745

NOAA Technical Report NMFS SSRF-745

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Dorsal Mantle Length— Total
Weight Relationships of Squids
Loligo pealei and ///ex illecebrosus
Fronn the Atlantic Coast of the
United States

Anne M. T. Lange and Karen L Johnson

March 1981

Vlarine Biological Laboratory
LIBRARY

OCT 14 1992

Woods Hole, Mass.

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

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NOAA Technical Report NMFS SSRF-745

.^OWMOS^^

^^^M^H^^"^

Dorsal Mantle Length— Total
Weight Relationships of Squids
Loligo pealei and ///ex illecebrosus
From the Atlantic Coast of the
United States

Anne M. T. Lange and Karen L Johnson
March 1981

Marine Biological Laboratory
LIBRARY

OCT 14 1992

Woods Hole, Mass.

U.S. DEPARTMENT OF COMMERCE

Philip M Klutznick, Secretary

National Oceanic and Atmospheric Administration

Richard A. Frank, Administrator

National Marine Fisheries Service

Terry L Leitzell, Assistant Administrator (or Fisheries

The National Marine Fisheries Service (NMFS) does not approve, rec-
ommend or endorse any proprietary product or proprietary material
mentioned in this publication. No reference shall be made to NMFS, or
to this publication furnished by NMFS, in any advertising or sales pro-
motion which would indicate or imply that NMFS approves, recommends
or endorses any proprietary product or proprietary material mentioned
herein, or which has as its purpose an Intent to cause directly or indirectly
the advertised product to be used or purchased because of this NMFS
publication.

CONTENTS

Introduction 1

Methods 1

Results 4

Statistical summary 4

Analyses of covariance 4

Discussion 13

Conclusions 13

Literature cited 16

Figures

1 . The northwest Atlantic area, considering in length-weight regression analyses for squid, showing (A)

survey strata and ICNAF Divisions and (B) geographical areas 2

2. Dorsal and ventral views of the squid, Loligo pealei and Illex illecebrosus, and features used for length
measurements 3

3. Seasonal (spring, summer, autumn) geographic distributions of Loligo pealei catches from U.S. bot-
tom trawl surveys in the northwest Atlantic, 1977 5-7

4. Seasonal (spring, summer, autumn) geographic distributions of Illex illecebrosus catches from U.S.
bottom trawl surveys in the northwest Atlantic, 1977 8-10

5. Plots of squid, Loligo pealei and Illex illecebrosus, overall length-weight relationships for the north-
west Atlantic, all data combined 17

Tables

1 . Survey cruises in the northwest Atlantic in which Illex illecebrosus and Loligo pealei were obtained

for length-weight analysis 1

2. Length-weight summary statistics for northwest Atlantic squid, Loligo pealei and Illex illecebrosus,

by sex, area, season, and year 11

3. Regression parameters and statistics for dorsal mantle length and total weight relationships of north-
west Atlantic squid, Loligo pealei and Illex illecebrosus, by sex, area, season, and year 12

4. Analysis of covariance of adjusted means and slopes of Loligo pealei length-weight regressions 14

5. Analysisof covariance of adjusted means and slopes of ///eAr///ecefcro5W5 length- weight regressions .... 15

6. Percentage overall errors in calculated sample weights of squid species versus empirical sample
weights using length-weight function for all data and for annual, seasonal, and area data by sex 16

lU

Dorsal Mantle Length — Total Weight Relationships of

Squids Loligo pealei and Illex illecebrosus from

the Atlantic Coast of the United States

ANNE M. T. LANGE AND KAREN L. JOHNSON'
ABSTRACT

Leng(h-weight data were collected from the Northwest Atlantic, for two commercially important species of
squid, Loligo pealei ani Illex illecebrosus, during nine research vessel cruises between 1975 and 1977. These data,
in total and by year, sex, season, and area of capture, were fit to length-weight relationships of the form
W = ai*. Analyses of covariance indicate that for each species, differences exist between relationships determined
for each area. For L. pealei, differences also exist between sex and among years and seasons. However, com-
parisons of sums of total observed weight versus sums of total weight, predicted by equations obtained for all
data within a given set, indicate that the net results of using a single equation for each species is about as precise
as using separate equations for each sex, area, season, and year. These equations are: H ' = 0.25662/.^*'^^^^ forL.
pealei and H= 0.04«10i '■''•''"' for /. illecebrosus.

INTRODUCTION

Two species of squid — the long-finned squid, Loligo pealei,
and the short-finned squid, Illex illecebrosus — are of commer-
cial importance off the northeastern United States. Loligo pealei
is distributed primarily from Cape Hatteras to the Gulf of
Maine with some seasonal occurrence in the Gulf of Mexico and
as far north as New Brunswick (Summers 1969). Commercial
concentrations of L. pealei are found primarily from Cape Cod
to about Baltimore Canyon. /Ilex illecebrosus ranges from New-
foundland to Florida with commercial concentrations from the
Middle Atlantic area, near Baltimore Canyon, to New-
foundland (Squires 1957). Until the late 1%0's these species
were taken commercially off the United States in quantities
ranging from 400 to 5,000 t (metric tons) per year (average 1 ,805
t for 1930-67). Comparable amounts (< 5,000 t) of /. il-
lecebrosus were taken annually off Newfoundland by coastal
Canadian fishermen. However, with development of interna-
tional fisheries in these areas, catches increased rapidly in the
early 1970's, reaching 56,700 t (/,. pealei and /. illecebrosus) in
1973 off the United States and 80,600 t (/. illecebrosus) in 1977
off Canada.

The life history and population dynamics of these two squid
species, especially /. illecebrosus, are not fully understood. The
relationship of growth in length to increase in weight can be
used, in conjunction with length-frequency samples from the
commercial fishery, to convert catch in weight to catch in
number. Population size in number may be more appropriate
than biomass in analyzing the status of the squid stocks, since
individuals increase weight so rapidly. Mesnil (1977), Summers
(1971), and Squires (1967) presented studies of the growth and
life cycles of these species but did not provide length-weight rela-
tionships. Mercer (1973p provided length-weight functions for
male and female /. illecebrosus from Newfoundland waters, but

'Northeast Fisheries Center Woods Hole Laboratory, National Marine
Fisheries Service, NOAA, Woods Hole, MA 02543.

^acer.M.C. 1973. Length-weight relationship of (he ommastrephid squid, //■
lex illecebrosus {LeSuew). Annu. Meet. Int. Comm. Northwest All. Fish. 1973, Res.
Doc. 72, Serial 3024. [Mimeogr.)

these may not be appropriate for /. illecebrosus off the United
States. Similar studies had not been made for L. pealei.

The objectives of this study were to: 1) calculate dorsal mantle
length-total weight relationships for Loligo pealei and Illex il-
lecebrosus from the northwest Atlantic off the U.S. coast; 2)
analyze differences in length-weight relationships from different
areas, seasons, and years, and by sex; and 3) determine the ap-
propriate application of these relations to empirical data fro."!
the commercial fishery (i.e., is a single relationship appropriate
for all areas, seasons, and sexes, or must several functions be
used to adequately represent the population?).

METHODS

Samples of L. pealei and /. illecebrosus, for length-weight
analysis, were collected from the Nova Scotian to Middle Atlan-
tic areas (Fig. 1) during research vessel bottom trawl surveys
conducted in 1975-77 (Table 1). Standard bottom tows, based
on a stratified random sampUng design (Grosslein 1969), were
made and subsamples of each species of squid taken from tows
in a given strata were frozen whole and returned to the North-
east Fisheries Center, Woods Hole Laboratory, Woods Hole,
Mass., for analysis. These were generally random subsamples,
but in areas or seasons, when few individuals in the upper or
lower size ranges were obtained, length stratified random
samples were used to ensure representation of the entire size

Table 1. — Survey cruises in the northwest Atlantic in which Illex illecebrosus and
Loligo pealei were obtained for length-weight analysis.

Year

Cruise
code

Country

Season

Area

1975

753

USA

Spring

758

USA

Autumn

1976

762

USA

Spring

766

USSR

Autumn

767

USA

Aummn

1977

771

USA

Spring

774

USA

Summer

775

Japan

Siunmer

778

USA

Autumn

Mid-Atlantic— Nova Scotia
Mid-Atlantic— Nova Sootia
Mid-Atlantic— Nova Scotia
Mid-Atiantic— Nova Scoda
Mid-Adantic— Nova Sootia
Mid-Adantic — Nova Scoria
Mid-Atlantic— Nova Sootia
Mid-Adantic— Georges Bank
Mid-Adantic— Nova Scotia

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Figure 1. — The northwest Allanlic area, considered in length-weight regression analyses for squid, showing (A) survey strata (strata numbers circled) and ICNAK
(International Commission For the Northwest Atlantic Fisheries) Divisions (such as 5Zw) and (B) geographical areas.

range. The length data, therefore, do not represent an unbiased
subsample of the survey catches.

Frozen samples were thawed prior to analysis. Dorsal mantle
length was measured from the apex of the tail fin to the
anterodorsal protuberance, to the nearest millimeter (Fig. 2);
total weight was measured to the nearest gram; and sex,
maturity, and stomach content information was recorded. All
data were audited and stored on computer files for statistical
analysis.

The form of the length-weight relationships was assumed to
be:

W=ALi>

where W= total weight (g),

L = dorsal mantle length (cm),
A and b = coefficients of regression.

Least squares regressions were fitted to the linearized form of

this function:

Y = a + bx

where Y = log^ ff,
X = loge L,
a = log^ A,
b = coefficient of regression.

Various regressions were fitted, with the Statistical Package
for the Social Sciences (SPSS) (Nie et al. 1975) SCAT-
TERGRAM subprogram, to combinations of the data, il-
lustrating effects of sex, season, year, and area differences on
the length-weight relationship. Pearson correlation coefficients
(r) were calculated for each regression to measure the strength of
the relationship and the goodness of the fit of the calculated
regression line to the empirical data.

One-way analyses of covariance were conducted using the
Biomedical Computer Programs (BMDP) (Dixon and Brown

ANTERODORSAL PROTUBERANCE

APEX OF FIN ■

Dorsal View

TAIL FIN

EYE

— ARMS

T.r'.WI '..:;>-,;.JM-J*^

-TENTACLES

Ventral View

lilex illecebrosus, The Short- finned Squid

APEX OF FIN

ANTERODORSAL PROTUBERANCE

■"^2^

TAIL FIN EYE

Dorsal View

— ARMS I — TENTACLES

Ventral View

Loligo pealei, The fjong- finned Squid

Figure 2.— Dorsal and ventral views of Ihe squid, Loligo pealei and Illex illecebrosus, and fealures used for length measurements.

1977), BMDPIV, to determine the significance of differences
between slopes and adjusted means of the various length-weight
functions (Winer 1971).

A total of 5,388 L. pealei and 2,798 /. illecebrosus were ob-
tained from nine cruises during the 3-yr study period (1975-77).
Of this total, 750 L. pealei and 20 /. illecebrosus were of indeter-
minable sex and not considered in this study. There were also
3,026 L. pealei and 193 /. illecebrosus which were damaged
during the capture or preserving process, preventing accurate
measurement of weight; these were also excluded.

The number of individuals in any sample does not necessarily
reflect the size of the survey catches or the relative abundance of
either species in any area, season, or year. This is often a func-
tion of time available to separate and freeze the samples.
Generally, however, both species are more available in autumn
than in spring, and while /. illecebrosus may be taken in great
quantities during the summer, L. pealei is usually too far inshore
to be captured in an offshore survey. Loligo pealei are most
abundant in the area south of Cape Cod and are only occa-
sionally found north of Georges Bank, while /. illecebrosus are
generally more available from southern New England and
Georges Bank areas, with significant catches also taken in the
Gulf of Maine and Nova Scotian areas. Examples of seasonal
distributions from U.S. surveys in 1977 are presented for L.
pealei and /. illecebrosus in Figures 3 and 4.

RESULTS

Statistical Summary

Statistical summaries of L. pealei and /. illecebrosus length
and weight data are presented in Table 2. Lengths ranged from
2.1 to 42.5 cm for L. pealei and from 4.9 to 45.0 cm for /. illec-
ebrosus, with an overall average of 17.0 and 22.3 cm. Weights
averaged 133 and 243 g, ranging from 4 to 752 g and from 3 to
861 g, for L. pealei and /. illecebrosus. Male L. pealei were con-
sistently larger (mean lengths and weights) in all areas, seasons,
and years, than female L. pealei; while on the average, female /.
illecebrosus were larger than the males of that species. Size com-
parisons, for each species, between areas and seasons were not
made, since not all samples were random with respect to length.

Regression parameters (a and b), standard errors of estimates,
and Pearson correlation coefficients (r) for L. pealei and /. illec-
ebrosus length- weight relations are presented in Table 3, by sex
and overall, for each year, season, and area. Correlation coeffi-
cients indicate that generally between 76% and 96% (r^ x 100)
of the variation between dorsal mantle length and total weight
of L. pealei may be accounted for by these regression equations.
The low value for the regression of females from siunmer
samples (64%) may possibly be explained by small sample size
(35 individuals) and a narrow range of lengths. For /.
illecebrosus, between 41 % and 96% of the variation is explained
by the various regressions. The relatively low correlations for /.
illecebrosus in some groups (all 1977 data, males in 1977 and in
spring, and all data from Georges Bank, the Gulf of Maine, and
Nova Scotia) indicate that regression equations may not always
be adequate for that species. However, examinations of
residuals about the regression lines, plotted against predicted
loge weights indicated no systematic departures from the fitted
equations which would imply a better model.

Comparison of the length-weight relationships of male versus
female L. pealei, for all samples, shows a difference in weight,

by sex, through the entire length range. This difference is also
evident when considering the relationships in each area sep-
arately. Generally, females less than about 13 cm are lighter
than males of the same length, while females greater than about
17 cm are heavier than the males. Length-weight relationships
by year (pooled over season and area) and those by season
(pooled over area and year) also showed differences between
sexes, again with females <13-17 cm weighing less than males at
the same lengths and those greater than that range weighing
more. The simimer sample shows only a slight difference be-
tween sexes. Comparisons of length-weight relationships by
year, season, and area, for each sex separately and combined,
indicate that differences in each category are more evident in the
male than in the female samples. Individuals of a given length,
for both sexes, were lightest in summer than spring, and heaviest
in the autumn, though larger females were heavier in the spring
than they were later in the year. The most robust males were
from the Middle Atlantic and southern New England areas,
while females from Georges Bank and southern New England
were heavier at any given length than those from the other areas.
The regressions for the Gulf of Maine are not given since the
weight of only five L. pealei were obtained.

Differences between the length-weight relationships of male
and female /. illecebrosus were not as consistent as those of L.
pealei. The overall /. illecebrosus regressions (pooled over year,
season, and areas) were almost identical. Though great dif-
ferences were exhibited between sexes in the spring and Nova
Scotian samples, the relationships from the other areas and
seasons were similar for each sex. Comparisons by year, season,
and area, overall and for each sex separately, indicate that the
greatest difference is exhibited by both males and females,
among areas, where the Nova Scotian samples had a nearly
linear length-weight relationship (b = 0.827 and 1.170 for males
and females and 1.242 overall).

Analyses of Covariance

Analysis of covariance was used to test if observed differences
in the regression equations of each species were statistically
significant (Tables 4, 5). In the analyses, the //g the adjusted
means are equal, is based on the prior assumption that the
slopes are equal. Significance in the test of equality of slopes in-
dicate differences in the populations, and the Hq is not tested.
Differences between sexes were examined with tests of slopes
and adjusted means, pooling data over all years, areas, and
seasons for each sex. Consistencies in these differences were
checked by testing differences between sex within each season
(data pooled over years and areas), within each area (data
pooled over seasons and years), and within each year (data
pooled over seasons and areas). Seasonal differences were
tested, with pairwise tests of data combined over all areas, sexes,
and years, for each season. Area and annual differences were
tested with data pooled over years, sexes, and seasons, and over
areas, sexes, and seasons.

Significant differences (P:i0.05) were exhibited in slopes be-
tween male and female L. pealei (Table 4a), with the slope of the
female equation significantly greater than for the males. This
difference was also significant during the spring and autumn,
and in each area, and year. In each case, the slope of the female
regression was significantly larger than for the males.

Tests between seasons (Table 4b) showed significant dif-
ferences in slopes between spring and summer and between sum-

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10

Table 2. — Lenglh-weighl summary statistics for nortliwest Atlantic squid, Loligo pealei and lUex illecebrosus, by sex, area, season, and year.

Species
and sex

Year

Season

Area

Dorsal mantle length (mm)

Total

weight (g)

n

T

SD

SB

Min.

Max.

jr

SD

SE

Min

Max.

Loligo pealei:

All Data

1,709

170.2066

58.43553

1.413533

21.0

425.0

133.4383

91.42767

2.21160

4.0

752.0

Males

All

All

All

915

190.2590

61.58830

2.036046

21.0

425.0

159.4230

100.7944

3.332I6I

4.0

752.0

Mid-Atlantic

409

190.8924

59.80818

2.957325

41.0

425.0

166.6308

104.2479

5.15473

4.0

734.0

S. New England

304

196.7039

53.81042

3.08624

65.0

402.0

170.4572

99.85371

5.727004

10.0

752.0

Georges Bank

164

173.0061

63.74359

4.977538

21.0

355.0

127.2927

90.42714

7.061172

7.0

526.0

Gulf of Maine

3

170.6667

10.01665

5.78312

161.0

181.0

120.0

23.00

13.27906

97.0

143.0

Nova Scotia

35

193.9714

61.40056

10.37859

98.0

310.0

133.2857

84.12161

14.21915

34.0

305.0

All

Spring

All

388

201.6959

69.22797

3.514519

21.0

425.0

173.9227

122.0835

6.197851

7.0

752.0

Summer

41

169.0244

46.19875

7.215032

90.0

298.0

95.82927

49.22444

7.687566

26.0

258.0

Autumn

486

181.8086

48.62424

2.20564

41.0

340.0

153.2119

80.65131

3.658417

4.0

570.0

1975

All

All

580

188.5931

60.11943

2.496323

21.0

425.0

163.9241

103.7126

4.306433

4.0

752.0

1976

All

All

212

200.783

57.14859

3.924981

41.0

374.0

172.2736

95.95537

6.590241

10.0

599.0

1977

All

All

123

175.5854

54.11841

4.879692

61.0

334.0

i 16.0488

82.82709

7.468266

9.0

460.0

Females

All

All

All

697

159.9928

37.227626

1.410083

54.0

286.0

115.8293

62.83559

2.380067

7.0

435.0

Mid-Atlantic

293

169.2423

37.53026

2.192542

54.0

286.0

130.6485

64.5405

3.770497

7.0

435.0

S. New England

243

162.251

34.21141

2.194662

59.0

275.0

117.2346

59.97084

3.847131

10.0

394.0

Georges Bank

124

136.7097

29.86794

2.68222

55.0

200.0

83.0

44.80145

4.023289

10.0

222.0

Gulf of Maine

2

168.0

18.38478

13.00001

155.0

181.0

134.0

35.35535

25.0

109.0

159.0

Nova Scotia

35

148.9143

42.70926

7.219182

70.0

227.0

97.28572

77.08994

3.03058

14.0

350.0

All

Spring

All

299

157.6522

38.48149

2.225442

55.0

275.0

111.4114

66.74384

3.859897

10.0

435.0

Summer

35

131.0857

14.64556

2.475552

100.0

158.0

58.39999

15.99117

2.703001

30.0

95.0

Autumn

363

164.7080

36.30104

1.905311

54.0

286.0

125.0055

58.99672

3.096525

7.0

403.0

1975

All

All

424

159.8962

39.81136

1.933411

54.0

286.0

121.9693

66.75272

3.2418

7.0

435.0

1976

All

Ail

178

166.6292

32.43434

2.431056

59.0

270.0

118.2416

55.62306

4.169125

10.0

374.0

1977

All

All

95

147.9895

30.31764

3.110524

82.0

255.0

83.90526

46.32266

4.752604

20.0

302.0

ftlex illecebrosus:

All Data

2,605

222.5766

40.73985

0.7982071

49.0

450.0

243.19

108.8574

2.132819

3.0

861.0

Males

All

All

All

1,074

204.0978

33.55382

1 .023858

49.0

450.0

196.7197

95.02876

2.899700

4.0

209.0

Mid-Atlantic

333

192.6877

31.55191

1.729034

75.0

254.0

164.1892

71.72276

3.930386

8.0

391.0

S. New England

217

192.5069

43.09842

2.925711

49.0

285.0

168.9309

86.65753

5.882696

4.0

430.0

Georges Bank

379

215.0607

25.76859

1.323644

120.0

450.0

220.4617

58.56674

3.008372

26.0

397.0

Gulf of Maine

77

223.5584

14.55865

1.662531

161.0

250.0

258.052

60.58702

6.904531

87.0

373.0

Nova Scotia

68

213.8235

28.77963

3.490043

65.0

277.0

215.2647

47.823875

5.799496

50.0

402.0

All

Spring

All

34

172.8235

26.97751

4.626604

128.0

241.0

118.6471

51.7903

8.881963

47.0

253.0

Summer

417

209.6906

19.74397

0.9668665

120.0

269.0

200.4149

59.33192

2.905497

4.0

428.0

Autumn

623

202.0610

39.55093

1.584575

49.0

450.0

195.488

83.51697

3.346037

4.0

428.0

1975

All

All

237

1%.1266

38.63312

2.50949

92.0

285.0

186.7722

93.99959

6.105929

16.0

397.0

1976

All

All

185

190.3297

44.57156

3.276966

49.0

265.0

171.8811

87.65227

6.444323

4.0

428.0

1977

All

All

652

210.9018

25.09465

0.9827825

120.0

450.0

204.4985

61.08788

2.392385

26.0

430.0

Females

All

All

All

I.5II

237.0735

37.97983

0.9770589

52.0

343.0

280.002

113.331

2.915523

4.0

861.0

Mid-Allanlic

362

222.8149

44.52104

2.339974

80.0

343.0

245.8232

125.4576

6.593907

10.0

794.0

S. Nevs England

268

225.8552

47.19168

2.882691

52.0

311.0

252.5933

133.1323

8.132354

4.0

861.0

Georges Bank

558

242.7867

29.46974

1.247553

82.0

301.0

290.2581

99.05467

4.193318

11.0

738.0

Gulf of Maine

165

252.5152

18.81023

1.464374

185.0

316.0

330.3696

90.3768

7.035824

78.0

713.0

Nova Scotia

158

252.2975

28.24924

2.247388

II 0.0

303.0

315.9810

74.4052

5.919359

139.0

523.0

All

Spring

All

17

131.0588

48.73341

11.33293

80.0

266.0

146.1176

117.7810

28.56609

10.0

408.0

Summer

556

231.1799

23.78857

1 .220907

139.0

290.0

247.3452

92.63647

3.928661

51.0

547.0

Autumn

938

241.5821

41.17207

1.344316

52.0

343.0

295.8582

120.4033

3.931305

4.0

861.0

1975

All

All

219

219.5434

47.2823

3.195042

82.0

316.0

244.9173

132.1029

8.926682

11.0

713.0

1976

All

All

304

242.523

44.75668

2.566972

52.0

343.0

305.6777

131.5025

7.542185

4.0

861.0

1977

All

All

988

239.2834

31.87256

1. 104001

80.0

303.0

279.8787

100.0517

3.183069

10.0

738.0

mer and autumn, with summer samples indicating smaller slopes
than either of the other seasons. Significant differences were
also evident in adjusted means between summer and autumn.

Differences in L. pealei length-weight regressions were also
found between areas (Table 4c). The slope from the southern
New England regression was significantly greater than that of
the Mid-Atlantic, Georges Bank, and Nova Scotia areas, in-
dicating statistical difference between each of these regression
pairs. Comparisons revealed that adjusted means from the Mid-

Atlantic area were significantly greater than from Georges Bank
or Nova Scotia, while the mean from the Nova Scotia regression
was also significantly less than from both Georges Bank and the
Gulf of Maine. There were no statistical differences in regres-
sions for the Mid-Atlantic and Gulf of Maine; southern New
England and the Gulf of Maine, and Georges Bank and the Gulf
of Maine.

Pairwise comparisons between years (Table 4d) produced no
significant difference in the slopes in any year. However, there

11

Table 3.~Regression parameters and statistics for dorsal mantle length (cm) and total weight (g) relationship of northwest Atlantic LoUgo pealei and lUex il-

lecebrosuSy by sex, area, season, and year.

Correlation

Intercept

Slope

coefficient

Species

Area

Season

Year

Sex

(a)

(b)

SEofft

(r)

Loligo pealei:
AU

AU

Spring

Summer

Autumn

AU

1975

1976

1977

AU

Mid-Atlantic
Southern New England
Georges Bank
Gulf of Maine
Nova Scotia

Illex illecebrosus:
All

AU

AU

1975

1976

1977

Spring All

Summer

Autumn

Mid-Atlantic
Southern New England
Georges Bank

AU

AU

-1.36015

2.15182

0.2861

0.95

Males

-0.86949

1.97528

0.3196

0.91

Females

-1.78605

2.32364

0.2038

0.94

AU

-1.41009

2.18743

0.2863

0.95

Males

-0.85092

1.98020

0.3303

0.91

Females

-1.58916

2.27017

0.2221

0.94

AU

-1.23862

2.10357

0.2691

0.95

Males

-0.23259

1.76347

0.3192

0.87

Females

-2.20362

2.45497

0.11%

0.97

AU

-1.61568

2.19236

0.1612

0.97

Males

-1.60828

2.17591

0.1547

0.98

Females

-2.16486

2.41658

0.1507

0.96

AU

-1.38547

2.14418

0.2736

0.97

Males

-0.88956

1.96453

0.3023

0.93

Females

-2.02656

2.40412

0.1859

0.97

AU

-0.78138

1.87046

0.1504

0.95

Males

-0.58210

1.79805

0.1539

0.96

Females

-0.89154

1.91773

0.1658

0.80

AU

-1.38983

2.18390

0.2711

0.94

Males

-0.93193

2.01763

0.3290

0.89

Females

-1.3%56

2.19463

0.2230

0.92

AU

-1.04605

2.05558

0.2803

0.92

Males

-0.97119

2.02414

0.3154

0.92

Females

-1.37391

2.18067

0.21%

0.93

AU

-1.77585

2.29771

0.1844

0.97

Males

-1.24814

2.10368

0.2528

0.93

Females

-2.48431

2.48431

0.1762

0.95

AU

-1.31404

2.11827

0.3566

0.96

Males

-0.26677

1.73782

0.40%

0.88

Females

-1.99225

2.41504

0.1798

0.95

AU

-

-

-

-

Males

-

-

-

-

Females

-

-

-

-

AU

-1.26702

2.06714

0.2491

0.95

Males

-1.01588

1.95655

0.2098

0.95

Females

-1.98178

2.36422

0.2537

0.94

AU

-3.03444

2.71990

0.2419

0.93

Males

-2.90355

2.58514

0.2753

0.89

Females

-3.12432

2.74348

0.2114

0.93

AU

-3.60800

2.91776

0.2252

0.95

Males

-3.86325

3.01297

0.2407

0.94

Females

-3.40628

2.84306

0.2054

0.96

AU

-3.48898

2.85430

0.2482

0.97

Males

-3.24850

2.79844

0.3193

0.94

Females

-3.78275

2.95017

0.1834

0.97

AU

-2.04101

2.40036

0.2281

0.85

Males

-1.09567

2.09151

0.25%

0.71

Females

-2.49809

2.54442

0.2166

0.87

AU

-3.43632

2.84756

0.2506

0.93

Males

-1.93149

2.32096

0.2554

0.81

Females

-3.87840

2.98569

0.1 %5

0.98

AU

-3.85026

2.98298

0.1501

0.92

Males

-5.54897

3.55229

0.17%

0.85

Females

-3.65525

2.91409

0.1719

0.91

AU

-2.90048

2.67582

0.2719

0.93

Males

-2.71526

2.62456

0.3189

0.90

Females

-2.95402

2.68939

0.2310

0.93

AU

-3.25968

2.79140

0.2474

0.93

Males

-3.06027

2.73143

0.3057

0.85

Females

-3.36896

2.82290

0.2185

0.95

AU

-3.64833

2.91003

0.2045

0.97

Males

-3.59821

2.90213

0.2285

0.97

Females

-3.72612

2.92964

0.1792

0.97

AU

-2.19814

2.45559

0.2213

0.85

Males

-1.24068

2.15026

0.2345

0.72

Females

-2.71228

2.61320

0.1067

0.87

12

Table 3.— Continued.

Correlation

Intercept

Slope

coefficient

Species

Area

Season

Year

Sex

(a)

W

SEofft

(r)

Gulf of Maine

Nova Scotia

All

-3.39896

2.84990

0.1466

0.88

Males

-4,77169

3.31502

0.1426

0.85

Females

-5.11873

3.37266

0.1291

0.89

All

1.67461

1.24241

0.2160

0.72

Males

2.82347

0.82687

0.2002

0.65

Females

1.95943

1.16965

0.1956

0.64

'Sample size too small to fit regression.

were significant results in tests of adjusted means, decreasing
from 1975 to 1977.

Differences in length-weight regressions for /. illecebrosus
were not as consistent as for L. pealei. Overall, the adjusted
mean was significantly greater for female than for male /. //-
lecebrocus (Table 5a.). The slope of the male regression was
significantly greater than the female's during the summer, in-
dicating statistical differences in the two regression lines, for
that season, while in autumn the adjusted mean of females was
greater than for males. There was no significant difference be-
tween regressions of either sex during the spring. Significant dif-
ferences in the slope of male and female regressions from the
Georges Bank and Nova Scotian areas indicate statistical dif-
ferences between sex in both these areas. The Mid-Atlantic area
is the only area that did not exhibit statistical significance in ad-
justed means between sexes. In all other areas females were
significantly larger than males. When compared by year, slopes
of male and female /. illecebrosus vvere only significantly dif-
ferent in 1977, but in both 1975 and 1976, adjusted means for
females were statistically greater than for males.

Differences in length-weight regressions due to seasons (Table
5b) were only significant for /. illecebrosus between the summer
and autumn, with the slope of the summer regression greater
than in autumn.

Tests of slopes were significant for all area comparisons
(Table 5c) except between the Mid-Atlantic and the Gulf of
Maine and between southern New England and the Gulf of
Maine, implying statistical differences between length-weight
regressions from all other areas. However, the adjusted mean
from the Gulf of Maine was also significantly greater than those
from either the Mid-Atlantic or the southern New England
areas, in pairwise comparisons.

Tests of slopes revealed significant differences between 1975
and 1977 and between 1976 and 1977 samples (Table 5d), in-
dicating thai separate equations were appropriate for these
areas. The 1975 adjusted mean was significantly greater than
that of 1976.

Comparisons of total calculated versus total empirical weights
were made for each species, for all data, and for various com-
binations of data (Table 6). Weights were calculated on an in-
dividual basis from sampled lengths, summed within length (cm)
interval and then summed over all lengtlis. Percent differences
were calculated between these values and those obtained by
summing the individual empirical weights for the data set.
Predicted weights were consistently less than empirical weights
due to bias in linearization by log transformations. These dif-
ferences were very small, ranging from 0.08% to 6.60% for L.
pealei and from 0.17% to i.dlVo for /. illecebrosus. This in-
dicates that the dorsal mantle length-total weight relationship

produces relatively precise approximations of total empirical
weight, and that the functions used for each species are fairly ac-
curate representations of this relationship.

DISCUSSION

Results of these analyses indicate that the weight of L. pealei
of a given size differs significantly, depending on the sex of the
individual. The consistency of this difference in tests within
areas, seasons, and years is evidence that it is not merely a pro-
duct of the statistical procedures employed. Major factors, in-
fluencing differences between sexes, are the relative weight of
gonads, with mature ovaries heavier than fully developed testes;
differences in rates of maturation, with females developing over
a longer time interval than males; and differential feeding during
different stages of maturation and at different sizes (Vinogradov
and Noskov 1979). This study also suggests significant seasonal
differences in the length-weight relationship of L. pealei. A
possible explanation of this is that in spring larger individuals
are more mature and, therefore, heavier than later in the year,
while in summer the many individuals which are not yet mature
begin to feed, so by autumn individuals throughout the size
range are heavier as a result of summer feeding. Area and an-
nual differences, also shown significant for L. pealei, may
possibly be explained by various physical and biological factors
such as temperature, nutrients, and availability of food.

Differences in length-weight relationships for various group-
ings of /. illecebrosus were less consistent than for L. pealei.
Overall, tests between sexes were not significant, except in sum-
mer samples (possibly due to maturation of males, or differen-
tial feeding). Seasonal and annual differences were not signifi-
cant for /. illecebrosus, but area differences proved to be impor-
tant. As with L. pealei these differences are most likely due to
physical and biological factors such as temperatures, nutrients,
and food availability.

CONCLUSIONS

This study indicates that differences in the length-weight rela-
tionships of Loligo pealei (by sex, year, season, and area) and of
Illex illecebrosus among areas (but not between sexes, seasons,
and years) do exist. However, comparisons within categories, of
sums of total empirical weight versus sums of total weight
predicted by equations obtained for all data within a given set,
indicate that the new results of using a single equation for each
species is approximately as precise as using separate equations
for each area, season, year, or sex. This implies that for pur-
poses of predicting total numbers taken in a fishery, from length

13

Table 4. — Analysis of covariance of adjusted means and slopes of LoUgo pealei length-weight regressions.

Test of adjusted means

Test of slopes

Adjusted means df

F-ratiol

df F-ratio'

a. Between sexes: all seasons, areas, and years combined; by seasons (area and year pooled); by area (season and year
pooled); and by year (season and area pooled).

Seasons

Overall N/A^

Season: Spring N/A

Summer 73 0.(X)l n.s.

Autumn N/A

Area: Mid-Atlantic N/A

Southern New England N/A

Georges Bank N/A

Gulf of Maine^ —

Year:

Factor
Spring

Spring
Summer

Nova Scotia
1975
1976
1977

vs. Summer
vs. Autumn
vs. Autumn

N/A
N/A
N/A
N/A

b. Between seasons: areas, years, and sexes pooled.

4.5358
4.6422

N/A
1,629
N/A

60.993*

c. Between pairs of areas: sexes, seasons, and years pcjled.

Area comparison
Mid-Atlantic

vs. S. New England N/A

Mid-Atlantic

vs.

Georges Bank

Mid-Atlantic

vs.

Gulf of Maine

Mid-Atlantic

vs.

Nova Scotia

S. New England

vs.

Georges Bank

S. New England

vs.

Gulf of Maine

S. New EngUnd

vs.

Nova Scotia

Georges Beink

vs.

Gulf of Maine

Georges Bank

vs.

Nova Scotia

Gulf of Maine

vs.

Nova Scotia

d. Be

Year comparison

1975

vs.

1976

1975

vs.

1977

1976

4.6220

4.5432

1,067

20.6O5'*

4.6220

4.6721

705

0.144 n.s.

4.6220

4.4403

771

N/A

29.764**

4.57%

4.6721

565

1.258 n.s.

4.5432
4.6721

4.5432
4.4403

4.6721
4.4403

N/A

369

435

73

0.747 n.s.

4.287*

4.396*

d. Between pairs of years: sex, seasons, and areas combined.

vs. 1977

4.6200
4.5649

4.6200
4.4379

4.5649
4.4379

1,501

1,304

632

9.275**

72.857**

42.700*

1,608

51.300*'

683

46.523*'

72

0.218 n.s.

845

5.737'

698

4.152'

543

25.187"

284

23.235**

66

5.054*

1,000

22.650"

400

47.078"

214

7.590"

843

5.533*

1,628

1.360 n.s.

935

7.163"

1,262 34.176"

1,066

704

770

926

564

630

368

434

72

1.785 n.s.

0.066 n.s.

0.010 n.s.
18.713*'

0.044 n.s.
11.215**

0.031 n.s.

0.182 n.s.

0.085 n.s.

1.500

2.401 n.s.

1,303

0.175 n.s.

631

2.358 n.s.

'• = PsO.05; •* = PsO.Ol; n.s. = not significant.

^N/A = test of adjusted means not applicable since test of slopes is significant.

^Sample size in the Gulf of Maine was inadequate for proper analysis.

14

Table S.— Analysis of covariance of adjusted means and slopes of Illex illecebrosus lenglh-weighl regressions.

Test of adjusted means

Tesi of slopes

Adjusied means df

F-ratio'

df

F-raiio

a. Between sexes: all seasons, areas and years combined; by seasons (area and year pooled); by area (season and year
pooled); and by year (season and area pooled).

I actor
Overall
Season; Spring

Summer

Autumn

Mid-Atlantic

Southern New England

Georges Bank

Gulf of Maine

Nova Scotia

1975
1976

1977

Area;

Year:

2.611

17.186**

2,610

1.353 n.s.

45

0.718 n.s.

44

3.599 n.s.

N/A-

998

30.168**

1,561

7.020**

1,560

1.140 n.s.

692

2.690 n.s.

691

0.855 n.s.

482

5.415*

481

0.160 n.s.

N/A

932

14.532**

239

51.376**

238

0.049 n.s.

N/A

222

4.409*

453

6.080*

452

3.625 n.s.

486

8.495**

485

3.361 n.s.

N/A

1,665

25.583**

b. Between seasons: years, areas, and sexes pooled.

Seasons

Spring

Spring
Summer

vs. Summer
\s. Autumn
vs. .^utumn

5.3076

5.3470

1,024

0.909 n.s.

1,023

1.410 n.s.

5.3076

5.3503

1,627

1.822 n.s.

1,626

0.993 n.s.

N/A

2,547

21.396**

c. Between pairs of areas: sexes, seasons, and years pooled.

Area comparison
Mid-Atlantic

s. So. New England

Mid-Atlantic

vs. Georges Bank

Mid-Atlantic

Mid-Atlantic

, Gulf of Maine

5.3363

5.4031

vs. Nova Scotia

S. New England

vs. Georges Bank

S. New England

vs. Gulf of Maine

S. New England

vs. Nova Scotia

5.3024
5.4031

George Bank

vs. Gulf of Maine

Georges Bank

vs. Nova Scotia

Gulf of Maine

vs. Nova Scotia

N/A

N/A

N/A

N/A

734

N/A

N/A

N/A

6.603*

13.956*

d. Between pairs of years: sex, seasons, and areas combined.

> ear comparison
1975

1975

1976

vs. 1976

1977

vs. 1977

5.3681
5.3348

960

N/A

7.208**

'* = P^0.05; •' = PiiO.Ol; n.s. = nol significant.

-N/A = lest of adjusted means not applicable since lest of slopes is significant.

1.193
1.637

940

924

1,430

733

717

1,177

1.161

464

5.310*

26.050**

0.131 n.s.

250.813**

60.111"

0.204 n.s.

401.683*

6.754*

159.471**

124.460**

959

0.917 n.s.

2,131

83.393**

2,166

86.398**

15

Table 6.

-Percentage overall error' in calculated sample weights of squid species versus empirical sample weights using length-weight functions for all data and

for annual, seasonal, and area data b\ sex.

Area

Season

Year

Loligo ,

pealei

/Ilex

illecebrosus

Number

%

Number

%

Sex

sampled

error

sampled

error

All

1,709

1.78

2,604

1.68

Males

915

3.73

1,073

2.08

Females

697

1.60

1,511

1.73

All

1,088

0.74

464

1.47

Males

580

3.77

237

2.07

Females

424

1.48

219

1.57

All

402

1.05

499

1.70

Males

212

2.95

185

3.18

Females

178

0.52

304

1.40

All

219

1.01

1,641

2.30

Males

123

1.28

651

0.17

Females

95

1.34

988

2.03

All

770

1.23

53

2.34

Males

388

3.76

34

5.62

Females

299

1.41

17

3.25

All

77

0.68

974

1.00

Males

41

0.99

916

0.26

Females

35

1.33

566

1.24

All

862

1.45

1,577

1.96

Males

486

4.04

623

2.63

Females

363

1.50

—

—

All

703

1.75

702

2.07

Males

409

2.07

333

2.14

Females

293

1.67

362

1.78

All

563

0.08

495

1.75

Males

304

3.58

217

2.63

Females

243

1.11

268

4.83

All

367

1.83

939

1.79

Males

164

6.60

378

1.86

Females

124

1.75

558

1.83

All

_2

-

242

0.95

Males

_2

-

77

0.95

Females

-

-

165

0.73

All

71

2.53

226

2.46

Males

35

1.97

68

1.76

Females

35

5.11

158

1.90

All

All

Spring

Summer

Autumn

All

1975

1976

1977

All

Mid-Allantic
Southern New England
Georges Bank
Gulf of Maine

Nova Scoiia

'Percentage error = (Total empirical weight-total calculated weight)/iotal empirical weight.
^Sample size too small lo fit regression.

frequency and total catch in weight data, a single equation ob-
tained from all samples is probably as accurate as applying dif-
ferent equations to catches from each sex, year, area, or season.
These equations for L. pealei and /. illecebrosus are plotted in
Figure 5. However, significant changes in this relationship, for
these short-lived species, could occur as a result of changes in
environmental factors.

LITERATURE CITED

W. J. DIXON (editor), and M. B. BROWN.

1977. BMDP-77, Biomedical Computer Programs. Pseries. Univ.
Calif. Press, 880 p. Berkeley, Calif.
GROSSLEIN, M. D.

1969. Groundfish survey program of BCF Woods Hole. Commer. Fish.
Rev. 3l(8-9):22.35.
MESNIL, B.

1977. Growth and life cycle of squid, Loligo pealei and Illex illecebrosus.

from the northwest Atlantic. Int. Comm. Northwest Atl. Fish., Sel.
Pap. 2:55-69.
NIE, N. H., C. H. HULL, J. C. JENKINS, K. STEINBRENNER. and
D. H. BENT.

1975. SPSS (Statistical Package lor the Social Sciences). 2d ed.
McGraw-Hill Book Co., N.V., 675 p.
SQUIRES, H. J.

1957. Squid, Illex illecebrosus (LeSueur). in the Newfoundland fishing

area. J. Fish. Res. Board Can. 14:693-728.
1967. Growth and hypothetical age of the Newfoundland bail squid, Illex
illecebrosus illecebrosus. J. Fish. Res. Board Can. 24:1209-1217.
SUMMERS. W. C.

1969. Winter population of Loligo pealei in the Mid-Atlantic Bight.

Biol. Bull. (Woods Hole) 137:202-216.
1971. Age and growth of Loligo pealei, a population study of the common
Atlantic coast squid. Biol. Bull. (Woods Hole) 141:189-201,
VINOGRADOV, V. I., and A. S. NOSKOV.

1979. Feeding of short-finned squid, Illex illecebrosus. and long-finned
squid, Loligo pealei, off Nova Scotia and New' England, 1974-75. Ini.
Comm. Northwest Atl. Fish., Sel. Pap. 5:31-36.
WINER. B. J.

1971. Statistical principles in experimental design. 2d ed. McGraw-Hill
Book Co., N.Y., 907 p.

16

SQUID LENGTH-WEIGHT RELATIONSHIPS

1000-1

o

t— I

liJ

□ -L. PEflLEI

X-I. ILLECEBROSUS

10 15 20 25 30 35 40

LENGTH (CM)

Figure S.— Plols of squid, LoUgo pealei and lUex illecebrosus, overall lenglli-weiglil relationship!^ for Ihe north»esl Allanlic. all data combined. (W

0.2S662L2I51«2 for /.. pealei and W = 0.048 lOL^ 7 1 wo f„r /. illecebrosus).

17

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