frequency of
survey cruises in each subarea. The unequal effort in each subarea re-
sulted from vessel scheduling problems and, in some cases, from.restric-
tions on European vessel operations in U.S. and Canadian waters (Berrien
et al., 1981). Different subareas were used for 1979 data (Figure 1).
They were based on oceanographic and biological. considerations, and were. °
selected so as to allow direct comparison with population-estimates from:
cohort analysis.

Ichthyoplankton was sampled with 61-cm bongos fitted with 0.505-mm
mesh nets. Smooth, double-oblique plankton hauls were made-at. each station
according to standard MARMAP I procedures (Jossi et al., 1975)...Sampling
extended from the surface to within 5 m of the bottom or to a maximum depth
of 200 m and was conducted at a vessel speed:of approximately 1.5 kts..~

Fish eggs were removed from the samples, identified and separated into
developmental stages. Numbers of eggs collected were adjusted to no./day/me
of sea surface area. Mortality rates were calculated on the observed. decline
in numbers with stage mean age. Numbers sampled/m¢/day ‘at ‘each station were

then adjusted for mortality to calculate numbers of eggs spawned/me/day*and


85

Table 6.--Spawning stock biomass estimates and stratified mean
catch-per-tow of the Georges Bank haddock stock.

Stratified

Spawning Stock Biomass (t) catch/tow
Year Larvae VPA (kg)
1977 48,699 60,596 - 23.13
1978 61,931 90,896 15.18
1979 127,533 78,826 26.87
1980 94,025 87,465 18.47
1981 * 65,534 40,701 11,77

1982 3,591 39,642 4.17



SMITH, P. E.
1972, The increase in spawning biomass of northern anchovy, Engraulis
mordax. Fish. Bull., 7U(3): 849-874.

STAUFFER, G. D.
1980. Estimate of the spawning biomass of the northern anchovy central
subpopulation for the 1979-8U fishing season. CalCOFI Rep., Vol. 21:
17-22.

WALSH, M., P. HOPKINS and P. RANKINE.
1983. Results of the North Sea mackerel eyy surveys in 1982. ICES, C.M.
1983/H:49. 24 p. (mimeo).


91

INTRODUCTION

Large scale plankton surveys have been conducted off the northeast
coast of the United States since the autumn of 1976 as part of a long-term
monitoring program (MARMAP) of the National Marine Fisheries Service.
Generally, six data gathering cruises per year, at various seasons, cover
the Gulf of Maine, Georges Bank, Southern New England, and Middle Atlantic
Bight waters out to the edge of the continental shelf. One objective of
these surveys is to produce an estimate of the total seasonal production
of eggs spawned by certain fish species. From egg abundance values,
estimates can be made of spawning stock size if other biological infor-
mation such as the sex ratios, fecundity, percent mature, and length fre-
quencies are available. Egg surveys often produce estimates of spawning
stock size which are consistent with estimates derived from other data
(see e.g., Saville, 1954; Simpson, 1959; Berrien et al., 1981; Lockwood

et al., 1981; Berrien, 1981; Berrien, 1983).

The estimated precision of egg surveys, and hence of the derived
spawning stock size estimates, is usually based only on the variability
of egg densities over space while the variability due to production
changing over time is ignored (Saville, 1964; Lockwood et al., 1981).
In this paper a technique is described which measures the effect of
varying production over time and space on the precision of estimates of
total seasonal egg production. The method is applied to survey results
for three species, Atlantic mackerel (Scomber scombus), silver hake
(Merluccius bilinearis) and yellowtail flounder (Limanda ferruginea) to

ascertain the approximate precision of the estimates of total egg pro-

duction.


96

Var(T ) = E[var(T. ; | ty, toses.stp)]
tp toreeesty tyetgreety 2 Leekrs

ot

L

VartE(Ty t

proverty | ty» tyse+-oty)I. (3)

The first term on the right hand side of equation (3) is the average
variance due to spatial differences in abundance, and the last term is
the variance of the expected abundance for a particular sequence taken

over all possible sequences of monthly surveys. Now if T., T. T

Poo2r ctr ek
are estimates of total egg production based on % systematic monthly

surveys taken with random starts then

i=l (4)

var(T) = 5 (Tt, -Tyelet)

is an unbiased estimate of its variance, and 2-var(T) is an unbiased
estimate of the variance of a single systematic survey conducted at

monthly intervals, i.e., of the left hand side of equation (3).




59

and mackerel stocks had reached extremely low levels which suggests replace-
ment (see Daan 1980) rather than competition as predator-prey or as predators
of a common food source. It remains to be seen if this shift in species
composition is a long-term trend or if, under the present management strategies
for mackerel and herring, a return to the pre-1960 species composition and
biomass levels will occur.

LITERATURE CITED

Aitchison, J. 1955. On the distribution of a positive random variable
having a discrete probability mass at the origin. J. Am. Stat.
Assoc. 50: 901-908.

Cameron, J. 1958. Studies on the Ammodytidae of Isle of Man Waters.
Ph.D Thesis, Univ. of Liverpool.

Clark, S. H. and B. E. Brown. 1977. Changes in biomass of finfishes and
squids from the Gulf of Maine to Cape Hatteras, 1963-1974, as deter-
mined from research vessel survey data. Fish. Bull., U. S. 75: 1-21.

Daan, N. 1980. A review of replacement of depleted stocks of other
species and the mechanisms underlying such replacement. Rapp.
P.-v. Reun. Cons. int. Explor. Mer, 177: 405-421.

Jossi, J. W., R. R. Marak and H. Petersen, Jr. 1975. MARMAP I survey
manual. At-sea data collection and laboratory procedures. MARMAP
Program Office, NMFS, NOAA, Wash., D. C

Livingstone, R., Jr. 1962. Underwater television of haddock (Melanogrammus
aeglefinus [Linnaeus]) in the cod-end. J. Cons. 27: 43-48.

Macer, C. T. 1965. The distribution of larval sandeels (Ammodytidae) in
the southern North Sea. J. Mar. Biol. Assoc. U. K. 45: 187-207.

Meyer, T. L., R. A. Cooper and R. W. Langton. 1979. Observations on the
relative abundance, behavior, and (384 habits of the American sand
lance, Ammodytes americanus DeKay (1842) from the Gulf of Maine.
Fish. Bull., U. S. 77: 243-253.

Norcross, J., W. H. Massmann and E. B. Joseph. 1961. Investigations of
inner continental shelf waters off lower Chesapeake Bay. Pt. 2.
Sand lance larvae, Ammodytes americanus. Ches. Sci. 2: 49-59.

Pennington, M. 1982. Efficient estimators of abundance for fish and
plankton surveys. Biometrics (in press).

Saville, A. and D. Schnack. 1981. Some thoughts on the current status
of studies of fish egg and larval distribution and abundance. Rapp.
P.-v. Reun. Cons. int. Explor. Mer, 178: 153-157.

Scott, J. S. 1968. Morphometric, distribution, growth and maturity of
offshore sand lance (A. dubius) on the Nova Scotia banks. J. Fish.
Res. Bd. Canada 25: 1775-1785.


65

7000-4 1978

Y= 16 1898.63Exp(-0.363x)
170.963

4000:

FREQUENCY

1980

S049 100109 sSo-189 m0-m9 wows moms

LENGTH INTERVAL immi Y= 15996.96Exp(-0.229X)

r=0.897

2004
3
3 0}
8000, 2
1979
4004
= r Y=2790.55Exp(0.243X)

40004 5) £30,977

S089 1do709 “So-189 mo0-29 wows moms
LENGTH INTERVAL, (mm!

FREQUENCY

S049 taco Moise wome sous moms
UENGTH INCTERrWRL, ewe

Figure 3. Length frequencies and fitted regressions fer sand lance,
Ammodytes sp., 1978-1980.


10

P. L. Berrien, N. A. Naplin, and M. R. Pennington

&

sf ooh
0 al i)
we Vedig Py ese
o Meh gx ue
‘on we
ra
x
5 . 7 1.
: est tas ween
wy ara pee
4
Als
ee a

eRCOeEKCY

a—onll para vest 2)

nee

Figure 2. Frequency distributions of non-transformed and log. ~
transformed values of eggs spawned /m’ /day.

calculated by a program written for this purpose. The
variance of k is estimated by:

vavonr=[ (8 : x) * “| :

\
gh n 2 sf
[ae + -(s + s)]

This formula, though approximate, takes into account
the fact that k is a function not only of ¥ but also of s°
and m. Confidence intervals can be generated by

assuming k (ora weighted sum of the k’s when estimat-
ing total) is approximately normally distributed with
standard error equal to y- (var k). It should be noted
that, when the proportion of zeros is zero, the A-
distribution is log-normal and the above estimators
may still be used,

The re-transformed mean density (k) was raised to
the number of eggs spawned in each stratum per day,
then multiplied by the number of days represented by
each survey in each stratum. The stratum estimates
were summed over time, resulting in the total number
of mackerel eggs spawned in 1977 in the area surveyed.

The number of days represented bya survey withina
stratum was determined by first calculating the mid-
point in time of sampling within each stratum, each
time it was surveyed. Then, for each midpoint, half the
days between the preceding midpoint and half between
the following midpoint were summed to produce the
number of days represented by that particular survey
in that stratum.

The estimate of total egg production for the season
was used to estimate the population size of mature
mackerel. A theoretical number of eggs spawned by
the mature females in the commercial fishery catch
was calculated. This theoretical egg production was
divided into the total season’s estimate of egg produc-
tion to derive a factor by which the commercial catch
could be multiplied to give an estimate of the total
spawning population.

RESULTS

Figures 3-5 show the densities of eggs spawned per
day during the 2nd through 7th surveys. No mackerel
eggs were taken during the first survey (5 March-8
April) given in Table |. Generally, the greatest concen-
trations of spawning occurred in near-shore waters in
strata 7 and 4 and in the inner half of continental shelf
waters in strata 2 and 3. Throughout the spawning
season, the greatest spawning intensity shifted toward
the north and east, occurring off New Jersey in late
April, off New Jersey and Long Island in early May,
and from Long Island to Nantucket in late May and
early June (Fig. 3 and 4).

Table 2 summarizes the results from calculations
used in deriving egg production estimates for individ-
ual strata as well as for the entire survey area and
season. The low rate of spawning (3.3 eggs/m’/day)
indicated by the second survey (mid-April) for most of
the Middle Atlantic Bight increased rapidly (to 76.3
eggs/m’/day) by the time of the third survey (late
April). The spawning rate decreased to slightly over
half that value and remained so throughout May, then
decreased during June to a very low level (0.36
eggs/m’/day).

In the more northeastern strata (nos. 3, 4, and 7) the
peak in spawning intensity occurred slightly later in


93

these adjusted values were used to derive the estimates of total egg
production for the entire season. For a more detailed account of
sampling and analysis procedures, see Berrien et al. (1981) and

Berrien (1981, 1983).

Statistical Methods

Data from a cruise was used to estimate the mean number of eggs
spawned/m/day at the time of each cruise. Only part of each survey
area contained the eggs of any particular species, and hence the pro-
portion of nonzeros in the sample estimates the fraction of the area in
which eggs occurred. It has been observed (Berrien et al., 1981; Berrien,
1981; Lockwood et al., 1981) that the distribution of the nonzero values
is often lognormal for egg data. A distribution with a proportion of
zeros such that the nonzero values are lognormally distributed is called
a h-distribution (Aitchison and Brown, 1957). The estimator (c) of the
arithmetic mean (Aitchison and Brown, 1957) and its variance [var(c)]

(Pennington, 1983) for the a-distribution are:
® exp(y)G_(s°/2), m1,
n 'm

c= xX, m1, (1)
7

0 m=0,


15

Atlantic Mackerel and Spawning Population Estimates

and Nantucket, Vineyard, Block Island, and Long
Island Sounds. Strata | and 6 are not shown in Figure

4 Bi nen
7 SY a\

sre

icy Ee WG) wT ab a ane ee

DATE ESERY FIFTH Dy GF FACIE MONDE INDIE SHED

Figure 6, Estimated daily egg production in four strata and in the
total Survey Area; Strata | and 6 are not shown, their contribu-
tions are insignificant.

6 as they would be represented by horizontal lines
extremely close to the zero-eggs/day line from 23
March to 5 May and 6 May to 2 July, respectively. The
inclusion of these insignificant abundances would
clutter the graph, obscuring the overall pattern.
Table 3 summarizes calculations used in estimating
the spawning population size. The total commercial
catch of mackerel by size and an assumed | : | sex ratio
was used to calculate the number of females in the
catch. The length frequencies of the mature mackerel
in the commercial catch were assumed to be propor-
tional to those of the spawning population. Using
percent-mature-at-length (Morse, pers. comm.) and
fecundity-at-length data (Morse, 1978), we calculated
the theoretical numbers of eggs spawned by the
females in the commercial catch (25.0608 x 10'* eggs).

Table 3. Calculations for Atlantic mackerel spawning population estimate.

Theoretical

Fork Total catch" Females? Percent Mature females egg production Mature females
length of fish in catch females in catch by catch in population
(cm) (No. x 10°) (No. x10") mature (No. x 10°) Fecundity” (No. x 10") (No. x 10°)

14 16 8.0

15 8 4.0

16 8 4.0

7 2 135

18 100 50.0

19 194 97.0

20 231 115.5

21 157 BS

2 124 62.0

23 237 118.5

24 890 445.0

25 2320 1 160.0

26 4 660 2330.0

27 4961 2 480.5

28 4860 2430.0

29 6 696 3348.0 16 53.6 202 085 0.0108 0.6485

30 16 758 8 379.0 13.4 1122.8 243 871 0.2738, 13.5843

3 27279 13 639.5 45.2 6 165.1 292 489 1.8032 74.5889

32 26 749 13.374. 80.0 10 699.6 348 780 3.7318 129.4499

33 21221 10 610.5 96.2 10 207.3 413 658 4.2223 123.4938

34 15 803, 7901.5 99.6 7 869.9 488 112 3.8414 95.2146

35 8351 4175.5 100.0 4175.5 573 209 2.3934 50.5176

36 6 161 3080.5 100.0 3080.5 670 102 2.0642 37,2697

cy 5 769 2 884.5 100.0 2 884.5 780 028 2.2500 34,8983

38 3.997 1998.5 100.0 1998.5 904 316 1.8073 24.1790

39 2 742 1371.0 100.0 1371.0 1 044 389 1.4319 16.5871

40 1517 758.5 100.0 758.5 1201 768 0.9115 9.1768

4l 383 191.5 100.0 191.5 1378 078 0.2639 2.3169

42 70 35.0 100.0 35.0 1575 049 0.0551 0.4235
Sum 162 289 50 613.3 25.0608 612.3489

“First quarter 1977 catch in ICNAF Subareas 5 and 6, submitted to ICNAF, E. Anderson, pers. comm.

"Calculated from total catch assuming a I:1 sex ratio.

“Based on 1978 NMFS, NEFC spring trawl survey data; W, Morse, pers. comm.

“From Morse (1978).


44

Jossi, J. Wo, 2. R. Marak and H. Petersen, Jr. 1975. MARMAP Survey I
manual. At-sea data collection and laboratory procedures. MARMAP Prograa
Office, NMFS, NOAA, Wash., DC.

Konstantinov, K. G. and A. S. Noskov. 1969. USSR research report, 1968.
ICNAF Redbook (part II): 99-117. .

Mari, A. and I. Ramos. 1979. Fecundity of silver hake on the Scotian
Shelf. ICNAF Res. Doc. 79/VI/86: & p. -

Nichols, J. T. and C. M. Breder, Jr. 1927. The marine fishes of New York and
southern New England. Zoologica, N.Y. Zool. Soc. 9(1): 192 p.

Nichy, F. E. 1969. Growth patterns on otoliths from voung silver hake,
Merluccius bilinearis (Mitch.). Int. Conm. Northwest Atl. Fish., Res.
Bull. 6: 107-117.

Pennington, M. 1983. Efficient estimates of abundance for fish and plankton
surveys. Bionetrica (in oress).

Sauskan, V. I. and V. P. Serebryaxov. 1968. Reproduction and developnent of
the silver hake (Merluccius bilinearis Mitchil]). Voor. Ikhtiol. 59:
500-521.

Saville, A. 1964. Estimation of the abundance of a fish stock fron ega and
larval surveys. Rapp. P.-v. Reun. Cons. int. Explor. Mer, 153: 164-179.

Sherman, K. 1980. MARMAP, a fisheries ecosysten study in the NW Atlantic:
Fluctuations in ichthyoplankton-zooplankton components and their potential
for impact on the systen. pp. 9-37. in F. P. Diener, F. J. Vernberg and
D. Z. Mirkes (eds.). Advanced concepts in ocean measurenents for marine
biology. Relle W. Baruch Inst. Mar. Biol. Coast. Res., Univ. So. Car.
Press.

Silverman, M. J. 1982. The distribution and abundance of silver hake,
Merluccius bilinearis, larvae off northeastern United States, 1977-80.
CM. 108276258.

Zweifel, J. 2. and R. L. Lasker. 1976. Prehatch and posthatch growth of
fishes - a general model. Fish. Bull., U. S. 74(3): 609-621.

MARMAP Contribution No. MED/NEFC 83-18


83

Measuring the Precision of Estimates of Total Egg Production

Based on Plankton Surveys *

by

Michael Pennington! and Peter Berrien?

IWational Marine Fisheries Service, NOAA
Northeast Fisheries Center
Woods Hole Laboratory
Woods Hole, Massachusetts 02543

2National Marine Fisheries Service, NOAA

Sandy Hook Laboratory
Highlands, New Jersey 07732

[(*MARMAP Contr. MED/NEFC, 83-39) }

Keywords: Plankton surveys; Egg production estimates

a

| Preceding page blank |


27

Table 3. Calculations for yellowtail flounder population estimate,

Theoretical Nature® Females? Fisn®
Total Reference? Percent Percent Mature Egg Production Females in in In
Length Catch of += Females «Females Females Females ‘ by Caten Population Population Population
(cm) Fish in Catch in Catch «Mature in Catch Fecundity’ {x 10-8) (10-3) (x 10-3) (10-3)
5 0 50.0
6 44000 50.0 22000 835.3 1670.5
7 voo090 50.0 50000 1888.3 3796.7
8 242000 50:0 124000 47079 9415.7
9 220000 50.0 119000 4176.3 8352.7
10 253000 50.0 126500 4802.8 9605.5
n $9000 50.0 29500 1120.9 2240.0
12 12000 50.0 6000, 227.8 455.5
13 50.0
14 17000 50.0 8500 327 645.4
15 20000 50.0 10000 373.7 759.3
16 0000 50.0 5000 139°8 97
7 50.0
ia 170¢0 50.0 8500 322.7 645.4
19 20000 50.0 0000 379.7 759.3
20 31900 50.0 15500, 588.5 10779
a 34000 50.0 47000 1786 2568.9
22 96000, 50.0 48000 14 ssa 148871 99 28.2 1822. 3544.8
3 68000 50.0 3acog 66 2251176722 398 855 1290.9 2581-7
a 68000, 50.0 3acoo, 11.8 4021208257 240 153.1 1290.0 2501.7
2 10000 52.4 79832 ni 13428243780 2273 5039.7 2381.6 5695.0
26 427000 ang goes = 22.3 13587283604 3953 518.9 2310.1 4821.3
2 205000, 46.5 95330 27.6 26280 © 328055 3621 997.7 3619-6 7783.2
2B 153000 44.6 6317) 32.8 22363377468 aa) 449.0, 2588.2 5203:9
29 1130¢0 ane sozis (38.0 igi0g 432192 8257 728.3 1906.7 9290.2
30 133000 49.2 s3879 83.3 231s 432582 viaot 878.7 2030.4 5049.6
n 136000 a6 56641 48.5 27480 5$9008 15361 1083.3 2150.5 5163.5
22 341000 42.6 144679 53.8 77768 631849 49138 2982.6 5493.0 12846.6
33 354000 40.5 157466 = 59.0 2988 111494 56089 3526.6 5978.5 13840.2
34 337000 45.8 V774zq 64.2 113952798345 30973 $326.4 8736.2 4693.1
35 399000 46.7 186421 69.5 129493892810 115613, 4916.4 7077.8 1$148.7
6 320009 48.6 198533 74,7 116133995313, 115638 aan) 5905.1 12183.3,
37 322000 52.6 169263 79.9 1353031106285 149684 $137.0 6426.3 12225.2
38 130000 55.4 105262 85.2 e964? 1226168 vogezz 3403.5 3996.1 7213.7
39 172000 59.5 vozso2 = 90.4 g2sez 1355414 125485 3515.9 3887.9 6530.3
40 38000 63.3 62018 95.8 59319 1494487, 88651 2252.1 2354.6 3720.7
4a 91900 67.3 si210 100.0 612101643860, 100621 2323.9 2323.9 3455.0
a 52000 70.2 36505 100.0 365081808017 65858 1386.0 1386.0 1974.3
a $4000 14:8 40396 100.0 403951976450, 73801 1833.7 1533.7 2080.2
43 3ecoo 79.6 30266 100.0 30266 «2158665 95335, 1437 1249.7 1462.7
4s 22000 84°93 19688 100.0 \eses 2354174 43385, 709.4 709.4 835.3
46 }0000 88.3 3836 100.0 8824 2562504 22637 335.4 335.4 79.7
a7 13000 91.6 17410, 100.0 vaio 2788186 48472 561.0 561.0 wha
48 34.8
39 000 35.5 7640 100.0 7640 3269800 24983, 290.1 290.1 303.7
50 10000 $6.0 9598 100.0 9598 1534850 33929 364.4 364.4 379.7
5 97.8
52 10000 $8.0 9go¢ 100.0 9904 4112308 40318 372.2 M22 379.7
3 98.0
sum 289000 1497674 4949.5 100707. 200881 .3

Apeference catch is the stratified catch per tow (multiplied by 1 x 108) from the NMFS spring groundfish survey; M. McBride, pers. comm,

percent females based on NMFS port sampling date from New Bedford, Massachusetts during first two quarters of 1976, 1977, and 1978;
S. Clark, pers. comm.

Percent females mature based on regression of data from Royce et al. (1959).
Fecundity from Howell and Kester (1977),
8These population estimates relate to those sizes caught during NMFS spring groundfish survey


1

Atlantic Mackerel and Spawning Population Estimates

& 3 te =
k me
\ 7
Re az
<0" a
2
ae
ae ;
ao"
68.
|
38"| 38°]
. |
70 |
APRIL 13 - 22 APRIL 14- MAY 13 (NORTH)
93 STATIONS | APRIL 24-APRIL 29 (SOUTH)
EGGS SPAWNED 'M“DAY 2-CRUISE_BOUNDARY~--
162 STATIONS |
[) None EGGS SPAWNED'M7/0AY
Dort0 EJ none
111-100 Bors
B 101-1000 36° Eii-t00 36"
BB 101-1000
7 Bi 001-5000 7 |
[Hl 5001-10000
pot Gf 7 ' *

Figure 3.

Distribution of Atlantic mackerel eggs during the second and third ichthyoplankton surveys, 1977.


55

This paper not to be cited without prior reference to the author

International Council for ICES C.M. 1982/G:59
the Exploration of the Sea Demersal Fish Committee

SPAWNING STOCK BIOMASS ESTIMATES OF SAND LANCE,
AMMODYTES SP., OFF NORTHEASTERN UNITED STATES,
DETERMINED FROM MARMAP PLANKTON SURVEYS, 1974-1980

by
Wallace Morse

U. S. Department of Commerce
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northeast Fisheries Center
Sandy Hook Laboratory
Highlands, New Jersey 07732 USA

ABSTRACT

Sand lance, Ammodytes sp., larvae from 18 MARMAP (Marine Resources
Monitoring, Assessment and Prediction) surveys from 1974-1980 were used
to estimate spawning stock biomass from Cape Hatteras, North Carolina to
Nova Scotia. A dramatic 50-fold increase in biomass occurred between 1974
to 1978 and then decreased to approximately one-third of the 1978 level in
1980. Changes in the species composition of the pelagic finfish community
suggest sand lance replaced Atlantic mackerel and Atlantic herring through
changes in energy flow within the ecosystem.

INTRODUCTION

Marine fish stocks off the northeastern United States were subjected
to intense fishing pressure during the late 1960's and early 1970's. By
1975 the fish biomass of the principal finfishes and squids found in shelf
waters between Cape Hatteras, North Carolina and Nova Scotia had been reduced
by approximately 50% (Clark and Brown 1977). During the period of reduced
biomass, 1974-1979, scientists at the Northeast Fisheries Center's Sandy
Hook Laboratory found evidence of a significant change in the ichthyofaunal
structure when they discovered a tremendous increase in sand lance larvae
abundance during winter MARMAP surveys (MARMAP is an acronym for Marine
Resources Monitoring, Assessment and Prediction; see Sherman (1980) for a
detailed description of the program). Abundance estimates of sand lance
larvae increased 20-fold from 490 x 109 in 1974, when they accounted for
less than 50% of the winter larval assemblage, to 9640 x 109 in 1979, when
they accounted for nearly 90% of the winter ichthyoplankton. (Sherman et al.
1981). The increase in larval abundance and evidence from other MARMAP
studies (e.g. bottom traw] surveys, diver observations and a significant
increase in sand lance as a predator food item) indicate that adult popula-
tions of sand lance larvae increased sharply since 1976.

Preceding page blank


108

68. Q {eer 4a"
Se
8
1,88 ‘|
wef SUBAREA 6 lag’
70 ,* "buBAREA : 7
} 8
ny a
w f SUBAREA 5 aa
©
©
me)
cS
>
- SUBAREA 4
72" \ ice
Le, 2,
42° 42°
“ SOUTHERN
¢ >f\ SUBAREA 3 NEW ENGLAND
Y/
Ke 3e"|
wv
70"
so
i, SUBAREA 2
5 MIDDLE
! ATLANTIC
. : 2
7 \ ¥ 36 36°
NN 5 Te 72.
~ :

\¢
ft «

Figure 1. Ichthyoplankton survey area ; subareas for 1977 (left) and 197S (right).

36°



1onv

'ar

“LL61 ‘ease ABAINS dVWHVW OU) UlYIIM UOHONpOId Hba Jepunoy je|Mo}jad Apep payewnsy “¢ aunbig

+ dv
—s

t HVA

110

Vauv WLOL

eerelerans

00€

oov

008

(g-01x) AV HSd GSNMvdS SDO93


viii

Figure 7. Estimated daily egy production in four subareas and in the tota
survey area; Subareas 6 and 7 not shown, but are included in the
total.

SILVER HAKE, Merluccius bilinearis, EGG CENSUS AND ADULT POPULATION ESTIMATE
FUR 1979 IN WATERS OFF EASTERN UNITED STATES

Figure 1. Distribution of silver hake eggs during the second, third
and fourth MARMAP ichthyoplankton surveys, 1979. Subarea
boundaries shown on left apply to all surveys.

Figure 2. Vistribution of silver hake eyys duriny the fifth, sixth and
seventh MARMAP ichthyoplankton surveys, 1979.

Figure 3. Estimated daily silver hake egy production in four subareas and in
the total survey area, 1979.

SPAWNING STOCK BIOMASS ESTIMATES OF SAND LANCE, Ammodytes sp., OFF

NORTHEASTERN UNITED STATES DETERMINED FRUM MARMAP PLANKTUN SURVEYS, 1974-1y¥8U

Figure 1. Station locations and analytical subareas of standard MARMAP
surveys.

Figure 2. Lenyth frequencies and fitted reyressions for sand lance,
Ammodytes sp., 1974-1977.

Figure 3. Length frequencies and fitted reyressions for sand lance,
Ammodytes sp., 1979-1980.

AN ASSESSMENT UF THE GEURGES BANK HAUDUCK STUCK BASED UN LARVAE CULLECTEU ON

MARMAP PLANKTON SURVEYS, 1977-1982

Figure 1. Standard MARMAP sampling locations and boundaries of subareas used
for analysis of haddock larvae.

Figure 2. Aye frequencies of haddock larvae for years 19//-1982.
MEASURING THE PRECISION OF ESTIMATES UF TOTAL EGG PRODUCTIUN BASED UN PLANKTON
SURVEYS

Figure 1. Ichthyoplankton survey area; subareas for 197/ (left) and 1979
(right).

Figure 2. Estimated daily Atlantic mackerel eyy production within the MARMAP
survey area, 1977.


30

> 1977 1980
iS) n=4785 n-=5573
Ww
320
©
iva
5
Z 10
{e)
iva
imi
Qa
50 1978 1981
n= 3726 n=5535
40
>
{e)
=a
4
3 30
©
ir
5
Z 20
{S)
jem
w
a
10
> 30 1979 1982
6) n=3716 n=101
za
Ww
3 20
Ww
ac
we
b
fa 10
ze
a

Figure 2.

10 20 30 40 50 60
AGE (DAYS)

Age frequencies of haddock larvae for years 1977-1982.

10 20 30 40 50 60
AGE (DAYS)


32

§,
&
©
40°
es
ae"
Jun 21 = 30 70.
N=94 .
Eags spawned/10 m@/day
None .
ON
F100 SSS
36"
ne
4
e
i
7

fe

g
we
40°
68
krlometers |
Coe)
Jul 30 = Aug 30 x
N= 159
Eggs spawned/10 m2/day
None +
I-10 ANS
N-100 Ls
36”
me

74°

Figure 4.

Distribution of yellowtail flounder eggs during the sixth and

seventh ichthyoplankton surveys, 1977.


and
“ony M2722 m-1, pm=-2 ¢2) ;
a exp(2y) {> Gils /2) - Cat Ge S*)} , m1,
x
var(c) = (4)? m=1,
QO, m=0,
where:
n is the sample size,
m is. the number of nonzero values,
y. is the sample mean of the nonzero log, values,
5? is the sample variance of the log, values,
xy is for m=1 the single nonzero value,
and

(m-1)2571 xd

With a computer it is easy to evaluate G(x) for given values of x and m.

m (m#1) (m+3)...(m+2j-3) jy

(2)

For smaller values of m.and/or larger values of x, the usual approximations

to G(x) such as expt (24) x) (Jones, 1956) are poor. For egg surveys,

c can be much more efficient in estimating the mean number of eggs spawned/

m/day than the ordinary sample mean (Pennington, 1983).


35

4

*Lb703
34} UL papn{dUL aue ynq ‘uMOYS JOU / pUue g SRauegns ‘eave AaAUuNS
{®}0} ay} UL pue seaueqns sno} UL UOLQONpoud Hha A Lep pazewizsz */ aunbiy

31VOIGNI HINOW HOV3 40 AVG HIJI4 AUBAR *31vO

ot T ony oz ch tine 02 oO U Nar oz oT AW (4 or

Tad oz or
+ trot sae

$ vauvans”
2 vauvans

€ vwauvans

V3UV ABAUNS TWAOL

00T

00d

008

(6-01 *) AVG Yd TANMYdS $993