1982_G_61.pdf (764.4Kb)

(1)

cited

without

prior reference to the author

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International Councbl for the Exp%oration of the Sea

STOCK SIZE OF NORTH-EAST ARCTIC COB 8i&4io,t~/ke&

ESTINTED FROM

ACO'USTIC

SURVEY

DATA

198%

ARVID HYLEN AND ODD MAICKEM Institute of Marine Researeh

Postboks 1878 5011 Bergen, Norway

ABS'E'MCT

Assessments of the total s t ~ c k and spawning stock of North East Arctic cod were carried

_{o u t}

on the basis of Norwegian suuvey data and comerebal landångs. The total stsck, i,e. fish which was 3 years old and older at

%

January 1982, was estimated to

580

millzon speeimens; the corresponding sgawning stsck amoun- ted to apprornimately

1 9 0

sraillioar specåmens. The estimates for the total stock were

i n

good agreement wåth those ueported by the Working Group on Arctic Fisheries, with exseptfon

of

the 6 year old fåsh (the 1976 yearelass) for whlch the present esti-mate Es w c h 1ower tkan the one reported by the Wsrkång Group. The estimated sgawnång stock såze was considerably larger than the Working Group estimate, because of the contri- butåons to tkis ctoek eomponent by fish whlch was less than 8 years old;

the

1975 yeaxclass (7 year old fish) contributed more thari % O per cent,

The Workipng Group on Arctic Fisheries and ACFM have several

times recsmnended to make use

0%

fishery independent

data

in

(2)

stock assessment. The recoimendation was based on the faet tkat fishery dependent data has during later years been less reli- able as compared wåth earlier years. This is mainly caused by changes in fiskery regirnes, introductfon of quota schemes and changes in fish distribution patterns due to kydrographical variations. In order to meet this recomendation an intensive survey activity on North-East Arctic cod and haddock has been introduced. The present work is an atterript to estimate the total

stock

and the spawning stock of North East Arctic cod at the begisining

of I 9 8 2

on the basis of the results from these surveys

^I

MATERIAL

%n the assessment we have used the results from a series of four surveys:

1. The Barents Sea acoustic curvey,

26

January- 5 March

1982

(DALEN et al.

1 9 8 2 ) .

2 .

The LofotenIVesterålen acoustic survey,

29

January-27

February 1982 (GOD@ et al.

1 9 8 2 ) .

3. The Mare acoustic survey, P6 March-7 April

1 9 8 2

(GODØ

et

al.

1 9 8 2 ) .

4. The Svalbard groundfish/trawl survey, September-October

1 9 8 1

(RANDA and SmBSTAD

1 9 8 2 ) .

Details of each survey åre given in the reportc referred to. In Fig.

1

are indieated the approximate areas covered by the acoustic surveys.

In additiom to survey data, preliminary commercial landing

statistics, including landings from foreign vessels, for the

period from P January to the date of the surveys in the respec-

tive areas were used. Biological data from Norwegian landings

in February as well

as

fro1111 the surveys were also taken into

account .

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ASSESSMENT OF

TOTALL STOCR

The nu1~1be-s of fLsk

by

age

a t 1

January

1882

were

a r r i v e d

at, by addilag together the 4982-comercia1 catches pris- to the acaustic

survegs

and the results from each

of

the surveys, The natural mortality between 1 January and the dates

o f

the surveys were

not aecsur1ted

for. Be1aw

is

given a br%e%

deserLg-

tåsn

of

each

of

the cananlpanents in

t%re

assessment.

Up to the 2% F'ebliwary the

total

landings

o f cod

north of the Lofoten islands

w e r e absut

86 000

tons

(Tab1.e

I n ) .

South

of

Lofoten the landlngs were

abcsut 18

000

t o n s

up to the end

of

March. These quantitfes

represeneed En

total about 27 millbion

6Esh ( T a b i e M ) .

In landings from the most northern areas (West and East-Finmark) the

1975

and

1 9 7 6

year classes were repre-

sefated

by aboant the same number. Further south the importance of the 1976 year class

wac

reduced, In total, the Eandings were predaminated by the

P975

year class. Very

small

quantities were

l a n d e d

from the Svalbard region between the survey which ended

t h e 7

Bctober

1981

anad 1 January

1982.

These landå.ngs were

t h e r e f o r e

neglested.

The Barents Se

The estimates arrived

at

during the different surveys, are given

%n

'Fable

113.

The Barerits Sea coxnponent was estl.mated to 408 mi.ll&an

_{f i a h}

(DALEN

et al, 1 9 0 2 ) ,

and the

1 9 7 5 -

and 4976- year classes were represeated by 74 and 73 million fish respec-

t i v e l y .

The Vester&lan

----p -.

An area

( V e s t e r å l e n ) btaeweegi

the area covered by the Barents

Sea

surveg

and the Lofoten survey was not worked later %kan the

end of

Januar7

(GOD@

e e

al.

1 9 8 2 ) .

At this time ccgd was record-

ed in

4 2 r e c % a n g l e s with an caverage

numbesl of

_{0 , 6}

rnillisn fbsh

p e r rectangke.

Assumirag

the

same abundance and geographica1

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distribution on the 20 February as in leate Janrrary the stock in the area was estimated to 25 million

f % s h .

In lack of represen- tative age dfstsibutions from research vessels, an age distri- bution from long

line

landings from the region in Pebruary was accepted to be approprfate for the stock ila the miådle of February (Table 1B). This age distribution was predominated by the 1975 year class.

The E..ofote

The st6c.k

%n

the Vestfjord and outside the Lofoten islands was estimated to about 80 million fåsh in the period 17-20 February (GOD@ et al. 1982). Only

a

limited number of length measure- ments and age readings existed from research vessels catches.

i

More

data

was available from comnercåal landings by gillnet,

long line, hand line and Danish seine. However, ROELEFSEN (1956) found that purse seine catches would give more represen- tative age distributians of the stack than the gears mentioned.

Age-distributions from purse seine catehes were available from March, and they were assmed to be representative for the stock at the appropråate time. These data showed a clear predominance of the 1975 year class. The 1976 year class was less abundant than in midwater traw1 catches taken by the research vessel

(GOD0 et a%. 1982).

The Helgeland region, fu-rther south, was not covered by sur- veys. This area has usually a low density

of

fish, indicated by small landings. In the first quarter of

1 9 8 2 ,

a total catch of 3000 tons was recorded which was only

₁₁₅

of the catches taken in the same period in the most southern survey area, Mare. The stock in the Helgeland region was therefore acsumed to be

115

of the estimated stock at

Mare or

equal to 2,3 million fish.

The age distributionn was assumed to be the same as at M@re

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The More

The s"iick o f f M@re _was e s t i n i a t e d t o a b s u t Il_ m i l l i o n f i a h a t t h e end a f March

(GOD0

e t a l , 1 9 8 2 ) , and _{t h e} 1975 y e a r c l a s s w a s predaminant i n t h e s t o c k (Table 1B1,

The Svalbard r e ~ å o n

%n P e b 7 ~ 1 ~ a ~ y t h e ~1b71ature p a r % , of the Svalbard s t o c k c o q o n e n t wou1.d $12 a3.0-ig the Nomegå.an c o a s t and aarcounted f o r by t h e

starveys i n February-Marc%4, bu% t h e i m a t u r e f i s h w i . l l s t a y i n ^, t h e r e g i o n , T h i s coal~onent was accounted f o r by d a t a c s % & e c t e d d u r i n g %tie grouindfksh saxrvey i n Septeen%ser-Qctobe~ 198% ( M N D A

\ cmd

SMEDSTAD

1982). By I-her swepl: axycua ~ n e t h o d the s t o c k was e s t i m a t e d t a about 40 i - n i 1 l i c . m £:i.st~ whlck wac redaaced by n a t u r a l . m o r t a l i t y (M-O,b?O) t o 36 -raai.ll%srl fic"raC

1

January 1 9 8 2 . When e x c l u d i n g t h e mature f i s k by applyfng a. d - i s t r i b ~ ~ t i o n f o r t h e r a t e of matiaration sfmiLar t o t h e r e s t o f t h e s t o c k ( s e e l a t e r ) , an estf.mate o f 28 m i l l i o n kmatuire f i s h a t t h e begin- nkng of 1982 was a r r i v e d a t , This compswent was predominated by t h e 1979 y e a r e l a s s (Table % B ) which was r e e o r d e d a s one of zihe most abundant y e a r s.1-asses i n t h e r e g i o n s i n c e t h e 1 9 7 0 y e a r c % a s s (RANDA, 1982 and p e r s o n a l caam1~nicati.0113.

T o t a l stocla estinnate

-

\ The sum o f starvey e s t i m a t e s arid l a a ~ d i n g s made up t h e t o t a l s t o c k s i z e i n t h e beglnning of 1982 (Table % B ) . It should be observed t h a t no c s r r e c t i o n was made f o r t h e n a t u r a l m o r t a l i t y in t h e p e r i o d p r i o r t o t h e s u r v e y s . The s t o c k s i z e of 3 y e a r o l d and o l d e r f i s k was a s s e s s e d t o a b s u t 1580 rniilllon. f i s h whieh conripares t o

630

m i l l i o n a r r i v e d a t by t h e A r c t i c F f s h e r % e s Working Group

(ANON,

1 9 8 2 ) . Good agreement was found f o r a l l

age groups exeept f o r t h e 6 y e a r o l d s , t h e 1976 y e a r c l a s s . The e s t i m a t e of t h i s y e a r e l a s s was onby 57% of t h e Worki-ng group e s t i m a t e 9 whish wac based on t h e a c o u s t f c survey in 1981, However, t h e survey e s t i m a t e f o r 1981 was n o t i n conforznity w i t h t h e e s t å m a t e s f o r this y e a r c l a s s %n e a r l i e r surveys (DALEN ^15t a l , 1482). I n 1981 ssnie d i f f i c u l t f e s i.11 d i s e r i m i n a t -

(6)

i n g between 5 and 4 y e a r olbds migkt have o c c t ~ r r e d and t h e

9976

y e a r c l a s s might t h u s kave been o v e r e s t i m a t e d i n t h e 198%

survey.

Further

studåes _of

this

problem a r e needed.

ASSESSMENT OF SPAWMENG

STQCK

The spawning s t o c k was eseimated on t h e b a s i s of t h e same d a t a a s

the

t o t a l s t o c k , B i o l s g i c a l samples from t h e a r e a s V e s t e r å l e n - MØre showed t h a t n e a r l y a l % f i s h b o t h i n t h e c o m e r e % a $ land-

åazgs and I.n t h e r e s e å r c h vesse'b c a t c h e s was mature f i s h and hence t h e t o t a l s t o c k w i t h i n t h e s e a r e a s was assumed t o be spawners ('rable

1

and 2 ) . The n e x t s t e - was t o exclude t h e immature f i s h from t h e Iandångs i n F i n m a r k and from t h e s t o c k e s t i m a t e of t h e Barents Sea and Svalbard coinponents. The s t o c k s i z e by bength f o r t h e B a r e n t s Sea component was s p l i t t e d i n m a t u r e ' s and % m a t u r e s s f o r each of t h e 4 a r e a s used i n a s s e s -

s i n g t h e s t o e k s å z e (DALEN e t a l . 1982). The age composition of mature f i s h was a r r i v e d a t by a p p l y i n g t h e r e s p e c t i v e a g e / l e n g t h keys. T o t a l age cornpositions f o r l a n d i n g s i n West- and East-Finnmark were e s t f m a t e d by a p p l y i n g t h e r e s p e c t i v e a r e a m a t u r i t y d i s t r i b u t i o n s found i n t h e survey.

The mature fis%- in t h e Svalbard component was on m i g r a t i o n t o t h e spawning grounds d u r i n g t h e p e r i o d of t h e a c o u s t i c suuveys and t h u s i n c l u d e d

In

t h e a c s u s t i c d a t a . The t o t a l spawning s t o c k a t t h e beginning of L982 was found by s u m i n g t h e l a n d i n g s and t h e s t o c k e s t i m a t e s of t h e d i f f e r e n t c o w o n e n t s (Table 2 ) ; i r e s u l t i n g i n a spawnlng s t s c k l e v e 1 of 188 m i l l i o n f i s h , predominated by t h e 1 9 7 5 y e a r e l a s s ,

D%SCUSSIQN

The s t o c k i n t h e Svalbard r e g i o n was a s s e s s e d by t h e swept a r e a method ( U N D A and

SMEDSTAD,

1 9 8 2 ) , assuming the f i s h i n g w i d t h of t h e t r a w l t o be 25 m , which i s h a l f t h e average rneasured d i s % a n c e between t h e o t t e r b o a r d s . For e s t å m a t i n g t h e shrimp s t o c k i n t h e B a r e n t s S e a , t h e f i s h i n g w i d t h of t h e t r a w l was taken t a be about 1 5 m (TEIGCMARK and

OYNES

1981). The e f f e c t i v e w i d t h o f t h e trawb may t h u a be d i s c u s s e d , b u t a t t h e p r e s e n t

(7)

low s t o c k l e v e l in t h e b>u~a.%ba.-d r e g i o n t h e t o e a l s t o c k s i z e wou%d rnot be v e r y s e n s i e i v e %O elaanges %n thås parameter

(Table

l),

The i r a v e s t i g a t i o n s %n ₁₉₈₂ _{d f d} not csvear t h e BesterALen a r e a s a t % s : f a e t o r å l y an t i m e , ThLs a r e a was surveyed i n l a t e J a n ~ ~ a x y , at a tfnae when t h e cod was p a s s i n g through on %he way $0 syawn- i n g ar.:as f t a r t h e r s o u t h . On the o t h e r hand mature fisgr 3,s caontå.r~~t::~i2s~",.y paseing k h i s a r e a from t h e n o r t h a t l e a a t up t o t h e end February. These f i s h e s a r e t h e b a s i s f o r the NomegLali fåshery i n t h e a r e a i n February and Marcb, a f f s h e r y which generally t a k e s p l a c e an t h e smie loucafitl.es t h r o u g h s u t t h e whole season. The a s s ~ m p t i s n made e h a t t h e fLsh was d i s t r i -

( b u t e d i n t h e same manxie:c i n . Februargr a s Pr1 l a t e January m+$.$:

t h u s h o l d good, b u t i t i s t h e most u n c e ~ ~ t a i n parameter i n t h e assessment of t h e s t s c k .

Less i n f o r m a t i o n on f i s h d i s t r i b u t t o n s and abundance waa a v a i l a b l e f o r t h e Helgeland r e g i a n , No s u r v e y s were c a r r i e d o u t and v e r y few b i o l o g i e a l d a t a from comnercfal landinga were ccsllected. We trave txsed f i s h e r y s t a t å s t i c a t o e s t i m a t e t h e s t o c k compoaaent and t h e figuaee arerived a t seerns o . A g r e a t number of fiskleranen a r e liuring i n % h a t p a r t o f Norway, and w i t h a s u f f i c i e n t h i g h fish derasi-ty i n t h a t regi-on t h e y would have p r e g e r r e d t o go f i a h i n g t h e r e . Pnstead most of them go f i s h i n g in Lofoten. O f c o u r s e , t h e e s t i m a t e d s t o e k coanponent, based on

l t h e c a t c h l e v e l c i n t h e t w s r e g i o n s (Helgeland and Mare) mfght be doubted, b u t on t h e o t h e r hand e r r o r s

in

t h e e s t i m a t e of

s t o c k l e v e l i n t h e Helgelarad r e g i o n woasld probably n o t be c r i t f c a l . f a r t h e assescments of t h e t o t a l s t o c k and t h e spawni.ng s t a c k .

Rased on a r e p r of t h e spawniaag

s t o c k a maturit- ed from t h e s t o c k

s i z e by age given Pn t h e Arctrc F i s h e r i e s Working Group Report

(ANQN,

1 9 8 2 ) .

ROLLEFSEN

( 1 9 5 6 ) å n d i c a t e d t h a t age d i s t r i b u t i o n s from piurse seine cateohes in Lofoten were r e p r e s e n t a t i v e f o r t h e s t o c k %n t h e a r e a . However, due to d i f f e r e n t geographica1 d i s t r j - b u t i o n of f i s b s i z e a n d segregatåon with _time

(S&TERSDfi

(8)

1958), no age distr%bution

from a

partåcular gear is represen- tative for the total spawning stock. In table

3

are given maturity diatributions from several authsrs. It is seen that the mataa.i-ity

rates

estimated from the results in the present papeu are much

h i g h e r

than $hose given by previsus autksrs. For exaqle, absut

2 1 3

of

the

7 year old ffsh was mature in the beginnång

of

1982, compared with an average of 13% f r the period 196&/47-197'7/78 given by P O N O W R E m B et al. (1980).

f 'Ehuc, the

queståon sf representative matuscity distributåons for

/ North-East Arctic

cod

seem to need further investigations.

I

ANOW 1982. Report

of

the

k r c t l c

Fåsheries Workång Group.

(

Copenhagen. 16-23 September 1981. Coun. Meet. int.

Sea, 1982(G:%)a 1-53. (Mimeo.)

P-

DALEN, J., HYLEN, A., NAKKEN; O., U N D A , K, and SMEDSTAD, O.M.

1982. Norwegian investågations on young cod and haddock in the Barents Sea during the winter 1982.

(G: 41)

:

1- 22. (Mimeo.)

GAEIROD, D. J. 1967. Populatåon dyitamles of the Arcto-Norwegian Cod. J. Pisk. Res.

_Bd,

Can., 24: 3.45-190.

GODØ, o.R., NAKKEN, O., NES, A. and SUNNANW, K. 1982.

ⁱ

Acsustic estiinates

of

spawning cod off Lofoten and Mare in

1 9 8 % . Coun.

Meet.

i=

1982

( G : 6 2 ) :

1-16. (Mimeo.)

P

HYLEN, A. and DICUGESUND,

8 .

1973. Reeruitment of young Arcto- Norwegian csd and

hadåsck

in relation to garent stock

PONOIMARENKO,

V . B . , PONOmREmB,

I.

Y a .

and YAMGINA, N.A. 1980.

Growth and maturation of the Lofoten-Barents Sea Cod.

(9)

9

Coun.

Meet, m

int.

Coun.

- (G:25): 1-28.

(Mimeo.

)

RANDA, M. and CMEDSTAD,

0 , M .

1982. The Nomegian Groundfish Survey

at

Bear Isla11d and West-Spitsbergen. Coun.

Meet. bnt.

p---.-=v

(G:4%): 1-17,

(Mime0

^e)

RANDA, M,

1982.

Re~ruitment

irradiees

f o r

the Arctic-Nomegian

cc~d f o r

the period 1965-1979

b a s e d

o r r a the interna- tional O-group fish surveys, 9)-igkMeet. int. - ^Coean.

l

Rollefsen, G. 1954.

Observatibons on ekse

csd and cod fisheries

\

36: 4 0 - 4 7 ,

-

ROLLEFSEN, G .

1956. InL~oductiora.

SÆTERSDAL, G. 1958.

Selective

processes in the skrei fisher- les. --

Coian.

Meet. in$. Coun.

9 . 5 8 ( 7 3 ) :

1 - 4 .

(Mimeo.)

TEEGSMARK,

G . and

OPNES, P, 1981. Results of a stratiffed bot-t-om

traw& smlevey for

chråmps (Pandalus borealis)

I %n the Barents Sea in May-June 1981. Coun. Meet. int.

( K : 2 1 ) :

1-19. (Mimeo.)

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