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C BIOLOGY AND FISHERIES OF

THE NORWEGIAN SPRING SPAWNING HERRING AND BLUE WHITING IN THE NORTHEAST ATLANTIC )

Proceed ings of the fourth Soviet-Norwegian Symposium

- _Bergen , 12-16 June 1989

E;.&..lJ:j T ~ lYVtoYl sf-o..&

Polar Research Institute of Marine Fisheries and Oceanography (PINRO) Murmansk

Institute of Marine Research Bergen

BIOLOGY AND FISHERIES OF THE NORWEGIAN SPRING SPAWNING HERRING AND

.b-L

BLUE WHITING IN THE NORTHEAST ATLANTIC

Proceedings of the fourth Soviet-Norwegian Symposium

Bergen, 12

-

^{16 June 1989}

Edi ted by

Terje Monstad

Institute of Marine Research, Bergen, Norway

CONTENTS

Page P r e f a c e . . .

... ⁴

Herring :

...

Section I: L i f e h i s t o r y

5

...

J . HAMRE

5

L i f e h i s t o r y and e x p l o i t a t i o n of t h e Norwegian s p r i n g spawning h e r r i n g .

E . I . SELIVERSTOVA..

... 4 1

Spawning s t o c k s t r u c t u r e and population f e c u n d i t y o f t h e Atlanto-Scandian h e r r i n g .

R . TORESEN..

... ⁸⁹

Long t e r m changes of growth and maturation i n t h e Norwegian spring-spawning h e r r i n g .

Section 11: Methodology and m o d e l s . . . 107

J . HAMRE and R. T O R E S E N . . . 107 S u r v i v a l t e s t s of i n t e r n a l l y tagged h e r r i n g .

...

A. DOMMASNES...

115

HM2 ( h e r r i n g model 2 ) . A s i n g l e s p e c i e s computer model of t h e Norwegian s p r i n g spawning h e r r i n g s t o c k .

S.N. RODIONOV and A.S. KROVNIN

...

¹²⁵

Northern hemisphere c l i m a t e changes and t h e i r e f f e c t s on envronment of Atlanto-Scandian h e r r i n g .

Herring and blue whiting:

...

Section 111: Fecundity, l a r v a e and j u v e n i l e s 135

A . I . KRYSOV AND L.R. E R G A K O V A . . .

135

D i s t r i b y t i o n and d r i f t of Atlanto-Scandian h e r r i n g l a r v a e i n Norwegian and Lofoten shallows i n 1983-1987.

...

V.P. SEREBRYAKOV, S.V. BELIKOV and E.S. TERESHCHENKO 153

Herring and b l u e whiting reproduction c a p a c i t y .

...

I. R~TTINGEN 165

The 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 a s j u v e n i l e s and r e c r u i t spawners.

Blue whiting:

Section IV: Life history ... ²⁰⁵ ...

V.S. BAKANEV 205

Dynamics of blue whiting abundance in the Norwegian Sea.

S.V. BELIKOV, V.A. ERMOLCHEV, N.A. ISAEV, and V.N. SHLEINIK... 219 USSR blue whiting research in the Northeast Atlantic

in 1982-1988.

T. MONSTAD. ... ²²⁷

Distribution and growth of blue whiting in the North-East Atlantic in 1980-1988.

...

Section V: Fecundity, larvae and feeding 269 S.V. BELIKOV and A.V. SCHEVCHENKO... 269

Investigations on the blue whiting spawning, larval distri- bution and drift west and north-west of the British Isles.

...

S.V. BELIKOV, TERESHCHENKO and N.A. ISAEV. 281 Population fecundity and yearclass strength of blue whiting

in the Northeast Atlantic.

N.V.

P L E K H A N O V A . . .

291 The conditions of blue whiting feeding in the Norwegian Sea

in the spring-summer period 1980-1987.

...

Section VI: Parasites, mortality and migration. 307 A.B. KARASEV... 307

Ecological and geographical analysis of the North-East Atlantic blue whiting parasitic fauna.

...

T. MONSTAD 319

Some aspects of mortality, condition factors and liver state with Anisakis-infection in blue whiting in the North-east Atlantic.

....

A.V. SHEVCHENKO, N.A. ISAEV and S.V. BELIKOV... 341 Some peculiarities of the blue whiting migrations in the

Northsast Atlantic in 1978-1988 in relation to stock composition and hydrographic conditions.

...

Section VII: Management 353

V. ZILANOV... ... ³⁵³

Problems of investigation and international management of the

blue whiting stock in the North-East Atlantic.

Many of t h e f i s h resources of t h e Norwegian Sea and adjacent waters a r e shared betweewn t h e Soviet Union and Norway and both c o u n t r i e s accomplish s c i e n t i f i c i n v e s t i g a t i o n s on t h e f i s h s t o c k s i n t h i s a r e a . To be a b l e t o coordinate t h i s work, t h e P o l a r Research I n s t i t u t e of Marine F i s h e r i e s and Oceanography (PINRO) i n Murmansk and t h e I n s t i t u t e of Marine Research i n Bergen a r e developing a programme of c l o s e cooperation, which i s under t h e a e g i s of t h e Mixed Soviet- Norwegian F i s h e r i e s Commision. A s a p a r t of t h i s programme a s e r i e s of symposia have been planned, d e a l i n g with important a s p e c t s of t h e f i s h s t o c k s and t h e i r enviroment i n t h e Northeast A t l a n t i c .

This volume p r e s e n t s t h e c o n t r i b u t i o n s presented t o t h e f o u r t h of t h e s e symposia, held i Bergen 12-16 June 1989, and d e l t with t h e Norwegian s p r i n g spawning h e r r i n g and t h e blue whiting s t o c k s . The t h r e e previous symposia focused on (1) t h e A r t i c cod, ( 2 ) t h e Barents Sea c a p e l i n and

( 3 )

t h e e f f e c t of oceanographic conditions on commercial f i s h s t o c k s i n t h e Barents Sea.

I n a d d i t i o n t o t h i s v e r s i o n i n t h e English language, t h e c o n t r i - butions w i l l a l c o appear i n a version i n t h e Russian language published by PINRO, Murmansk.

The e d i t o r of t h i s v e r s i o n i s responsible f o r some modest e d i t o r i a l changes i n some of t h e c o n t r i b u t i o n s i n which i t has n o t been p o s s i b l e t o o b t a i n t h e a u t h o r s approval. It i s , however, believed t h a t t h i s has n o t r e s u l t e d i n any change of meaning o r i n l o s s of c l a r i t y of t h e paper. The f i n a l English t e x t of a l l t h e Soviet c o n t r i b u t i o n s except one, were i n advance a l s 0 given t o t h e Soviet s c i e n t i s t s .

The e d i t o r i s indebted t o Ole J . Gullaksen f o r review and r e v i s i o n of t h e English grammar of t h e t e x t .

Bergen, October 1990

Herring

S e c t i o n I: L i f e h i s t o r y .

LIFE HISTORY AND EXPLOITATION OF THE NORWEGIAN SPRING SPAWNING HERRING

Johs. Hamre

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 i s a review of t h e h i s t o r y and e x p l o i t a t i o n of t h e Norwegian s p r i n g spawning h e r r i n g s t o c k . I n a v i r g i n s t a t e t h e biomass of t h i s s t o c k may have ranged from

15

t o 20 m i l l i o n tonnes and i t was t h e most important f i s h r e s o u r c e i n t h e Northeast A t l a n t i c . The a d u l t s t o c k u t i l i z e d t h e r i c h plankton production along t h e P o l a r Front i n t h e Norwegian Sea b u t spawned d u r i n g w i n t e r on t h e Norwegian w e s t c o a s t . These spawners formed t h e b a s i s f o r t h e l a r g e s t f i s h e r y i n Europe f o r c e n t u r i e s . The young and adolescent h e r r i n g a r e d i s t r i b u t e d i n Norwegian c o a s t a l w a t e r s and i n t h e Barents Sea where they c o n s t i t u t e t h e most important prey s p e c i e s f o r many s t o c k s of p r e d a t o r s , both of f i s h , b i r d s and mammals.

Due t o t e c h n i c a l advances t h e e x p l o i t a t i o n of t h e h e r r i n g i n c r e a s e d tremendously i n t h e 1960's and t h e a d u l t s t o c k was f i s h e d o u t completely i n 1970. Some small components of j u v e n i l e h e r r i n g d i d however s u r v i v e , and spawned on t h e t r a d i t i o n a l spawning grounds i n 1973. A f t e r spawning t h e h e r r i n g d i d n o t m i g r a t e t o t h e t r a d i t i o n a l f e e d i n g a r e a i n t h e Norwegian Sea, b u t remained i n Norwegian c o a s t a l w a t e r s throughout t h e y e a r . I n l a t e r y e a r s t h e s t o c k has recovered s l o w l y , b u t t h e o l d t r a d i t i o n a l migration p a t t e r n of h e r r i n g between t h e P o l a r Front a r e a and t h e Norwegian c o a s t h a s n o t y e t been r e t a i n e d . It i s concluded t h a t t h e break down of t h e l i f e c y c l e s of t h e h e r r i n g i s t h e prime reason f o r t h e r e c e n t c r i s i s which h a s developed i n t h e Barents Sea s t o c k s and f i s h e r i e s .

LIFE HISTORY

-

h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n

...

INTRODUCTION

The p r e s e n t paper reviews t h e h i s t o r y of t h e f i s h e r y and r e s e a r c h on t h e Norwegian s p r i n g spawning h e r r i n g and t h e r e g u l a t i o n measures i n t r o d u c e d t o conserve t h e s t o c k i n r e c e n t y e a r s . I n conclusion emphasis i s l a i d on t h e importance of t h e s t o c k f o r t h e balance i n t h e p r e d a t i o n / p r e y r e l a t i o n s h i p i n t h e ecosystem of t h e Norwegian Sea and Barents Sea.

STOCK IDENTITY

The term "Atlanto-Scandian h e r r i n g " was introduced by Johansen

(1919)

and i s used a s a common name f o r t h r e e s t o c k s : Norwegian s p r i n g spawners, I c e l a n d i c s p r i n g spawners, and I c e l a n d i c summer spawners.

The Norwegian s p r i n g spawners a r e t h e l a r g e s t of t h e s e s t o c k s , w i t h spawning grounds s i t u a t e d mainly along t h e Norwegian c o a s t . STOCK STRUCTURE

Whether t h e Norwegian spring-spawning h e r r i n g c o n s t i t u t e a s i n g l e homogeneous s t o c k has been t h e s u b j e c t of c o n f l i c t i n g s c i e n t i f i c views. Broch (1908) found t h a t t h e v e r t e b r a l counts o f t h e spawners were n o t t h e same throughout t h e t o t a l d i s t r i b u t i o n range. Lea (1929) observed t h a t t h e s c a l e s of young h e r r i n g from n o r t h e r n and s o u t h e r n Norway d i f f e r e d i n t h e p a t t e r n of t h e i r w i n t e r r i n g s , r e f l e c t i n g d i f f e r e n c e s i n t h e i r growth r a t e s d u r i n g adolescence. I n t h e l i g h t of such d i f f e r e n c e s , Schnackenbeck (1931) concluded t h a t t h e Norwegian spawning p o p u l a t i o n was d i v i s i b l e i n t o a t l e a s t two " r a c e s " , and O t t e s t a d (1934) s p l i t t e d t h e s t o c k i n t o a n o r t h e r n and a s o u t h e r n component with spawning grounds t o t h e n o r t h and s o u t h of More r e s p e c t i v e l y . RunnstrØm (1937,1941), on t h e o t h e r hand, claimed t h a t such a s t r i c t s e p a r a t i o n was n o t c o n s i s t e n t with t h e a v a i l a b l e evidences.

Østvedt (1958) found t h a t t h e r e was an i n c r e a s i n g i n t e r m i x i n g of t h e two t y p e s with age, and t h a t t h e p r o p o r t i o n s of t h e two t y p e s v a r i e d c o n s i d e r a b l y between y e a r c l a s s e s . H e concluded t h a t h e r r i n g of t h e two growth t y p e s could n o t be members of d i f f e r e n t " r a c e s " . The r e s u l t s of t h e tagging experiments c a r r i e d o u t on t h e Norwegian spawning grounds and i n t h e oceanic f e e d i n g a r e a s (Dragesund and Jakobsson, 1963) a l s o show t h a t t h e spawners change t h e i r grounds from y e a r t o y e a r along t h e Norwegian c o a s t . I n l i g h t of a l l t h e a v a i l a b l e evidences i t i s t h e r e f o r e reasonable t o assume t h a t t h e Norwegian s p r i n g spawners a r e members of a s i n g l e s t o c k and t h a t t h e two d i s t i n c t i v e growth types a r e h e r r i n g which o r i g i n a t e from d i f f e r e n t n u r s e r y a r e a s .

DISTRIBUTION AND MIGRATION 1. Adult h e r r i n g

Knowledge of t h e d i s t r i b u t i o n and migration of t h e a d u l t h e r r i n g i s obtained from s e v e r a l s o u r c e s , such a s r a c i a l a n a l y s i s ( F r i d r i k s s o n , 1 9 6 3 ) , t a g g i n g experiments ( F r i d r i k s s o n and Aasen, 1952; Jakobsson, 1963) and a c o u s t i c surveys (Devold, 1963 ; Anon.

,

1964 ; and Jakobsson,

1971).

For many y e a r s t h e s e surveys were c a r r i e d o u t j o i n t l y by Denmark, I c e l a n d , Norway and t h e USSR.

l

I LIFE HISTORY

-

h e r r i n g

l L i f e k i s t o r y and e x p l o i t a t i o n .

. .

1

2. H e r r i n g p e r i o d s

For c e n t u r i e s t h i s h e r r i n g has been t h e b a s i s f o r one o f t h e l a r g e s t f i s h e r i e s i n Norway, and f o r more than 100 y e a r s t h e s u b j e c t of s c i e n t i f i c i n v e s t i g a t i o n s . I n

1857

t h e Norwegian Government gave Dr.Axel Boeck

(1871)

t h e t a s k of i n v e s t i g a t i n g t h e s o - c a l l e d " s p r i n g h e r r i n g " . Boeck brought t o g e t h e r many h i s t o r i c a l f a c t s about t h e Norwegian s p r i n g h e r r i n g f i s h e r y and he found t h a t t h e f i s h e r y had p e r i o d s of high abundance a l t e r n a t i n g w i t h p e r i o d s of extreme s c a r c i t y . According t o Boeck, t h e symptoms of a Norwegian h e r r i n g p e r i o d approaching i t s end a r e t h a t t h e h e r r i n g a r r i v e l a t e r each y e a r a t t h e Norwegian c o a s t , which had been t h e s i t u a t i o n i n t h e 1870's.

Boeck found s i m i l a r p e r i o d i c i t y i n t h e h e r r i n g f i s h e r y o f Bohuslan i n Sweden and suggested t h a t t h i s f i s h e r y could o r i g i n a t e from t h e Norwegian s p r i n g spawning h e r r i n g s t o c k . Boeck's view t h a t t h e s p r i n g h e r r i n g could l e a v e t h e u s u a l spawning grounds c r e a t e d g r e a t f e a r among t h e fishermen, and t h e Norwegian Government asked G.O. S a r s t o i n v e s t i g a t e t h i s problem.

A f t e r t h r e e y e a r s of i n v e s t i g a t i o n G.O.Sars succeeded i n drawing a f a i r l y c o r r e c t p i c t u r e of t h e l i f e h i s t o r y o f t h e Norwegian h e r r i n g . He b e l i e v e d t h a t t h e " s p r i n g h e r r i n g " l i v e d i n t h e s u r f a c e l a y e r s of t h e open s e a between S c o t l a n d , Norway and I c e l a n d , f e e d i n g on copepods, and a t t a i n i n g m a t u r i t y when b e i n g about 6 y e a r s o l d . The spawning a r e a was l o c a t e d o f f t h e Norwegian c o a s t between Stavanger and K r i s t i a n s u n d , from which t h e l a r v a e were s p r e a d northwards by t h e c u r r e n t s . I n t h e y e a r s 1868-1874 g r e a t q u a n t i t i e s of s o - c a l l e d " l a r g e h e r r i n g " were caught o f f n o r t h e r n Norway i n t h e autumn. O r i g i n a l l y he regarded t h e " l a r g e h e r r i n g " a s a s p e c i a l t r i b e w i t h unknown spawning grounds b u t l a t e r he found t h a t t h e connection between t h e " s p r i n g h e r r i n g " and " l a r g e h e r r i n g " f i s h e r i e s was c l o s e r t h a n he e a r l i e r b e l i e v e d . With r e s p e c t t o a l t e r n a t i n g h e r r i n g p e r i o d s , G.O. S a r s views were d i f f e r e d from t h o s e of Boeck. S a r s had found j u v e n i l e h e r r i n g f u r t h e r o f f t h e c o a s t than was u s u a l and considered i t l i k e l y t h a t t h e h e r r i n g would soon r e t u r n t o t h e o l d spawning grounds. H e q u e s t i o n e d whether h e r r i n g p e r i o d s r e a l l y d i d e x i s t i n t h e Norwegian h e r r i n g f i s h e r i e s and thought i t u n l i k e l y t h a t t h e r e should be any connection between t h e " s p r i n g h e r r i n g " and t h e h e r r i n g r e s p o n s i b l e f o r t h e g r e a t h e r r i n g f i s h e r i e s i n Bohuslan.

Jensen

(1881)

and Buck

(1888)

continued t h e h e r r i n g s t u d i e s i n t h e f o l l o w i n g y e a r s and d e s c r i b e d t h e h e r r i n g on t h e w e s t c o a s t as "new h e r r i n g " c o n s i s t i n g of a mixture of immature and mature h e r r i n g which i n s i z e became s i m i l a r t o t h e s p r i n g h e r r i n g . The h e r r i n g spawned on t h e u s u a l spawning grounds b u t was f a r less abundant a s b e f o r e 1870.

The mature h e r r i n g found i n shallow a r e a s o f f n o r t h e r n Norway i n 1868-

1874

were i n v e s t i g a t e d by Boeck and S a r s and were d e s c r i b e d a s h e r r i n g of t h e same s i z e a s t h e " s p r i n g h e r r i n g " , b u t i n much b e t t e r c o n d i t i o n . The o v a r i e s showed t h a t they were n o t ready t o spawn. I n December, t h e " l a r g e h e r r i n g " disappeared from n o r t h e r n Norway b u t t h e i r spawning ground was never observed.

During t h e w i n t e r o f

1877,

g r e a t s c h o o l s o f h e r r i n g were discovered p e n e t r a t i n g t h e Bohuslan s k e r r i e s , and f o r 20 w i n t e r s i n s u c c e s s i o n , a g r e a t h e r r i n g f i s h e r y was c a r r i e d o u t t h e r e . The h e r r i n g had been a b s e n t s i n c e 1808, b u t s i m i l a r f i s h i n g p e r i o d s i n t h i s a r e a a r e t r a c e d back i n h i s t o r y f o r about 1000 y e a r s , and i t l o o k s a s i f t h e Bohuslan and Norwegian " s p r i n g h e r r i n g " f i s h i n g p e r i o d s occured a l t e r n a t e l y . A t t h e time of t h e Bohuslan f i s h e r y , h e r r i n g f i s h e r i e s als0 grew up on

LIFE HISTORY

-

h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n

...

t h e Norwegian s i d e of t h e border t o Sweden (Ljungman, 1882; 0 . P e t t e r s s o n , 1922; Devold 1963)

.

During t h e w i n t e r of 1895-96 Norwegian fishermen caught g r e a t q u a n t i t i e s of l a r g e h e r r i n g i n t h e Skagerak f o r t h e l a s t t i m e . It was a l s o t h e l a s t w i n t e r i n which g r e a t h e r r i n g f i s h e r i e s o c c u r r e d i n s i d e t h e s k e r r i e s i n Bohuslan. The f o l l o w i n g w i n t e r h e r r i n g c o n c e n t r a t i o n s along t h e c o a s t of western Norway were of t h e same magnitude a s i n t h e good f i s h i n g w i n t e r s b e f o r e 1870 (Buvik, 1895-99)#

I n t h e autumn of 1896 onwards, g r e a t s c h o o l s of h e r r i n g were d i s c o v e r e d o f f Møre. They were c a l l e d " l a r g e h e r r i n g " , and an e x t e n s i v e h e r r i n g f i s h e r y began on them. These h e r r i n g s c h o o l s disappeared b e f o r e Christmas, b u t i n January new s c h o o l s a r r i v e d and moved southwards a l o n g t h e c o a s t and were l a t e r caught from Haugesund southwards t o Lindesnes. These s c h o o l s were c a l l e d " s p r i n g h e r r i n g " . I n t h e beginning of t h i s c e n t u r y t h e h e r r i n g f i s h e r i e s had two s e a s o n s , one based on t h e " l a r g e h e r r i n g " , t h e o t h e r on t h e " s p r i n g h e r r i n g " . The l a r g e h e r r i n g a r r i v e d each y e a r l a t e r i n t h e c o a s t a l w a t e r s and a f t e r 1921 no h e r r i n g a r r i v e d i n t h e Møre r e g i o n b e f o r e t h e 1st o f January. I n t h e 1 9 3 0 ' s t h e h e r r i n g spawned i n e a r l y February, whereas t h e spawning i n t h e 1 9 5 0 ' s took p l a c e i n e a r l y March.

Simultaneously t h e d i s t r i b u t i o n a r e a decreased and t h e c e n t e r of spawning moved northwards. The spawning grounds s o u t h o f Bergen were abandoned i n t h e l a t e

l95O1s,

and i n l a t e r y e a r s t h e spawning h a s been c o n c e n t r a t e d on t h e c o a s t from M@re t o Lofoten (Devold, 1963).

The simultaneous changes i n t h e spawning time and i n t h e displacement of t h e spawning grounds northwards gave rise t o a renewed d i s c u s s i o n of a l t e r n a t i n g h e r r i n g p e r i o d s between t h e r i c h Bohuslan f i s h e r y and t h e w i n t e r h e r r i n g f i s h e r y on t h e Norwegian west c o a s t . I n a s e r i e s of a r t i c l e s and p u b l i c a t i o n s i n t h e 1 9 5 0 ' s Finn Devold supported t h e theory o f a l t e r n a t i n g h e r r i n g p e r i o d s and p r e d i c t e d t h a t t h e displacement of t h e spawning grounds and t h e d e l a y i n t h e spawning t i m e i n d i c a t e d t h e end of t h e h e r r i n g f i s h e r y on t h e Norwegian w e s t c o a s t (Devold 1950,1955,1959,1960,1963,1964). Devold a l s 0 developed an h y p o t h e s i s which e x p l a i n e d t h e p r o c e s s e s which governed t h e r e l a t i o n between t h e spawning behaviour and t h e m i g r a t i o n . H i s b a s i c assumption was t h a t i t t a k e s a l i t t l e more t h a n one y e a r between s u c c e s s i v e spawnings. The h e r r i n g w i l l then a r r i v e a t t h e Norwegian c o a s t l a t e r each y e a r and a l s o l e a v e t h e c o a s t l a t e r . When p o s t spawners a r e l e a v i n g l a t e , t h e y have t o p a s s t h e a r e a on t h e Norwegian c o n t i n e n t a l s h e l f a f t e r t h e copepods have e n t e r e d s u r f a c e l a y e r s , i n A p r i l . The h e r r i n g w i l l t h e r e f o r e s t a r t f e e d i n g h e r e and w i l l move northwards o f f t h e Norwegian c o a s t .

I n t h e autumn, t h e h e r r i n g used t o m i g r a t e t o t h e c o l d a r c t i c water i n t h e E a s t I c e l a n d i c C u r r e n t f o r w i n t e r i n g . Being o f f n o r t h e r n Norway they w i l l be f a r from t h e a r c t i c water of t h e E a s t I c e l a n d i c C u r r e n t . Cold w a t e r w i l l , however, be a v a i l a b l e n e a r t h e Norwegian c o a s t , where t h e w i n t e r c o o l i n g of t h e c o a s t a l w a t e r s w i l l have s t a r t e d , and t h e s e w a t e r s w i l l t h e r e f o r e b e invaded f o r w i n t e r i n g . S i n c e t h e temperature of t h e c o a s t a l water of n o r t h e r n Norway is h i g h e r t h a n t h a t of t h e E a s t I c e l a n d i c C u r r e n t , t h e gonads of t h e s e h e r r i n g w i l l develop f a s t e r and spawning w i l l t a k e p l a c e e a r l i e r than i n t h e preceding season. A f t e r spawning t h e s e h e r r i n g w i l l l e a v e t h e Norwegian c o a s t e a r l y , and r e t u r n f o r f e e d i n g along t h e P o l a r Front e a r l i e r than u s u a l . The n e x t autumn t h e i r spawning m i g r a t i o n w i l l t h e r e f o r e s t a r t e a r l y . , and t h e m i g r a t i n g s c h o o l s w i l l have t o p a s s through water masses of a h i g h e r temperature than u s u a l . The Norwegian c o a s t a l

LIFE HISTORY

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h e r r i n g

9

L i f e h i s t o r y aiid e x p l o i t a t i o n

...

w a t e r s o f f More, where t h e h e r r i n g u s u a l l y a r r i v e , have a s u r f a c e temperature above 10 C i n t h e autumn. The h e r r i n g w i l l avoid t h i s warm o water and move toward t h e B a l t i c water of a temperature of s i x t o seven degrees. The h e r r i n g may then pass through t h e Norwegian Channel i n t o t h e Skagerak, and spawn o f f t h e Norwegian s o u t h c o a s t , and o f f Bohuslan. A f t e r spawning t h e h e r r i n g invade t h e c o a s t a l a r e a s of Bohuslan, and t h e s o u t h - e a s t c o a s t of Norway where t h e y spend t h e

" r e s t i n g t i m e " i n c o l d water. The delay i n spawning t i m e by y e a r s w i l l however i n c r e a s e t h e chances t h a t t h e h e r r i n g meet c o l d B a l t i c water i n t h e Skagerak on t h e spawning migration. I f t h e B a l t i c water is t o o c o l d , t h e h e r r i n g w i l l f i n d warmer spawning grounds f u r t h e r west. I f t h e h e r r i n g have t o l e a v e a spawning ground and f i n d a new one, they w i l l r e t u r n t o t h i s new ground f o r t h e succeeding spawnings. I n t h i s way t h e h e r r i n g a r e d r i v e n o u t of t h e Skagerak, and l a t e r a l s o have t o avoid t h e s o u t h e r n spawning grounds i n western Norway. I n t h i s way r i c h h e r r i n g p e r i o d s of t h e Bohuslan and of t h e Norwegian w e s t c o a s t may a l t e r n a t e and t h e hypothesis a l s o e x p l a i n e t h e i n t e r m e d i a t e occurrence of t h e " l a r g e h e r r i n g " w i n t e r i n g i n t h e n o r t h Norwegian f j o r d s .

Devolds h y p o t h e s i s was s t r o n g l y opposed by Swedish s c i e n t i s t s (Andersson 1950, 1956, Hoglund 1959,1960,1977). Based on s i z e and age composition a n a l y s i s of t h e Bohuslan h e r r i n g , t h e y claimed t h a t t h i s s t o c k had no connections with t h e Norwegian s p r i n g spawning h e r r i n g , b u t was r e l a t e d t o t r i b e s which were u s u s a l l y f i s h e d i n t h e North Sea, Skagerak and K a t t e g a t .

The Norwegian west c o a s t h e r r i n g f i s h e r y c o l l a p s e d i n t h e 1960's due t o d e p l e t i o n of t h e s t o c k by t h e f i s h e r y . The f e e d i n g migration t o t h e P o l a r Front a r e a was i n t e r r u p t e d i n t h e e a r l y 1 9 7 0 ' s . and i n t h e subsequent y e a r s t h e postspawners have been f e e d i n g o f f t h e Norwegian c o a s t and have wintered i n t h e Norwegian f j o r d s a s presupposed by Devold's h y p o t h e s i s . The maturing o f t h e h e r r i n g h a s , however, n o t developed a s p r e d i c t e d . The h e r r i n g have matured i n February-March a s they d i d i n t h e 1960's and have spawned on t h e t r a d i t i o n a l spawning grounds from More t o Lofoten. I n 1989 a s m a l l component a l s o spawned , on t h e southern grounds f o r t h e f i r s t t i m e s i n c e 1959, and t h i s spawning took p l a c e r a t h e r l a t e i n t h e spawning season ( f i r s t h a l f of March)

.

l

3.

Migration p a t t e r n

The migration o f t h e a d u l t h e r r i n g s t o c k i s recorded i n d e t a i l s i n c e t h e e a r l y 1950's. A f t e r spawning most of t h e s p e n t h e r r i n g moved l northwestwards i n t o t h e Norwegian Sea where they f e d on zooplankton.

The l a r g e r f i s h reached t h e P o l a r Front i n June and J u l y and some

l

l c r o s s e d i n t o t h e c o l d water. The l i m i t of t h e summer f e e d i n g migration extended from t h e Spitsbergen-Jan Mayen a r e a i n t h e n o r t h t o t h e western borders of t h e E a s t I c e l a n d i c Current i n t h e s o u t h . The l a r g e r f i s h moved f u r t h e r t o t h e northwest than t h e s m a l l e r f i s h (Marty, 1959; Marty and Wilson, 1960).

During t h e autumn t h e h e r r i n g was found i n t h e southwestern p a r t of t h e Norwegian Sea along t h e borders of t h e E a s t I c e l a n d i c Current. The r i p e n i n g h e r r i n g wintered i n an a r e a o f f East I c e l a n d . I n December and January prespawning c o n c e n t r a t i o n s moved towards t h e Norwegian c o a s t . Devold (1951,1959,1963) d e s c r i b e d i n d e t a i l t h e spawning migration towards t h e c o a s t i n t h e 5 0 ' s . H e found t h a t t h e h e r r i n g g a t h e r i n cold-water pockets b e f o r e p e n e t r a t i n g t h e warm A t l a n t i c Current i n t o t h e c o l d e r Norwegian c o a s t a l water. The h e r r i n g u s u a l l y a r r i v e a t ^{t h e}

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h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n

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Norwegian c o a s t o f f Mare and spread f a r t h e r s o u t h and n o r t h t o spawn.

T h i s d e s c r i p t i o n of t h e d i s t r i b u t i o n and migratory p a t t e r n of t h e a d u l t s t o c k r e f e r s t o a s t a t e when t h e s t o c k was a t a r e l a t i v e l y h i g h l e v e l . Between l950 and 1962 t h e s t o c k d e c l i n e d . The spawning was g r a d u a l l y d i s p l a c e d northwards, and a f t e r 1959 spawning s o u t h of Bergen was n e g l i g i b l e (Devold, 1963; Dragesund, 1970)

.

I n 1950-1962 t h e main summer f e e d i n g grounds v a r i e d somewhat b u t remained i n t h e Iceland-Jan Mayen a r e a , b u t i n 1963-1966 a s t o c k component f e d and wintered i n an a r e a s o u t h of BjØrnøya ( F i g l ) The d e n s e s t summer c o n c e n t r a t i o n s were u s u a l l y found n e a r t h e b o r d e r s of t h e E a s t I c e l a n d i c C u r r e n t . I n t h e autumn t h e h e r r i n g assembled on t h e w i n t e r i n g grounds s i t u a t e d n e a r t h e s o u t h e r n and southwestern b o r d e r s of t h e E a s t I c e l a n d i c Current.

Jan H a y e p

---r Feeding migratio

20' 10' O'

Fig. 1 Migration of Norwegian s p r i n g spawning h e r r i n g p r i o r t o 1970.

4.

Migration p a t t e r n a f t e r 1970

The summer and autumn f i s h e r y f o r a d u l t h e r r i n g terminated i n 1969, and s i n c e then no h e r r i n g have been recorded i n t h e P o l a r F r o n t a r e a of t h e Norwegian Sea. The w i n t e r h e r r i n g f i s h e r y on t h e spawning grounds decreased s h a r p l y a f t e r i967 b u t continued on t h e d e p l e t e d s t o c k u n t i l

1971.

The s t o c k of immature h e r r i n g was almost d e p l e t e d i n 1969, and immature f i s h recorded i n t h e e a r l y 1 9 7 0 ' s belonged mainly t o t h e 1969 y e a r c l a s s .

The u s e of h e r r i n g f o r r e d u c t i o n purposes was p r o h i b i t e d i n Norway from January

1971.

T h i s r e g u l a t i o n probably prevented t h e complete e x t i n c t i o n of t h e 1969 y e a r c l a s s . Purse s e i n e r s f i s h i n g f o r c a p e l i n r e p o r t e d c o n c e n t r a t i o n s of young h e r r i n g o f f t h e c o a s t of Finnmark d u r i n g t h e w i n t e r of 1971, and s e v e r a l c a t c h e s of f a t h e r r i n g were r e l e a s e d t h a t y e a r because of t h e ban on t h e i n d u s t r i a l f i s h e r y . T h i s

LIFE HISTORY

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h e r r i n g

L i f e h i s t o r y and e x p l o i t a t i o n

...

l a s t remnant of t h e s t o c k probably survived a s j u v e n i l e s somewhere i n t h e Barents Sea o r i n t h e n o r t h e a s t e r n p a r t of t h e Norwegian Sea.

I n 1972, f i v e p u r s e s e i n e r s w e r e c h a r t e r e d t o survey t h e spawning grounds. P r a c t i c a l l y no spawning h e r r i n g were recorded (Dragesund, B j e r k e , and S a n g o l t , 1972). The absence o f spawning h e r r i n g and h e r r i n g l a r v a e i n 1972 and t h e very low abundance o f t h e 1970-1972 y e a r c l a s s e s i n t h e spawning s t o c k demonstrates t h a t t h e a d u l t s t o c k of Norwegian spring-spawning h e r r i n g c o l l a p s e d i n t h e e a r l y 1970's.

I n November 1972 s h o a l s of maturing h e r r i n g were recorded o f f western Finnmark ( i n t h e Ingøy Deep), and i n January 1973 a Norwegian p u r s e s e i n e r l o c a t e d h e r r i n g s h o a l s some 50 nm northwest of Ingøy. Most of t h e s e h e r r i n g belonged t o t h e 1969 y e a r c l a s s , and were obviously on t h e i r way t o t h e c o a s t t o spawn. Maturing h e r r i n g o f t h e 1969 y e a r c l a s s were found, l a t e r i n 1973, o f f V e s t e r å l e n and Lofoten. These h e r r i n g probably spawned i n t h e Lofoten a r e a i n March, because h e r r i n g l a r v a e were found t h e r e i n A p r i l . The t r a d i t i o n a l spawning grounds o f f Mgre and Trgndelag were surveyed throughout t h e spawning season i n

1973.

No c o n c e n t r a t i o n of spawning h e r r i n g was found, b u t g i l l - n e t c a t c h e s of h e r r i n g with running gonads i n d i c a t e d t h a t some spawning took p l a c e . This was l a t e r confirmed by t h e l a r v a l survey t h a t y e a r . The spawning s t o c k o f f Møre was a l c o dominated by t h e 1969 y e a r c l a s s

(Dragesund, Bjerke, and S a n g o l t ,

1973).

Two components of immature h e r r i n g survived t h e heavy e x p l o i t a t i o n i n t h e 1 9 6 o t s , one i n t h e Barents Sea and t h e o t h e r on t h e west c o a s t of Norway. Both components spawned f o r t h e f i r s t time i n 1973, one o f f t h e Mgre c o a s t , t h e o t h e r o f f Lofoten. According t o r e c o r d i n g s of maturing h e r r i n g i n 1973, t h e n o r t h e r n component was by f a r t h e l a r g e r . A f t e r spawning, t h e h e r r i n g d i d n o t l e a v e t h e c o a s t a s i n p r e v i o u s y e a r s , b u t migrated i n t o i n s h o r e w a t e r s t o f e e d d u r i n g summer and autumn. No spawning was observed o f f Lofoten i n t h e w i n t e r of 1974. The n o r t h e r n component migrated southward, and s i n c e

1974

spawning h a s taken p l a c e on t h e t r a d i t i o n a l spawning grounds o f f Møre and Trgndelag (Dragesund e t . a l 1980).

The t r a d i t i o n a l migration p a t t e r n of t h e h e r r i n g was t h u s i n t e r r u p t e d i n t h e e a r l y 7 0 ' s and h a s n o t y e t been r e t a i n e d . The two s t o c k components have developed a s s e p a r a t e u n i t s , with d i f f e r e n t spawning grounds, f e e d i n g a r e a s and w i n t e r i n g l o c a l i t i e s ( F i g u r e

3 ) .

The s o u t h e r n component has\spawned on t h e s o u t h e r n c o a s t o f f Møre and some y e a r s a l s 0 f u r t h e r s o u t h . A s a l r e a d y mentioned, s h o a l s of spawning h e r r i n g were i n

1989

recorded on t h e s o u t h e r n spawning grounds i n t h e beginning of March. These grounds have been abandoned by t h e h e r r i n g s i n c e t h e l a t e 1950's. The s o u t h e r n component has f e d d u r i n g summer and autumn o f f t h e c o a s t of Møre and Trøndelag, and wintered i n t h e f j o r d s of n o r t h e r n Møre. The s o u t h e r n component has u s u a l l y l e f t t h e w i n t e r i n g a r e a i n l a t e January and a r r i v e d a t t h e spawning ground i n t h e e a r l y February. Growth r a t e , r e c r u i t m e n t and age s t r u c t u r e of t h e h e r r i n g i n d i c a t e t h a t t h i s s t o c k component has developed a s a s e p a r a t e u n i t . This i s a l s 0 supported by t h e recovery of tagged h e r r i n g . The s o u t h e r n component of s p r i n g spawners has t o some e x t e n t been mixed with autumn spawners and h e r r i n g from l o c a l s t o c k s which spawn i n t h e f j o r d s .

The n o r t h e r n component has spawned i n t h e a r e a from n o r t h e r n Møre (Buagrunnen) t o Lofoten. This h e r r i n g has spawned some weeks l a t e r t h a n t h e h e r r i n g of t h e s o u t h e r n component. The n o r t h e r n component has

LIFE HISTORY

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h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n

...

a l c o f e d on t h e Norwegian s h e l f d u r i n g summer and autumn, b u t more o f f s h o r e and f a r t h e r n o r t h . The s h o a l s have moved northwards d u r i n g t h e summer and have u s u a l l y been found o f f Lofoten i n t h e e a r l y autumn. I n September t h e y have migrated i n t o t h e V e s t f j o r d e n a r e a and wintered i n t h e f j o r d s o f Lofoten and V e s t e r å l e n . The h e r r i n g have r e t u r n e d t o t h e same f j o r d s every y e a r b u t when t h e abundant B a r e n t s Sea component of t h e

1983

y e a r c l a s s migrated t o t h e c o a s t a l a r e a f o r w i n t e r i n g i n t h e autumn 1986, t h e w i n t e r i n g a r e a was expanded t o i n c l u d e s e v e r a l new f j o r d s i n t h e same r e g i o n .

I n t h e y e a r s 1988 and

89

most of t h e 1983 y e a r c l a s s wintered i n t h e i n n e r p a r t of V e s t f j o r d e n . When t h e 1983 y e a r 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 t h e s e p a r a t i o n of t h e h e r r i n g i n two d i f f e r e n t s t o c k u n i t s disappeared. Tag r e t u r n s from t h e w i n t e r f i s h e r y i n 1989 do, h o w e v e r , i n d i c a t e t h a t t h e Barents Sea component of t h e

1983

y e a r c l a s s h a s invaded a l l spawning grounds on More, whereas t h e h e r r i n g from t h e More-Trondelag a r e a a r e d i s p l a c e d t o spawning grounds f a r t h e r t o t h e

s o u t h ( F i g .

3 B ) .

5.

D i s t r i b u t i o n of young and a d o l e s c e n t h e r r i n g

U n t i l t h e beginning of t h e 1 9 6 0 ' s l i t t l e was known about t h e d i s t r i b u t i o n and m i g r a t i o n of t h e e a r l y s t a g e s of Norwegian s p r i n g spawners. Devold (1950) showed t h a t O-group h e r r i n g of t h e r i c h 1950 y e a r c l a s s were d i s t r i b u t e d f a r o f f s h o r e i n t h e n o r t h e a s t e r n p a r t of t h e Norwegian S e a , and he suggested t h a t only p a r t of t h e t o t a l O-group p o p u l a t i o n e n t e r e d t h e Norwegian f j o r d s . From l a t e r i n v e s t i g a t i o n s i t can b e s t a t e d t h a t t h e d i s t r i b u t i o n of t h e young and a d o l e s c e n t h e r r i n g i s widespread, ranging from t h e f j o r d s of n o r t h e r n

Fig. 2. D i s t r i b u t i o n of young h e r r i n g . ( l ) n u r s e r y a r e a , ( 2 ) l a r v a l d i s t r i b u t i o n ,

(3)

d i r e c t i o n of p o s t - l a r v a l d r i f t t o t h e o f f s h o r e n u r s e r y a r e a .

LIFE

HISTORY

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h e r r i n g

L i f e h i s t o r y and e x p l o i t a t i o n

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A RECAPTURED

o" 5" 15"

Fig.

3.

D i s t r i b u t i o n of t a g r e t u r n s . A=

r e t u r n s from t h e w i n t e r f i s h e r y i n

1979,

B = r e t u r n s from t h e w i n t e r f i s h e r y i n

1989,

C= r e t u r n s from c a t c h e s taken i n t h e n o r t h e r n and s o u t h e r n w i n t e r i n g a r e a s of t h e h e r r i n g d u r i n g l a t e autumn.

LIFE HISTORY

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h e r r i n g L i f e h i s t o r y aiid e x p l o i t a t i o n

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Norway t o t h e open ocean of t h e Norwegian Sea and t h e B a r e n t s Sea

(Dragesund and Hognestad, 1960; Devold, 1968; Jakobsson, 1968;

Dragesund, 1 9 7 0 ) . When r e c r u i t m e n t c o n d i t i o n s a r e f a v o u r a b l e , most of t h e j u v e n i l e h e r r i n g a r e found i n t h e B a r e n t s Sea ( R ~ t t i n g e n ,

1987).

F i g u r e 2 shows a schematic i l l u s t r 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 of t h e e a r l y s t a g e s . Soon a f t e r h a t c h i n g , t h e l a r v a e rise i n t o t h e upper water l a y e r s and a r e t r a n s p o r t e d northwards from t h e spawning grounds.

During t h e northward d r i f t , p a r t of t h e l a r v a e accumulates a t t h e e n t r a n c e t o t h e f j o r d s a l o n g t h e Norwegian c o a s t . I n l a t e summer and e a r l y autumn O-group h e r r i n g a r e g e n e r a l l y recorded i n t h e t o p water l a y e r s a l o n g t h e Norwegian c o a s t and i n t h e B a r e n t s Sea (Dragesund, 1970; Anon., 1970). The o f f s h o r e d i s t r i b u t i o n i s , however, more v a r i a b l e and i s c l o s e l y r e l a t e d t o y e a r c l a s s s t r e n g t h , and hence t h e i n f l o w of A t l a n t i c water t o t h i s r e g i o n ( s e e s e c t i o n

5 ) .

I n l a t e autumn a major p a r t of t h e O-group i n o f f s h o r e waters i s c o n c e n t r a t e d along t h e f r o n t s between t h e c o l d a r c t i c water and t h e warmer water masses o f f t h e Spitsbergen-Bear I s l a n d and i n t h e c e n t r a l and s o u t h e a s t e r n p a r t s of t h e Barents Sea. The h e r r i n g remain i n t h i s a r e a d u r i n g t h e f o l l o w i n g w i n t e r and s p r i n g . During s p r i n g and e a r l y summer, t h e I-group h e r r i n g d i s t r i b u t e d i n t h e n o r t h e r n and n o r t h e a s t e r n p a r t of t h e Barents Sea move southwards. A t t h e same time, h e r r i n g of t h e same a g e , which have wintered i n t h e f j o r d s of n o r t h e r n Norway, m i g r a t e from t h e c o a s t and mix w i t h t h e open-sea c o n c e n t r a t i o n s . During t h e f o l l o w i n g w i n t e r t h e 2-group h e r r i n g a r e found i n almost t h e same a r e a , although t h e d i s t r i b u t i o n i s more r e s t r i c t e d t o c o a s t a l banks and t o t h e c e n t r a l and s o u t h e r n p a r t of t h e B a r e n t s Sea.

During summer and autumn p a r t of t h e 2-group h e r r i n g , t h e f a s t e s t growing f i s h , move westward i n t o t h e Norwegian Sea. However, most of t h e f i s h remain i n t h e B a r e n t s Sea and i n t h e a r e a o f f Finnmark f o r a n o t h e r y e a r b e f o r e they s t a r t t h e westward m i g r a t i o n i n t o t h e Norwegian Sea t o j o i n t h e a d u l t s t o c k . The s l o w e s t growing f i s h s t a r t t h e i r e m i g r a t i o n from t h e B a r e n t s Sea d u r i n g t h e 4-group s t a g e . The a d o l e s c e n t h e r r i n g moving i n t o t h e Norwegian Sea u s u a l l y have an o c e a n i c s t a g e b e f o r e they mature. Some i n d i v i d u a l s mature a f t e r one y e a r , o t h e r s a f t e r two o r t h r e e y e a r s (Dragesund e t . a l 1 9 8 0 ) .

This d i s t r i b u t i o n and m i g r a t i o n p a t t e r n of young and a d o l e s c e n t h e r r i n g i n t h e B a r e n t s Sea i s i n accordance with t h e o b s e r v a t i o n s of t h e movement of t h e

1983

y e a r c l a s s ( R ~ t t i n g e n ,

1989).

The c o a s t a l component of t h e

1983

y e a r c l a s s from t h e f j o r d s i n Finnmark mixed with t h e B a r e n t s Sea component i n

1984

and t h e mixed s t o c k l e f t t h e B a r e n t s Sea d u r i n g t h e s p r i n g and t h e summer 1986. Most o f t h e s e h e r r i n g had a one y e a r o c e a n i c s t a g e b e f o r e they matured and spawned f o r t h e f i r s t time i n

1988.

I n 1963-66 t h e 4-years o l d immature h e r r i n g wintered i n t h e Bear I s l a n d w i n t e r i n g a r e a , b u t most of t h e 1983 y e a r c l a s s wintered a s immature i n V e s t f j o r d e n a s

4

y e a r o l d s . RECRUITMENT AND AGE COMPOSITION

The age s t r u c t u r e of t h e a d u l t h e r r i n g s t o c k has been known s i n c e t h e beginning of t h i s c e n t u r y ( H j o r t , 1926)

.

I n a v i r g i n s t a t e , t h e l i f e span of h e r r i n g i s about 20-25 y e a r s . The m a t u r a t i o n of a y e a r c l a s s t a k e s p l a c e about some f i v e y e a r s , which means t h a t t h e a d u l t s t o c k may c o n s i s t of a s much a s 15-20 y e a r c l a s s e s . The r e c r u i t m e n t i s more- over v a r i a b l e and t h e s e f a c t o r s govern t h e age s t r u c t u r e of t h e s t o c k

LIFE HISTORY

-

h e r r i n g

L i f e h i s t o r y m-d e x p l o i t a t i o n

...

and t h e s t a b i l i t y of s t o c k abundance. The age composition of h e r r i n g from 1908 onwards compared with g e n e r a l i n f o r m a t i o n on s t o c k abundance i n d i c a t e t h a t t h e s t o c k recovered g r a d u a l l y a t t h e end o f t h e previous c e n t u r y . An e x t r a o r d i n a r y s t r o n g y e a r c l a s s was r e c r u i t e d i n 1904 which may have r e b u i l t t h e spawning s t o c k t o a l e v e l of

5

t o 10 m i l l i o n tonnes i n t h e second decade of t h i s c e n t u r y (Marty and Fedorov, 1963). Three r i c h y e a r c l a s s e s occured between 1900-1930, t h e y e a r c l a s s e s 1904,

1918

and 1923. The 1930's c o n s t i t u t e d a p e r i o d of good r e c r u i t m e n t and o n l y t h e y e a r c l a s s e s

1931

and 1936 were poor. I n t h e 1 9 4 0 ' s t h e r e were t h r e e r i c h y e a r c l a s s e s , t h o s e of

1943, 1944

and

1947

and a n o t h e r v e r y abundant y e a r c l a s s occurred i n 1950. According t o Marty and Fedorov t h e p e r i o d i c i t y of occurrence of abundant y e a r c l a s s e s ranged from one t o

14

y e a r s , whereas a seven y e a r s i n t e r v a l had been t y p i c a l from 1923 t o 1950. The a u t o r s a l s o showed t h a t t h e occurrence of abundant y e a r c l a s s e s c o i n s i d e d with i n c r e a s i n g i n f l o w o f warm water t o t h e B a r e n t s S e a , which a f f e c t s t h e mean Kola Meridian temperature. I n a r e c e n t paper S æ t e r s d a l and Loeng

(1984)

have shown t h a t a s i m i l a r c o r r e l a t i o n does e x i s t between t h e temperature of t h e Kola Meridian and r e c r u i t m e n t s u c c e s s f o r Northeast A r c t i c cod.

S i n c e 1950 abundant h e r r i n g y e a r c l a s s e s have o c c u r r e d i n 1959 and i960 c o i n s i d i n g with a warm c l i m a t e i n t h e Barents Sea. I n t h e e a r l y 7 0 t s , a n o t h e r warm p e r i o d occured, b u t a t t h a t time t h e spawning s t o c k of h e r r i n g was d e p l e t e d . I n r e l a t i o n t o spawning s t o c k t h e h e r r i n g y e a r c l a s s

1973

was known e x t r a - o r d i n a r y s t r o n g . The l a t e 1 9 7 0 ' s was a c o l d p e r i o d i n t h e B a r e n t s Sea. The c l i m a t i c c o n d i t i o n s improved i n t h e e a r l y 8 0 ' s and s t r o n g y e a r c l a s s e s were r e c r u i t e d i n t h e y e a r s 1983-85. The h e r r i n g y e a r c l a s s e s 1984-85 were however d e p l e t e d by i n c r e a s e d p r e d a t i o n from a very s t r o n g 1983 y e a r c l a s s of cod.

Recruitment a f t e r 1985 h a s been poor.

P l o t s of VPA-estimates of r e c r u i t m e n t v e r s u s spawning s t o c k biomass a r e shown i n F i g u r e 10 f o r t h e y e a r s 1950 onwards.The VPA f i g u r e s a r e d e r i v e d from t h e c a t c h i n number by y e a r c l a s s e s a d j u s t e d by a c o n s t a n t n a t u r a l m o r t a l i t y by age groups. V a r i a t i o n s i n t h e m o r t a l i t y due t o p r e d a t i o n o r o t h e r forms of s t o c k i n t e r a c t i o n s have n o t been accounted f o r . Judging from t h e s t o c k i n t e r r e l a t i o n s h i p observed i n r e c e n t y e a r s i t is assumed t h a t t h e s e r e c r u i t m e n t f i g u r e s a r e g r o s s l y u n d e r e s t i m a t e d , p a r t i c u l a r l y t h e r e c r u i t m e n t i n warm p e r i o d s when t h e cod have had f a v o u r a b l e r e c r u i t m e n t c o n d i t i o n s . The s t o c k - r e c r u i t m e n t p l o t demonstrates a l i n e a r r e l e a t i o n s h i p between s t o c k biomass and r e c r u i t m e n t when r e c r u i t m e n t c o n d i t i o n s a r e f a v o u r a b l e . When u s i n g c a t c h - r e l a t e d r e c r u i t m e n t f i g u r e s , t h i s a p p l i e s t o t h e f i r s t y e a r c l a s s which i s r e c r u i t e d i n a good r e c r u i t m e n t p e r i o d . The y e a r c l a s s e s of t h e subsequent y e a r s may however a l s o have been abundant a s O-group h e r r i n g , b u t may have been reduced a t a young age by p r e d a t i o n from abundant y e a r c l a s s e s of cod.

EXPLOITATION

The main f i s h e r y on a d u l t h e r r i n g has been t h e w i n t e r h e r r i n g f i s h e r y d u r i n g t h e spawning season. I n t h e p e r i o d 1925-1960 t h e w i n t e r h e r r i n g c a t c h e s were s h a r e d about e q u a l l y by p u r s e s e i n e r s and d r i f t e r s . E a r l i e r i n t h i s c e n t u r y t h e l a n d s e i n e was a l s o e x t e n s i v e l y used.

O r i g i n a l l y t h e p u r s e - s e i n e f i s h e r y was c a r r i e d o u t by v e s s e l s equipped with a p u r s e s e i n e o p e r a t e d from two d o r i e s . The r i n g - n e t technique w i t h power block r e p l a c e d t h e two-dory system i n t h e e a r l y 1 9 6 0 1 s , and most of t h e h e r r i n g h a s been caught by t h i s technique i n l a t e r y e a r s .

LIFE HISTORY

-

h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n

...

Y E A R

F i g .

4 .

T o t a l c a t c h of a d u l t h e r r i n g 1925-1970.

The annua1 c a t c h e s from t h e a d u l t h e r r i n g f i s h e r y o v e r t h e p e r i o d 1925-1970 a r e shown i n F i g u r e

4.

D e t a i l s of t h e h e r r i n g c a t c h e s 1950-

1988

a r e given i n Table 1. Although t h e c a t c h e s f l u c t u a t e d c o n s i d e r a b l y , they d i d n o t show any major t r e n d up t o 1947. T h e r e a f t e r t h e c a t c h e s r o s e s t e a d i l y t o about one m i l l i o n tonnes i n 1954-1956, when t h e r i c h l950 y e a r c l a s s s t a r t e d t o r e c r u i t t o t h e spawning s t o c k . The c a t c h e s then f e l l s t e a d i l y , up t o 1963, t o a l e v e 1 n e a r t h a t of t h e p o o r e s t y e a r of t h e prewar p e r i o d . There was a recovery i n 1964 when t h e r i c h y e a r c l a s s e s of 1959 and 1960 e n t e r e d t h e s t o c k . From 1965 onwards a r a p i d d e c r e a s e i n t h e s t o c k s i z e took p l a c e , and t h e w i n t e r - h e r r i n g f i s h e r y c o l l a p s e d i n 1970.

The summer and autumn f i s h e r y on a d u l t s , took p l a c e on t h e f e e d i n g grounds a l o n g t h e P o l a r Front i n t h e Norwegian Sea. T h i s f i s h e r y was l o c a t e d f o r a l o n g p e r i o d o f f n o r t h e r n and n o r t h e a s t e r n I c e l a n d (Jakobsson, 1963). The f i s h i n g season normally l a s t e d from June t o e a r l y September, and up t o 1950 t h e s t o c k was mainly e x p l o i t e d by I c e l a n d i c and Norwegian v e s s e l s .

I n t h e e a r l y 19601s new t e c h n i c a l advances improved t h e technique i n t h e I c e l a n d i c f i s h e r y , a s they d i d i n t h e Norwegian h e r r i n g f i s h e r y , and t h e f i s h e r y extended seawards. During t h e 1 9 6 0 ' s t h e f i s h e r y took p l a c e f a r o f f s h o r e i n t h e Norwegian Sea, and t h e f i s h i n g season l a s t e d u n t i l October-November. I n 1966 when t h e r e c o r d c a t c h of a d u l t h e r r i n g was t a k e n , I c e l a n d caught 40% whereas Norway and USSR caught about

30%

of t h e t o t a l c a t c h each (Table 2 ) .

The S o v i e t d r i f t n e t f i s h e r y on f e e d i n g h e r r i n g i n t h e Norwegian Sea s t a r t e d i n 1950. I n i t i a l l y , t h e f i s h e r y was p u r e l y a summer o n e , e x p l o i t i n g t h e grounds between S p i t s b e r g e n , J a n Mayen, and I c e l a n d . I n

LIFE HISTORY

-

h e r r i n g

L i f e h i s t o r y and e x p l o i t a t i o n

...

1952 an autumn and w i n t e r f i s h e r y s t a r t e d along t h e migratory r o u t e s of t h e prespawning c o n c e n t r a t i o n s towards t h e spawning grounds o f f t h e Norwegian c o a s t .

The change i n t h e migratory p a t t e r n of t h e a d u l t s t o c k d u r i n g t h e 1 9 6 0 ' s s t r o n g l y i n f l u e n c e d t h e l o c a t i o n of t h e summer and autumn f i s h e r y . Off I c e l a n d i t became n e g l i g i b l e and most of t h e summer and autumn f i s h e r y i n t h e 1960's took p l a c e o f f t h e s h e l f s o u t h and, west o f Bear I s l a n d - S p i t s b e r g e n . From t h e 1 9 7 0 ' s onwards most of t h e h e r r i n g h a s been caught i n Norwegian c o a s t a l w a t e r s w i t h i n a range of some 20 n.m. o f f t h e c o a s t .

Y E A R

F i g .

5.

The c a t c h of young and a d o l e s c e n t h e r r i n g . ( 1 ) t h e t o t a l c a t c h , ( 2 ) t h e c a t c h of s m a l l h e r r i n g .

I n a d d i t i o n t o t h e f i s h e r y on a d u l t s , t h e young and a d o l e s c e n t h e r r i n g were f i s h e d a t t h e Norwegian c o a s t and i n t h e f j o r d s ( F i g u r e

5 ) .

Almost a l l t h e c a t c h e s were taken with p u r s e s e i n e , and from 1964 onwards t h e r i n g - n e t technique was used and t h e e f f i c i e n c y i n c r e a s e d . The most important s m a l l - h e r r i n g f i s h e r y o c c u r r e d i n t h e f j o r d s from l a t e autumn t o e a r l y s p r i n g .

STOCK ASSESSMENT

The abundance of t h e Norwegian s p r i n g spawning h e r r i n g s t o c k has been a s s e s s e d by v a r i o u s methods. Marty and Fedorov (1963) a s s e s s e d t h e s t o c k abundance and y e a r c l a s s s t r e n g t h f o r t h e p e r i o d 1904-1960 on t h e b a s i s of c a t c h by y e a r c l a s s e s i n s u c c e s i v e y e a r s a f t e r a method

developed by Denzhavin (1922). Dragesund and Jakobsson (1963)

e s t i m a t e d s t o c k s i z e and t o t a l m o r t a l i t y r a t e f o r t h e p e r i o d 1953-1960 on t h e b a s i s of t a g r e t u r n s from i n t e r n a l t a g g i n g experiments and Østvedt (1963) e s t i m a t e d t o t a l m o r t a l i t y from c a t c h and e f f o r t d a t a i n t h e d r i f t n e t f i s h e r y f o r t h e p e r i o d 1950-1960. The ICES Working Group on Atlanto-Scandian h e r r i n g ( h e r e a f t e r termed t h e Working Group), has i n two r e p o r t s (Anon. 1970, 1977) a s s e s s e d t h e s t a t e of t h e s t o c k f o r t h e p e r i o d

1953-1959,

u s i n g d a t a from v a r i o u s s o u r c e s . A conventional VPA f o r t h e y e a r s 1950-1971 i s p u b l i s h e d by Dragesund and U l l t a n g

(1978)

and t h e r e s u l t s of a somewhat a d j u s t e d v e r s i o n of t h i s a r e shown i n F i g u r e

7

(Dragesund e t . a l 1980)

.

The ICES Working Group r e s u l t s a r e i n c l u d e d f o r comparison. I n t h e p e r i o d

1975

onwards, t h e s t o c k h a s been a s s e s s e d by VPA, t a g g i n g and a c o u s t i c methods.

LIFE HISTORY

-

h e r r i n g L i f e h i s t o r y and e x p l o i t a t i o n

...

Fig.

6.

( I ) Abundance i n d i c e s of some year c l a s s e s of Norwegian s p r i n g spawning h e r r i n g i n b i l l i o n s of f i s h , s t o c k values of h e r r i n g from t h r e e year o l d s and o l d e r , ( 2 ) mature h e r r i n g ,

(3)

by y e a r s i n m i l l i o n metric c e n t n e r s (Marty and Fedorov 1963).

Fig.

7.

Estimated spawning stock ( S ) , f i s h i n g m o r t a l i t y ( F ) and recruitment ( X ) of h e r r i n g 1950-1973 a s l year o l d . The

broken l i n e shows s t o c k e s t i m a t e s given by t h e Working Group.

LIFE HISTORY

-

h e r r i n g

L i f e h i s t o r y and e x p l o i t a t i o n

...

The s t o c k abundance e s t i m a t e s of h e r r i n g o l d e r t h a n

3

y e a r s f o r t h e p e r i o d 1904 t o 1960 a r e shown i n Figure 6 (Marty and Fedorov, 1963).

The n a t u r a l m o r t a l i t y h a s n o t been accounted f o r i n t h e s e e s t i m a t e s . According t o t h i s method, t h e accumulated c a t c h e s ranged between 1 . 5 and 2.0 m i l l . tonnes p r i o r t o 1925. Assuming t h a t t h e f i s h i n g m o r t a l i t y a t t h a t t i m e was lower than t h e n a t u r a l m o r t a l i t y , Marty and Fedorow found t h a t t h e s t a n d i n g s t o c k biomass must have been f i v e t o s i x t i m e s g r e a t e r t h a n t h e accumulated c a t c h f i g u r e s o r i n an o r d e r of magnitude of 10 m i l l . tonnes. For t h e 1 9 5 0 ' s t h e Dezhavin's method gave a s t o c k e s t i m a t e of 7 t o

8

m i l l . tonnes. Assuming t h a t t h e f i s h i n g m o r t a l i t y i n t h e 1 9 5 0 ' s was

5

times h i g h e r t h a n t h e n a t u r a l m o r t a l i t y t h e a u t h o r concluded t h a t t h e s t o c k may have remained on a s t e a d y s t a t e l e v e l of an o r d e r of magnitude of 1 0 m i l l . tonnes throughout t h e whole p e r i o d under s t u d y .

According t o t h e VPA ( F i g u r e 7 ) , t h e spawning s t o c k s i z e was a t a l e v e 1 of about 9 m i l l i o n tonnes i n l950 and decreased t o about 7 m i l l i o n tonnes i n 1953. From 1954 t o 1957 t h e s t r o n g 1950 y e a r c l a s s g r a d u a l l y r e c r u i t e d t o t h e spawning s t o c k , r e s u l t i n g i n an i n c r e a s e i n s t o c k s i z e t o about 10 m i l l i o n tonnes i n 1957. The s t o c k t h e n decreased t o about 2 . 5 m i l l i o n tonnes i n 1963 mainly a s a r e s u l t of poor r e c r u i t m e n t . From 1963 t o 1965 t h e spawning s t o c k s i z e i n c r e a s e d a g a i n , r e a c h i n g about

3.7

m i l l i o n tonnes i n

1965.

From 1966 onwards t h e r e was a r a p i d d e c r e a s e i n spawning s t o c k s i z e owing t o an almost complete l a c k of r e c r u i t m e n t t o t h e a d u l t s t o c k and r a p i d l y i n c r e a s i n g f i s h i n g m o r t a l i t i e s . The rise i n F d u r i n g t h e y e a r s 1963-1966 was caused by i n c r e a s i n g f i s h i n g e f f o r t , b u t t h e f u r t h e r l a r g e i n c r e a s e i n F i n 1967 onwards was probably mainly t h e e f f e c t of d e c r e a s i n g s t o c k s i z e caused by b o t h t h e i n c r e a s e i n f i s h i n g m o r t a l i t y i n previous y e a r s and t h e f a i l u r e i n r e c r u i t m e n t ( U l l t a n g 1 9 7 6 ) .

Y E A R - C L 4 S S 1

F i g .

8.

Year-class s t r e n g t h i n number a s O-group and

4

y e a r o l d s (broken l i n e ) , 1950-1969 (Dragesund e t a l . 1 9 8 0 ) .

L i f e h i s t o r y and e x p l o i t a t i o n

...

Comparing t h e p r e s e n t e s t i m a t e s of s t o c k s i z e and r a t e of e x p l o i t a t i o n of a d u l t s from VPA with e a r l i e r Working Group e s t i m a t e s , i t can be concluded t h a t t h e Working Group assessed t h e s i t u a t i o n more o r less c o r r e c t l y u n t i l t h e r a p i d i n c r e a s e i n f i s h i n g e f f o r t s t a r t e d i n t h e e a r l y 1 9 6 0 1 s , i . e . b e f o r e t h e i n t r o d u c t i o n o f t h e r i n g - n e t technique.

T h e r e a f t e r t h e Working Group badly overestimated t h e s t o c k s i z e .

The e x p l o i t a t i o n r a t e of young h e r r i n g was a l s o high d u r i n g t h e p e r i o d 1950-1969. I n F i g u r e

8

a r e given t h e VPA e s t i m a t e s of y e a r c l a s s s t r e n g t h a s O and

4

y e a r s o l d i n t h e p e r i o d . The F i g u r e shows t h a t y e a r c l a s s e s i n t h e 1 9 5 0 ' s which have t r a d i t i o n a l l y been d e s c r i b e d a s weak, were a l l of what could be c a l l e d normal s t r e n g t h 1 0 * 1 0 ~ t o 3 0 . 1 0 ~ f i s h a t t h e O-group s t a g e . However, y e a r c l a s s of s t r e n g t h s l e s s t h a n 20.

lo9

a s O-group s u r v i v e d t h e f i s h e r y o n l y i n s m a l l q u a n t i t i e s t o reach t h e age of

4

y e a r s . The 1965 y e a r c l a s s w a s t h e f i r s t one i n t h e p e r i o d s t u d i e d which r e a l l y should be c l a s s i f i e d a s weak a t t h e O-group s t a g e (Dragesund and U l l t a n g ,

1978).

The VPA c l e a r l y shows t h a t t h e f i s h i n g p r e s s u r e , on young and a d o l e s c e n t h e r r i n g i n g e n e r a l and on a d u l t h e r r i n g i n t h e y e a r s 1965- 1968, was t h e primary f a c t o r i n t h e c o l l a p s e of t h i s h e r r i n g s t o c k . A s mentioned p r e v i o u s l y some few h e r r i n g of t h e 1969 y e a r c l a s s s u r v i v e d a s j u v e n i l e s i n t h e e a r l y 1 9 7 0 ' s i n t h e Barents Sea and some v e r y few s u r v i v e d on t h e More c o a s t . These s t o c k components have i n l a t e r y e a r s been a s s e s s e d by an a c o u s t i c method and by t a g g i n g a s a d u l t s . An echo abundance survey of O-group h e r r i n g i n t h e Norwegian f j o r d s were i n i t i a t e d i n

1975

and extended t o cover t h e d i s t r i b u t i o n a r e a of O-group h e r r i n g i n t h e Barents Sea s i n c e

1983.

The survey a r e c a r r i e d o u t i n November-December and t h e technique used i s t h e same a s t h a t a p p l i e d f o r c a p e l i n (Nakken and Dommasnes

1975).

The r e s u l t s appear from t h e t e x t t a b l e below:

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

Year comp

.

^Sea

1975

1 . 0

1976

3.8

1977 o. 4 l978

1 . 2

1979

3.4

1980 0.2

1981

O. 2

1982 2.9

1983

13.7

35.7

1984 1 . 4

6 . 2

1985

1 . 0

41.5

1986 0.4 O

1987

0 . 3 O

1988

2 . 5 9

8

These r e c r u i t m e n t f i g u r e s a r e n o t comparable t o t h e back c a l c u l a t e d r e c r u i t m e n t number of l-group h e r r i n g ( R 1 ) d e r i v e d from t h e VPA. I n t h e s t o c k p r o g n o s i s t h e a c o u s t i c O-group e s t i m a t e s have been used a s i n d i c e s of r e c r u i t m e n t a t age

3

by s c a l i n g t h e number down by a c a l c u l a t e d conversion f a c t o r of 0.51 (Anon. 1986).

Compared t o t h e p e r i o d b e f o r 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 t h e r e c r u i t m e n t i n l a t e r y e a r s h a s been extremely low e x c e p t f o r t h e