S e c t i o n 11: Methodology and models
SURVIVAL TESTS OF INTERNALLY TAGGED HERRING
Johannes Hamre and Reidar Toresen I n s t i t u t e of Marine Research
P.O. Box 1870 Nordnes N-5024 Bergen, Norway
ABSTRACT
Two s e p a r a t e s u r v i v a l tests w e r e run i n an indoor b a s i n . Herring was tagged applying i n t e r n a l metal t a g s a s used i n t h e annua1 tagging experiments on t h e Norwegian spring-spawners. The m o r t a l i t y caused by t a g g i n g was s e v e r e i n t h e f i r s t few weeks a f t e r r e l e a s e , d e c l i n i n g t o a normal l e v e 1 i n about
8
weeks. The s u r v i v a l of tagged h e r r i n g i n t h e two t e s t s v a r i e d s u b s t a n t i a l l y , and t h e c o e f f i c i e n t was c a l c u l a t e d t o be 0.74 and 0.91 r e s p e c t i v e l y . The d i f f e r e n c e i s e x p l a i n e d by t h e d i f f i c u l t i e s i n h a n d l i n g h e r r i n g i n c a p t i v i t y .METHODOLOGY AND MODELS S u r v i v a l tests o f i n t e r n a l l y tagged h e r r i n g
INTRODUCTION
Tagging of f i s h i s a f r e q u e n t l y a p p l i e d method f o r s t u d y i n g m i g r a t i o n s , and t o a s s e s s t h e m o r t a l i t y and t h e abundance o f f i s h s t o c k s . P r a c t i c a l d i f f i c u l t i e s have been encountered because h e r r i n g i s v e r y s e n s i t i v e t o handling. Dahlgren (1933) t e s t e d t h e performance of d i f f e r e n t t y p e s of t a g s by comparative experiments, and found t h a t t h e most s u c c e s s f u l method proved t o be an i n t e r n a l b e l l y t a g . T h i s method was i n t r o d u c e d i n t h e Norwegian-Icelandic t a g g i n g scheme
(1947-1952), with t h e aim t o v e r i f y t h e t h e o r y t h a t t h e h e r r i n g caught d u r i n g summer o f f t h e n o r t h e r n c o a s t of I c e l a n d were i d e n t i c a l t o t h e Norwegian w i n t e r h e r r i n g ( F r i d r i k s s o n 1944, F r i d r i k s s o n and Aasen 1 9 5 0 ) . The d a t a from t h i s experiment were l a t e r used t o a s s e s s t h e abundance of t h e s t o c k (Dragesund and Jakobsson 1963).
I n
1975,
a new t a g g i n g programme f o r h e r r i n g was s t a r t e d and s i n c e t h e n a t o t a l of 30-40 000 tagged h e r r i n g have been r e l e a s e d e v e r y s p r i n g a t d i f f e r e n t l o c a l i t i e s on t h e Norwegian west c o a s t .The b a s i c assumptions u n d e r l y i n g t h e u s e of t a g g i n g d a t a i n s t o c k abundance s t u d i e s are d i s c u s s e d by Aasen (1958). The s u r v i v a l o f tagged h e r r i n g i s a c r u c i a l f a c t o r i n t h i s r e s p e c t , and m o r t a l i t y experiments were c a r r i e d o u t i n 1948,
49
and 50 ( F r i d r i k s s o n and Aasen 1950). The c o n c l u s i o n s drawn from t h e s e experiments w e r e t h a t t h e t a g g i n g d i d n o t a f f e c t t h e h e r r i n g s e r i o u s l y when p r o p e r l y executed on f i s h i n good c o n d i t i o n , b u t no e s t i m a t e of s u r v i v a l was made.Dragesund and Jakobsson (1963) concluded however, t h a t when t h e t o t a l r e t u r n s from each experiment where examined, t h e r e was a s i g n i f i c a n t v a r i a t i o n i n r e t u r n s from t h e v a r i o u s r e l e a s e s even w i t h i n t h e same experiment. The same has been experienced i n t h e r e c e n t y e a r s . T h i s v a r i a t i o n may be due t o v a r y i n g t a g g i n g m o r t a l i t y and shedding, b u t may a l s 0 be due t o non random mixing of t h e tagged h e r r i n g i n more than one s t o c k u n i t .
MATERIAL AND METHODS
Two s e p a r a t e s u r v i v a l t e s t s were accomplished, ane i n 1987, t h e o t h e r i n
1988.
The f i s h was caught by p u r s e s e i n e on t h e c o a s t of western Norway and brought t o Bergen i n t a n k s on a commercial p u r s e s e i n e r , A r r i v i n g i n Bergen, t h e h e r r i n g was t r a n s f e r e d t o an outdoor b a s i n a t t h e I n s t i t u t e of Marine Research.T e s t no. 1.
Before t a g g i n g , t h e h e r r i n g was adapted t o l i f e i n c a p t i v i t y f o r 11 weeks t o be s u r e t h a t only h e a l t h y f i s h were used i n t h e t e s t . A f t e r
5
weeks of t h e accomodation p e r i o d , t h e f i s h was moved t o an i n d o o r ,
185
m 3
,
b a s i n a s shown s c h e m a t i c a l l y i n F i g u r e 1. Here they dwelled f o r6
weeks b e f o r e t h e test s t a r t e d . During t h e accomodation p e r i o d and i n t h e test p e r i o d , t h e f i s h was f e d k r i l l (Euphausiacea), copepods
(Calanus s p . ) and p e l l e t s o f d r y food. The f i s h was t r e a t e d with Flumequine on two o c c a t i o n s , t o p r e v e n t t h e o u t b u r s t of v i b r i o s i s . A t o t a l o f 962 f i s h were used i n t h e test. About h a l f of t h e a (498) were tagged while t h e r e s t (464) remained untagged a s a c o n t r o l group.
A s m a l l s e i n e n e t was used t o c a t c h t h e f i s h i n t h e b a s i n and t h e t a g g i n g was done a p p l y i n g t h e same method a s used i n t h e annua1 t a g g i n g programme. A metal t a g was s h o t i n t o t h e b e l l y of t h e f i s h u s i n g a t a g g i n g p i s t o l a s d e s c r i b e d by F r i d r i k s s o n and Aasen 1950.
METHODOLOGY AND MODELS
S u r v i v a l tests of i n t e r n a l l y tagged h e r r i n g
F i g u r e 1. Shape and dimensions of t h e experimental t a n k
The number of dead h e r r i n g was recorded c u r r e n t l y and t h o s e f i s h e s were examined f o r t a g s u s i n g a t a g d e t e c t o r . Other c h a r a c t e r i s t i c s such a s l e n g t h , weight, s e x , m a t u r a t i o n and stomach c o n t e n t were a l s o r e c o r d e d i n
3
samples of approx. 100 f i s h each, a f t e r 9 ,14
and 24 weeks r e s p e c t i v e l y . The t e s t was ended a f t e r 30 weeks. When ended,3
tagged h e r r i n g were found i n t h e g u t t e r and
45
t a g s were found on t h e f l o o r of t h e b a s i n . Of t h e t o t a l of 962 f i s h used i n t h e t e s t , 922 were recovered. 40 h e r r i n g were m i s s i n g , which were probably l o s t through t h e g u t t e r .T e s t no. 2 .
The f i s h was k e p t f o r accomodation i n t h e outdoor b a s i n f o r
4
weeksand moved t o t h e indoor b a s i n where t h e y were k e p t f o r a n o t h e r
4
weeks b e f o r e t h e t e s t s t a r t e d . During t h e accomodation p e r i o d , and i n t h e test p e r i o d a s w e l l , t h e f i s h was f e d copepods o n l y . No t r e a t m e n t with Flumequine was n e c e s s a r y because t h e r e was no s i g n of v i b r i o s i s i n t h e s t o c k.
400 f i s h were tagged a p p l y i n g t h e same method a s p r e v i o u s l y used and no c o n t r o l group of untagged h e r r i n g was a p p l i e d .
Records of dead h e r r i n g were c o l l e c t e d c u r r e n t l y a s i n t h e p r e v i o u s experiment and 1 sample of 100 f i s h was taken a f t e r
8
weeks. The experiment was ended a f t e r17'
weeks. When ended,6
f i s h were missing and probably l o s t through t h e g u t t e r .RESULTS
Length d i s t r i b u t i o n s of t h e h e r r i n g used i n t h e tests a r e shown i n T a b l e 1. There i s no s i g n i f i c a n t d i f f e r e n c e i n l e n g t h between t h e
METHODOLOGY
AND
MODELS S u r v i v a l tests of i n t e r n a l l y tagged h e r r i n gtagged and untagged f i s h .
The d a t a of t h e f i r s t t e s t grouped by week a r e given i n t h e t e x t t a b l e below :
S u r v i v a l s Deaths Samples
Week
s2 S m m m
1 2 3 M 1 M2
1 498 464 962 1 1
2
35 3
3
104
4 3
0Sl and S2 d e n o t e numbers of tagged and untagged h e r r i n g a t t h e beginning of t h e week, and ml and m t h e corresponding numbers o f dead h e r r i n g recorded d u r i n g t h e week. 'm i s a c a l c u l a t e d f i g u r e r e f e r i n g t o t h e h e r r i n g l o s t through t h e gutte&. Ml and M2 a r e number of f i s h sampled d u r i n g t h e experiment.
I n c a l c u l a t i n g t h e s u r v i v a l , one h a s assumed t h a t t h e l o s t h e r r i n g belongs t o t h e group which f o r some reason h a s d i e d d u r i n g t h e e x p e r i - ment. Judging from t h e t r e n d i n t h e d e a t h r a t e , t h e t a b l e shows t h a t t h e m o r t a l i t y due t o t a g g i n g i s ended, a f t e r 6 weeks. The
43
un- recorded dead h e r r i n g have been a l l o c a t e d t o t h e p e r i o d s b e f o r e and a f t e r t h e7.
week i n t h e same p r o p o r t i o n a s t h e recorded ones (64 t o 24). T h i s g i v e s 31 dead h e r r i n g a l l o c a t e d t o t h e f i r s t p e r i o d and 12 h e r r i n g t o t h e l a s t one. Assuming t h a t t h e l a t t e r group i s e q u a l l y d i s t r i b u t e d on tagged and untagged h e r r i n g , t h e number of s u r v i v i n g' tagged h e r r i n g a t t h e beginning of t h e
7.
week i s found by summation of t h e samples and t h o s e which have d i e d , i . e .347
+ 13 +6
= 366 i n d i v i d u a l s . T h i s g i v e s a t o t a l i n s t a n t a n e o u s m o r t a l i t y c o e f f i c i e n t(Z) o f :
During t h e n e x t
7
weeks 11 dead i n d i v i d u a l s were recorded. I f w e assume t h a t 113 of t h e 12 l o s t h e r r i n g d i e d d u r i n g t h i s p e r i o d , t h e t o t a l m o r t a l i t y amounts t o 15 i n d i v i d u a l s . T h i s g i v e s a Z v a l u e ofConsidering t h i s a s t h e n a t u r a l m o r t a l i t y i n t h e s t o c k , t h e m o r t a l i t y due t o t a g g i n g i s e s t i m a t e d t o : Z = 0.291. which corresponds t o a
METHODOLOGY AND MODELS
S u r v i v a l t e s t s of i n t e r n a l l y tagged h e r r i n g
c o e f f i c i e n t of s u r v i v a l S = 0.74. T h i s c o e f f i c i e n t i n c l u d e s t h e shedding which i s e s t i m a t e d t o 46 i n d i v i d u a l s (498
-
(366 +55
+3 1 ) ) ,
p l u s s some
5-6
of t h e specimens recorded a s dead unmarked h e r r i n g which have l o s t t h e i r t a g s d u r i n g t h e t h r e e f i r s t weeks. T h i s means t h a t some 10-
l1%
of t h e tagged h e r r i n g have l o s t t h e i r t a g s .The d a t a from t h e second test a r e summarized i n t h e t e x t t a b l e below:
Also i n t h i s experiment t h e i n c r e a s e d m o r t a l i t y due t o t a g g i n g i s o v e r a f t e r
7
weeks. 6 specimens were l o s t i n t h i s t e s t , and i t i s assumed t h a t t h e s e d i e d d u r i n g t h e f i r s t7
weeks. Two specimens d i e d from t h e8
t o t h e 16 week, which shows t h a t t h e n a t u r a l m o r t a l i t y i n t h e t e s t p e r i o d can be regarded a s i n s i g n i f i c a n t ( l e s s t h a n 1g ) .
A l t o g e t h e r ,13
specimens had l o s t t h e i r t a g s and assuming t h a t a l l shedding of t a g s had taken p l a c e d u r i n g t h e f i r s t7
weeks, t h e c o e f f i c i e n t of s u r - v i v a 1 can be taken a s t h e t o t a l s u r v i v a l a f t e r t h e f i r s t7
weeks minus t h e 1 0 untagged specimens i n t h e samples.Only 3
%
of t h e tagged h e r r i n g i n t h i s test had l o s t t h e i r t a g s . DISCUSSIONThe r e s u l t of t h e tests i s only r e p r e s e n t a t i v e f o r t h a t p a r t of t h e t a g g i n g m o r t a l i t y which i s caused by t h e h a n d l i n g of t h e f i s h d u r i n g t h e t a g g i n g o p e r a t i o n and t h e i n j u r i e s caused by t h e i n s e r t i o n of t h e t a g . The m o r t a l i t y caused by t h e c a t c h i n g o p e r a t i o n and t h e b r a i l i n g of t h e f i s h on board t h e s h i p w i l l add t o t h e t o t a l t a g g i n g m o r t a l i t y i n p r a c t i c e , and t h e s u r v i v a l c o e f f i c i e n t s d e r i v e d from t h e s e e x p e r i - ments a r e t h e r e f o r e t o be considered a s maximum v a l u e s . I n j u r i e s caused by t h e p u r s e s e i n e o p e r a t i o n and b r a i l i n g of t h e f i s h t o t h e t a n k s may v a r y with weather c o n d i t i o n s and a r e d i f f i c u l t t o measure by experimental t e c h n i q u e s . It i s , however, experienced t h a t damage of t h e s k i n and l o s s of s c a l e s reduce t h e s u r v i v a l o f h e r r i n g and
METHODOLOGY AND MODELS S u r v i v a l t e s t s of i n t e r n a l l y tagged h e r r i n g
t h e s k i n and l o s s of s c a l e s reduce t h e s u r v i v a l of h e r r i n g and although no h e r r i n g w i t h apparent damage of t h e s k i n i s a c c e p t e d f o r t a g g i n g , i t i s r e a s o n a b l e t o assume t h a t such i n j u r i e s c o n t r i b u t e s i g n i f i c a n t l y t h e t o t a l tagging m o r t a l i t y . Another f a c t o r which obviously b i a s t h e s u r v i v a l e s t i m a t e i n t h e s e tests is t h e absence of p r e d a t o r s . The tagged h e r r i n g are no doubt more v u l n e r a b l e t o p r e - d a t i o n d u r i n g t h e p e r i o d of recovery than t h e untagged p o p u l a t i o n . The s i g n i f i c a n t d i f f e r e n c e between t h e s u r v i v a l estimates of t h e two tests i s assumed t o be a consequence of t h e d i f f e r e n t c o n d i t i o n o f t h e tagged f i s h . I n t h e f i r s t c a s e , t h e h e r r i n g was more d e n s e l y s t o c k e d , and t h e f i s h was s u f f e r i n g from an o u t b u r s t of v i b r i o s i s some
3
weeks b e f o r e t h e t a g g i n g took p l a c e . Although t h e sample which was tagged appeared t o have recovered, t h e n a t u r a l m o r t a l i t y i n t h e untagged p o p u l a t i o n was r e l a t i v e l y high when t h e t a g g i n g was executed. These circumstances c o n s t i t u t e d an a d d i t i o n a l s t r a i n on t h e tagged f i s h , which i s n o t p r e s e n t i n n a t u r e . Only t h e r e s u l t s of t h e second test a r e t h e r e f o r e regarded a s r e p r e s e n t a t i v e f o r t h e t a g g i n g m o r t a l i t y of i n t e r n a l t a g g i n g by t h e p r e s e n t method. The test confirms t h e con- c l u s i o n drawn by F r i d r i k s s o n and Aasen (1950) t h a t t h e t a g g i n g do n o t a f f e c t t h e h e r r i n g s e r i o u s l y when t h e f i s h i s i n good c o n d i t i o n . The m o r t a l i t y caused by t h e t a g g i n g o p e r a t i o n under f a v o u r a b l e c o n d i t i o n s i s e s t i m a t e d t o be about 10%. b u t may i n c r e a s e c o n s i d e r a b l y i f t h e c o n d i t i o n of t h e f i s h i s poor. It may be noted t h a t even t h e shedding of t a g s may i n c r e a s e when t a g g i n g h e r r i n g i n poor c o n d i t i o n .REFERENCES
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1958.
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1933.
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F r i d r i k s s o n , A .
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F r i d r i k s s o n , A. and Aasen, O. 1950. The Norwegian-Icelandic h e r r i n g t a g g i n g experiments. Report No. 1. F i s k D i r . S k r . S e r . H a v U n d e r s . , g ( l l ) : l - 4 3 .
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Dragesund, 0. and Jakobsson, J . 1963. Stock S t r e n g t h s and Rates o f M o r t a l i t y of t h e Norwegian S p r i n g Spawners a s I n d i c a t e d by Tagging Experiments i n I c e l a n d i c Waters.
Rapp. P.-v. Reun. Cons. perm. i n t . Explor. Mer,
I
&
+
:
83-90.Michel, C . , Gerard, J . - P . , Fourbet, B. C o l l a s , R . e t C h e v a l i e r , R.
1980. Emploi de l a Flumequine c o n t r e l a Furonculose d e s Salmonides: E s s a i s Therapeutiques e t P e r s p e c t i v e s P r a c t i q u e s . B u l l e t i n F r a n c a i s d e P i s c i c u l t u r e , No. 277. : 154-162.
