The 1983 yearclass.pdf (1.830Mb)

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THE

1983

YEAR CLASS OF NORWEGIAN SPRING SPAWNING HERRING AS JUVENILES AND RECRUIT SPAWNERS

I n g o l f Rottingen

I n s t i t u t e of Marine Research P.O. Box 1870 Nordnes N-5024 Bergen, Norway

ABSTRACT

T h i s paper g i v e s t h e geographical d i s t r i b u t i o n and t h e migrations of t h e

1983

y e a r c l a s s of Norwegian s p r i n g spawning h e r r i n g i n t h e p e r i o d

1983-1989.

These migrations a r e compared w i t h h e r r i n g migrations of e a r l i e r p e r i o d s . F u r t h e r , t h e a c o u s t i c abundance e s t i m a t e s of t h i s y e a r c l a s s i s ^reviewed.

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166 FECUNDITY, LARVAE AND JUVENILES The

1983

y e a r c l a s s o f Norwegian spawning h e r r i n g a s . . .

INTRODUCTION

The s t o c k of Norwegian s p r i n g spawning h e r r i n g collapsed i n t h e l a t e 1960's (Dragesund e t a l . 1980). From a l e v e 1 of approximately z e r o i n 1972 t h e spawning s t o c k recovered i n a slow b u t s t e a d y manner t o a l e v e l of about

0.5

m i l l i o n tonnes i n 1983 ( H a m r e 1989). This was, however, f a r below t h e average s t o c k s i z e i n t h e p e r i o d p r i o r t o t h e s t o c k c o l l a p s e . The s t r e n g t h o f t h e y e a r c l a s s e s i n t h e p e r i o d 1970- 1982 was a l s 0 below t h e average y e a r c l a s s s t r e n g t h of e a r l i e r p e r i o d s

.

I n

1983

l a r g e amounts of O-group h e r r i n g were recorded i n t h e Barents Sea, i n d i c a t i n g favourable c o n d i t i o n s f o r s u r v i v a l and growth of t h e h e r r i n g l a r v a e and O-group. S i n c e t h e n , information on t h i s y e a r c l a s s h a s been o b t a i n e d by:

1) Acoustic surveys

2 ) Sampling commercial c a t c h e s

3)

^Tagging

R e s u l t s from t h e s e surveys and i n v e s t i g a t i o n s a r e given i n papers p r e s e n t e d t o t h e ICES S t a t u t o r y Meetings by t h e p r e s e n t a u t h o r ( R ~ t t i n g e n 1984,1985,1986,1987 and 1988). i n ICES Working Group r e p o r t s (Anon. 1984,1985,1986,1987,1988 and

1989)

and i n unpublished c r u i s e r e p o r t s t o t h e I n s t i t u t e o f Marine Research.

The aim of t h i s paper w i l l be t h e following:

1) To make a c h r o n o l o g i c a l review of t h e s e a s o n a l geographical d i s t r i b u t i o n and v a r i o u s a s p e c t s of t h e behaviour and b i o l o g y of t h e 1983 y e a r c l a s s from i t s b i r t h i n s p r i n g of 1983 t o 1988/89 when t h e bulk o f t h i s year c l a s s r e c r u i t e d t o t h e spawning s t o c k .

2 ) Discuss t h e abundance e s t i m a t e s obtained f o r t h e 1983 y e a r c l a s s .

3)

O u t l i n e t h e migration p a t t e r n s which t h e 1983 y e a r c l a s s h a s undertaken, and compare t h e s e with migration p a t t e r s from p r e v i o u s t i m e p e r i o d s .

RESULTS

Geographical d i s t r i b u t i o n YEAR

1983

The spawning i n

1983

A t t h e end of t h e 1 9 7 0 ' s and beginning of t h e 1980's r e l e a s e and r e c a p t u r e d a t a showed t h a t tagged h e r r i n g d i d n o t mix randomly w i t h i n spawning s t o c k of Norwegian s p r i n g spawning h e r r i n g , b u t t h a t t h e spawning s t o c k c o n s i s t e d o f a t l e a s t two u n i t s o r "components" ( H a m r e

1989).

I n 1983, t h e s e u n i t s (one s o u t h e r n and one n o r t h e r n ) , were e s t i m a t e d t o be of approximately t h e same s i z e . The s o u t h e r n u n i t spawned mainly on t h e t r a d i t i o n a l spawning grounds on t h e c o a s t a l banks s o u t h of 6 3 O ~ , th e n o r t h e r n u n i t spawned n o r t h o f 63ON. The Working group on Atlanto-Scandian h e r r i n g has e s t i m a t e d t h e t o t a l spawning s t o c k t o 615 thousand tonnes i n 1983. T h i s e s t i m a t e was d e r i v e d from a VPA run which was tuned t o t h e

1984

spawning s t o c k e s t i m a t e o b t a i n e d by t a g g i n g (Anon.

1988).

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The

1983

y e a r c l a s s of Norwegian spawning h e r r i n g as...

Fig. 1. Norwegian s p r i n g spawning h e r r i n g .

M. Number of l a r v a e on Gulf 111 s t a t i o n s , A p r i l 6 t h

1983.

B . Number of l a r v a e p e r m* s u r f a c e 14-21 A p r i l

1983.

( B j ø r k e , unpublished d a t a ) .

n . i

l . . .. ... . . . <_._. . : . .. . . .. . .. .. ..I:. ' ;.

-

^{. ..}^I..:^{. .}. . . . . . .... . .. .: .. .. . . . . . . ...

. . : - . : . . . . ..

:> :...;, ' .- .-,

, . ..

.. ..

.. . _.:^:_i..,?__.._:.. ^:

. . . _.-.

'n- . . _.,,.-. '._ ^'

...*... ^c...-:.. .._ '.

.. .:

. . .. .

.. . _ _{- .}.__.. ....-

. . - ^,...

Norwegian s p r i n g spawning h e r r i n g

D i s t r i b u t i o n of p o s t l a r v a e 20 June-l6 J u l y

1983.

( B j ø r k e , unpublished d a t a ) .

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168 FECUNDITY, LARVAE AND JUVENILES The 1983 y e a r c l a s s of Norwegian spawning h e r r i n g a s . . .

A p r i l 1983

-

h e r r i n g l a r v a e

The f o l l o w i n g paragraph on h e r r i n g l a r v a e i n 1983 i s a summary from Bjørke ( p e r s . c o m ) . On A p r i l

5

f o u r s t a t i o n s u s i n g a Gulf 111 plankton r e c o r d e r were taken i n t h e a r e a from S t a t t t o SmØla. The number of l a r v a e i s shown i n F i g l a . Most of t h e l a r v a e were newly h a t c h e d , b u t t h e r e were o b s e r v a t i o n s of l a r v a e up toward

14

mm. T h i s i n d i c a t e s t h a t h a t c h i n g took p l a c e on t h e spawning f i e l d s on More i n l a s t week of March

1983.

I n t h e p e r i o d 14-21 A p r i l h e r r i n g l a r v a e were recorded from S t a t t t o Bodo ( F i g l b ) . 5200 l a r v a e , of which 390 were l a r g e r than 12 mm, were taken i n

1983.

T h i s was u n t i l then t h e l a r g e s t number of l a r v a e observed s i n c e t h e s t o c k c o l l a p s e i n t h e l a t e 1 9 6 0 ' s .

The d i s t r i b u t i o n of t h e h e r r i n g l a r v a e ( F i g 1) may be taken a s an i n d i c a t i o n o f t h e e x t e n t of t h e spawning i n

1983.

The g e n e r a l conclusion i s t h a t t h e r e seems t o have occured a widespread spawning i n 1983 from S t a t t and northwards t o Boda, b u t t h e main spawning seems t o have occured i n t h e t r a d i t i o n a l spawning sites o f f Mgre.

June-July 1983

P o s t l a r v a e o f f n o r t h e r n Norway were recorded on a survey i n t h e p e r i o d 20 June-l6 J u l y

1983.

The sampling was done by p e l a g i c t r a w l . F i g 2 shows t h e d i s t r i b u t i o n of t h e h e r r i n g p o s t l a r v a e . (H. B j ~ r k e , unpublished d a t a ) . The main c o n c e n t r a t i o n s were found o f f TromsØflaket

(Approximately

7 1 ° ~ ,

I ~ O E ) . The western l i m i t o f t h e d i s t r i b u t i o n i s n o t recorded. The main p a r t of t h e p o s t l a r v a e i s found r e l a t i v e l y c l o s e t o t h e s h o r e .

Fig.

3.

Norwegian s p r i n g spawning h e r r i n g .

D i s t r i b u t i o n of O-group, I n t e r n a t i o n a l O-group survey August-September 1983 (Anon

1983).

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The 1983 y e a r c l a s s of Norwegian spawning h e r r i n g a s . . , . . .

August-September 1983

The d i s t r i b u t i o n of t h e O-group recorded d u r i n g t h e i n t e r n a t i o n a l O-group c r u i s e i n t h e Barents Sea i n t h e p e r i o d 21 August-8 September

1983

i s given i n F i g

3

(Anon 1983).This i s a t r a w l s u r v e y , t h e dense and v e r y dense a r e a s shown i n F i g

3

a r e d e f i n e d a c c o r d i n g t o t h e c a t c h of O-group h e r r i n g i n t h e t r a w l s t a t i o n s . The O-group h e r r i n g have now, compared with t h e p o s t l a r v a e s i t u a t i o n i n June-July, a f a r more o f f s h o r e and e a s t e r n d i s t r i b u t i o n . I n 1983, O-group h e r r i n g were found on a l a r g e r number o f s t a t i o n s and t h e number o f specimens a t each s t a t i o n was h i g h e r than p r e v i o u s l y observed on t h e i n t e r n a t i o n a l O-group s u r v e y s . These surveys s t a r t e d i n 1965.

November

1983

F i g

4

^shows t h e a r e a where O-group h e r r i n g was recorded i n November

1983.

Bad weather and some t e c h n i c a l d i f f i c u l t i e s l i m i t e d t h e i n v e s t i g a t i o n a r e a d u r i n g t h i s survey. There i s t h e r e f o r e a p o s s i b i l i t y t h a t O-group h e r r i n g were l o c a t e d i n o t h e r a r e a s of t h e B a r e n t s Sea t h a n shown i n F i g

4.

However, i f t h e f i g u r e shows t h e main d i s t r i b u t i o n a r e a , t h e n a c o n s i d e r a b l e e a s t t o s o u t h e a s t m i g r a t i o n of t h e O-group h e r r i n g took p l a c e i n t h e l a t e autumn months of

1983.

F i g .

4.

D i s t r i b u t i o n of O-group November

1983.

I n t e g r a t o r o u t p u t p r e s e n t e d a s t o t a l i n t e g r a t e d s c a t t e r i n g c r o s s s e c t i o n p e r n a u t i c a l m i l e m u l t i l p l i e d by 10.

A O-group h e r r i n g survey was c a r r i e d o u t i n t h e f j o r d and c o a s t a l a r e a s of northwest and n o r t h Norway i n November 1983. T h i s was p a r t of a y e a r l y i n v e s t i g a t i o n series t h a t s t a r t e d i n 1975 ( R ~ t t i n g e n 1987a).

The abundance of O-group h e r r i n g recorded i n t h e f j o r d a r e a s i n 1983 was c o n s i d e r a b l y h i g h e r than i n t h e p e r i o d 1975-1982.

S c e n a r i o a t t h e end of 1983

By t h e end of

1983

i t was c l e a r t h a t t h e

1983

y e a r c l a s s of Norwegian s p r i n g spawning h e r r i n g was abundant and d i s t r i b u t e d o v e r wide a r e a s i n t h e B a r e n t s Sea and i n t h e f j o r d and c o a s t a l a r e a s of Norway. But

@J s t r o n g was t h i s y e a r c l a s s ? Was i t comparable t o t h e l a r g e year c l a s s e s of t h e 1 9 5 0 ' s and 1960's? Was i t by t h e end of

1983

p o s s i b l e t o make any q u a n t i t a t i v e comparisons with o t h e r y e a r c l a s s e s ?

Dragesund (1970) made i n v e s t i g a t i o n s o f t h e s t r e n g t h of t h e y e a r c l a s s e s 1959-1965 a s O-group, and he a l s o measured t h e subseguent y e a r c l a s s s t r e n g t h a t r e c r u i t m e n t t o t h e spawning s t o c k . However, t h e

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methodology, equipment and c a l i b r a t i o n methods used d u r i n g t h e s e i n v e s t i g a t i o n s were d i f f e r e n t from t h o s e a p p l i e d i n

1983.

T h i s makes a d i r e c t comparison between a c o u s t i c abundance e s t i m a t e s from t h e 1 9 6 0 ' s and 1 9 8 0 ' s impossible.

Based on t h e r e s u l t s from t h e i n t e r n a t i o n a l O-group surveys i n t h e B a r e n t s Sea t h e Working group on Atlanto-Scandian h e r r i n g i n October 1983 c a l c u l a t e d an abundance index f o r t h e O-group h e r r i n g i n 1979 and 1983. The r e s u l t i s given i n t h e t e x t t a b l e below:

Year

1979 1983

Abundance index

8 431

The number of t h e 1979 y e a r c l a s s a s

4

y e a r o l d f i s h was e s t i m a t e d by t a g g i n g t o 1350 x

lo6

i n d i v i d u a l s (Anon.

1984).

Assuming a t l e a s t an equal abundance of O-group h e r r i n g i n t h e c o a s t a l a r e a s i n

1983

a s i n 1979 t h e Working group s t a t e d : " T h e Working group concluded t h a t t h e 1983 y e a r c l a s s was very s t r o n g a s O-group compared t o any y e a r c l a s s s i n c e t h e c o l l a p s e of t h e s t o c k i n t h e l a t e 1 9 6 0 ~ , and t h a t i t could w e l l t u r n o u t t o be of t h e same o r d e r of magnitude a s t h e y e a r c l a s s e s produced i n t h e p e r i o d 1961-66. These y e a r c l a s s e s had an avcerage s t r e n g t h of

l 7

x 109 i n d i v i d u a l s i n terms of VPA e s t i m a t e s of O-group f i s h (Dragesund and U l l t a n g ,

1978).

The corresponding average of

4

y e a r o l d f i s h f o r t h e y e a r c l a s s e s 1961-1966 was 1507 x

lo6

i n d i v i d u a l s .

"

^(Anon

1984) .

YEAR 1984

I

^January

^l984

Herring of t h e

1983

y e a r c l a s s (now I-group) were recorded d u r i n g t h e i n v e s t i g a t i o n s o f spawning c a p e l i n . F i g

5

g i v e s t h e t r a w l s t a t i o n s taken d u r i n g t h e s e i n v e s t i g a t i o n s . The t r a w l s t a t i o n s w i t h c a t c h e s o f I-group of h e r r i n g a r e marked with f i l l e d symbols. I f F i g .

4

is r e p r e s e n t a t i v e o f t h e d i s t r i b u t i o n i n November

1983,

t h e c a t c h e s i n January

1984

i n d i c a t e t h a t t h e h e r r i n g had migrated northwards.

May- June

1984

F i g 6 g i v e s t h e geographical d i s t r i b u t i o n of t h e I-group h e r r i n g i n t h e B a r e n t s Sea i n May-June

1984

(Toresen

1984).

There were two main d i s t r i b u t i o n a r e a s . I n t h e e a s t e r n p a r t of t h e B a r e n t s Sea t h e I-group h e r r i n g were d i s t r i b u t e d from n o r t h of t h e Rybachi p e n i n s u l a (approx.

70° 30

'

N , 32O ,O0

'

E) t o t h e Goose Bank a r e a ( approximately

73O

00 'N, 4 8 O 0 0 ' ~ ) . There were more o r less continuous r e c o r d i n g s o f I-group h e r r i n g a s a s c a t t e r i n g l a y e r i n 100-150m depth ( F i g

7 )

o v e r a d i s t a n c e of approximately 250 n a u t i c a l m i l e s . The o t h e r d i s t r i b u t i o n a r e a o f f t h e Finnmark c o a s t t o about 50 n a u t i c a l miles o f f s h o r e . I n t h i s a r e a some of t h e I-group h e r r i n g formed s c h o o l s n e a r t h e s u r f a c e , and t h e r e were some mixing w i t h a d u l t c a p e l i n .

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The

1983

y e a r c l a s s of Norwegian spawning h e r r i n g a s . . .

Fig.

5.

Number of I-group p e r trawled n a u t i c a l m i l e , January

1984.

F i g .

6.

D i s t r i b u t i o n of I-group i n May-June

1984.

I n t e g r a t o r o u t p u t a s i n F i g .

4 .

Modified from Toresen

1984.

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FECUNDITY, LARVAE AND JUVENILES The

1983

F i g .

7.

Echogram showing s c a t t e r i n g l a y e r of I-group a t 100 m d e p t h . Goose Bank. (Approx. 7 2 O ~ , 4 7 O ~ )

,

May

1984

(Toresen

1984) .

November-December

1984

A survey of t h e f j o r d and c o a s t a l a r e a s of Norway, u t i l i z i n g t h e same c o u r s e l i n e s a s t h e corresponding survey i n November-December 1983, showed t h a t t h e

1983

y e a r c l a s s was d i s t r i b u t e d o v e r much s m a l l e r a r e a s t h a n t h e y e a r b e f o r e . However,there s t i l l remained c o n s i d e r a b l e c o n s e n t r a t i o n s of t h i s y e a r c l a s s i n some f j o r d a r e a s , e s p e c i a l l y i n n o r t h e r n Norway. F i g

8

shows a t y p i c a l r e c o r d i n g of t h e I-group h e r r i n g from a f j o r d i n n o r t h e r n Norway.

S c e n a r i o a t t h e end of

1984

The corresponding surveys on t h e c o a s t and f j o r d a r e a s i n November

1983

and November

1984

showed t h a t t h e abundance ( i n numbers) and g e o g r a p h i c a l d i s t r i b u t i o n a r e a o f t h e

1983

y e a r c l a s s had decreased c o n s i d e r a b l y i n t h e s e a r e a s i n t h i s p e r i o d . T h i s was due t o e m i g r a t i o n a n d l o r m o r t a l i t y .

U n f o r t u n a t e l y , i t cannot be s t a t e d with a b s o l u t e c e r t a i n t y i f any of t h e O-group of t h e

1983

y e a r c l a s s i n t h e f j o r d s of n o r t h e r n Norway emigrated from t h e f j o r d s and joined t h e o f f s h o r e p o p u l a t i o n i n t h e B a r e n t s Sea. Due t o t h e p o s s i b l e underestimate of t h e

1983

y e a r c l a s s d u r i n g t h e a c o u s t i c survey i n November

1983,

t h e abundance e s t i m a t e s from t h e s u r v e y s i n

1984

i n t h e B a r e n t s Sea could n o t g i v e any c l e a r answer t o t h e q u e s t i o n i f t h e o f f s h o r e p a r t of t h e

1983

y e a r c l a s s had i n c r e a s e d i n

1984

due t o e m i g r a t i o n from t h e f j o r d s . However, F i g

6

shows t h a t I-group h e r r i n g were d i s t r i b u t e d c l o s e t o t h e e n t r a n c e of t h e f j o r d s e a s t of S ~ r ø y a (approximately 2 3 O ~ ) i n June 1984. T h i s may b e h e r r i n g which h a s emigrated from t h e f j o r d s . Although a major p a r t of t h e O-group h e r r i n g i n 1983 were d i s t r i b u t e d i n t h e f j o r d s from

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The 1983 year c l a s s of Norwegian spawning h e r r i n g a s . .

. . . ^.

Fig.

8.

Echogram of I-group i n U l l s f j o r d , northern Norway, December

1984.

S Ø r ~ y a t o Lofoten, t h e r e were no records of I-group h e r r i n g i n t h e open s e a o u t s i d e t h i s c o a s t a l a r e a .

Based on t h e information a v a i l a b l e by October 1984, t h e Working Group r e s t a t e d t h e i r o p i n i o n l i n a more confident way, about t h e

1983

year c l a s s i n t h e following manner: " A s observed l a s t y e a r , and confirmed i n t h i s y e a r ' s r e p o r t , t h e 1983 year c l a s s i s s t r o n g and i n view of t h e g r e a t l y improved prospects f o r recruitment t o t h e spawning s t o c k , a f i s h i n g m o r t a l i t y on t h e a d u l t component of t h e s t o c k i n t h e order of F = 0.05 w i l l have very l i t t l e e f f e c t on t h e long-term development of t h e s t o c k .

"

(Anon.

1985) .

January

1985

F i g

9

g i v e s an i n d i c a t i o n of t h e d i s t r i b u t i o n of t h e

1983

year c l a s s i n t h e e a s t e r n p a r t of t h e Barents Sea i n January 1985. The a c o u s t i c survey i n January

1985

was designed t o cover t h e d i s t r i b u t i o n a r e a f o r cod, some a r e a s where 11-group h e r r i n g may have been d i s t r i b u t e d may n o t have been surveyed. This may p a r t i c u l a r y be t h e c a s e f o r t h e n o r t h e r n borders of t h e h e r r i n g d i s t r i b u t i o n .

However, t a k i n g t h e r e s u l t s from t h e January survey a s an i n d i c a t i o n of t h e g e n e r a l d i s t r i b u t i o n , i t can be seen t h a t t h e d i s t r i b u t i o n of t h e h e r r i n g i s , i n g e n e r a l , a l i t t l e more t o t h e e a s t than t h e d i s t r i b u t i o n i n June 1984 ( F i g

6 ) .

The behaviour had changed, i n January t h e h e r r i n g mostly occured i n schools i n c o n t r a s t t o t h e s c a t t e r i n g l a y e r s i n June

1984.

There were a l s o c o n c e n t r a t i o n s of c a p e l i n i n t h e same a r e a a s t h e h e r r i n g . The sonar and echo recordings

(10)

J. / ' t FEL'UNUI'I'Y, LAKVAE AND JUVENILES The 1983 year c l a s s of Norwegian spawning h e r r i n g a s . . .

Fig.

9.

D i s t r i b u t i o n of

1983

year c l a s s i n January

1985.

I n t e g r a t o r output a s i n Fig.

4.

The Norwegian c a p e l i n winter f i s h e r y took mainly place within t h e small frame shown i n t h e f i g u r e .

of c a p e l i n and h e r r i n g were d i f f i c u l t t o d i s c r i m i n a t e and t h i s caused considerable d i f f i c u l t i e s i n c a r r y i n g o u t t h e Norwegian c a p e l i n winter f i s h e r y i n January

1985.

The a r e a where t h e c a p e l i n f i s h e r y took place i s within t h e frame included i n F i g

9.

A maximum by-catch of 10%

h e r r i n g was enforced i n t h e Norwegian c a p e l i n winter f i s h e r y i n

1985.

The by-catch s t a t i s t i c s show t h a t approximately 2500 tonnes of II- group h e r r i n g were caught i n the Norwegian and 1800 tonnes i n t h e USSR winter c a p e l i n f i s h e r y i n 1985 (Anon 1986).

Fig 10 gives the d i s t r i b u t i o n of t h e 1983 y e a r c l a s s i n May

1985

( H a m r e and Dommasnes 1985). Compared with January a westerly migration has taken p l a c e , and t h e e a s t e r n border is now approximately a t 4 0 ° ~ . The h e r r i n g was recorded both a s small schools and a s s c a t t e r i n g l a y e r s form 50 m t o 100 m depth. I n some p a r t s of t h e d i s t r i b u t i o n a r e a t h e h e r r i n g was mixed with c a p e l i n , t h e c a p e l i n l a y e r was u s u a l l y deeper than t h e h e r r i n g recordings.

Returning t o t h e c o a s t a l a r e a s , a tagging survey was conducted on t h e Norwegian c o a s t south of 6 8 0 ~ i n April-May. Small schools of h e r r i n g of t h e

1983

year c l a s s were recorded o f f More and Helgeland. This h e r r i n g had a f a r g r e a t e r growth r a t e than t h e h e r r i n g recorded i n t h e Barents Sea. ( F i g 11).

(11)

The

1983

year c l a s s of Norwegian spawning h e r r i n g a s . . .

D i s t r i b u t i o n of t h e

1983

year c l a s s i n May

1985.

Numbers denote tonnes p e r naut. m i l e 2 . (Hamre and Dommasnes

1985).

Length d i s t r i b u t i o n of t h e

1983

year c l a s s i n May

1985).

September

1985

F i g 12 shows t h e d i s t r i b u t i o n of t h e 1983 year c l a s s i n September 1985 A comparison with Fig 10 (May 1985) shows t h a t t h e r e was no major change i n geographical d i s t r i b u t i o n of t h e

1983

year c l a s s i n t h e Barents Sea during t h e summer season of

1985.

I n September t h e h e r r i n g were mostly d i s t r i b u t e d i n dense schools near t h e s u r f a c e during daytime, b u t t h e r e were a l s a recorded schools of h e r r i n g down t o 100-150 m depth. During n i g h t time t h e schools were d i s s o l v e d and t h e

(12)

176 FECUNDITY, LARVAE AND JWENILES The i983 y e a r c l a s s of Norwegian spawning h e r r i n g a s . . .

Fig. 1 2 . Norwegian s p r i n g spawning h e r r i n g .

1983

year c l a s s i n September

1985.

Numbers denote tonnes p e r naut. m i l e 2 .

Fig.

13. 1983

year c l a s s i n November

1985.

Numbers denote tonnes per naut. mile2.

(13)

The

1983

h e r r i n g was recorded i n s c a t t e r i n g l a y e r s . Some O-group h e r r i n g and j u v e n i l e cod and haddock were recorded t o g e t h e r with t h e 11-group h e r r i n g .

November

1985

F i g

13

shows t h e d i s t r i b u t i o n of t h e 1983 y e a r c l a s s i n November 1985.

The h e r r i n g of t h e

1983

y e a r c l a s s occurred t o g e t h e r with O-group h e r r i n g . Only t h e a r e a west of

4 1 O ~

was surveyed. F i g 11 and

13

show t h a t a comprehensive migration had taken p l a c e eastwards during a time i n t e r v a l of 2 months.The h e r r i n g i n t h e e a s t e r n p a r t of t h e d i s t r i b u t i o n a r e a were mostly recorded a s a s c a t t e r i n g l a y e r i n t h e upper

5Om

of t h e water masses.

I n November

1984

considerable amounts of I-group h e r r i n g were recorded i n t h e f j o r d s of Northern Norway, e s p e c i a l l y n o r t h of

69ON.

^Very

l i t t l e 11-group h e r r i n g were recorded i n t h e s e a r e a s i n November 1985, by t h i s time t h e f a r g r e a t e r p a r t of t h e h e r r i n g of t h e 1983 year c l a s s had migrated from t h i s a r e a . South of Lofoten (68ON) no h e r r i n g of t h e 1983 year c l a s s were found i n t h e f j o r d a r e a s i n November 1985.

I

Scenario a t t h e end of 1985

I

Two d i f f e r e n t "populations" of t h e

1983

y e a r c l a s s could s t i l l be recognized:

A ) I n t h e Barents Sea, t h e main c o n c e n t r a t i o n s of t h e

1983

year c l a s s undertook a western migration i n t h e w i n t e r months, from an a r e a around 4 0 ° ~ to an a r e a o f f e a s t e r n Finnmark and Kola. I n t h e summer season t h e geographical d i s t r i b u t i o n remained r e l a t i v e l y c o n s t a n t , but i n October a migration t o t h e e a s t e r n p a r t of t h e Barents Sea took p l a c e . I n winter t h e h e r r i n g i n t h e Barents Sea occurred t o g e t h e r with c a p e l i n , i n autumn t h e concentrations of t h e 1983 y e a r c l a s s were mixed with O-group h e r r i n g

(1985

year c l a s s ) .

B ) On t h e c o a s t , h e r r i n g of t h e

1983

y e a r c l a s s migrated from t h e i n n e r p a r t of t h e f j o r d s where they were d i s t r i b u t e d a s O-group. Minor p a r t s of t h e h e r r i n g were found i n t h e o u t e r c o a s t a r e a s south of 68ON i n s p r i n g . F u r t h e r , t h e 1983 year c l a s s began t o appear i n t h e c o a s t a l h e r r i n g f i s h e r y i n autumn of

1985.

This h e r r i n g had a l a r g e r growth r a t e than t h e h e r r i n g d i s t r i b u t e d i n t h e Barents Sea.

YEAR i986 January

1986

F i g

14

shows t h e d i s t r i b u t i o n of 111-group h e r r i n g i n January

1986.

This was t h e most e a s t e r n d i s t r i b u t i o n of t h e

1983

y e a r c l a s s t h a t had been observed s i n c e June

1984.

From about 38OE and eastwards, t h e h e r r i n g was recorded a s a " c a r p e t H n e a r t h e bottom. A t some l o c a t i o n s , (approximately 7Z0N, 4 6 0 ~ ) . denser c o n c e n t r a t i o n s appeared a s

"columns" r i s i n g up t o 50m from t h e s e a bed. West of 38OE, some l a r g e schools of h e r r i n g were d e t e c t e d , p a r t i c u l a r y i n t h e a r e a n o r t h and e a s t of t h e Skolpen Bank. I n t h e period January-April 1986 a f i s h e r y on t h e

1983

year c l a s s of h e r r i n g was c a r r i e d o u t by USSR i n ICES a r e a I ( e a s t e r n p a r t of t h e Barents S e a ) . The t o t a l c a t c h i n t h i s f i s h e r y was approximately 25 thousand tonnes.

(14)

178

FECUNDITY, LARVAE AND JUVENILES The 1983 year c l a s s of Norwegian spawning h e r r i n g a s . . .

Fig.

14.

D i s t r i b u t i o n of t h e 1983 year c l a s s i n January 1986.

Numbers denote tonnes p e r naut. mile2.

Spawning season, February-March 1986 ¹

,

!

I n 1986 h e r r i n g of t h e

1983

year c l a s s appeared f o r t h e f i r s t time on t h e spawning grounds o f f More. About

7%

of t h e h e r r i n g i n t h e spawning a r e a s ( l a r g e v a r i a t i o n s from a r e a t o a r e a ) belonged t o t h i s year c l a s s . This was h e r r i n g with a l a r g e r growth r a t e than t h a t of t h e h e r r i n g of t h e same year c l a s s i n the Barents Sea. However, l e s s than 10% of t h e

1983

year c l a s s which appeared on t h e spawning grounds had maturing gonads and may t h e r e f o r e have been r e c r u i t spawners, t h e rest were immature f i s h .

May 1986

Fig

15

g i v e s t h e d i s t r i b u t i o n i n May 1986. There was now an extended east-west d i s t r i b u t i o n i n a " b e l t " of approximately 40-50 n a u t i c a l miles width. The h e r r i n g was mostly recorded a s a s c a t t e r i n g l a y e r i n 150-200 m depth. The d e n s i t y of t h e h e r r i n g was much lower than recorded during previous surveys.

Herring were a l s 0 recorded i n t h e c o a s t a l a r e a s . During a tagging survey i n April 1986 schools c o n s i s t i n g of

1983

year c l a s s h e r r i n g only were recorded i n t h e o u t e r c o a s t a l a r e a s between 66ON and 6 7 0 ~ . This h e r r i n g had a l a r g e r growth r a t e than t h e h e r r i n g i n t h e Barents s e a ( F i g 1 6 ) .

(15)

The 1983 y e a r c l a s s of Norwegian spawning h e r r i n g a s . . .

F i g .

15. 1983

y e a r c l a s s i n May

1986.

Numbers denote tonnes p e r n a u t . m i l e 2 .

Fig.16. Norwegian s p r i n g spawning h e r r i n g .

1983

y e a r c l a s s i n May 1 9 8 6 ~

(16)

FECUNDITY, LARVAE AND JWENILES The 1983 year c l a s s of Norwegian spawning h e r r i n g a s . . .

Fig.

17. 1983

year c l a s s i n August 1986.

- B a r e n t s e a w e s t ( M a y 8 6 )

_ _ - W

O f f T r o m s ( A u g u s t 8 6 )

Fig.

18.

Length d i s t r i b u t i o n of t h e o f f s h o r e d i s t r i b u t e d h e r r i n g i n May 1986 (Barents Sea) and August

1986

(Norwegian S e a ) .

(17)

The

1983

August 1986

By t h i s t i m e t h e 1983 year c l a s s had emigrated from t h e Barents Sea and t h e r e were o b s e r v a t i o n s of s c a t t e r e d c o n c e n t r a t i o n s up t o 150 n a u t i c a l miles of t h e c o a s t of Norway from 6 4 0 ~ t o 70°N ( F i g

17)

.The main c o n c e n t r a t i o n s were found n o r t h of 68ON. I n t h i s p e r i o d t h e h e r r i n g were l o c a t e d i n v a r i o u s depths from n e a r t h e s u r f a c e t o depths o f 200-300m. The s o n a r r e c o r d i n g s n e a r t h e s u r f a c e c o n s i s t e d of s m a l l s c h o o l s , t h e l a r g e r s c h o o l s were l o c a t e d i n depths of

5Om

and deeper. The mean l e n g t h of t h e

1983

y e a r c l a s s had i n c r e a s e d c o n s i d e r a b l y s i n c e t h e h e r r i n g l e f t t h e Barents Sea ( F i g

18).

November

1986

The h e r r i n g i n t h e o f f s h o r e a r e a s had c o n c e n t r a t e d n e a r e r t h e c o a s t , between 66ON and 6 7 0 ~ . ( F i g

19) .

The h e r r i n g were now l o c a t e d i n s c h o o l s n e a r t h e s u r f a c e d u r i n g n i g h t t i m e

(O-5Om)

and n e a r bottom o r down t o 250-300m depth d u r i n g daytime. The s i z e of t h e s c h o o l s showed l a r g e v a r i a t i o n s , d u r i n g n i g h t t h e h e r r i n g o f t e n s p l i t i n t o small l o o s e s c h o o l s .

I n autumn 1986 t h e 1983 y e a r c l a s s became abundant i n t h e c a t c h e s i n Norwegian h e r r i n g f i s h e r y , The f i s h e r y took p l a c e i n t h e f j o r d a r e a s were t h e h e r r i n g had wintered s i n c e t h e s t o c k c o l l a p s e and t h e m i g r a t i o n t o t h e f e e d i n g and w i n t e r i n g grounds i n t h e Norwegian Sea terminated. The

1983

year c l a s s occurred t o g e t h e r w i t h o l d e r h e r r i n g on t h e w i n t e r i n g grounds.

Fig.

19.

D i s t r i b u t i o n of t h e 1983 y e a r c l a s s i n November 1986.

(18)

1983

S c e n a r i o a t t h e end of 1986

A v e r y small f r a c t i o n of t h e 1983 y e a r c l a s s ( l e s s than 1%) seemed t o be r e c r u i t spawners i n w i n t e r 1986. These h e r r i n g spawned on t h e t r a d i t i o n a l spawning grounds o f f More. They were n o t h e r r i n g o r i g i n a t i n g from t h e Barents Sea n u r s e r y a r e a .

I n 1986 t h e two types of h e r r i n g of t h e 1983 year c l a s s could s t i l l be recognized. Some h e r r i n g were recorded on t h e t r a d i t i o n a l spawning s i t e s o f f M Ø r e i n February-March,in t h e o u t e r c o s t a 1 a r e a s i n s p r i n g and i n w i n t e r i n g a r e a s i n some f j o r d s from October/Nowember. These h e r r i n g had a l a r g e growth r a t e .

But by f a r t h e l a r g e r p a r t of t h e 1983 y e a r c l a s s was i n w i n t e r l e a r l y s p r i n g of 1986 l o c a t e d i n t h e e a s t e r n p a r t of t h e Barents s e a . I n s p r i n g of 1986 a fundamental change i n t h e d i s t r i b u t i o n of t h e 1983 y e a r c l a s s took p l a c e . I n May-June t h e whole o f f s h o r e p o p u l a t i o n of t h e

1983

y e a r c l a s s migrated westwards o u t of t h e Barents Sea and i n t o t h e Norwegian Sea o f f t h e Norwegian c o a s t . The " s t a y " i n t h e Barents Sea n u r s e r y a r e a had t h u s terminated.

YEAR

1987

January

1987

F i g 20 shows t h e w i n t e r i n g d i s t r i b u t i o n a r e a of t h e h e r r i n g (January

1987).

During day t i m e t h e h e r r i n g occurred i n s c h o o l s i n 100-200m d e p t h , d u r i n g n i g h t time t h e h e r r i n g ascended t o t h e upper ?Om and o f t e n occurred i n l a r g e dense s c h o o l s .

F i g . 20. Norwegian s p r i n g spawning h e r r i n g .

D i s t r i b u t i o n of t h e 1983 y e a r c l a s s i n January 1987.

(19)

Spawning s e a s o n , February-March 1987

T h i s y e a r t h e

4

y e a r o l d h e r r i n g dominated t h e b i o l o g i c a l samples from t h e t r a d i t i o n a l spawning s i t e s o f f Møre. The g e o g r a p h i c a l d i s t r i b u t i o n o f t h e 1983 y e a r c l a s s i s given i n F i g 21, On t h e spawning grounds t h e h e r r i n g mostly o c c u r r e d i n l o o s e s c h o o l s o r i n s c a t t e r i n g l a y e r s . There were observed o n l y a few dense s c h o o l s i n February-March 1987.

The h e r r i n g of t h e 1983 y e a r c l a s s were mixed with o l d e r h e r r i n g on t h e spawning f i e l d s . About 40-60% of t h e 1983 y e a r c l a s s which was

1983

y e a r c l a s s on t h e spawning sites o f f Møre i n February/March

1987.

recorded on t h e spawning grounds were r e c r u i t spawners. But t h e g r e a t e r p a r t of t h e

1983

y e a r c l a s s were s t i l l immature and t h e r e f o r e d i d n o t appear on t h e spawning grounds. The average l e n g t h of t h e h e r r i n g of t h e

1983

y e a r c l a s s i n t h e spawning a r e a s was approximately 28 cm. However, one sample from t h e s o u t h e r n p a r t of t h e d i s t r i b u t i o n a r e a had a mean l e n g t h of

31

cm. This may have been h e r r i n g of c o a s t a l o r i g i n

.

April-May 1987

The main o f f s h o r e c o n c e n t r a t i o n s were now l o c a t e d t o t h e n o r t h of t h e spawning sites ( F i g 2 2 ) , and t h e e x t e n s i o n of t h e d i s t r i b u t i o n a r e a had i n c r e a s e d .

I n April-May 1987 s c h o o l s c o n s i s t i n g o f

1983

y e a r c l a s s o f h e r r i n g were recorded i n t h e o u t e r c o a s t a l a r e a between 6 6 O ~ and 6 7 0 ~ . However, according t o t h e l e n g t h d i s t r i b u t i o n s , t h i s was obviously n o t t h e same type of h e r r i n g a s w a s recorded i n t h e same a r e a i n April-May i n

1985

and 1986. The mean l e n g t h of t h e h e r r i n g was a c t u a l l y g r e a t e r i n 1986 than i n

1987

( F i g 2 3 ) , i n d i c a t i n g t h a t t h e f a s t growing h e r r i n g i n t h i s a r e a i n 1985 and 1986 had been r e p l a c e d by a h e r r i n g with a slower growth r a t e i n

1987.

The "new" h e r r i n g i n t h i s a r e a probably o r i g i n a t e d from t h e n u r s e r y a r e a s i n t h e B a r e n t s Sea.

(20)

1983

.,..

.<" e... .I.. e... e...

.,..

^i."

.."

..r ..r ..r I.. i I," i... ,I.. I... I."

....

^i,..^t... <."

'."

^.I

1 1 -

-

^"

^..

D i s t r i b u t i o n of t h e 1983 year c l a s s i n May

1987.

O/o

4

O

---+- 8 3 year d a s s in 1986

3 O

-

^{8 3}year class in 1987

2

o

1

o

Fig.

23. 1983

year c l a s s i n Norwegian c o a s t a l waters o f f Helgeland (between

6 5 0 ~

and

6 8 O N )

i n April

1986

and April

1987).

(21)

LARVAE

The

1983

y e a r d a s s of Norwegian spawning h e r r i n g a s . . .

June-July

1987

The m i g r a t i o n of t h e o f f s h o r e d i s t r i b u t e d h e r r i n g continued northwards; t h e d i s t r i b u t i o n a r e a f o r J u l y

1987

i s given i n F i g 24. I n t h e p e r i o d A p r i l - J u l y

1987

t h e h e r r i n g mostly occurred i n small s c h o o l s n e a r t h e s u r f a c e . The h e r r i n g r e c o r d i n g s were mixed with plankton r e c o r d i n g s .

1983

y e a r c l a s s i n J u l y 1987.

August

1987

Medio August

1987

t h e

1983

year c l a s s concentrated i n t h e a r e a west of Lofoten ( F i g 2 5 ) . Compared with t h e p e r i o d A p r i l - J u l y , t h e behaviour of t h e h e r r i n g had changed. The h e r r i n g concentrated i n a r a t h e r dense s c a t t e r i n g l a y e r i n about 10-20m depth d u r i n g most of t h e Bay. This was t y p i c a l " f a t h e r r i n g " , with a l o t of f a t i n t h e i n t e s t i n e a r e a . The gonads were poorly developed.

I

I September

1987

I n September t h e main c o n c e n t r a t i o n s of h e r r i n g had migrated i n t o t h e V e s t f j o r d a r e a ( F i g 2 6 ) . By t h i s t i m e t h e h e r r i n g began t o make e x t e n s i v e v e r t i c a l m i g r a t i o n s . During day t i m e t h e h e r r i n g were recorded i n s c h o o l s a t 250 m t o 300 m depth, r i s i n g towards t h e s u r f a c e and d i s p e r s i n g d u r i n g n i g h t . The gonads were c o n s i d e r a b l y more developed than i n August.

(22)

The 1983 year c l a s s of Norwegian spawning h e r r i n g a s . . .

1983

year c l a s s i n August

1987.

Fig.

26.

D i s t r i b u t i o n of t h e 1983 year c l a s s i n September

1987.

(23)

The

1983

year c l a s s i n November

1987.

(24)

188 1983

November

1987

I n October t h e h e r r i n g migrated f u r t h e r i n t o t h e V e s t f j o r d , and by November t h e h e r r i n g which s i n c e

1983

had been d i s t r i b u t e d o f f s h o r e , were now l o c a t e d i n t h e t r i b u t a r y f j o r d s of t h e V e s t f j o r d ( F i g 2 7 ) . Here t h e h e r r i n g occurred i n enormous s c h o o l s , o f t e n extending over s e v e r a l n a u t i c a l m i l e s . The h e r r i n g undertook v e r t i c a l m i g r a t i o n s ( F i g 2 8 ) . The gonads were f u r t h e r developed, and t h e amount of f a t i n t h e i n t e s t i n e had c l e a r l y decreased compared with August/ September. The h e r r i n g wintered i n t h e V e s t f j o r d u n t i l t h e end of January

1988.

F i g . 28, Norwegian s p r i n g spawning h e r r i n g

Echo r e c o r d i n g s d u r i n g daytime (upper) and n i g h t t i m e

( l o w e r ) of t h e

1983

y e a r c l a s s from approximately t h e same l o c a t i o n i n t h e Ofotf jord i n November

1987.

(25)

The 1983 y e a r c l a s s o f Norwegian spawning h e r r i n g a s . . .

S c e n a r i o a t t h e end of i987

A minor p a r t of t h e 1983 y e a r c l a s s matured and spawned on t h e t r a d i t i o n a l spawning sites i n 1987. A f t e r spawning t h e h e r r i n g d i d n o t resume t h e f e e d i n g m i g r a t i o n r o u t e s from t h e t i m e p r i o r t o t h e s t o c k c o l l a p s e , i . e . t o t h e J a n Mayen- North I c e l a n d a r e a . The f e e d i n g a r e a s i n 1987 were from t h e c o a s t a l a r e a s of n o r t h e r n Norway between 6 4 0 ~ and 70°N and e x t e n d i n g approximately 200 n a u t i c a l miles i n t h e Norwegian Sea. I n August t h e h e r r i n g c o n c e n t r a t e d w e s t of t h e Lofoten I s l a n d s , and i n September t h e y migrated i n t o t h e V e s t f j o r d , and i n October f u r t h e r east i n t o t h e t r i b u t a r y f j o r d s of t h e V e s t f j o r d . The w i n t e r i n g a r e a s i n

1987188

^{( F i g}

17)

were t h u s s l i g h t l y d i f f e r e n t from 1986187, t h e l a t t e r w i n t e r i n g a r e a was i n t h e o u t e r p a r t of t h e V e s t f j o r d ( F i g 2 0 ) .

YEAR

1988

February 1988

According t o d a t a from t h e f i s h e r i e s , t h e main p a r t of t h e 1983 y e a r

c l a s s appeared on t h e spawning sites o f f Møre i n mid-February. F i g 29 l g i v e s t h e a r e a where spawning h e r r i n g were recorded i n t h e p e r i o d

22.2-19.3

1988.

The main spawning grounds were from S t a t t ( 6 2 O ~ ) t o K r i s t i a n s u n d , and some spawning was a l s 0 recorded n o r t h t o Vikna.

D i s t r i b u t i o n of t h e 1983 year c l a s s on t h e spawning s i t e s o f f Møre i n FebruaryIMarch

1988.

(26)

There were very few r e c o r d s of spawning h e r r i n g i n t h e Lofoten- V e s t e r å l e n a r e a . The spawning grounds were e s s e n t i a l l y t h e same a s i n t h e p e r i o d 1974-1987. I n 1988, approximately

95%

of t h e spawning s t o c k c o n s i s t e d of 1983 y e a r c l a s s h e r r i n g . During day time t h e h e r r i n g on t h e spawning grounds were d i s t r i b u t e d "hard" down t o t h e bottom and were v e r y d i f f i c u l t t o observe on t h e echo r e c o r d e r . Only i n a few r e s t r i c t e d a r e a s could s c h o o l s b e seen n e a r t h e bottom. However, d u r i n g n i g h t t i m e t h e h e r r i n g r o s e and d i s p e r s e d i n t h e upper 100 meters of t h e water masses. F i g 30 shows a t y p i c a l n i g h t r e c o r d i n g on t h e spawning f i e l d s i n February

1988.

The main spawning commenced by t h e end of February i n t h e southernmost p a r t of t h e d i s t r i b u t i o n a r e a . Spawning on spawning grounds s o u t h of S t a t t was n o t resumed t o any e x t e n t i n 1988.

Nighttime echo r e c o r d i n g of spawning h e r r i n g . More, February 1988.

A p r i l

1988

The f e e d i n g m i g r a t i o n i n

1988

seems t o have followed t h e same p a t t e r n a s i n

1987.

The s p e n t h e r r i n g have moved i n a n o r t h e r n d i r e c t i o n from t h e spawning grounds and t h e geographical d i s t r i b u t i o n a t t h e end of A p r i l

1988

i s o u t l i n e d i n F i g

31.

The d i s t r i b u t i o n a r e a is l o c a t e d o f f t h e Norwegian c o a s t mainly between 640N and 6 8 O ~ and e x t e n d i n g approximately 150 n a u t i c a l m i l e s westwards.

May

1988

The g e o g r a p h i c a l d i s t r i b u t i o n i n May 1988 i s shown i n F i g 32. Compared t o t h e end of A p r i l 1988 t h e h e r r i n g have migrated f u r t h e r n o r t h and a r e d i s p e r s e d over a wider a r e a .

(27)

FECUNDITY, LARVAE AND

The

1983

Fig.

31. 1983

year c l a s s i n April

1988.

Fig.

32.

D i s t r i b u t i o n of t h e 1983 year c l a s s i n May 1988.

(28)

192 FECUNDITY, LARVAE AND JUVENILES The

1983

August

1988

The h e r r i n g migrated eastwards d u r i n g summer, and were l o c a t e d i n t h e o u t e r p a r t of t h e V e s t f j o r d i n August(Fig

33).

^However, some h e r r i n g were d i s t r i b u t e d west of t h e Lofoten I s l a n d s were t h e main c o n c e n t r a t i o n s were l o c a t e d i n August

1987

( F i g 2 5 ) . The h e r r i n g were recorded a s a more o r less continuous l a y e r a t t h e bottom (approximately depth 200-250 m ) and t o about 30-40111 above bottom. But from midnight t o approximately

4

a.m., t h e h e r r i n g r o s e and formed a s c a t t e r i n g l a y e r i n t h e upper 50 meters of t h e water masses.

F i g .

33. 1983

y e a r c l a s s i n August

1988.

(29)

The

1983

November 1988

By November 1988, a s was t h e c a s e i n November 1987, t h e h e r r i n g had migrated f u r t h e r i n t o t h e V e s t f j o r d and were now l o c a t e d i n t h e t r i b u t a r y f j o r d s . I n 1988 t h e main c o n c e n t r a t i o n s were found i n O f o t f j o r d , T y s f j o r d and Lavangen. The behaviour was s i m i l a r t o t h a t of November 1987.

S c e n a r i o a t t h e end of

1988

I n

1988

t h e major p a r t of t h e

1988

y e a r c l a s s matured and spawned. The spawning and f e e d i n g m i g r a t i o n s i n

1988

were s i m i l a r t o

1987,

t h u s t h e

1983

y e a r c l a s s seemed t o have e s t a b l i s h e d t h e spawning and w i n t e r i n g a r e a s and t h e m i g r a t i o n c y c l u s . T h i s c y c l u s was d i f f e r e n t from t h a t of t h e t i m e p r i o r t o t h e s t o c k c o l l a p s e , a s t h e

1983

y e a r c l a s s d i d n o t resume t h e f e e d i n g m i g r a t i o n t o t h e Jan MayenINorth I c e l a n d a r e a .

YEAR 1989 February-March

1989

F i g

34

g i v e s t h e d i s t r i b u t i o n of h e r r i n g on t h e spawning f i e l d s i n February-March

1989.

The main spawning f i e l d s a r e s i m i l a r t o

1988.

F i g .

34. 1983

y e a r c l a s s on t h e spawning s i t e s i n FebruaryIMarch

1989.

(30)

However, spawning h e r r i n g were recorded o f f Karmøy (approximately 59ON) and t h e r e were a l s 0 r e p o r t s of spawning h e r r i n g from a r e a s f u r t h e r s o u t h , perhaps t o Siragrunnen (approximately

58ON)

P r i o r t o 1955, t h e s e were important spawning grounds f o r t h e Norwegian s p r i n g spawning h e r r i n g . F i g

35

g i v e s t h e l e n g t h and age d i s t r i b u t i o n of t h e h e r r i n g from t h e spawning a r e a a t KarmØy. T h i s was p r a c t i c a l l y t h e same l e n g t h and age d i s t r i b u t i o n a s t h e h e r r i n g on t h e spawning sites o f f M Ø r e . A t p r e s e n t i t i s n o t known i f t h i s h e r r i n g had t h e i r n u r s e r y a r e a i n t h e B a r e n t s S e a , o r i f they a r e of c o a s t a l o r i g i n .

F i g .

35.

Length and age d i s t r i b u t i o n of spawning h e r r i n g a t Karmøy, March

1989.

Acoustic abundance estimates

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

1983

y e a r c l a s s have been made by t h e u s e of a c o u s t i c techniques. The procedures, development h i s t o r y , t h e o r e t i c a l b a s i s and t h e a p p l i c a t i o n of t h i s technique t o p e l a g i c f i s h i n n o r t h e r n waters a r e d e s c r i b e d i n a paper t o t h e S o v i e t - Norwegian symposium on Barents Sea c a p e l i n i n August

1984

(Dommasnes and R ø t t i n g e n 1985).

A c e n t r a l key i n t h e a c o u s t i c abundance e s t i m a t i o n i s t h e t a r g e t s t r e n g t h

-

f i s h l e n g t h r e l a t i o n which i s used t o c o n v e r t t h e a c o u s t i c d a t a t o number o f f i s h . The O-group h e r r i n g i n Norwegian w a t e r s have been measured a c o u s t i c a l l y s i n c e 1975 ( R ø t t i n g e n 1987a). The f o l l o w i n g t a r g e t s t r e n g t h

-

l e n g t h r e l a t i o n has been u t i l i z e d t o c o n v e r t t h e a c o u s t i c d a t a t o number of f i s h d u r i n g t h e s e surveys:

This i s t h e same t a r g e t s t r e n g t h

-

l e n g t h r e l a t i o n a s i s u t i l i z e d f o r a b s o l u t e abundance e s t i m a t e s o f Barents Sea c a p e l i n , and i t s o r i g i n is a combination o f :

1) Counting c a p e l i n t r a c e s on t h e echogram paper and r e l a t i n g t h i s t o t h e a c t u a l i n t e g r a t o r v a l u e o b t a i n e d from t h e r e c o r d i n g .

2 ) The l e n g t h dependant dimension

(19.1

logL where L i s t h e l e n g t h of t h e f i s h ) o r i g i n a t e s from experimental measurements o f s e v e r a l c l u p e o i d f i s h (Dalen e t a l . 1976).

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FECUNDITY, LARVAE AND JUVENILES

195

The t a r g e t s t r e n g t h

-

l e n g t h r e l a t i o n i s n o t based on O-group h e r r i n g d a t a e x c l u s i v e l y , and abundance e s t i m a t e s of O-group and young h e r r i n g based on t h i s conversion f a c t o r should be used with c a r e when a p p l i e d i n an a b s o l u t e s e n s e . However, t h i s was t h e only t a r g e t s t r e n g t h

-

l e n g t h r e l a t i o n " a v a i l a b l e " when t h e s y s t e m a t i c O-group h e r r i n g i n v e s t i g a t i o n s s t a r t e d i n 1975.

The Working group on Atlanto-Scandian h e r r i n g has t h u s n o t a p p l i e d t h e s e e s t i m a t e s a s a b s o l u t e , they have a p p l i e d t h e e s t i m a t e s a s abundance " i n d i c e s " , and a non-biological "conversion f a c t o r " has been used t o convert t h e O-group number f o r a c e r t a i n y e a r c l a s s t o number of r e c r u i t spawners

4

y e a r s l a t e r . Other d i f f i c u l t i e s have been encountered d u r i n g t h e a c o u s t i c survey work on t h e

1983

y e a r c l a s s i n t h e Barents Sea. The survey i n November 1983 was s e v e r e l y hampered by bad weather and t h e t o t a l d i s t r i b u t i o n a r e a was t h e r e f o r e probably n o t covered. I n 1984 and e s p e c i a l l y i n 1985 t h e h e r r i n g r e c o r d i n g s were mixed with c a p e l i n , making an e x a c t e s t i m a t i o n of t h e h e r r i n g abundance d i f f i c u l t . I n January l986 t h e h e r r i n g were recorded c l o s e t o t h e bottom. Table 1 g i v e s t h e abundance e s t i m a t e s of t h e

1983

year c l a s s u s i n g t h e t a r g e t s t r e n g t h

-

l e n g t h r e l a t i o n d e s c r i b e d above.

Table 1. Acoustic abundance e s t i m a t e s of immature

1983

y e a r c l a s s (TS ⁼

19.

i i o g ~

-

74.0)

Barents Sea ( F i g

6)

C o a s t a l a r e a s

Barents Sea ( F i g 1 0 ) Barents Sea ( F i g 1 2 ) Barents Sea ( F i g

1 4 )

Barents Sea

There h a s been c o n s i d e r a b l e d i s c u s s i o n of t h e " r e a l " t a r g e t s t r e n g t h v a l u e f o r h e r r i n g (Anon. 1987b). There h a s now been p r e s e n t e d s t r o n g evidence f o r a c c e p t i n g a g e n e r a l "20 logL" dependance i n t h e t a r g e t s t r e n g t h

-

l e n g t h r e g r e s s i o n equation f o r h e r r i n g . However, t h e t a r g e t s t r e n g t h i s n o t a f i x e d v a l u e . It i s s t r o n g l y r e l a t e d t o t h e swimbladder a r e a and volume and w i l l change due t o p h y s i o l o g i c a l changes of t h e swimbladder with depth and f i s h c o n d i t i o n . Thus t h e i n t e r c e p t v a l u e i n t h e t a r g e t s t r e n g t h -1ength r e g r e s s i o n e q u a t i o n w i l vary according t o season, depth e t c .

From t h e chronological review given i n t h e p r e s e n t p a p e r , i t can be s e e n t h a t h e r r i n g have been recorded with v a r y i n g behaviour according t o season, geographical d i s t r i b u t i o n e t c . , some examples a r e given below :

(32)

196 FECUNDITY, LARVAE AND JWENILES The 1983 y e a r c l a s s of Norwegian spawning h e r r i n g a s . . .

1) r e c o r d i n g s of I-group i n small schools i n deeper w a t e r , summer season ( F i g

7 ) .

2) V e r t i c a l m i g r a t i o n , a d u l t h e r r i n g i n w i n t e r i n g a r e a s . The " c o r r e c t "

t a r g e t s t r e n g t h v a l u e w i l l probably change d r a m a t i c a l l y from n i g h t t o day s i t u a t i o n ( F i g 2 8 ) .

3 )

Night s c a t t e r i n g l a y e r , spawning a r e a s ( F i g 3 0 ) .

By u s i n g o n l y one TS

-

v a l u e one should of c o u r s e be c a r e f u l t o compare e s t i m a t e s made d u r i n g d i f f e r e n t times of y e a r and/or day. The most r e l i a b l e r e s u l t s w i l l be obtained by comparing e s t i m a t e s made under t h e same c o n d i t i o n s , i . e . t h e same time of t h e y e a r .

From 1987 t h e abundance e s t i m a t e s of t h e 1983 y e a r c l a s s of h e r r i n g have been used a s a b s o l u t e e s t i m a t e s i n t h e assessment work o f t h e Working Group. Taken i n t o account t h e information a v a i l a b l e i n October 1987, t h e Working Gsoup on Atlanto-Scandian h e r r i n g recommended t h e following t a r g e t s t r e n g t h

-

l e n g t h equation f o r u s e i n a c o u s t i c abundance e s t i m a t i o n s of a d u l t Norwegian s p r i n g spawning h e r r i n g :

TS = 20.0 logL

-

71.9 (Foote 1987, Anon.

1988)

This v a l u e i s based on " i n - s i t u " t a r g e t s t r e n g t h measurements of a d u l t h e r r i n g and may n o t be t h e c o r r e c t t a r g e t s t r e n g t h

-

l e n g t h r e l a t i o n f o r O-group and young h e r r i n g .

Table 2 g i v e s t h e a c o u s t i c a b s o l u t e e s t i m a t e s of t h e

1983

y e a r c l a s s obtained s i n c e August

1987

by t h e u s e of t h e recommended t a r g e t s t r e n g t h - l e n g t h e q u a t i o n . The e s t i m a t e s of t h e a d u l t h e r r i n g o b t a i n e d i n

1987

a r e lower than t h e e s t i m a t e s i n

1988

and

1989.

Reasons f o r t h i s may be dense s c h o o l i n g i n V e s t f j o r d / O f o t f j o r d ( F i g 28) with a p o s s i b l e a c o u s t i c shadowing. F u r t h e r , t h e h e r r i n g of c o a s t a l o r i g i n may n o t have r e c r u i t e d t o t h e main s t o c k i n

1987.

Table 2. Acoustic abundance e s t i m a t e s of a d u l t

1983

y e a r c l a s s (TS = 20.0 logL

- 71.9)

YEAR

l987

i988 1989

PERIOD ABUNDANCE COMMENTS

( N x

Aug 4100 Off Lofoten ( F i g 25)

S e p t 2000 Vestf jord ( F i g 26)

Nov 2800 V e s t f j / O f o t f j o r d ( F i g 27)

Feb 6805 Spawning a r e a ( F i g 29)

Feb

5118

Spawning a r e a ( F i g

34)

(33)

Migration

I n autumn

1983

t h e O-group h e r r i n g were d i s t r i b u t e d i n two g e o g r a p h i c a l l y d i f f e r e n t n u r s e r y grounds:

1) The main p a r t o f t h e O-group population was d i s t r i b u t e d i n t h e o f f s h o r e r e g i o n s of t h e Barents Sea

2 ) A minor p a r t of t h e population was d i s t r i b u t e d i n t h e f j o r d a r e a s of northwestern and n o r t h e r n Norway

I t h a s been p o s s i b l e t o map t h e g e n e r a l migration r o u t e s of t h e p a r t o f t h e p o p u l a t i o n d i s t r i b u t e d i n t h e Barents Sea. T h i s p o p u l a t i o n has probably been augmented by h e r r i n g which s p e n t t h e i r f i r s t ( o r f i r s t and second) w i n t e r i n t h e f j o r d s of n o r t h e r n Troms and Finnmark and then emigrated t o t h e o f f s h o r e a r e a s of t h e Barents Sea. (The t e r m

"component" should t h e r e f o r e be used with c a r e t o d i s c r i m i n a t e t h e h e r r i n g i n t h e f j o r d s and o f f s h o r e a r e a s r e s p e c t i v e l y , a s "component"

i n d i c a t e s a s t a t i c s i t u a t i o n with minimum i n t e r c h a n g e ) . The migrations of t h e h e r r i n g d i s t r i b u t e d i n t h e f j o r d a r e a s have been more d i f f i c u l t t o follow.

1) T h i s h e r r i n g s t a y e d i n t h e Barents Sea u n t i l May-June 1986, i . e . a t i m e p e r i o d of 3 y e a r s . F i g 36 g i v e s a schematic p r e s e n t a t i o n of t h e m i g r a t i o n s which t h e h e r r i n g i n t h e o f f s h o r e r e g i o n s of t h e Barents Sea c a r r i e d o u t i n t h e p e r i o d i t s t a y e d i n t h e Barents Sea. The w i n t e r i n g a r e a s were i n g e n e r a l l o c a t e d f u r t h e r t o t h e e a s t than t h e f e e d i n g a r e a s .

Fig.

36.

Migration r o u t e s (schematic) f o r t h e

1983

y e a r c l a s s i n t h e Barents Sea.