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P. Fossum, H. Bj~rke og R. Sætre Fiskeridirektoratets Havforskningsinstitutt

Postboks 1870, 5024 Bergen

SAMMENDRAG

Denne rapporten gir noen forelopige resultater fra sildelarveunder- s~kelsene på Møre i april 1986. Den behandler horisontal- og verti- kalfordeling av larvene i relasjon til det fysiske miljoet samt deres vekst og næringsopptak.

Gytefeltene kommer klart frem i fordelingen av de minste larvene.

Feltene var de samme som ble funnet i 1985. I tillegg fant det sted en mindre gyting ute

på

eggakanten. Hovedtrekkene i sirkulasjons- monsteret synes

å

være det samme som i 1985. Ved

å

kombinere hydro- grafiske data, larvefordeling og drivboyer ser det ut for at man kan få frem både larvenes viktigste driftsruter samt områder hvor larvene holdes tilbake i 10-15 dager.

Larvepopulasjonen i 1986 var totalt dominert av plommesekklarver.

Antall larver større enn 12

mm

var omkring 10% av det som ble funnet

i

samme periode i 1985.

1

1986 ble det også observert lavere vekst og næringsopptak hos larvene enn i 1985. Alt dette tyder på at rekrutteringen til sildebestanden i 1986 var dårligere enn i 1985.

Storstedelen av larvene ble funnet dypere enn

60 m.

Innslaget av ny-

klekkede larver Øket med dypet mens eldre larver ble hovedsaklig

funnet i de Øvre 40

m.

Forste næringsopptak ble funnet i 3-6 dagers

gamle larver. Dietten var dominert av rauåte larver.

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STUDIES ON HERRING M V A E OFF CdESTERN FIORWAY E61e

1986

by

P. Fossum, H . Bjarke and R . Sætre I n s t i t u t e of Marine Research P. O . Box 1870, N-5024 Bergen

Norway

ABSTRACT

T h i s r e p o r t g i v e s some p r e l i m i n a r y r e s u l t s from a s t u d y on t h e spawning grounds of t h e Norwegian spring-spawning h e r r i n g i n A p r i l 1986. I t d e a l s with t h e h o r i z o n t a l and v e r t i c a l d i s t r i b u t i o n of h e r r i n g l a r v a e i n r e l a t i o n t o t h e p h y s i c a l environment a s w e l l a s growth and d i e t .

The spawning a r e a can c l e a r l y be seen i n t h e d i s t r i b u t i o n of l a r v a e

<

⁹mm and t h e s e were t h e same a s i n 1985. I n a d d i t i o n , a s m a l l e r spawning a r e a o f f s h o r e a t t h e c o n t i n e n t a l s l o p e was i d e n t i f i e d .

The main f e a t u r e s of t h e c i r c u l a t i o n p a t t e r n of t h e a r e a seems t o be t h e same a s i n

1985.

The combined u s e of hydrography, l a r v a e d i s t r i - b u t i o n and Argos d r i f t e r s seem a b l e t o r e v e a l both t h e l a r v a l d r i f t a s w e l l a s r e t e n t i o n a r e a s with a r e s i d e n c e time of 10-15 d a y s ,

The l a r v a l population i n 1986 was t o t a l l y dominated by yolksac l a r v a e . The number of l a r v a e

>

12 mm was about 10% of t h a t found d u r i n g t h e same p e r i o d i n 1985, I n 1986 a slower growth and a lower f e e d i n g r a t i o i n a l l l a r v a l s t a g e s was observed compared t o 1985, T h i s i n d i - c a t e poorer recruitment i n 1986 than i n 1985.

The m a j o r i t y of t h e l a r v a e were found deeper than 60 m opposed t o 1985. The percentage of newly hatched l a r v a e i n c r e a s e d with depth.

Older l a r v a e were found mainly i n t h e upper 40 m. Patchy d i s t r i b u t i o n made a comparison between l a r v a e caught a t day and a t n i g h t d i f f i c u l t . F i r s t f e e d i n g was observed i n 3-6 days o l d l a r v a e . The d i e t of t h e l a r v a e was dominated by copepods n a u p l i i . A s h r i n k a g e of 40-50% i n dryweight and

3-7%

i n l e n g t h due t o p r e s e r v a t i o n was observed.

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Sampling of l a r v a e of t h e Norwegian spring-spawning h e r r i n g has been c a r r i e d o u t f o r a long period ( e . g . WLBORG 1960, DRAGESUND 1970, SELI- VERSTOV 1974 and BJØRKE 1 9 8 1 ) . The main o b j e c t i v e of t h e s e i n v e s t i g a - t i o n s has been t o l o c a t e spawning a r e a s and t o o b t a i n t h e f i r s t i n d i - c a t i o n of t h e r e c r u i t m e n t . The i n c r e a s e of t h e h e r r i n g s t o c k i n more r e c e n t y e a r s and development of new g e a r s and methods, a c t u a l i z e t h e formulation of a p r o j e c t t o s t u d y t h e r e c r u i t m e n t mechanisms.

I n

1985

a p i l o t study was c a r r i e d o u t (BJØRKE, FOSSUM and SÆTRE, 1 9 8 6 ) . The p r o j e c t was l a t e r included i n a n a t i o n a l program t o s t u d y t h e p o s s i b l e consequences on f i s h eggs and l a r v a e of o i l explo- r a t i o n on t h e Norwegian c o n t i n e n t a l s h e l f n o r t h of 6 2 ' ~ (FØYN and BJØRKE, 1986). T h i s program i s given t h e acronym HELP (Havforsknings- i n s t i t u t t e t s Egg- og Larveprogram) and i s supposed t o l a s t f o r t h e p e r i o d e 1986-90.

The o b j e c t i v e s of HELP i s t o :

-

o b t a i n d e t a i l e d knowlegde of t h e d i s t r i b u t i o n i n s p a c e and time of t h e important commercial f i s h s p e c i e s d u r i n g t h e i r e a r l y l i f e s t a g e along t h e Norwegian c o a s t ,

-

s t u d y t h e r e p r o d u c t i v e biology of t h e same s p e c i e s .

-

s t u d y t h e r e c r u i t m e n t mechanisms of t h e Norwegian spring-spawning h e r r i n g and t h e Arcto-Norwegian cod.

-

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

The p r e s e n t r e p o r t g i v e s some p r e l i m i n a r y r e s u l t s from t h e i n v e s t i - g a t i o n on t h e l a r v a e of t h e Norwegian spring-spawning h e r r i n g i n 1986.

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MATERIALS AND METRODS

The s t u d y was c a r r i e d o u t during t h e p e r i o d s 29 March

- ⁷

A p r i l and

9 - 18

A p r i l . The southern p a r t of t h e a r e a was covered d u r i n g both t h e s e p e r i o d s ( F i g . l ) . Herring l a r v a e were sampled with a modified c o n i c a l n e t of 0.5 m* opening and

375

p m mesh s i z e (ELLERTSEN e t a l .

1984)

from 150 m ( o r

5

m above t h e bottom) t o t h e s u r f a c e . The v e r t i - c a 1 d i s t r i b u t i o n s of temperature, s a l i n i t y , n u t r i e n t s and c h l o r o p h y l l c o n t e n t s were observed by Nansen h a u l s . Five Argos s a t e l l i t t e - t r a c k e d , d r i f t i n g buoys were deployd. These were equipped with a 10 m 2 window b l i n d drogue a t t a c h e d t o t h e buoys v i a a 30 m t e t h e r l i n e .

The m a t e r i a l f o r t h e v e r t i c a l s t u d i e s was d e r i v e d from two experiments on Buagrunnen; one from 5-7 A p r i l with a Mocness l m 2 sampler(mesh 3 7 5 ~ ) (WIEBE e t a l . ) ,and one from A p r i l

5

and 6 with a opening/closing Juday n e t (mesh 375p and opening O.

5m2

⁾

.

Dif f i c u l t i e s i n changing of n e t s a t p r e c i s e depths arosed d u r i n g t h e Mocness experiment and t h i s caused a s l i g h t overlapping of depth i n t e r v a l s (Table 1.) About 50 m ³ was f i l t e r e d with t h e Mocness sampler w i t h i n each depth i n t e r v a l and about 1 0 m 3 with t h e v e r t i c a l n e t . To confirm abundance of l a r v a e a v e r t i c a l plankton hau1 was made between each Mocness h a u l . Bottom depth v a r i e d between 120 and 90 m d u r i n g t h e Mocness experiment.

During t h e sampling with t h e Juday n e t t h e s h i p was anchored a t a depth of 120 m .

The h e r r i n g l a r v a e used t o morphometric measurements and g u t c o n t e n t a n a l y s i s were preserved i n

4%

formalin i n 10

%.

s e a water

.

Only t h e food organisms t h a t could be recognized through t h e e p i t h e l i u m of t h e g u t were examined, because of g u t c o n t e n t voidance i n h e r r i n g l a r v a e d u r i n g c a t c h i n g and f i x a t i o n (HAU

1981).

No q u a n t i t a t i v e a n a l y s e s of t h e d i e t of t h e h e r r i n g l a r v a e was performed due t o t h e same reason.

The same procedure was followed i n 1986 a s w i t h t h e 1985 m a t e r i a l (BJØRKE, FOSSUM & SAXRE 1986) and a comparative a n a l y s i s between t h e s e two sets of d a t a could t h u s be made.

The h e r r i n g l a r v a e used t o d e s c r i b e t h e h o r i z o n t a l d i s t r i b u t i o n were measured on board. Standard l e n g t h (SL) measurements of 50 h e r r i n g l a r v a e p e r hau1 ( i f p r e s e n t ) were taken t o n e a r e s t mm below. For morphometric measurements i n t h e l a b o r a t o r y a m a t e r i a l of 647 h e r r i n g

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l a r v a e were analysed

.

From each s t a t i o n 20 l a r v a e ( i E p r e s e n t ) were c l a s s i f i e d according t o DOYLE (1977) and ØIESTAD (1983). and measured t o n e a r e s t 0 . 1 mm below. V i s i b l e prey organisms were d i s s e c t e d o u t of t h e g u t and c l a s s i f i e d i n t o one of t h e following two groups; copepod eggs o r copepod n a u p l i i . The l a r v a e were then r i n s e d i n f r e s h w a t e r , d r i e d t o c o n s t a n t weight and weighed on a Cahn e l e c t r o b a l a n c e t o t h e n e a r e s t pg.

Because of shrinkage due t o p r e s e r v a t i o n (THEILACKER & DORSEY 1 9 8 0 ) , a r e p r e s e n t a t i v sample of h e r r i n g l a r v a e ( N = 47) from t h e whole a r e a of d i s t r i b u t i o n were s e p e r a t e d i n t o d i f f e r e n t s t a g e s when f r e s h onboard.

They were measured t o n e a r e s t O . l m m below, r i n s e d i n f r e s h water and brought t o t h e l a b o r a t o r y where they were d r i e d t o c o n s t a n t weight and weighed on a Cahn e l e c t r o b a l a n c e t o t h e n e a r e s t pg. This sample r e p r e - s e n t an e s t i m a t e of t h e t r u e s t a n d a r d l e n g t h and d r y weight i n t h e l a r v a l p o p u l a t i o n , and a comparison between t h e s e l a r v a e and t h e preserved ones g i v e s information of t h e shrinkage d u r i n g f i x a t i o n .

RESULTS AND DISCUSSION

Hydrography

Surface temperatures ( F i g . 2 ) and s a l i n i t i e s ( F i g . 3 ) were

4.5

O - 6 . 5 ' ~ and 33-35%. r e s p e c t i v e l y . The n o r t h e r n p a r t of t h e a r e a was c l e a r l y i n f l u e n c e d by A t l a n t i c Water masses while i n t h e s o u t h e r n p a r t C o a s t a l Water was dominant. The same p a t t e r n could be s e e n i n t h e s u r f a c e d i - s t r i b u t i o n of n i t r a t e and s i l i c a t e ( F i g s . 4-5) with high v a l u e s i n t h e n o r t h e r n and low v a l u e s i n t h e s o u t h e r n p a r t . The s u r f a c e d i s t r i b u t i o n of c h l o r o p h y l l g ( F i g .

6 )

showed very low v a l u e s i n t h e n o r t h e r n a r e a . The h i g h e s t c o n c e n t r a t i o n s were found along t h e s h e l f break i n t h e c e n t r a l a r e a .

Fig.

7

shows t h e t y p i c a l v e r t i c a l hydrographic s t r u c t u r e from t h e s o u t h e r n (SECTION A ) , t h e c e n t r a l (SECTION B ) and t h e n o r t h e r n (SECTION C ) p a r t of t h e i n v e s t i g a t e d a r e a . The l o c a t i o n of t h e s e c t i - ons appear i n Fig. 1. C o a s t a l Water ( S

<

3 5 % . ) covers t h e upper 100 m i n t h e s o u t h e r n and c e n t r a l s h e l f a r e a . I n t h e northernmost s e c t i o n

(SECTION C ) water of c o a s t a l o r i g i n i s seen a t t h e outermost s t a t i o n s . T h i s i s probably a r e s u l t of t h e s p l i t t i n g of t h e Norwegian C o a s t a l

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Current f u r t h e r south a l s o i n d i c a t e d i n t h e d i s t r i b u t i o n of s u s f a c e s a l i n i t y ( F i g . 3 ) . According t o LJØEN and NAli(KEN

(1969)

t h e Norwegianr C o a s t a l Current s p l i t s i n t o two branches between

63' and 6 4 ' ~ ~

The main branch run p a r a l l e l and c l o s e t o t h e c o a s t on t h e e o a s t a l s i d e of Haltenbanken (Area F, F i g .

1 7 ) .

The o t h e r branch follows t h e edge of

t h e c o n t i n e n t a l s l o p e on top of t h e A t l a n t i c water.

SECTION A was c a r r i e d o u t twice;

31

March and

16

A p r i l ( F i g , 71, The a n g l e of t h e s l o p i n g i n t e r f a c e between t h e C o a s t a l and t h e A t l a n t i c Water have decreased d u r i n g t h e f i r s t p a r t of A p r i l r e s u l t i n g i n a more seaward e x t e n t i o n of t h e C o a s t a l Water. There i s a pronounced r e - d u c t i o n of t h e n i t r a t e c o n t e n t i n t h e upper l a y e r s from t h e end of March t o mid-April i n d i c a t i n g t h a t a phytoplankton blsom

has

occurred between t h e o b s e r v a t i o n s . During t h e same p e r i o d e t h e c o n t e n t s of c h l o r o p h y l l g i n t h e upper 30 m of t h e s e c t i o n i n c r e a s e d from 0 - 1

-

0 . 3 t o

1 . 5 - 4.5

^mg/m3 ( F i g .

8 ) .

Though t h e s u r f a c e c h l o r o p h y l l v a l u e s

9-18

A p r i l i n t h e n o r t h e r n a r e a i s low ( F i g .

G),

reminiseences of a precedent phytoplankton bloom a r e seen i n SECTION C ( F i g ,

8 ) .

F i g .

9

shows t h e d r i f t i n g t r a c k s from t h e Argos kuoys. The bottom topography of t h e a r e a i s r a t h e r complica.ted and t h i s i n f l u e n c e s t h e c i r c u l a t i o n p a t t e r n . There a r e f o u r major shallow banks i n t h e a r e a : Buagrunnen ( C ) , F r ~ y a b a n k e n (D ) , Haltenbanken ( F ) and Sklinnabanken

( E ) . The l o c a t i o n of t h e s e a r e seen i n F i g .

17.

Around t h e s e banks t h e topographic s t e e r i n g of t h e c u r r e n t favour an a n t i - c y c l o n i c e i r c u - l a t i o n . North of Buagrunnen and of F r ~ y a b a n k e n th e water mainly flows eastwards and merge i n t o t h e channel between Haltenbanken

a d

t h e c o a s t . This seems t o be t h e main r o u t e f o r t h e northward d r i f t i n g l a r v a e . The c u r r e n k speed of t h e upper l a y e r of t h i c a r e a i s between 30 and 60 cm/s which means

7-15

n a u t i c a l miles/day, OE t h e two Argos buoys which were d r i f t i n g f u r t h e r northward. one ended up a t

66'~ 26

May and t h e o t h e r one c l o s e t o 6 9 ' 3 0 ' ~ a t

18

June ( F i g , L O )

H o r i z o n t a l l a r v a e d i s t r i b u t i o n

The h a t c h i n g of h e r r i n g l a r v a e s t a r t e d i n t h e southernmost a r e a around

15

March and a t Buagrunnen (Area C , F i g .

17)

around L A p r i l , A t both l o c a t i o n s t h e maximum h a t c h i n g occurred i n mid-April (BJØRKE, HANSEN and MELLE,

1987) .

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The h o r i z o n t a l d i s t r i b u t i o n of h e r r i n g l a r v a e of t h r e e d i f f e r e n t l e n g t h groups from t h e f i r s t coverage 29 March

- 7

A p r i l i s shown i n F i g s .

11-13.

The d i s t r i b u t i o n of t h e youngest l a r v a e ( F i g . l i ) i n d i - c a t e t h r e e s e p a r a t e d spawning a r e a s ; Buagrunnen, c l o s e t o t h e s h o r e i n t h e southernmost a r e a and a t t h e s h e l f break around 6 3 ' ~ . A s can be seen t h e r e a r e very few l a r v a e

L

¹²mm ( F i g .

1 3 ) .

During t h e second coverage (9-18 A p r i l ) t h e t o t a l number of l a r v a e

< 9

mm i s h i g h e r ( F i g .

1 4 ) .

Two of t h e apparent spawning a r e a s a r e t h e same a s on t h e previous coverage. A d d i t i o n a l l y , t h e r e seems t o be a minor spawning n e a r FrØyabanken (Area D, Fig. 1 7 ) . The number of l a r v a e

L

¹² mm ( F i g . 1 6 ) i s only about 10% of t h a t found d u r i n g t h e same p e r i o d i n

1985

(BJØRKE, FOSSUM and SÆTRE, 1 9 8 6 ) . T h i s may i n d i - c a t e t h a t t h e recruitment success i n 1986 was c o n s i d e r a b l y lower than i n

1985.

Off t h e southernmost c o a s t a l spawning a r e a (Area A , Fig.

17)

a s w e l l a s a t Buagrunnen t h e Argos d r i f t e r s i n d i c a t e r e t e n t i o n a r e a s of t h e l a r v a e with a recidence time of t h e water of 10-15 days. Fig.

17

i s an attempt t o summarize t h e information on t h e l a r v a l d r i f t . It i s based on l a r v a e d i s t r i b u t i o n , t h e t r a c k s of t h e Argos d r i f t e r s and on hydrography. The d r i f t i n g time from t h e spawning a r e a s t o t h e p a s s i n g of t h e 6 5 ' ~ l a t t i t u d e seems t o be 40-50 days from t h e southernmost spawning a r e a and 20-30 days from Buagrunnen. A s a s i t g n l f i c a n t pso- p o r t i o n of t h e l a r v a e p o p u l a t i o n i s below t h e drogue depth of t h e Argos buoys and a s d i s p e r s i o n mechanisms i s n o t c o n s i d e r e d , t h e c a l - c u l a t e d d r i f t i n g times is probably underestimates.

V e r t i c a l l a r v a e d i s t r i b u t i o n .

Table 1 shows t h e number of l a r v a e p e r m 2 s u r f a c e s a p l e d d u r i n g t h e Mocness experiment. Larvae without yolk s a c and without t h e c h a r a c t e r i s t i c s of s t a g e 2a d e s c r i b e d by DOYLE (1977) a r e o m i t t e d from t h e t a b l e . Although t h e Mocness sampling w i t h i n t h e a r e a was l o c a t e d by abundance of l a r v a e i n v e r t i c a l n e t - h a u l s , some of t h e Mocnes tows were without any l a r v a e . This i n d i c a t e patchy d i s t r i b u t i o n of t h e l a r v a e

.

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Table 1. Number of l a r v a e p e r m 2 s u r f a c e s m p l e d d u r i n g t h e Mocness experiment.

Date

5

A p r i l 6 A p r i l

Hour

18

20 21 23 24 02 04 06 07 09 12 14 15

Dep t h

t a b l e continued:

Date 6 A p r i l

7

A p r i l

Hour 16 17

19

20 21 22 23 00 02 03 04 05 07

Dep t h

t a b l e continued:

Date 7 A p r i l

Hour 08

O9

10 11 12 13

14

15 16 17 20 T o t a l

Depth

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F i g .

18

shows t h e v e r t i c a l d i s t r i b u t i o n of l a r v a e when a l l depth i n - t e r v a l s above 80 m were sampled. Nearly 60 % of t h e l a r v a e were found i n t h e 80-56 m depth i n t e r v a l . Most of t h e s e l a r v a e were newly h a t - ched, i . e . s t a g e l a . The percentage of t h e s e l a r v a e i n c r e a s e d with depth and only few were found i n t h e upper 20 m . The percentage of t h e o l d e r s t a g e s , however, i n c r e a s e d i n t h e upper l a y e r s and s t a g e 2a were found only i n t h e s u r f a c e l a y e r .

F i g .

19

shows t h e d i s t r i b u t i o n d u r i n g broad d a y l i g h t i . e . between 09 and 15 h r s . GMT. More than

55%

of t h e l a r v a e were found i n t h e 80-65 m i n t e r v a l . F i g . 20 shows t h e v e r t i c a l d i s t r i b u t i o n of t h e l a r v a e d u r i n g darkness i . e . between 21 and 02 h r s . GMT. S t i l l most of t h e l a r v a e were found i n t h e 80-85 m i n t e r v a l and s t a g e I b was dominating. The number of l a r v a e caught a t n i g h t were much lesser t h a n t h a t caught a t d a y l i g h t . T h i s i s probably caused by a patchy d i s t r i b u t i o n of l a r v a e

(Table 1 ) . T h i s i s most probably a l s o t h e reason f o r t h e absence of l a r v a e i n t h e deepest hau1 a t n i g h t . Because of t h e patchy d i s t r i b u t i - on of t h e l a r v a e i t i s d i f f i c u l t t o make any comparison between s t a g e d i s t r i b u t i o n of l a r v a e caught a t d a y l i g h t and i n d a r k n e s s .

Table 2. Number of l a r v a e p e r m 2 s u r f a c e sampled d u r i n g t h e c l o s i n g n e t experiment.

Date

5

A p r i l 6 A p r i l

Hour

Og

11

13 14 17 19

21 23 01 03 05 07 T o t a l

Dep t h

Table 2 shows t h e number of l a r v a r p e r m 2 s u r f a c e d u r i n g t h e c l o s i n g n e t experiment. Larvae without yolk s a c and w i t h s u t t h e c h a r a c t e r i s t i c s of s t a g e 2 a d e s c r i b e d by DOYLE (1977) a r e omitted from

(11)

t h e t a b l e . F i g . 21 shows t h e v e r t i c a l d i s t r i b u t i o n of t h e l a r v a e

Fn

Table 2. Most of t h e l a r v a e were found i n t h e 100-81 m i n t e r v a l and t h e m a j o r i t y of t h e s e were i n s t a g e l b . During t h i s experiment newly hatched were recorded i n a l l depth i n t e r v a l s without any c l e a r p a t - t e r n . Older l a r v a e , however, were mainly found i n t h e upper l a y e r s .

During a s i m i l a r experiment i n 1985 i n t h e same a r e a (BJØRKE, FOSSUM and SÆTRE 1986) more than 65% of t h e l a r v a e were caught i n t h e upper 60 m . I n c l u d i n g t h e l a r v a e omitted from Table l and Table 2 t h e percentage of l a r v a e i n t h e upper 60 m were 12% d u r i n g t h e Mocness experiment and

14%

d u r i n g t h e c l o s i n g n e t experiment i n 1986. I n 1985 t h e h i g h e s t abundance of l a r v a e were found i n t h e middle of t h e pyc- n o c l i n e . I n 1986 t h e pycnocline was less pronounced than i n

1985

( F i g . 7 S e c t i o n A ) . I n 1985 few newly hatched l a r v a e ( 1 a r v a e

<

9mm)were found. These two f a c t s might e x p l a i n t h e h i g h e r abundance of l a r v a e i n t h e deeper i n t e r v a l s observed i n 1986.

Lengthlstage d i s t r i b u t i o n of f i x e d l a r v a e .

Table

3

shows t h e l e n g t h d i s t r i b u t i o n of f i x e d h e r r i n g l a r v a e caught i n 1986 c l a s s i f i e d according t o DOYLE (1977) and ØIESTAD (1983). Fig.

Length (mm)

la

l b 1c 1 d 2a TOT

...

005

l 1

006 167 38 8 70 283

007 515 353 71 271

1210

008 749 1049 158 515 2471

009 400 1547 474 617 3038

010

57 761 712 397

2

19-29

011

24 6

1

87 25 197

012 1

7 31 9 48

013 4 3 7

014

2 2

015

1 1

...

TOT

1888 3774 1491 1995 39 9187

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

I n Table

4

t h e d a t a of shrinkage due t o formalin f i x a t i o n i s given.

Table

4.

P e r c e n t shrinkage d u r i n g formalin f i x a t i o n

S t a g e Nos of l a r v a e Shrinkage i n Shrinkage i n Fixed Unfixed l e n g t h

(g)

d r y weight%)

(13)

The t a b l e shows t h a t t h e s h r i n k a g e both i n l e n g t h and weight i s r e h - t i v e l y c o n s t a n t between t h e d i f f e r e n t s t a g e s . The shrinkage i n l e n g t h i s r e l a t i v e l y moderate, while t h e shrinkage i n weight i s very l a r g e and t h e weight i s almost halved d u r i n g t h e f i x a t i o n p e r i o d . The d i f - f e r e n c e s i n mean l e n g t h of t h e same s t a g e s between t h e l a r v a e i n Table

4

and t h e ones r e p r e s e n t e d i n Fig. 24 might be due t o more a c c u r a t e measurements of t h e l a r v a e i n Table

4.

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

The m a t e r i a l i n t h i s examination was sampled d u r i n g t h e second coverage and c o n s i s t s of 647 h e r r i n g l a r v a e of s t a n d a r d l e n g t h 6.2-14.5 mm.

The bulk of t h e l a r v a e belonged t o t h e yolk s a c s t a g e s l a - l d . Few l a r v a e had s t a r t e d t o develope t h e d o r s a l f i n , s t a g e 2 a , and t h e development of t h e l a r v a l population was delayed compared t o t h e 1985 s e a s o n , when most of t h e l a r v a e sampled i n t h e same area and a t t h e same time were i n t h e 2a s t a g e (BJØRKE

,

FOSSUM & SÆTRE 1 9 8 6 ) .

The mean s t a n d a r d l e n g t h , d r y weight and number of l a r v a e i n each s t a g e a r e shown i n Table

5.

Table

5.

The l a r v a l m a t e r i a l sampled i n 1986.

Substage Nos. of Mean s t a n d a r d Mean d r y

l a r v a e l e n g t h (mm) SD weight (ligl SD

(14)

The mean h a t c h i n g weight cmd t h e mean weight of t h e Larvae I n

the

dif- f e r e n t y o l k s a c s t a g e s was unchanged compared t o t h e 1985 m a t e r i a l

(BJØRXE

,

FOSSUM & SÆTRE 1986)

.

The delayed development of t h e l a r v a l population i n 1986 compared t o 1985, seemes t o be due t o t h e l a t e h a t c h i n g t h i s y e a r . Mastirnum bat- ching was observed i n mid A p r i l

,

(BJØRKE, HANSEM and MELLE 1987) a d l a r v a e hatched e a r l i e r i n t h e season a r e probably vanished.

A s t a n d a r d l e n g t h l d r y weight p l o t of t h e p r e s e n t m a t e r i a l i s shown i n F i g . 22. There i s no s t r i c t r e l a t i o n s h i p between t h e s t a n d a r d l e n g t k and t h e dry weight, i n d i c a t e d by a e x p o n e n t i a l c o r r e l a t i o n c o e f f e s c i - e n t r 2 = 0 . 4 0 , i n c o n t r a s t t o t h e E985 m a t e r i a l with a corresponding c o r r e l a t i o n c o e f f i s c i e n t r 2 =0.81.

There seemes t o be s i g n i f i e a n t l e s s growth of t h e h e r r i n g l a r v a e i n i986 than i n 1985, with a d e c r e a s e of t h e growth parameter ( s l o p e ) from 0 . 1 8 t o 0.11. The same p r e s e r v a t i o n procedure was followed both i n 1985 and 1986, and t h i s i n d i c a t e t h a t t h e l a r v a l population i n 1986 was exposed t o more marginale food c o n d i t i o n s than i n t h e previous y e a r .

Some of t h e v a r i a t i o n i n t h e d a t a may be introduced through t h e pre- s e r v a t i o n , a s t h e r e i s a s t r o n g e r l e n g t h l weight r e l a t i o n s h i p i n t h e p l o t of t h e l a r v a e n o t exposed t o Eormalin ( F i g . 2 3 ) . Therefore t h e n e c e s s i t y of a comparable p r e s e r v a t i o n procedure and t o s t u d y t h e l e n g t h

/

weight r e l a t i o n s h i p of unpreserved and presesved l a r v a e muct be s t r e s s e d .

F i g . 24 shows t h e l e n g t h frequency d i s t r i b u t i o n of t h e l a r v a e i n t h e d i f f e r e n t s t a g e s . The jump i n s t a n d a r d l e n g t h from s t a g e La t o l b Is probably due t o t h e s e n s i t i v e n e s s of t h e newly hatched l a r v a e t o band- l i n g . They a r e e a s i l y exposed t o shrinkage d u r i n g c a t c h i n g . Exeept f o r t h i s t h e l e n g t h frequency d i s t r i b u t i o n of t h e y o l k s a c l a r v a e seemes t o be comparable t o t h e one from t h e previous y e a r .

The d i e t of t h e l a r v a e d u r i n g S t a g e s l a - 2 a , r e p r e s e n t i n g a t i m e span e s t i m a t e d t o be 23 days (BJØRKE, FOSSUM & SÆTRE 1986) i s shown i n Fig. 25. The dominating food organism through t h i s p e r i o d was copepod

(15)

a a u p l i i which contributec!

80 %

t o t h e g t t c c a n t e - a t , Tkie only o t h e r food orgmism found was copepod e g g s (20%j, The youngest l a r v a e found with g u t c o n t e n t were

3-6

days o l d . I n t h i s period copepod eggs and copepod n a u p l i i were of e q u a l importmce

,

S u t e r on t h e d i e t was dominated o*

copepod n a u p l i i . No copepod e g g s were found i n Larvae o l d e r t h m

11

days. There i s a pronounced reduction i n t h e f e e d i n g r a t i o (number of food organisms p e r l a r v a l lut) i n a l l ctagec from 298"o 1986,

The reduced f e e d i n g r a t i o and growth parameter t o g e t h e r with t h e t o t a l dominance of yolksac Larvae a s Late a s mid A p r i l , i n d i c a t e

1986

a s a y e a r with poor r e c r u i t m e n t of t h e Norweglan cpring- spawning h e r r i n g , L n v e s t i g a t i o n s c a r r i e d o u t i n May gave a d d i t i o n a l information of t h l s (Nedseaas p e r s , comm,), a d t h e O-group Index e s t a b l i s h e d l a t e i n t h e autumn confirmed t h a t t h i s y e a r c l a c s was a poor one ( R a t t i n g e n p e r s * comm. ) ,

CONCEUCIONS

The spawning a r e a can c l e a r l y be seen i n t h e d i s t r i b u t i o n of l a r v a e

<

9

mm and t h e s e were t h e same a s i n

2985.

I n a d d i t i o n a s m a l l e r spaw- n i n g a r e a o f f s h o r e a t t h e c o n t i n e n t a l s l o p e was i d e n t i f i e d ,

The main f e a t u r e s of t h e c i r c u l a t i o n p a t t e r n of t h e a r e a seems t o be t h e same a s i n

198s.

The combined use of bydrography, l a r v a e d i s t r i b u - t i o n and Argos d r i f t e r s ceem a b l e t o r e v e a l b o t h t h e Larval d r i f t as welI a s r e t e n t i o n a r e a s with a r e s i d e n c e t i m e of

10-15

days,

The l a r v a l population i n l986 was t o t a l l y dominuted by yolksac l a r v a e . The number of l a r v a e

>

L2 mm woc about 18% of t h a t found d u r i n g t h e same p e r i o d i n

1985, In

1986 a slower growth a d a lower f e e d i n g r a t i o i n a l l l a r v a l s t a g e s was observed compared t o 2985, T h i s i n d i c a t e poorer r e c r u i t m e n t i n 1986 t k m i n

1985,

The m a j o r i t y of t h e l a r v a e weie found deeper than 60 m a s opposed t o

1985.

The percentage of newly hatched Earvae I.ncreased with depth.

Older l a r v a e were found mainly i n t h e upper 40 m , Patchy d i s t r i b u t i o n made a comparison between l a r v a e caugbt a t day and a t n i g h t d i f f i c u l t .

Mapping of t h e e a r l i e s t s t a g e of l a r v a l development i n s t e a d of tlie s m a l l e s t l a r v a e groups g i v e s a b e t l e r Xocation of the spawning

(16)

grounds ,

F i r s t f e e d i n g was observed i n 3-6 days o l d l a r v a e . The d i e t of t h e l a r v a e was dominated by copepod n a u p l i i . A shrinkage of 40-45% i n dryweight and

3-7%

i n l e n g t h due t o p r e s e r v a t i o n was observed.

REFERENCES

BJØRKE, H . 1981. D i s t r i b u t i o n of f i s h eggs and l a r v a e from Stad t o Lofoten d u r i n g A p r i l 1976-80. Pp 583-603

& I

Roald Sætre and Martin Mork (Eds.) The Norwegian Coastal Current. U n i v e r s i t y of Bergen

1981: 895

p.

BJØRKE, H . , P. FOSSUM and R . SÆTRE, 1986. D i s t r i b u t i o n , d r i f t and c o n d i t i o n of h e r r i n g l a r v a e o f f western Norway i n 1985. Coun

.

Meet. i n t . Coun. Explor. Sea, (H:39):

1-15.

BJØRKE, H., K . HANSEN and W. MELLE,

1987.

S i l d e k l e k k i n g og s e i g y t i n g på More i

1986.

I n s t i t u t e of Marine ~ e s e a r c h ' s Egg- and Larvae Program (HELP)

,

Report 1987, No.

4.

DOYLE, M . J .

1977.

A morphological s t a g i n g system f o r t h e l a r v a l development of t h e h e r r i n g , (Clupea harengus L . ) . J . mar. b i o l . A s s . ,

51:

^859-867.

DRAGESUND, 0 . 1970. F a c t o r s i n f l u e n c i n g y e a r - c l a s s s t r e n g t h of Nor- wegian s p r i n g spawning h e r r i n g . FiskDir. Skr. S e r . HavUnders.,l5

:

381-450.

ELLERTSEN, B . , P. FOSSUM, P. SOLEMDAL, S. SUNDBY and S. TILSETH,

1984.

A c a s e s t u d y on t h e d i s t r i b u t i o n of cod l:.rvae and a v a i l a b i l i t y of prey organisms i n r e l a t i o n t o p h y s i c a l p r o c e s s e s i n Lofoten.

I n : E. DAHL, D.S. DANIELSEN, E . MOKSNESS and P . SOLEMDAL ( E d s . ) , The Propagation of Cod Gadus morhua L. F l ~ d e v i g e n r a p p o r t s e r . ,

L:

453 - 477.

(17)

FØYN, L , and K . BJØRKE,

1986,

S t r a t e g i e s i n assescment of p o t e n t i a l o i l p o l l u t i o n e f f e c t s on t h e f i s h r e s o u r c e s . Coun. Meet. i n t . Coun. Explor. Sea, (E:34).

HAY, D.E.

1981.

E f f e c t s of c a p t u r e and f i x a t i o n on g u t c o n t e n t s and body s i z e of P a s i c i c h e r r i n g l a r v a e . Rapp. P.-v. Reun. Cons.

perm. i n t . Explor. Mer,

a:

^395-400.

LJØEN, R . and 0 . NAKKEN, 1969. On t h e hydrography of t h e s h e l f water o f f Møre and Helgeland. F i s k D i r . Skr. S e r . HavUnders

. ^, 15:

²⁸⁵

-

294.

SELIVERSTOV, A.S.

1974.

V e r t i c a l migrations of l a r v a e of t h e A t 1 a n t ~ - Scandian Herring (Clupea harengus L . ) P. 253-262

&

BLAXTER, J . H . S. e d . The e a r l y l i f e h i s t o r y of f i s h . Springer-Verlag. B e r l i n .

THEILACKER, G. and DORSEY, K . 1980. Larval f i s h d i v e r s i t y , a summer of l a b o r a t o r y and f i e l d r e s e a r c h . I O C Workshop Report no. 28:

105-142.

WIBORG, K.F. 1960. I n v e s t i g a t i o n s on eggs and l a r v a e of commercial f i s h e s i n Norwegian c o a s t a l and o f f s h o r e waters i n

1957-58.

F i s k . - D i r . Skr. S e r . HavUnders., 12

( 7 ) :

1-27.

WIEBE, P.H., BURT, K . H . , BOYD, S.H. and MORTON, A.W., 1976. A m u l t i p l e opening/closing n e t and environmental s e n s i n g system f o r sampling zooplankton. J . Mar

.

^Res.

^, 34:

^313-326.

ØIESTAD, V . 1983. Growth and s u r v i v a l of h e r r i n g l a r v a e and f r y (Clupea harengus L . ) exposed t o d i f f e r e n t f e e d i n g regimes i n experimental ecosystems; outdoor b a s i n s and p l a s t i c bags. Ph. d , t h e s i s : l - 2 9 9 . U n i v e r s i t y of Bergen.

(18)

F i g . l . Grid o f s t a t i o n s , 29 March - 1 8 A p r i l 1986. B a t h y m e t r i c c o n t o u r s f o r each 100 m a r e i n c l u d e d . I n s e r t e d map shows t h e l o c a t i o n o f t h e s t u d i e d a r e a .

(19)

(20)

Fig. 3 . S u r f a c e c a l i n i t y 9-18 April 1986.

(21)

F i g . 4 . S u r f a c e v a l u e s of n i t r a t e 9-18 A p r i l 1 9 8 6 .

(22)

F i g . 5 . S u r f a c e v a l u e s of s i l i c a t e 9-18 A p r i l 1 9 8 6 .

(23)

Fig. 6. Surface values of chlorophyll a 9-18 April 1986.

(24)

.

l

SECTION A 16 APRIL 1986

14 APRIL 1986

F i g . 7 . Hydrographic s e c t i o n A , B and C . L o c a t i o n of t h e s e i s i n d i c a t e d i n F i g . l .

(25)

(26)

Ei DEPLOYMENT POSITION A RECOVERY POSITION

F i g . 9. T r a c k s o f t h e d r i f t i n g Argos buoys drogued a t 30 m depth.

(27)

Fig. 10. T r a c k s o f two o f t h e Argos buoys f u r t h e r n o r t h .

(28)

F i g . 11. D i s t r i b u t i o n o f h e r r i n g larvae < 9 mm ( ~ / m 2 ) , 29 March-7 April 1986.

(29)

2 F i g . 1 2 . D i s t r i b u t i o n of h e r r i n g l a r v a e between 9 a n d 11 mm (N/m ) ,

29 March - 7 A p r i l 1 9 8 6 .

(30)

(31)

F i g . 14- D i s t r i b u t i o n o f h e r r i n g l a r v a e < 9 mm (N/m 2 ) 9-18 A p r i l 1 9 8 6 .

(32)

4" ^{5 O} 6" 7 - '8 ^{9 O} ^10- ^11' ^{l z O}

I l l

30i 300 200

500 LOG LOC

i : 3 0 8

. . .

6 5'-

300

. . . . . .

6 1 0

.

e . .

HERRING LARVAE ^-

9 m m 5 (Nlrn2) < 12mm 9 - 18 APRIL 1986

F i g . 1 5 . D i s t r i b u t i o n o f h e r r i n g l a r v a e between 9 and 11 mm ( ~ / m 2 )

,

9-18 A p r i l 1986.

(33)

F i g . 1 6 . D i s t r i b u t i o n o f h e r r i n g l a r v a e > 11 mm (N/m 2 ) , 9-18 A p r i l 1986.

(34)

F i g . 1 7 . Observed spawning a r e a s , ( c i r c l e s ) and t e n t a t i v e l a r v a l d r i f t r o u t e s . The i n d i c a t e d d r i f t i n g time i s u n t i l p a s s i n g t h e 65 o N l a t i t u d e .

(35)

VERTICAL OISTRI3UTION m s s

VERTICAL DISTRIBUTION

m 5 5 _FIAGE

r I

IERTiCAL CICTRIEUTION

mNES5

t . . . r I . . n ~ I . 9 5 x 8 . . . . i . r . * l . . - - r

0 1 0 2 0 3 0 w 5 0 m

PER CENT

F i g . 18. V e r t i c a l d i s t r i b u t i o n o f l a r v a e ; number, s t a g e and p e r c e n t a g e f o r t h e Mocness m a t e r i a l .

(36)

VERTICAL OISTRIBUTION

W3PeSf DAY VERTICAL DISTRIBUTION

ICEPESS OAY STAGE

iUSESS DAY

F i g . 19. V e r t i c a l d i s t r i b u t i o n of l a r v a e ; number. s t a g e and percentage f o r the Mocness m a t e r i a l during day time.

(37)

YERTIChL DISTRIBUTION

t C M 3 3 N I C F T

KUES-3 N1W STAGE

VERTICAL DISTRIBUTIOM

FPXXZSS N I W

z I

F i g . 20. V e r t i c a l d i s t r i b u t i o n o f l a r v a e ; number, stage and p e r c e n t a g e f o r t h e Mocness m a t e r i a l d u r i n g n i g h t .

(38)

-ING NET

l

CLOSINS HET _STAGE

=OS ING NE7 s I

PER CENT

F i g . 2 1 . V e r t i c a l d i s t r i b u t i o n o f l a r v a e ; n u m b e r , s t a g e and.

p e r c e n t a g e f o r t h e c l o s i n g n e t .

(39)

STANDARD LENGTH

(M

F i g . 22. The l e n g t h / d r y w e i g h t p l o t o f t h e p r e s e n t h e r r i n g l a r v a e m a t e r i a l .

I

DRY WEIGHT (PLI)

STANDARD LENGTH

(MM)

F i g . 2 3 . The l e n g t h / d r y w e i g h t p l o t o f t h e l a r v a e n o t exposed t o f o r m a l i n f i x a t i o n .

Fiskeridirektoratets Havforskningsinstitutt Postboks 1870

5024 Bergen

1987 r

l

P,Solemdal og P,Bratland: KLekkeforlØp for lodde

i

Varangerfjorden 1986,

Nr.

2 , T,Waug

og SeSundby: Kveitelarver og milj8, UndersGkelser på gytefeltene ved SGrØya.

r

3

B,BjØrke, KaHansen og S.Sundby: Postlarveunder- sØkelser i 1986.

Nr, 4 , H,Bj@rke, K,Hansen og @,Melle: Sildeklekking

og

seigyting på MØre 1986,

Nr.

_{5 ,}

H,BjØrke and SeSundby: Abundance indices for the Arcto-Norxqegian cod in 1979-1986 based on larvae investigations.

Nr. 6, P,Fossum: Sult under larvestadiet - ^{en viktig}

rekrutteringsmekanisme

?