Management of marine species

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H e l g o l ~ n d e r Meeresunters. 33, 641-661 (1980)

M a n a g e m e n t of marine species

P. Korringa

Feithlaan 8, 1985 G J Driehuis NH, The N e t h e r l a n d s

ABSTRACT: Marine fish a n d shellfish constitute important natural resources. Provided t h e y are wisely exploited, t h e y are not liable to exhaustion but continue to r e n e w themselves. Wise exploitation requires s o u n d m a n a g e m e n t , a n d for s u c h m a n a g e m e n t one should b e w e l l informed about the factors g o v e r n i n g the fluctuations in the stocks a n d about the costs of exploitation. A century of scientific fisheries r e s e a r c h p r o v i d e d a w e a l t h of information on reproduction, migration a n d growth of commercially important s p e c i e s of fish and shellfish a n d about the losses the stocks suffer t h r o u g h natural causes such as predation, diseases a n d parasites, a n d through the fishery itself. Such information is available for areas w h i c h are intensively fished. In fertile waters, the approximate growth increase of fish stocks is some 15 % by w e i g h t year -1. If one w e r e to harvest this 15 % only, to b e c o n s i d e r e d as interest on this natural capital, a n d to leave the capital itself untouched, one could go on fishing for ever. There w o u l d b e no overfishing or stock depletion. For sound m a n a g e m e n t w e n e e d not only ecological data but also information on economic fishery aspects, e. g. on size a n d p o w e r of t h e fleet, type of fish-finding apparatus installed, costs of n e t t i n g a n d w a g e s , fuel r e q u i r e d p e r fishing trip, a n d on the capital invested. Further w e n e e d statistical information on the l a n d i n g s a n d on t h e proceeds. Such information is available in countries w h i c h participate intensively in fishing. Therefore, one w o u l d assume that g o v e r n m e n t s w h i c h are well informed by their fishery biologists about fluctuations in stocks of fish a n d shellfish a n d by their economists on various aspects of the exploitation w o u l d apply sound m a n a g e m e n t to ensure that fishing m a y continue for m a n y years to come without depletion. A n u m b e r of e x a m p l e s r e l a t e d to the North East Atlantic area, w h e r e intensive fishing is carried out a n d from w h e r e a w e a l t h of scientific information is available, m a k e s clear that cases of s o u n d m a n a g e m e n t are h a r d to trace.

Editorial note: Professor Dr. Pieter Korringa d i e d shortly before the symposium. In his last letter h e r e q u e s t e d that his p a p e r b e r e a d to the auditorium. After p a y i n g tribute to this disting- u i s h e d colleague, Professor Dr. Otto Kinne r e a d his paper. The texts of tribute a n d p a p e r follow below.

TRIBUTE TO P R O F E S S O R PIETER K O R R I N G A

Dear M r s Korringa ! Ladies and G e n t l e m e n ! C o l l e a g u e s and Friends!

It is with great sorrow a n d s a d n e s s that I stand h e r e i n s t e a d o f a m a n d i s t i n g u i s h e d b y a l o n g a n d successful career as a fisheries biologist: Pieter Korringa. H e a n d I h a d a g r e e d that h e w o u l d present, at this s y m p o s i u m , an Introductory Paper, b a s e d l a r g e l y on h i s o w n e x p e r i e n c e a n d c o n c e r n e d with the m a n a g e m e n t of m a r i n e species. In spite of

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642 P. K o r r i n g a

the fact that P i e t e r h a d b e e n s e r i o u s l y ill for s o m e time, h e p r o m i s e d to do h i s b e s t to c o m p l e t e the p a p e r a n d to p r e s e n t it h e r e p e r s o n a l l y , i f at all p o s s i b l e . P i e t e r Korringa s p e n t the last days o f h i s l i f e d i c t a t i n g the m a n u s c r i p t for this paper. H e d i e d on J u l y 13,

1979.

Born on F e b r u a r y 16, I913, at H e e m s t e d e , The N e t h e r l a n d s , P i e t e r Korringa b e c a m e a h i g h l y regarded, i n t e r n a t i o n a l l y p r o m i n e n t s h e l l f i s h biologist and a d i s t i n g u i s h e d teacher. For m a n y y e a r s h e s e r v e d as Director o f the N e t h e r l a n d s Institute for F i s h e r y I n v e s t i g a t i o n s at I J m u i d e n . H i s m a j o r s c i e n t i f i c a c c o m p l i s h m e n t s i n c l u d e research on s h e l l f i s h cultivation a n d s t o c k m a n a g e m e n t o f c o m m e r c i a l fishes. P i e t e r Korringa w a s Extraordinary Professor at the U n i v e r s i t y o f A m s t e r d a m . On n u m e r o u s occasions h e s e r v e d h i s c o u n t r y as a d e l e g a t e to i n t e r n a t i o n a l organizations.

H i s l a s t m a j o r a c c o m p l i s h m e n t was a f o u r - v o l u m e treatise on the f a r m i n g o f m a r i n e organisms. F i s h e r y s c i e n c e s a n d m a r i n e e c o l o g y h a v e s u f f e r e d a g r e a t loss. W e shall m i s s P i e t e r Korringa's leadership, a d v i c e and criticism.

L a d i e s a n d G e n t l e m e n , I w o u l d l i k e y o u n o w to rise a n d s t a n d for a m i n u t e in m e m o r y o f Professor Dr. P i e t e r Korringa.

T h a n k you. P i e t e r Korringa, w e shall a l w a y s r e m e m b e r y o u in our hearts!

I N T R O D U C T I O N

T h e stocks of fish a n d shellfish constitute o n e of the n a t u r a l resources m a n has e x p l o i t e d since time i m m e m o r i a l . It is a l w a y s wise to k e e p a n eye o n t h e future a n d therefore to a v o i d w a s t e f u l e x p l o i t a t i o n of n a t u r a l resources w h i c h might, i n d u e course, l e a d to c o m p l e t e d e p l e t i o n . T h e great a d v a n t a g e of a l i v i n g resource like a stock of fish or shellfish is that it c a n r e j u v e n a t e itself w h e n carefully e x p l o i t e d so that s u s t a i n e d profitability is a realistic aim. S o u n d m a n a g e m e n t is therefore a p r e r e q u i s i t e just as i n other i n d u s t r i a l e n t e r p r i s e s of our time. Por such m a n a g e m e n t o n e s h o u l d h a v e i n s i g h t s into the v a r i o u s factors w h i c h d e t e r m i n e cost a n d m a g n i t u d e of p r o d u c t i o n a n d b e able to i d e n t i f y l i m i t i n g factors so that a d e q u a t e m e a s u r e s c a n b e t a k e n to p r e v e n t s t a g n a t i o n i n the d e v e l o p m e n t of the i n d u s t r y c o n c e r n e d . Poresight is r e q u i r e d , e x p e c i a l l y i n our time, s i n c e the e c o n o m i c a n d social p a r a m e t e r s are l i a b l e to c h a n g e almost overnight.

T h e p r o d u c t i v i t y of the sea, b a s e d o n the c a r b o n - d i o x i d e a s s i m i l a t i o n b y the phyto- p l a n k t o n , is n o t affected b y the f i s h i n g industry, a n d i n the more fertile waters o n e m a y count on a n a n n u a l i n c r e m e n t i n w e i g h t of the fish stock of some 15 %, a n i n c r e m e n t s i m p l y d u e to growth of the fish. W e r e w e to h a r v e s t this 15 % - to b e c o n s i d e r e d as the i n t e r e s t of this n a t u r a l c a p i t a l - a n d l e a v e t h e c a p i t a l itself u n t o u c h e d , w e could expect to go o n f i s h i n g for m a n y years w i t h o u t o b s e r v i n g signs of d e p l e t i o n or overfishing.

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e c o n o m i c a n d social aspects of the f i s h i n g i n d u s t r y it s h o u l d b e p o s s i b l e to find a b a s i s for s o u n d fishery m a n a g e m e n t . We could a i m at the s o - c a l l e d " m a x i m u m s u s t a i n a b l e y i e l d , " e x p r e s s e d i n tons of fish, or l e a d the m a n a g e m e n t to the m a x i m u m s u s t a i n a b l e profit, e x p r e s s e d i n m o n e t a r y units.

Theoretically, s o u n d m a n a g e m e n t of the f i s h i n g i n d u s t r y m u s t b e possible, e v e n i n w a t e r s w h e r e m o r e t h a n o n e c o u n t r y operates. W h e t h e r such is the case c a n b e c o n c l u d e d from the e x a m p l e s p r e s e n t e d i n this paper, d e a l i n g w i t h the fisheries i n the n o r t h - e a s t e r n A t l a n t i c area, as w e l l as fisheries i n streams a n d lakes, e s t u a r i e s a n d coastal waters, a n d the h i g h seas.

I shall d o c u m e n t h e r e past d e v e l o p m e n t s a n d activities, as w e l l as refer to the p r e s e n t state-of-the-art of the m a n a g e m e n t of m a r i n e species b y p r e s e n t i n g 7 e x a m p l e s - the oyster Ostrea edulls, the b l u e m u s s e l Mytilus edulls, the b r o w n s h r i m p Crangon crangon, the sole Solea solea, the h e r r i n g C1upea harengus, the s a l m o n of the River R h i n e a n d the b o w h e a d w h a l e Balaena mysticetus - a n d a brief r e v i e w of the d e v e l o p - m e n t from Z u y d e r Sea to Lake IJssel. T h e m a j o r c o n c l u s i o n s d r a w n are t h e n p r e s e n t e d i n the f i n a l section.

THE OYSTER

T h e r e w a s a time w h e n oysters Ostrea edulls a b o u n d e d i n the s h a l l o w e r parts of the North Sea. Very rich n a t u r a l b e d s w e r e f o u n d i n the Firth of Forth, i n the Dutch W a d d e n Sea, a n d i n the w a t e r s of S c h l e s w i g - H o l s t e i n k n o w n as the " F i s k a l i s c h e Austernb~inke." M i l l i o n s of oysters w e r e fished there a n n u a l l y to b e s h i p p e d to the cities w h e r e t h e y w e r e sold for w h a t is n o w c o n s i d e r e d as a r i d i c u l o u s l y low price. Entire s h i p l o a d s of oysters w e r e d i s p a t c h e d from the Firth of Forth to Z e a l a n d , w h e r e oyster d e a l e r s g r a d e d t h e m a n d stored t h e m i n l a r g e s e a - w a t e r b a s i n s prior to s h i p m e n t to cities i n B e l g i u m a n d G e r m a n y . W h e n a real n e t of r a i l w a y s s p r e a d all over Europe the m a r k e t for such a p e r i s h a b l e p r o d u c t as the oyster w i d e n e d c o n s i d e r a b l y a n d the d e m a n d i n c r e a s e d rapidly. T h e oyster fishers g l a d l y r e s p o n d e d b y i n c r e a s i n g the i n t e n s i t y of fishing, a n d for a w h i l e b u s i n e s s was good.

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m i g h t b e n e f i t from this extra work. H e n c e , m a n y y o u n g oysters are lost, a n d from the m o m e n t a d u l t oysters b e c o m e so scarce that fertilization of all the eggs o n the gills of the m o t h e r oysters is n o l o n g e r e n s u r e d , the n a t u r a l b e d will collapse.

No l i v i n g oysters c a n n o w a d a y s b e f o u n d on the former n a t u r a l b e d s i n t h e Firth of Forth a n d i n the W a d d e n Sea, t h o u g h e n v i r o n m e n t a l c o n d i t i o n s h a v e h a r d l y c h a n g e d at all. This is the m o r e d e p l o r a b l e since t h e s e p o p u l a t i o n s of Ostrea edulis s h o w e d good larval d e v e l o p m e n t at w a t e r t e m p e r a t u r e s as low as 15 ~ to 16 ~ w h e r e a s the p o p u l a - tions from Brittany a n d the O o s t e r s c h e l d e r e q u i r e 18 ~ at least, a n d the W a d d e n Sea oyster e v i d e n t l y c o u l d - s t a n d severe w i n t e r w e a t h e r for a p r o l o n g e d period. It was a s s u m e d for a l o n g t i m e that the p o p u l a t i o n s s h o w i n g such i n t e r e s t i n g q u a l i t i e s w e r e i r r e t r i e v a b l y lost, b u t n o w there is some hope. Some years ago i n the cadre of the Delta project, the G r e v e l i n g e n - a b o d y of salt w a t e r b e t w e e n the isles of G o e r e e - O v e r f l a k k e e a n d S c h o u w e n - D u i v e l a n d i n the S. W. of T h e N e t h e r l a n d s - b e c a m e cut off from the sea a n d from fresh w a t e r b o d i e s further east. Oysters h a v e occurred there since t i m e i m m e m o r i a l , b u t r e p r o d u c t i o n w a s a l w a y s very scanty. It w a s a surprise, therefore, that r e p r o d u c t i o n s h o w e d a sharp i n c r e a s e after c o m m u n i c a t i o n w i t h the sea w a s severed, t h o u g h t h e n u m b e r of m o t h e r oysters r e m a i n e d low. E v i d e n t l y l a r v a l survival is m u c h b e t t e r u n d e r the n e w conditions, p r e s u m a b l y b e c a u s e predators such as anchovies, c t e n o p h o r e s a n d the like, w h i c h d e v o u r m i l l i o n s of p e l a g i c oyster larvae, c a n no l o n g e r e n t e r the G r e v e l i n g e n b o d y of sea water.

R e c e n t e v i d e n c e gives hope for the future: t h e u n u s u a l l y low w a t e r t e m p e r a t u r e s i n the cool s u m m e r of 1978 l e d to a c o m p l e t e failure of spaffall i n the Oosterschelde, b u t i n the G r e v e l i n g e n good n u m b e r s of spat c o u l d b e o b s e r v e d o n t h e e x p e r i m e n t a l collectors, d e s p i t e the fact that w a t e r t e m p e r a t u r e s s t a y e d w e l l u n d e r 18 ~ (the critical l e v e l for the O o s t e r s c h e l d e oysters). Moreover, the w i n t e r of 1978-1979 was very l o n g a n d cold w i t h ice o n the w a t e r for m a n y w e e k s i n succession. Despite these u n f a v o u r a b l e conditions, the y o u n g oysters i n the G r e v e l i n g e n d i d not suffer a p p r e c i a b l e losses. O n e m a y s u r m i s e that the w i l d G r e v e l i n g e n stock shows the s a m e e x c e l l e n t q u a l i t i e s as the former W a d d e n Sea a n d Firth of Forth oysters: l a r v a l d e v e l o p m e n t at low w a t e r t e m p e r a t u r e s a n d h a r d i n e s s i n severe winters. T h e Dutch G o v e r n m e n t , i n c o o p e r a t i o n w i t h the oyster farmers of Yerseke, is a t t e m p t i n g to protect this stock of oysters, a n d to avoid its b e c o m i n g m i x e d w i t h the O o s t e r s c h e l d e stock, i n a n effort to d e v e l o p the salt Gre- v e l i n g e n b a s i n into a n u r s e r y g r o u n d for oysters from w h i c h the j u v e n i l e oysters c a n later b e t r a n s f e r r e d to the O o s t e r s c h e l d e plots for further growth a n d f a t t e n i n g . Cool s u m m e r s a n d severe winters, w h i c h r e p e a t e d l y interfere w i t h the d e v e l o p m e n t of the oyster stocks, will then, hopefully, n o l o n g e r e n d a n g e r the D u t c h oyster industry. It is here, i n the c o o p e r a t i o n b e t w e e n the g o v e r n m e n t a n d the oyster farmers that real m a n a g e m e n t b e g i n s , after h u n d r e d s of years of m i s m a n a g e m e n t of t h e n a t u r a l oyster beds. Oyster f a r m i n g o n the plots of the O o s t e r s c h e l d e is q u i t e a different thing, a case of p r i v a t e e n t e r p r i s e b y oyster farmers o p e r a t i n g o n plots l e a s e d from the g o v e r n m e n t .

THE BLUE MUSSEL

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good, s i n c e t h e i r m a i n e n e m y , t h e s e a s t a r

Asterias rubens,

c a n n o t a t t a c k t h e m t h e r e as it is l i a b l e to p r e d a t i o n b y s e a - g u l l s . M u s s e l s e e d w h i c h s e t t l e d in d e e p e r w a t e r often d i s a p p e a r s in a r a t h e r short time. T h e t i d a l z o n e is, h o w e v e r , not t h e b e s t p l a c e for r a p i d g r o w t h a n d f a t t e n i n g , s i n c e w a t e r rich in p l a n k t o n r e a c h e s t h e m u s s e l s h e r e o n l y i n t e r m i t t e n t l y . T h e m u s s e l s on t h e b e d s in t h e i n t e r t i d a l z o n e - t h o s e a t t a c h e d to b r e a k w a t e r s i n c l u d e d - a r e g e n e r a l l y of i r r e g u l a r size a n d a g e a n d r a t h e r p o o r in t h e q u a l i t y of t h e i r e d i b l e p a r t s and, therefore, of little i m p o r t a n c e as h u m a n food.

Still, a n a t u r a l m u s s e l b e d c o n s t i t u t e s a b i o l o g i c a l l y v e r y rich r e s o u r c e . H e r e one f i n d s u p to 10 k g of m u s s e l s p e r s q u a r e m e t r e , a d e n s i t y of a n i m a l s one w i l l r a r e l y f i n d e l s e w h e r e . W e should, h o w e v e r , b e w a r e of m a k i n g c o m p a r i s o n s w i t h t h e s i t u a t i o n on the l a n d , for e x a m p l e , w i t h t h e n u m b e r of c o w s on a g i v e n p a s t u r e . This not o n l y b e c a u s e m u s s e l s consist of o n l y a b o u t 25 % of m e a t , w e t w e i g h t , b u t also b e c a u s e t h e y do not l i v e from t h e food p r o d u c e d on t h e a c r e a g e t h e y a r e a c t u a l l y g r o w i n g on, b u t r a t h e r from t h e p h y t o p l a n k t o n p r o d u c e d in a far l a r g e r a r e a a n d c a r d e d to t h e m b y the t i d a l currents. A c o m p a r i s o n w i t h a m o d e r n b i o - i n d u s t r y of c h i c k e n s or w i t h a n a p a r t m e n t h o u s e full of p e o p l e is m o r e realistic.

W h a t u s e h a v e w e m a d e of this rich r e s o u r c e ? L o n g a g o f i s h e r m e n from Z e a l a n d f o u n d t h a t t r a n s f e r of m u s s e l s from n a t u r a l b e d s to sites w i t h b o t h sufficient s h e l t e r a n d p l e n t y of food - b u t w h e r e t h e y w o u l d not s e t t l e n a t u r a l l y - c o u l d l e a d to r a p i d g r o w t h a n d f a t t e n i n g a n d thus, in m u c h s h o r t e r t i m e t h a n is o b s e r v e d in oysters, to a p r o d u c t fit for t h e m a r k e t a n d for t h e h u m a n t a b l e . It took, h o w e v e r , a l o n g t i m e b e f o r e this p r a c t i c a l e x p e r i e n c e c o u l d b e a p p l i e d on l a r g e r scale. O n e h a d first of all to b e s u r e t h a t o n e c o u l d h a r v e s t t h e m u s s e l s t r a n s f e r r e d to t h e f a t t e n i n g g r o u n d s , oneself, t h a t is, t h a t o t h e r f i s h e r m e n w o u l d not b e n e f i t from t h e work. Therefore, r e a l d e v e l o p m e n t of a m u s s e l i n d u s t r y b e c a m e o n l y p o s s i b l e w h e n t h e g o v e r n m e n t l e a s e d p l o t s to p r o s p e c t i v e m u s s e l f a r m e r s a n d o r g a n i s e d p r o p e r p o l i c e p a t r o l to e n s u r e t h a t n o b o d y w o u l d t r e s p a s s on o t h e r p e o p l e ' s g r o u n d s . This h a p p e n e d a b o u t 100 y e a r s ago, a n d s i n c e t h e n t h e D u t c h m u s s e l i n d u s t r y h a s d e v e l o p e d p r o p e r l y . S o m e m a n a g e m e n t b y t h e g o v e r n m e n t t o o k p l a c e : to a v o i d w a s t e f u l e x p l o i t a t i o n , t h e n a t u r a l m u s s e l b e d s w e r e c l o s e d a n d o n l y o p e n e d for a l i m i t e d n u m b e r of d a y s or w e e k s w h e n t h e g o v e r n m e n t a l a d v i s o r s t h o u g h t it w i s e to do so. T h e n t h e m u s s e l f a r m e r s from Z e a l a n d c o u l d g e t t h e i r b o a t - l o a d s of m u s s e l s e e d from t h e n a t u r a l b e d s in t h e W a d d e n S e a to p l a n t t h e m on t h e i r plots in t h e Z e a l a n d w a t e r s ; after 1950 t h e y also u s e d n e w l y i n s t a l l e d p l o t s i n t h e w e s t e r n s e c t i o n of t h e D u t c h W a d d e n Sea, from w h e r e one n o w a d a y s h a r v e s t s 70 % of t h e t o t a l p r o d u c t i o n of m a r k e t a b l e m u s s e l s , w h i c h a m o u n t s to s o m e 100 000 000 k g p e r year.

F o r m e r l y , m u s s e l s e e d w a s also f i s h e d on t h e n a t u r a l b e d s in t h e W a d d e n S e a a n d in t h e n o r t h e r n p a r t of t h e Z u y d e r S e a as f e e d for d u c k farms in t h e c e n t r e of t h e c o u n t r y and, at t h e t e r m i n a t i o n of W o r l d W a r I, also l a r g e c o n s i g n m e n t s of w i l d m u s s e l s w e r e s h i p p e d , from the n a t u r a l b e d s in t h e W a d d e n S e a to the h u n g r y p e o p l e in d e f e a t e d G e r m a n y , b u t it w a s c l e a r t h a t this m a r k e t w o u l d o n l y b e a t e m p o r a r y o n e c o n s i d e r i n g t h e p o o r q u a l i t y of t h e p r o d u c t .

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THE B R O W N SHRIMP

T h e b r o w n s h r i m p

Crangon crangon

a b o u n d s in t h e c o a s t a l w a t e r s of t h e e a s t e r n s h o r e of the N o r t h Sea, from the Straits of D o v e r to 3utland. It is r a t h e r small, u p to 6 cm long, b u t of a n e x q u i s i t e flavour. A f i s h e r y for b r o w n s h r i m p d e v e l o p e d in d u e course a l o n g t h e u s u a l e m p i r i c a l lines, not g u i d e d b y scientific a d v i c e or official r e g u l a t i o n s ; o n c e it h a d b e e n e s t a b l i s h e d , t h e f i s h e r m e n c l a i m e d t h a t it w a s t h e i r l a w f u l r i g h t to m a k e a l i v i n g t h a t w a y . First o n e f i s h e d from t h e b e a c h e s , a n d h o r s e s w e r e often u s e d on the B e l g i a n s e c t i o n of t h e coast; l a t e r b o a t s c a m e into u s e s t a r t i n g w i t h s a i l i n g vessels, t h e n b o a t s e q u i p p e d w i t h e n g i n e s . T h e s e o p e r a t e d a l o n g t i m e w i t h t r a w l s k e p t o p e n b y doors, b u t in d u e c o u r s e t h e f i s h e r m e n f o u n d t h e b e a m t r a w l m o r e efficient. It is o n l y l o g i c a l w h e n f i s h i n g for c r e a t u r e s as s m a l l as b r o w n s h r i m p t h a t one u s e s f i n e - m e s h e d n e t s a l t h o u g h a b y - c a t c h c a n n o t b e a v o i d e d . H o w e v e r , it t o o k a l o n g t i m e b e f o r e one l e a r n e d m o r e a b o u t t h e p r a c t i c a l i m p o r t a n c e of t h e d i s c a r d s , a n d of the i m p a c t of t h e d e s t r u c t i o n of c r e a t u r e s o t h e r t h a n s h r i m p on t h e f i s h e r y e l s e w h e r e . Sets of s h a k i n g s i e v e s w e r e in u s e on the s h r i m p e r s to p r o d u c e a m a r k e t a b l e p r o d u c t free of a l i e n objects, a n d l a r g e r fishes w e r e t a k e n out b y h a n d b e f o r e one p r o c e e d e d to b o i l t h e s h r i m p o n b o a r d . It w a s not u n t i l a b i o l o g i s t of t h e " N e t h e r l a n d s I n s t i t u t e for F i s h e r y I n v e s t i g a t i o n s " u n d e r t o o k a m o r e d e t a i l e d s t u d y on t h e b r o w n s h r i m p a n d its f i s h e r y t h a t w e r e a l i z e d h o w m a n y y o u n g flatfishes, e s p e c i a l l y p l a i c e a n d sole, c o u l d b e e n c o u n t e r e d in t h e c a t c h e s at c e r t a i n t i m e s of t h e y e a r , e s p e c i a l l y in the W a d d e n S e a a n d in the Z e a l a n d e s t u a r i e s , t h e m o s t i m p o r t a n t n u r s e r y g r o u n d s for N o r t h S e a flatfish. Of course, t h e f i s h e r m e n m u s t h a v e s e e n this, b u t d i d not w o r r y a b o u t it, s i n c e t h e y f i s h e d e x c l u s i v e l y for s h r i m p s , w h e r e a s o t h e r f i s h e r m e n , often from o t h e r s e c t i o n s of t h e c o u n t r y w e r e after flatfish. T h e flatfishes i n t h e b y - c a t c h e s w e r e s m a l l , b u t often e x t r e m e l y n u m e r o u s . Sufficient i n f o r m a t i o n w a s a v a i l a b l e on g r o w t h a n d n a t u r a l m o r t a l - ity of t h e s e s m a l l flatfishes to a l l o w c a l c u l a t i o n of t h e d e l e t e r i o u s effect t h e b r o w n s h r i m p f i s h e r y e x e r t e d o n t h e flatfish f i s h e r y e l s e w h e r e i n t h e N o r t h Sea. It t u r n e d out t h a t t h e d a m a g e d o n e to t h e r e c r u i t m e n t of sole a n d p l a i c e , e x p r e s s e d in t e r m s of m o n e y , e x c e e d e d b y far t h e p r o c e e d s of t h e s h r i m p fishery.

For a f i s h e r y a d m i n i s t r a t o r s u c h i n f o r m a t i o n is u n w e l c o m e n e w s , for one c a n n o t p r o h i b i t a f i s h e r y w h i c h for c e n t u r i e s h a s p r o v i d e d a l i v i n g to m a n y f i s h e r m e n . W e r e the c a u s a l r e l a t i o n b e t w e e n t h e g a t h e r i n g of b r o w n s h r i m p s a n d flatfish k n o w n p r i o r to t h e d e v e l o p m e n t of a p r o f e s s i o n a l s h r i m p fishery, t h e n it w o u l d h a v e b e e n w i s e to d e c i d e to p r o t e c t t h e flatfish in a n effort to e x p l o i t t h e n a t u r a l r e s o u r c e s as r a t i o n a l l y as p o s s i b l e , b u t it is - for a f i s h e r i e s a d m i n i s t r a t i o n - a l m o s t i m p o s s i b l e to cut short a n a l r e a d y e x i s t i n g f i s h e r y w i t h a l o n g t r a d i t i o n . This w o u l d not o n l y l e a d to fierce p r o t e s t from those w h o m a k e a l i v i n g t h a t w a y , b u t w o u l d also u p s e t p u b l i c o p i n i o n a n d w o u l d l e a d to s t r o n g o p p o s i t i o n in P a r l i a m e n t , d e s p i t e t h e e c o n o m i c l o g i c of s u c h a d e c i s i o n .

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w a s the d e v e l o p m e n t of a n i n g e n i o u s a p p a r a t u s to b e i n s t a l l e d a b o a r d w h i c h c o u l d s i e v e t h e c a t c h i n w a t e r in s u c h a w a y t h a t b o t h y o u n g f l a t f i s h e s a h d j u v e n i l e s h r i m p r e t u r n u n d a m a g e d , a l i v e a n d k i c k i n g , to t h e i r n a t u r a l e n v i r o n m e n t . T h e D u t c h G o v e r n m e n t d e c i d e d to p r o m o t e t h e i n t r o d u c t i o n of this a p p a r a t u s on t h e s h r i m p e r s of t h e D u t c h f l e e t a n d s u b s i d i s e d its p u r c h a s e . It could, h o w e v e r , not c o m p e l a l l s h r i m p fishers to b u y this s p e c i a l e q u i p m e n t a n d to u s e it, b u t s i n c e t h e f i s h e r m e n o b s e r v e d t h a t it is also a l a b o u r - s a v i n g d e v i c e , t h e r e h a s b e e n a g e n e r a l t e n d e n c y to i n t r o d u c e it on t h o s e s h i p s w h i c h l e n d t h e m s e l v e s to it. This w a y t h e d e l e t e r i o u s effect of t h e s h r i m p f i s h e r , / o n t h e flatfish f i s h e r y e l s e w h e r e in t h e N o r t h S e a c a n b e r e d u c e d to s u c h a n e x t e n t t h a t b o t h f i s h e r i e s c a n r e a s o n a b l y co-exist.

THE SOLE

Of all t h e fishes c a u g h t in t h e N o r t h S e a t h e sole Solea solea b r i n g s b y far t h e h i g h e s t p r i c e p e r kg. C o n t r a r y to t h e e v e n t s in most o t h e r s p e c i e s of a p p r e c i a b l e c o m m e r c i a l v a l u e t h e sole c a t c h e s m a d e in our t i m e a r e d e f i n i t e l y h i g h e r t h a n t h o s e m a d e e a r l i e r i n t h e century. O n e w o u l d s u p p o s e t h a t t h e l a r g e r a n d f a s t e r s h i p s a n d t h e m o r e efficient g e a r w o u l d e x p l a i n t h e g r e a t e r sole l a n d i n g s i n p o s t - w a r y e a r s , b u t t h e r e is s c i e n t i f i c e v i d e n c e , b a s e d on e g g - c o u n t s in t h e p l a n k t o n , w h i c h i n d i c a t e s t h a t t h e s t o c k of N o r t h S e a sole m u s t r e a l l y h a v e b e e n of l e s s e r m a g n i t u d e e a r l i e r in t h e century.

T h e D u t c h f i s h i n g i n d u s t r y , s p e c i a l i z e d in e x p o r t of f l e s h t a b l e fish, h a s c o n c e n t r a t e d its efforts m o r e a n d m o r e on c a t c h i n g sole. S p e c i a l i z e d units w e r e b u i l t for this p u r p o s e . T h e b e s t c a t c h e s c o u l d b e m a d e shortly after s u n s e t w h e n t h e sole b e g i n s to forage, a n d a g a i n just b e f o r e s u n r i s e w h e n it g e t s h u n g r y again~ h o w e v e r , s i n c e one h a s l e a r n e d to use w h o l e s e r i e s of t i c k l e r c h a i n s , w h i c h c h a s e t h e sole out of the s a n d a n y t i m e of t h e day, t h e sole c a t c h e s a r e no l o n g e r l i m i t e d to t h e d a r k hours of t h e night.

M o r e a n d m o r e units w e r e b u i l t s p e c i a l l y for t h e sole f i s h e r y a n d i n t h e m i d - 1 9 5 0 s t h e d a y c a m e w h e n t h e f i n a n c i a l p r o c e e d s of the sole f i s h e r y s u r p a s s e d t h o s e of the h e r r i n g fishery, w h i c h h a d l o n g p r e d o m i n a t e d i n the D u t c h f i s h i n g i n d u s t r y . T h e N o r t h S e a sole f i s h e r y b e c a m e m o r e a n d m o r e a D u t c h b u s i n e s s , a n d n o w 80 to 85 % of t h e sole c a u g h t is t a k e n b y D u t c h vessels. T h i s w o u l d m a k e it p o s s i b l e to d e v e l o p a s o u n d m a n a g e m e n t for this fishery. I n t e r n a t i o n a l a g r e e m e n t w o u l d h a r d l y b e n e c e s s a r y , for all m e a s u r e s t a k e n w o u l d o p e r a t e p r a c t i c a l l y e x c l u s i v e l y on b e h a l f of t h e D u t c h fishery.

W h a t h a p p e n e d ? S c i e n t i f i c i n v e s t i g a t i o n s m a d e c l e a r t h a t r e p r o d u c t i o n s h o w s s h a r p f l u c t u a t i o n s i n t h e sole, s h a r p e r t h a n i n m a n y o t h e r fish s p e c i e s . T h o u g h t h e n u m b e r of e g g s p r o d u c e d d u r i n g t h e s p a w n i n g s e a s o n w i l l not s h o w m a j o r d e v i a t i o n s from t h e a v e r a g e , t h e s u c c e s s of r e p r o d u c t i o n v a r i e s l a r g e l y . Poor y e a r s , in d u e c o u r s e l e a d i n g to at m o s t a m o d e s t r e c r u i t m e n t , a l t e r n a t e w i t h g o o d y e a r s p r o d u c i n g e x c e l l e n t c a t c h e s a few y e a r s later. U n f o r t u n a t e l y r e a l l y r i c h y e a r c l a s s e s s e e m to occur o n l y a b o u t o n c e i n t e n years. V e r y g r e a t n u m b e r s of j u v e n i l e soles w e r e , for i n s t a n c e , p r o d u c e d in t h e y e a r s 1947, 1958, a n d p a r t i c u l a r l y 1963, a n d 1969 g a v e a r e a s o n a b l y g o o d b i r t h rate. A b o u t 21/2 y e a r s l a t e r t h e first " r e c r u i t s " m a k e t h e i r a p p e a r a n c e in t h e catches. T h e q u e s t i o n of w h i c h factors a r e to b e h e l d r e s p o n s i b l e for s u c c e s s or f a i l u r e in r e p r o d u c t i o n is still far from b e i n g a n s w e r e d , b u t e v e n if one k n e w one w o u l d still h a v e to w a i t a n d s e e w h a t n a t u r e h a s in m i n d .

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m a r k e t for soles is e x c e l l e n t i n m a n y E u r o p e a n c o u n t r i e s b i g m o n e y will b e m a d e w h e n the catches are good. Thered:ore a rich y e a r class i n c i t e s the f i s h e r m e n to e n l a r g e their fleet, w h i c h shows c o n s e q u e n t l y n e a t p e a k s r o u g h l y 4V2 years after the b i r t h of each rich y e a r class. T h e 1973-1974 p e a k i n the n u m b e r of fishery u n i t s is, however, h i g h e r t h a n could b e e x p e c t e d o n the b a s i s of the size of the 1969 y e a r class only, b u t easy terms for g e t t i n g m o n e y from the b a n k s w o r k e d out that way. T h e m o n e y m a d e is not o n l y i n v e s t e d i n more ships, b u t also i n b i g g e r a n d s t r o n g e r ships for this s a m e type of fishery. A b i g g e r ship w i t h a s t r o n g e r e n g i n e m a k e s b e t t e r catches, t h o u g h it also r e q u i r e s g r e a t e r i n v e s t m e n t a n d h i g h e r costs for fuel a n d gear. F i s h e r m e n are a b o v e all k e e n o n great catches a n d therefore t e n d to b u i l d ships w h i c h are b i g g e r a n d stronger t h a n those of their colleagues. This w o u l d n o t m a t t e r if at the s a m e time one r e d u c e d the n u m b e r of u n i t s i n t h e sole fishery, b u t n e i t h e r the f i s h i n g i n d u s t r y itself, n o r the g o v e r n m e n t has the p o w e r to a c h i e v e this. T h e f i n a l result is a fleet too b i g a n d too strong for the sole there is to catch. Surely, the stock of soles does n o t k e e p p a c e w i t h the size of the fleet. T h e f i s h e r m e n saw the catches m a d e p e r h o u r f i s h i n g d e c l i n e a l a r m i n g l y a n d t r i e d to c o m p e n s a t e this b y b u i l d i n g still b i g g e r a n d s t r o n g e r ships. For a n i n d i v i d u a l f i s h e r m a n this m a y s e e m to help, b u t the total catches w i l l n o t go up. O n the contrary. N o w the b a n k s w h i c h offered m o n e y on too easy terms b e g i n to realize that b r a n d - n e w ships s p e c i a l i z e d for the sole fishery are n o t such a good g u a r a n t e e for their m o n e y w h e n there is not e n o u g h fish to b e c a u g h t to cover the r u n n i n g expenses.

Scientific e v i d e n c e shows that b i g g e r catches could b e m a d e b y a further i n c r e a s e i n the m e s h size of the trawl nets, t h o u g h this w o u l d i n i t i a l l y l e a d to a r e d u c t i o n i n the catches, b u t also that the Dutch cutter fleet s p e c i a l i z e d for the sole fishery is m u c h too strong. With a fleet a b o u t o n e third of the p r e s e n t size o n e could catch the s a m e total t o n n a g e of sole as today. But the q u e s t i o n arises, w h o is g o i n g to give w a y a n d h o w o n e c a n p r o h i b i t the b u i l d i n g of y e t a n o t h e r ship for the sole fishery. A s m a l l e r fleet l a n d i n g the s a m e a n n u a l catches as today w o u l d g r e a t l y i n c r e a s e the r e m u n e r a t i o n of each i n d i v i d u a l ship, b u t h o w could o n e r e a c h this goal o n the b a s i s of the p r e s e n t fishery laws a n d r e g u l a t i o n s ? T h e scientists k n o w that e v e n a fleet as l a r g e as t o d a y will n o t e x t e r m i n a t e the North Sea sole a n d that a d e p l e t e d stock m a y i n d u e course recover w h e n the f i s h i n g i n t e n s i t y is f i n a l l y r e d u c e d b e c a u s e one loses too m u c h m o n e y o p e r a t i n g i n the p r e s e n t way. But t h e y are not too sure that n a t u r e w i l l r e a d i l y p r o d u c e a good stock of soles once t h e f i s h i n g i n t e n s i t y w o u l d b e d r a s t i c a l l y reduced. T h e r e is such a t h i n g as the " s t o c k - r e c r u i t m e n t r e l a t i o n " w h i c h m e a n s that recovery of a stock will t a k e a l o n g time once the total n u m b e r of eggs p r o d u c e d d u r i n g the s p a w n i n g s e a s o n has d r o p p e d b e l o w a critical level. T h e biologists s t u d y i n g the North Sea sole are afraid that this critical l e v e l is a l r e a d y operating, a n d therefore dare no l o n g e r p r o p h e s y that a good y e a r class w i l l occur at least once i n t e n years.

W h a t m a n a g e m e n t w o u l d b e c o n c e i v a b l e to s a f e g u a r d the future of the D u t c h sole fishery i n w h i c h so m u c h m o n e y h a s b e e n i n v e s t e d a n d for w h i c h t h e r e is n o t e n o u g h fish?

THE HERRING

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food in t h e d a r k h o u r s of t h e n i g h t , w o u l d g e t e n t a n g l e d b y its g i l l covers. In t h e p e r i o d b e t w e e n W o r l d W a r I a n d W o r l d W a r II o n e o b s e r v e d s y m p t o m s of s e r i o u s o v e r f i s h i n g i n d e m e r s a l s p e c i e s s u c h as flatfishes a n d g a d o i d s in t h e N o r t h Sea, b u t not in t h e h e r r i n g fishery. S a m p l e s of h e r r i n g c a u g h t in t h e drift n e t s a p p e a r e d to consist of s e v e r a l y e a r classes, s o m e t i m e s u p to ten. T h u s t h e e x i s t i n g f l u c t u a t i o n in t h e s t r e n g t h of t h e i n d i v i d u a l y e a r c l a s s e s w a s h a r d l y r e f l e c t e d in t h e size of t h e catches. W h e n it w a s d e c i d e d in 1946 to i n t r o d u c e i n t e r n a t i o n a l r e g u l a t i o n s to p r e v e n t o v e r f i s h i n g in t h e N o r t h Sea, p e l a g i c fishes s u c h as h e r r i n g a n d m a c k e r e l w e r e c o n s i d e r e d to b e so p l e n t i f u l t h a t t h e y n e e d e d no p r o t e c t i o n at all. No l e g a l m i n i m u m size w a s c o n s i d e r e d n e c e s s a r y for t h e h e r r i n g .

Drift n e t t i n g r e v i v e d after W o r l d W a r II, b u t in a d d i t i o n f i s h e r m e n b e g a n m o r e a n d m o r e to u s e f i n e - m e s h e d t r a w l n e t s to catch t h e h e r r i n g c l o s e to t h e b o t t o m d u r i n g d a y l i g h t hours. This b e c a m e p o s s i b l e b y u s e of b o a t s w i t h s t r o n g e r e n g i n e s w h i c h c o u l d m o v e the n e t w i t h a s p e e d f a s t e r t h a n t h a t of h e r r i n g t r y i n g to e s c a p e b y s w i m m i n g . G r a d u a l l y t h e t r a w l s c a u g h t m o r e a n d m o r e h e r r i n g a n d f i n a l l y drift n e t s b e c a m e o b s o l e t e in t h e D u t c h fishery. This d e v e l o p m e n t w a s f u r t h e r e d b y t h e i n t r o d u c t i o n of e l e c t r o n i c f i s h - f i n d i n g e q u i p m e n t w h i c h m a d e it p o s s i b l e to l o c a t e t h e h e r r i n g schools w i t h c o n s i d e r a b l e p r e c i s i o n . S i n c e h e r r i n g schools a r e s o m e t i m e s o b s e r v e d in m i d w a t e r , a p e l a g i c t r a w l w a s d e v e l o p e d to c h a s e t h e h e r r i n g w h e r e v e r it o c c u r r e d .

This d e v e l o p m e n t l e d to a n o t e w o r t h y i n c r e m e n t of t h e f i s h i n g i n t e n s i t y for h e r r i n g , a n d t h e r e b y to a r e d u c t i o n of t h e n u m b e r of y e a r c l a s s e s f o u n d in t h e catches. T h e i n t e n s i v e f i s h e r y m a d e it v i r t u a l l y i m p o s s i b l e for t h e h e r r i n g to r e a c h a n a g e of 10 to 15 y e a r s , as it c o u l d w i t h s o m e g o o d l u c k in e a r l i e r times. In r e a l i t y the c a t c h e s m a d e in the l a s t f e w y e a r s consist v i r t u a l l y e x c l u s i v e l y of t h e y e a r class w h i c h is b e i n g r e c r u i t e d , h e r r i n g of t h r e e y e a r s old, w h e r e a s h e r r i n g of e a r l i e r y e a r c l a s s e s r e p r e s e n t o n l y a m i n o r i t y in t h e catches. T h e stock w h i c h s p a w n s i n t h e C h a n n e l l a t e in t h e y e a r a n d c o n g r e g a t e s a l o n g t h e e a s t c o a s t of E n g l a n d in l a t e s u m m e r a n d e a r l y a u t u m n s u f f e r e d m o r e from i n t e n s i v e t r a w l i n g t h a n a n y o t h e r stock of N o r t h S e a h e r r i n g a n d lost t h e r e b y m u c h of its f o r m e r i m p o r t a n c e .

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Fig. 1. Dramatic events in the stocks of North Sea herring under the influence of drastically increased fishing intensity

w i t h all force after the m a c k e r e l a n d after the North Sea h e r r i n g proper. It w a s e s p e c i a l l y this latter d e v e l o p m e n t w h i c h b r o u g h t the North Sea stock of h e r r i n g d o w n to a p a r t i c u l a r l y low ebb. T h e I n t e r n a t i o n a l C o u n c i l for the E x p l o r a t i o n of the Sea w a r n e d the North-East A t l a n t i c Fisheries C o m m i s s i o n that too h e a v y a toll was l e v i e d of the North Sea h e r r i n g a n d that o n l y drastic m e a s u r e s could s a f e g u a r d the future of the h e r r i n g fishery. T h e C o u n c i l n o t e d that the 1973 y e a r class w a s of r e a s o n a b l e m a g n i t u d e , a b l e to secure a good offspring, b u t that later y e a r classes w e r e poor or e v e n e x t r e m e l y poor. Therefore, the C o u n c i l a d v i s e d that f i s h i n g 1973 y e a r class b e a b s t a i n e d from i n a n effort to offer the North Sea h e r r i n g a n o p p o r t u n i t y to r e v i v e its stocks. T h e North-East A t l a n t i c Fisheries C o m m i s s i o n d i s c u s s e d this a d v i c e seriously, b u t the f i s h i n g i n d u s t r y r e f u s e d to follow it b e c a u s e the h e r r i n g w e r e u r g e n t l y n e e d e d . All o n e d i d at this very late m o m e n t w a s to i n t r o d u c e a m i n i m u m l e g a l size for h e r r i n g , w h i c h m e a n t that the D a n i s h fish- m e a l i n d u s t r y w o u l d n o l o n g e r b e a l l o w e d to fish p u r p o s e l y for j u v e n i l e h e r r i n g i n the North Sea. It could, however, fish for sprat, a n d a m o n g the sprat o n e often finds j u v e n i l e h e r r i n g s as a by-catch.

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g i v e n to f i s h i n g for direct h u m a n c o n s u m p t i o n , b u t o n w h a t basis could one c o m p e l a g i v e n c o u n t r y to e a t the fish it catches i n s t e a d of f e e d i n g it to pigs a n d c h i c k e n s after r e d u c i n g it to fish m e a l ?

T h e future s e e m s v e r y g l o o m y for the North Sea h e r r i n g fishery. T h e a d v i c e of the scientists to give the 1973 y e a r class a c h a n c e to p r o d u c e offspring w a s f l u n g to the w i n d s a n d h e n c e this y e a r class w a s w i p e d out b y the 1976 fishery. Later y e a r classes are so poor that o n e c a n h a r d l y expect a r e v i v a l of the stocks, e v e n w h e n t h e y are c o m p l e t e l y left i n peace. T h e d a n g e r is t h e n that sprat t a k e s over from the h e r r i n g i n the North Sea, i n the s a m e w a y the a n c h o v y took t h e p l a c e of the over-fished s a r d i n e i n the coastal w a t e r s of California. Stocks of d e m e r s a l fishes such as flatfishes a n d g a d o i d s will n o t r u n t h e risk of b e i n g fished d o w n to s u c h a low e b b as s c h o o l i n g p e l a g i c fishes such as h e r r i n g a n d m a c k e r e l . With m o d e r n f i s h - f i n d i n g e q u i p m e n t a n d m o d e m g e a r o n e could trace a n d catch the very last school of t h e s e p e l a g i c fishes, w h e r e a s the d e m e r s a l fishes, w h i c h do n o t c o n c e n t r a t e to such a n extent, will b e left a l o n e w h e n t h e catch p e r u n i t of effort drops b e l o w a g i v e n level.

T h o u g h all c o u n t r i e s f i s h i n g for h e r r i n g i n the North Sea are seriously c o n c e r n e d a b o u t the p r e s e n t state of t h e stocks, it s e e m s h a r d l y p o s s i b l e to r e a c h a g r e e m e n t l e a d i n g to s o u n d m a n a g e m e n t . T h e r e is no s o u n d l e g a l basis to stop the i n d u s t r i a l fishery a n d t h e r e are no i n t e r n a t i o n a l f u n d s to b u y it out. Every t o n of j u v e n i l e h e r r i n g t a k e n as a b y - catch r e d u c e s the future stock of a d u l t h e r r i n g b y four tons - the n a t u r a l m o r t a l i t y t a k e n into a c c o u n t - b u t o n l y a strict control c o u l d enforce o b e d i e n c e to l i m i t i n g the b y - c a t c h of the i n d u s t r i a l fishery to the t o n n a g e a g r e e d u p o n . C o u n t r i e s t r a d i t i o n a l l y f i s h i n g for h e r r i n g d e s t i n e d for direct h u m a n c o n s u m p t i o n are v e r y h e s i t a n t to accept r e g u l a t i o n s r e s t r i c t i n g t h e i r catches, as l o n g as the r e a l c a u s e of all the t r o u b l e i n the h e r r i n g world, the i n d u s t r i a l fishery, h a s n o t d i s a p p e a r e d a n d as l o n g as the quotas are n o t b a s e d o n the former catches for h u m a n c o n s u m p t i o n only.

THE S A L M O N OF THE RIVER RHINE

O n c e the River R h i n e t e e m e d w i t h s a l m o n S a l m o salar. In the years f o l l o w i n g 1869, for w h i c h r e l i a b l e statistics are a v a i l a b l e , 50 000 to 60 000 s a l m o n p e r y e a r w e r e c a u g h t i n its d o w n r i v e r section. A l m o s t all w e r e b i g fishes w e i g h i n g some 10 kg each. O n l y 14 % of the catches c o n s i s t e d of m a l e s p a r t i c i p a t i n g for the first t i m e i n the run, w e i g h i n g some 2 k g each. T h e K r a l i n g s e V e e r n e a r R o t t e r d a m was t h e n t h e b i g m a r k e t for s a l m o n . H u g e nets w e r e u s e d to catch t h e m i g r a t i n g s a l m o n ; t h e y w e r e o p e r a t e d e i t h e r from some type of raft or from a fixed i n s t a l l a t i o n o n the river b a n k . O r i g i n a l l y , the n e t s w e r e d r a w n i n b y h a n d , b u t i n t h e shore i n s t a l l a t i o n s one could m a k e u s e of a h o r s e - m i l l for this h e a v y work. In d u e course, it w a s d e c i d e d to m a k e u s e of s t e a m p o w e r to d r a w i n the nets. This m a d e it p o s s i b l e to u s e still l a r g e r nets, b l o c k i n g off the river h e r m e t i c a l l y . Since then, t h r e e such l a r g e n e t s w e r e o p e r a t e d i n turns, b u t few of the m i g r a t i n g s a l m o n got a c h a n c e to escape. T h e catches i n c r e a s e d s h a r p l y w i t h the i n t r o d u c t i o n of s t e a m p o w e r a n d i n the years f o l l o w i n g 1880 o n e c o u l d often b r i n g more t h a n 100 000 s a l m o n to the m a r k e t . But this could n o t last. Too few s a l m o n could r e a c h the s p a w n i n g g r o u n d s i n the u p r i v e r tributaries. First the p e r c e n t a g e of s m a l l s a l m o n w e n t up, n e x t the total catches d r o p p e d a l a r m i n g l y .

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c a l l e d " S a l m o n Treaty," w h i c h l e d to i n t e r r u p t i o n of f i s h i n g for s a l m o n d u r i n g the w e e k - e n d s a n d d u r i n g a close s e a s o n late i n s u m m e r , b u t the e x p e c t e d a n d forecasted r e t u r n of l a r g e catches of s a l m o n from the River Rhine d i d n o t occur. In fact, the m e a s u r e s t a k e n came too late and, moreover, o v e r f i s h i n g w a s followed b y the c o n s t r u c t i o n of more a n d more weirs a n d b a r r a g e s for s h i p p i n g a n d h y d r o - e l e c t r i c stations, w h i c h m a d e it i m p o s s i b l e for the s a l m o n to r e a c h their s p a w n i n g g r o u n d s i n the tributaries. Here a n d there fish p a s s e s w e r e constructed, b u t t h e y w e r e e v i d e n t l y not of a d e s i g n a p p r e c i a t e d b y the salmon, a n d those fishes w h i c h d i d m a n a g e to b y p a s s the b a r r a g e s f o u n d their h a b i t a t deteriorated: i n s t e a d of w a t e r r u n n i n g swiftly over g r a v e l beds, the s a l m o n f o u n d a b o v e the b a r r a g e s almost s t a g n a n t w a t e r w i t h a m u d d y bottom, totally u n s u i t a b l e as s p a w n i n g g r o u n d . T h e n c a m e the r a p i d i n d u s t r i a l p o l l u t i o n of the w a t e r of the River Rhine w h i c h g a v e the last few s a l m o n c a u g h t a n a u s e a t i n g p h e n o l flavour (Fig. 2).

Was there no p r o p e r m a n a g e m e n t at all? E v i d e n t l y not. It is i n c r e d i b l e that the disastrous results of h e r m e t i c a l l y b l o c k i n g off the river b y a series of n e t s h a u l e d w i t h s t e a m p o w e r w e r e not f o r e s e e n a n d forestalled. T o w a r d s the e n d of the n i n e t e e n t h c e n t u r y it was d e c i d e d to r e l e a s e h a t c h e r y - r e a r e d s a l m o n i n a n effort to r e v i v e t h e once so p r o s p e r o u s stock, b u t t h o u g h m u c h m o n e y w a s s p e n t this w a y the goal w a s not realised. A c o m b i n a t i o n of overfishing, b a r r a g e s a n d w a t e r p o l l u t i o n h a d d e t e r i o r a t e d the s i t u a t i o n for the s a l m o n so drastically that a r e v i v a l of the stock h a d b e c o m e i m p o s s i b l e . Of course, o n e c a n c o n c e i v e of i n t e r n a t i o n a l m e a s u r e s to check the serious i n d u s t r i a l p o l l u t i o n of the River Rhine, n o w v i r t u a l l y a n o p e n sewer. Such m e a s u r e s w o u l d b e costly a l t h o u g h b e n e f i c i a l for other interests too, b u t w h o w o u l d s u g g e s t t a k i n g a w a y the weirs a n d b a r r a g e s to restore the s a l m o n ' s s p a w n i n g g r o u n d s i n the u p r i v e r areas? For e c o n o m i c r e a s o n s it s e e m s m u c h w i s e r to rely on p u r c h a s i n g fresh s a l m o n from Norway, w h e r e s a l m o n are r e a r e d to c o n s u m p t i o n size i n n e t t i n g p e n s p l a c e d i n w e l l - s h e l t e r e d fjords.

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THE BOWHEAD WHALE

B e t w e e n the y e a r s / 5 9 4 - 1 5 9 7 three n o w famous v o y a g e s w e r e u n d e r t a k e n b y W i l l e m Barents, J a c o b v a n H e e m s k e r k c k a n d J a n Cornelisz. Rijp. T h e y w e r e o r d e r e d to s e e k a n e w route to J a p a n , C h i n a a n d t h e Indies, since the t r a d i t i o n a l route v i a the C a p e of Good H o p e w a s r a t h e r d a n g e r o u s b e c a u s e of the w a r w i t h Spain. It w a s on the third v o y a g e that t h e y c a m e as far as the Isle of Nova Z e m b l a w h e r e t h e y s t a y e d d u r i n g the Arctic w i n t e r i n a h u t m a d e from the ship's timber, T h e survivors r e t u r n e d the n e x t s p r i n g i n o p e n boats to the i n h a b i t e d world, T h e y h a d n o t f o u n d a n a l t e r n a t e route to the Indies, b u t t h e y r e p o r t e d o n l a r g e schools of w h a l e s t h e y h a d o b s e r v e d i n the n o r t h e r n waters, e s p e c i a l l y a r o u n d the Isle of S p i t s b e r g e n (Svalbard), It w a s a type of w h a l e w h i c h differed s o m e w h a t from the A t l a n t i c Right Whale, for w h i c h t h e B a s q u e s a n d the British h a d b e e n h u n t i n g for m a n y years. Its h e a d w a s v e r y high, a n d the b a l e e n s or w h a l e - b o n e s w e r e c o r r e s p o n d i n g l y long.

It took some t i m e before p r a c t i c a l u s e w a s m a d e of this information, b u t i n d u e course ships s a i l e d n o r t h to catch w h a l e s . British a n d D u t c h ships a r r i v e d almost s i m u l t a n e o u s l y , i n l a t e r years followed b y ships from other nations. After some d i s p u t e a n d q u a r r e l l i n g each c o u n t r y m a d e u s e of its o w n b a y to o p e r a t e a l a n d station for w h a l i n g . T h e Dutch s e t t l e m e n t w a s a p p r o p r i a t e l y c a l l e d " S m e e r e n b u r g " .

T h e d e m a n d for w h a l e oil a n d b a l e e n s was great at that t i m e a n d soon p r o s p e r i t y s p r e a d a m o n g those directly or i n d i r e c t l y e n g a g e d i n w h a l i n g i n the arctic waters. But it w o u l d n o t a n d could n o t last, b e c a u s e f i s h i n g w a s so i n t e n s e that n a t u r e could not c o m p e t e w i t h these losses t h r o u g h r e p r o d u c t i o n a n d growth. O n e d i d not t h i n k i n such terms at that time b u t it w a s n o t e d that the n u m b e r of w h a l e s i n S p i t s b e r g e n w a t e r s d e c l i n e d d r a m a t i c a l l y a n d that it b e c a m e difficult to o p e r a t e from a l a n d station. At that time, the D u t c h u s e d a l a n d s t a t i o n o n the Isle of J a n M a y e n . But h e r e too w h a l e s d i s a p p e a r e d i n d u e course. T h e f i s h i n g p a t t e r n h a d to b e c h a n g e d from u s i n g a l a n d s t a t i o n to p e l a g i c w h a l i n g t h o u g h the latter m e t h o d was more c u m b e r s o m e a n d pro- d u c e d a w h a l e oil of inferior q u a l i t y since b o i l i n g o p e r a t i o n s h a d to b e c a r r i e d out after r e t u r n to the h o m e country. T h e w h a l e r s did n o t b e l i e v e that t h e y w e r e to b l a m e for the d e c l i n e of t h e stocks. T h e y a s s u m e d that w h a l i n g just scared the w h a l e s w h i c h t h e n w i t h d r e w to i n a c c e s s i b l e ice fields f u r t h e r north.

T h e r e a l i t y was, however, that b o w h e a d w h a l e s

Balaena mysticetus

b e c a m e more a n d more scarce, e v e n i n t h e w a t e r s west of G r e e n l a n d , a n d arctic w h a l i n g c a m e to a n e n d late i n the 18th c e n t u r y w h e n it was no l o n g e r r e m u n e r a t i v e to h u n t

for

b o w h e a d w h a l e s . N a r r a t i v e s like that of the w h a l e s ' " F r a n k e n d a a l " give a good i m p r e s s i o n of the s i t u a t i o n i n the years 1786-1787. W h a l i n g w a s s t o p p e d b e c a u s e it h a d b e c o m e a n i m p o s s i b l e e n t e r p r i s e from the e c o n o m i c p o i n t of view, c a u s e d b y d r o p p i n g prices for w h a l e oil a n d b a l e e n s , a n d b y the great scarcity of whales.

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T h e y still catch a b o w h e a d w h a l e o c c a s i o n a l l y but, u n f o r t u n a t e l y , n o w a d a y s switch over from t h e i r old p r i m i t i v e gear to more m o d e r n e q u i p m e n t . This will m a k e it all the more difficult for the r e d u c e d stock of b o w h e a d w h a l e s to recover.

A s i m i l a r sad story, b a s e d o n l a c k of m a n a g e m e n t , c o u l d b e told a b o u t a n t a r c t i c w h a l i n g i n o u r time. W h e n the d e m a n d for w h a l e oil w a s great after the S e c o n d World War, s e v e r a l c o u n t r i e s sent large factory ships to the Antarctic O c e a n to h u n t for b l u e w h a l e s a n d fin w h a l e s . In d u e course the catch p e r d a y d i m i n i s h e d , b u t the w h a l e r s f o u n d q u i t e a few e x p l a n a t i o n s for this fact other t h a n that it could h a v e b e e n c a u s e d b y their o w n activities. T h e r e w a s a n I n t e r n a t i o n a l W h a l i n g C o m m i s s i o n , a d v i s i n g the g o v e r n m e n t s i n v o l v e d o n the best w a y of o p e r a t i n g i n antarctic waters. T h e scientists i n this c o m m i s s i o n h a d the d u t y to d e m o n s t r a t e as a c c u r a t e l y as p o s s i b l e w h a t effect f i s h i n g h a d o n the w h a l e stocks. I d e a l m a n a g e m e n t w o u l d b e h a r v e s t i n g the r e n t of this n a t u r a l c a p i t a l alone, t a k i n g the t o n n a g e a d d e d to the stocks each y e a r b y growth a n d r e p r o d u c - tion. But the scientists could not a g r e e o n the b e s t w a y to d e t e r m i n e the a g e of the whales, a n d thus could not p r o d u c e r e l i a b l e figures o n growth a n d reproduction. I n such cases g o v e r n m e n t a l a u t h o r i t i e s are i n c l i n e d to l i s t e n to i n d u s t r y r a t h e r t h a n to q u a r r e l - l i n g scientists. The w h a l i n g i n d u s t r y was not w i l l i n g to r e d u c e its catches i n such a w a y that it could b e c o n s i d e r e d as a n e c o n o m i c sacrifice a n d thus h u n t i n g w e n t o n i n d i s c r i m i - n a t e l y . T h e result is w e l l k n o w n : the stocks s h o w e d signs of d e p l e t i o n w h i c h m a d e e c o n o m i c e x p l o i t a t i o n more a n d more difficult, e s p e c i a l l y w h e n the price of w h a l e oil d r o p p e d d r a m a t i c a l l y b y a n i n c r e a s i n g p r o d u c t i o n of v e g e t a b l e fats i n tropical countries. S e v e r a l c o u n t r i e s s t o p p e d antarctic w h a l i n g for e c o n o m i c reasons, b u t the USSR a n d J a p a n c o n t i n u e d . T r u e m a n a g e m e n t is at p r e s e n t out of the question.

Experts from F A O i n f o r m e d us some years ago that the fin w h a l e w o u l d r e q u i r e 40 years, the b l u e w h a l e at least 80 years to recover their stocks to a l e v e l of e c o n o m i c i m p o r t a n c e , p r o v i d e d w e s t o p p e d w h a l i n g c o m p l e t e l y now. This is n o t a n effort of m a n a g e m e n t b u t just a k i c k i n the air. No g o v e r n m e n t is w i l l i n g to i m p o s e severe restrictions on its i n d u s t r i e s on b e h a l f of such a l o n g - t e r m possible benefit. G o v e r n m e n t officials a n d political l e a d e r s are r a t h e r t h i n k i n g i n terms of b e n e f i c i a l d e v e l o p m e n t s w i t h i n their terms of office. Therefore w e c a n n o t hope for s o u n d m a n a g e m e n t of w h a l e stocks. O n the other h a n d , c o m p l e t e e x t e r m i n a t i o n is not to b e expected. Long before that t i m e it will b e c o m e e c o n o m i c a l l y i m p o s s i b l e to c o n t i n u e w h a l i n g , i n a n y case w h e r e l a r g e factory ships are used.

FROM ZUYDER SEA TO LAKE IJSSEL

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rich p l a n k t o n a n d b o t t o m f a u n a o n w h i c h fishes a d a p t e d to low s a l i n i t i e s could thrive. It could b e e x p e c t e d that c y p r i n i d s such as the b r e a m

(Abramis brama)

w o u l d thrive there, t o g e t h e r w i t h the ruff

(Acerina cernua),

a s m a l l m e m b e r of the p e r c h family, a n d that the smelt

(Osmerus eperlanus],

b e i n g very e u r y h a l i n e , w o u l d survive here, p o s s i b l y as stock of r a t h e r s m a l l i n d i v i d u a l s , b u t all these w o u l d h a r d l y b e of a n y direct v a l u e for the fishery. It w o u l d b e of c o n s i d e r a b l e i n t e r e s t if the c o m m o n p e r c h

(Perca fluviatilis)

a n d the p i k e - p e r c h

(Lucioperca lucioperca)

w o u l d thrive i n the n e w Lake IJssel, for these fishes are w e l c o m e o n the m a r k e t . O n e felt q u i t e sure that p e r c h stock w o u l d soon increase, b u t for the p i k e - p e r c h , o r i g i n a l l y a n o n - i n d i g e n o u s species, some d o u b t s e e m e d justified. A b o v e all o n e h o p e d for t h e d e v e l o p m e n t of a rich stock of eels, the most v a l u a b l e of the fresh w a t e r fishes o c c u r r i n g i n the w a t e r s of T h e N e t h e r l a n d s . T h e elvers, b o r n i n the Sargasso Sea, h a d to m a k e their e n t r y from the n o r t h a n d w o u l d f i n d the e n c l o s i n g d a m i n t h e i r way. H o w w o u l d t h e y t a c k l e this obstacle? It is true that two groups of locks h a d b e e n c o n s t r u c t e d i n the e n c l o s i n g d a m w h i c h w o u l d facilitate t h e i r p a s s a g e s if t h e y could find them, b u t the e n g i n e e r s i n c h a r g e i n s i s t e d on k e e p i n g the s a l i n e w a t e r s from the o p e n s e a a w a y from Lake IJssel. I n i t i a l l y the elvers p a s s e d the locks i n t h e s a m e w a y as t h e ships for w h i c h t h e y h a d b e e n constructed, b u t on t h e basis of scientific i n v e s t i g a t i o n s a n i n g e n i o u s system of n o c t u r n a l m a n i p u l a t i o n s w i t h the doors of the locks w a s d e v e l o p e d i n d u e course; this l e d to l a r g e - s c a l e p a s s a g e of elvers into Lake IJssel w i t h o u t a n y i n t r u s i o n of salt water. W o u l d the elvers stay i n Lake IJssel or w o u l d t h e y m a k e their w a y into the h i n t e r l a n d ? F o r t u n a t e l y , m a n y j u v e n i l e eels s t a y e d i n Lake IJssel, w h i c h w a s r i c h e r i n food t h a n most of the waters further u p s t r e a m .

T h e t r a n s i t i o n from Z u y d e r Sea to Lake IJssel w o u l d offer a n e x c e l l e n t o p p o r t u n i t y to c h a n g e the p a t t e r n of the fishery i n such a w a y that o n e could s p e a k of a r a t i o n a l e x p l o i t a t i o n of the n a t u r a l resources. A b i l l h a d b e e n p a s s e d w h i c h facilitated f i n a n c i a l c o m p e n s a t i o n for those of the old Z u y d e r Sea f i s h e r m e n w h o w o u l d lose t h e i r living. Therefore, there w a s a good o p p o r t u n i t y to set u p a n e n t i r e l y n e w p a t t e r n for the fishery i n Lake IJssel. If the e e l w a s to b e c o m e the l e a d i n g species, it w o u l d b e wise to catch silver eels p r e p a r i n g for m i g r a t i o n to t h e i r s p a w n i n g grounds, for t h e n t h e y r e a c h t h e i r h i g h e s t m a r k e t v a l u e . This is the system so effectively u s e d i n the L a g o o n of C o m a c c h i o i n Italy. For a v a r i e t y of r e a s o n s the p l a n n i n g t u r n e d out differently. C a t c h i n g eels e x c l u s i v e l y as silver eels w o u l d n o t only r e d u c e the f i s h i n g s e s a s o n to a few m o n t h s a year, w h e r e a s there w a s a good d e m a n d for eels t h r o u g h o u t the s u m m e r season, b u t w o u l d also b e e x c l u s i v e l y b e n e f i c i a l for those f i s h e r m e n w h o o p e r a t e d i n the m i g r a t i o n routes of the eels, d e p r i v i n g f i s h e r m e n e l s e w h e r e a r o u n d the Z u y d e r Sea from c a t c h i n g eels. M o r e o v e r all this h a p p e n e d d u r i n g the i l l - f a m e d d e p r e s s i o n years a n d the M i n i s t r y i n s i s t e d o n k e e p i n g a large n u m b e r of s m a l l f i s h e r m e n i n the fishery r a t h e r t h a n to o p e r a t e w i t h a s m a l l e r n u m b e r of s t r o n g e r units. It w a s e v e n s u g g e s t e d m a k i n g use of s a i l i n g vessels only, a n d to a b s t a i n from u s i n g e n g i n e p o w e r for r e a s o n s of economy.

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656 P. Korringa

y e a r a n d the success of t h e silver eel fishery some s e v e n years later. This m a d e it e v e n p o s s i b l e to forecast the results of the silver eel fishery. To p r e v e n t the i m m a t u r e eels from b e i n g c a u g h t at too s m a l l a size, a m i n i m u m l e g a l size of 28 cm w a s i n t r o d u c e d ; to p r e v e n t too h i g h a f i s h i n g i n t e n s i t y for i m m a t u r e eels n o e n g i n e s s t r o n g e r t h a n 25 hp w e r e a l l o w e d i n the f i s h i n g boats o p e r a t i n g i n Lake IJssel. T h e advice to stick to s a i l i n g vessels only was n o t a c c e p t e d b y the f i s h e r m e n , for t h e y soon f o u n d out that e n g i n e s w o u l d allow t h e m to o p e r a t e i n almost a n y type of w e a t h e r a n d w o u l d l e a d to b e t t e r e c o n o m i c results.

It w a s n o easy m a t t e r to enforce the m i n i m u m l e g a l size for i m m a t u r e eels, b u t the 25 h p rule s e e m e d to work q u i t e well. A r o u n d 1960 the e e l fishery i n Lake IJssel d i d n o t s e e m to flourish as w e l l as before; i n particular, the fishery for silver eels s h o w e d m u c h p o o r e r results t h a n forecast o n the b a s i s of the i m m i g r a t i o n of elvers. Scientific r e s e a r c h carried out b y the N e t h e r l a n d s Institute for F i s h e r y I n v e s t i g a t i o n s r e v e a l e d the cause of the decline. T h e l a c k of silver eels h a d to b e a s c r i b e d to a n i n c r e a s e d fishery with the eel trawls, this n o t b e c a u s e more ships p a r t i c i p a t e d i n the fishery, b u t r a t h e r b e c a u s e clever f i s h e r m e n h a d l e a r n e d to a b u s e the 25 hp r u l e i n s e v e r a l ways. A faster b o a t a p p e a r e d to l e a d to g r e a t e r catches a n d b e t t e r proceeds. Other f i s h e r m e n s a w this h a p p e n a n d soon followed the e x a m p l e , t h o u g h d a n g e r o u s a n d illegal. It soon t u r n e d out that some of the boats w o r k e d i n reality w i t h a horse p o w e r of 60 to 80 i n s t e a d 25. No s m a l l w o n d e r that the silver e e l catches h a d d e c l i n e d so drastically! T h e scientific report also m a d e clear that the i n t e n s i v e trawl fishery for i m m a t u r e eels m a d e it v i r t u a l l y i m p o s s i b l e for the stocks of p e r c h a n d p i k e - p e r c h to develop, since too m a n y j u v e n i l e s p e c i m e n s f o u n d a n u n t i m e l y d e a t h i n t h e f i n e - m e s h e d nets.

T h e report l e d to a serious clash i n the M i n i s t r y a n d e v e n to d i s m i s s a l of its Director of Pisheries. A s p e c i a l c o m m i s s i o n w a s set u p i n w h i c h b o t h p r o f e s s i o n a l f i s h e r m e n a n d s p o r t - f i s h e r m e n w e r e d u l y r e p r e s e n t e d . It could only corroborate the a l l e g a t i o n s of the biologists that the f i s h i n g i n t e n s i t y h a d g o n e u p a l a r m i n g l y since the 25 h p limit b e c a m e grossly a b u s e d a n d the 28-cm m i n i m u m l e g a l size for eels w a s not a l w a y s observed. T h e p r o f e s s i o n a l f i s h e r m e n e v e n a d m i t t e d that t h e y often fished for eels i n the f o r b i d d e n coastal zone, the s p a w n i n g a n d n u r s e r y g r o u n d s for p e r c h a n d p i k e - p e r c h , t h o u g h d u l y d e l i m i t e d b y lights, a n d that the i n s t a l l a t i o n of r a d i o t e l e p h o n e s on their vessels m a d e it possible to k e e p each other i n f o r m e d o n the w h e r e a b o u t s of the p a t r o l l i n g police- vessels. No s m a l l w o n d e r that m a n y p i k e - p e r c h nests w e r e d e s t r o y e d a n d that the trawls m a d e a terrible s l a u g h t e r of the j u v e n i l e p e r c h a n d p i k e - p e r c h . S o m e t h i n g h a d to b e d o n e to restore the former p r o d u c t i v i t y of Lake IJssel. R e d u c t i o n of the f i s h i n g i n t e n s i t y , e s p e c i a l l y of the trawl fishery, s e e m e d i m p e r a t i v e , b u t o n e h e s i t a t e d to t a k e such a drastic m e a s u r e a n d c o n s i d e r e d for the t i m e b e i n g a s t e p - b y - s t e p r e d u c t i o n of this fishery.