POTENTIAL FISHERIES YIELD OF A MOOREA FRINGING REEF (FRENCH POLYNESIA) BY THE ANALYSIS OF THREE DOMINANT FISHES

ATOLL RESEARCH BULLETIN NO. 305

POTENTIAL FISHERIES YIELD OF A MOOREA FRINGING REEF (FRENCH POLYNESIA) BY THE ANALYSIS OF THREE DOMINANT FISHES

BY

RENE GALZIN

ISSUED BY

THE SMITHSONIAN INSTITUTION WASHINGTON, D.C., U.S.A.

AUGUST 1987

POTENTIAL FISHERIES YIELD OF A MOOREA FRINGING REEF (FRENCH POLYNESIA) BY THE ANALYSIS OF THREE DOMINANT FISHES

BY

RENE GALZIN*

RESUME

La connaissance du stock exploitable est une donnge indispensable pour toute gestion rationnelle du milieu. Dans les 110 pays possCdant des r6cifs coralliens, les poissons rgcifaux occupent une place importante dans 116conomie de subsistance et de march6 local. D e r6centes estimations font 6tat d l u n potentiel de piche commercialisable dans l'avenir de l'ordre de

6

millions de tonnes (1110 des pgcheries mondiales)

,

^{dont seulement} 5% seraient actuel lement exploi t6s.

Tout polyn&ien 6tant un picheur qui apporte sa famille, avec le poisson, une part importante des proteines animales dans l'alimentation; il est trks difficile, en PolynCsie franqaise, dlobtenir des donn6es fiables sur les statistiques de p6che et donc du stock exploitable. Dans ce travail nous donnons une approximation de ce rendement de pcche pr6visionnel pour un rCcif frangeant de l'ile de Moorea, en 6tudiant la Dynamique des Populations (biologie, reproduction, stock, croissance, biomasse et production) de trois espkces dominantes du lagon de Moorea. Si cette approche slav&re exacte, elle devrait constituer la m6thode la plus simple pour estimer les productions ichtyologiques dans les r6cifs coralliens soumis

A

des piicheries de subsistance et d'exploitation commerciale.

...

ECOLE PRATIQUE DES HAUTES ETUDES- LABORATOIRE DE BIOLOGIE MARINE ET MALACOLOGIE- 55 RUE DE BUFFON- 75005 PARIS.

and

ANTENNE MUSEUMIEPHE- CENTRE DE L'ENVIRONNEMENT DE MOOREA- BP 1013 MOOREA- POLYNESIE FRANCAISE.

INTRODUCTION

R e c e n t s t u d i e s have shown t h a t many c o r a l r e e f s a r e c a p a b l e o f y i e l d i n g a t o t a l f i s h c a t c h o f 18- 24 T . K ~ ' ~ ( H i l l , 1978; A l c a l a , 1 9 8 1 ; Munro, 1987). T h e r e a r e , however, n o e s t i m a t e s f o r t h e p r o d u c t i v i t y a n d y i e l d o f f i s h e s a s s o c i a t e d w i t h c o r a l r e e f s i n F r e n c h P o l y n e s i a . T h i s s t u d y was d e s i g n e d t o d e t e r m i n e t h e f i s h e r i e s y i e l d from a p a r t o f t h e f r i n g i n g r e e f on t h e i s l a n d of Moorea, F r e n c h P o l y n e s i a .

T h i s a r e a , however, h a s a d i f f e r e n t assemblage of f i s h e s compared t o some o f t h e o t h e r r e e f s t h a t have been s t u d i e d . T h e r e a r e fewer s p e c i e s i n F r e n c h P o l y n e s i a due t o i t s i s o l a t i o n i n t h e e a s t e r n p a r t o f t h e I n d o - P a c i f i c p r o v i n c e , and m o r e o v e r , t h e assemblage of f i s h e s i s dominated by r e l a t i v e l y few s p e c i e s ( G a l z i n , 1986a).

I n t h i s p a p e r , I h a v e assumed t h a t i t may b e p o s s i b l e t o e s t i m a t e t h e b i o m a s s and p r o d u c t i v i t y o f whole g r o u p s of f i s h e s by s t u d y i n g t h e p o p u l a t i o n dynamics of t h e dominant s p e c i e s . Because most f i s h i n P o l y n e s i a f a l l i n t o 3 g r o u p s

G.

h e r b i v o r e s , omnivores a n d c a r n i v o r e s , I o n l y c o l l e c t e d d a t a on t h r e e s p e c i e s . They a r e :

11

The h e r b i v o r e C t e n o c h a e t u s s t r i a t u s (Quoy e t Gaimard

,

¹⁸²⁴⁾ 'Waito". I t i s common t h r o u g h o u t t h e I n d o - P a c i f i c ( s p r i n g e r , 19821, and i s t h e m o s t a b u n d a n t s p e c i e s o f s u r g e o n f i s h i n t h e l a g o o n s of h i g h i s l a n d s i n F r e n c h P o l y n e s i a ( G a l z i n , 1 9 8 5 ) . I t i s n o t a c o m m e r c i a l l y i m p o r t a n t s p e c i e s , however, b e c a u s e i t i s sometimes c i g u a t o x i c . 21 The omnivore S t e g a s t e s n i g r i c a n s (LacepGde, 1803) " A t o t i " . I n F r e n c h P o l y n e s i a , t h i s s p e c i e s d o e s n o t o c c u r on t h e o u t e r s l o p e a t d e p t h s g r e a t e r t h a n 3m, b u t it i s e x t r e m e l y a b u n d a n t i n a l l t h e f r i n g i n g r e e f s . A t o t i i s a p u g n a c i o u s t e r r i t o r y h o l d e r ( ~ l l e n , 1975). One of i t s f a v o r i t e h a b i t a t s is dead c o r a l c o l o n i z e d by f i l a m e n t o u s a l g a e . 3 1 The c a r n i v o r e S a r g o c e n t r o n microstoma G u n t h e r , 1859 "Araoe". I t i s t h e most a b u n d a n t o f t h e l a r g e n o c t u r n a l l y a c t i v e f i s h e s i n t h e l a g o o n of Moorea i s l a n d .

I n t h i s p a p e r I p r e s e n t d a t a on t h e b i o l o g y , biomass and growth o f t h e s e t h r e e s p e c i e s . These d a t a a r e t h e n a n a l y z e d t o p r o v i d e a n e s t i m a t e o f t h e p r o d u c t i v i t y o f t h e s e f i s h e s a n d , of t h e f i s h e r i e s y i e l d from one p a r t of t h e r e e f of Moorea i s l a n d .

MATERIAL ABD METHODS

A r e a and d u r a t i o n of e t u d y . T h i s s t u d y was c a r r i e d o u t o n t h e n o r t h w e s t e r n p a r t o f Moorea I s l a n d , 1 7 " 3 0 1 S ; 149"501W ( ~ i ~ . l ) . F u r t h e r d e t a i l s of t h i s a r e a a r e g i v e n i n G a l z i n and P o i n t i e r (1985).

A l l s a m p l e s were c o l l e c t e d between August 1982 and O c t o b e r 1983.

F o r t h e feeding h a b i t s t u d y o f

---

C t e n o c h a e t u s s t r i a t u s and S t e g a s t e s n i g r i c a n s e v e r y two h o u r s and f o r 2 4 h o u r s , 10 f i s h e s were

c o l l e c t e d i n a n e i g h b o u r i n g f r i n g i n g r e e f . An e m p t i n e s s i n d e x (number o f empty s t o m a c h s

.

1 0 0 number o f examined f i s h e s ' I ) g i v e s some i n d i c a t i o n s o n t h e d a i l y rythm o f f e e d i n g . The S a r g o c e n t r o n m i c r o s t o m a stomach c o n t e n t s were o n l y a n a l y z e d w i t h f i s h c a p t u r e d by r o t e n o n e . The o c c u r e n c e i n d e x ( f ) i s t h e p e r c e n t a g e o f f i s h e s c o n t a i n i n g a s p e c i a l k i n d o f p r e y on t h e number o f f i s h e s w i t h f u l l stomachs. Numerical p e r c e n t a g e s a n d p e r c e n t a g e s by w e i g h t of e a c h p r e y w e r e c a l c u l a t e d .

The r e p r o d u c t i o n of t h e s e 3 f i s h was o n l y s t u d i e d by d i v i n g o b s e r v a t i o n s o f t h e b e h a v i o r and by t h e a n a l y s i s o f t h e monthly change o f t h e Gonadosomatic i n d e x (GSI ⁼ Weight o f - t h e gonad -

. ¹⁰⁶

w e i g h t o f t h e f i s h - I ) . The 1 2 9 8 ~ t e n o c h a e t u s s t r i a t u s , 1270 S t e g a s t e s n i g r i c a n s and 202 S a r g o c e n t r o n m i c r o s t o m a , examined w e r e c a p t u r e d by r o t e n o n e e v e r y month d u r i n g 1 5 months.

The total number, h b i o m a s s and t h e b e h a v i o r o f t h e s e 3 s p e c i e s a r e d i f f e r e n t . S o , i n o r d e r t o s t u d y t h e p o p u l a t i o n dynamics o f e a c h s p e c i e s , d i f f e r e n t p r o c e d u r e s w e r e u s e d . F o r C t e n o c h a e t u s s t r i a t u s t h e a c c u r a c y o f t h e d i v i n g c o u n t s

armel el in-~ivien

e t a 1 . , 1 9 8 5 ) was good enough t o u s e t h i s s a m p l i n g method f o r t h e s t o c k - s t u d y . The biomass was c a l c u l a t e d by m u l t i p l y i n g t h e number o f i n d i v i d u a l s c o u n t e d by t h e mean w e i g h t o b t a i n e d a f t e r a monthly r o t e n o n e s a m p l i n g o n a n e i g h b o u r i n g r e e f . S t e g a s t e s n i g r i c a n s i s v e r y d i f f i c u l t t o c o u n t w h i l e d i v i n g , s o t h r e e d i f f e r e n t methods w e r e u s e d _{- .} ( G a l z i n , 1 9 8 5 ) : a d i r e c t e v a l u a t i o n by d i v i n g c o u n t s a n d two i n d i r e c t e v a l u a t i o n s by r o t e n o n e s a m p l i n g w i t h t a g g i n g ( ~ a i l e ~ , 1951;

Schumacher e t Eschmeyer, 1 9 4 3 ) and w i t h o u t t a g g i n g (De L u r y , 1947).

S a r g o c e n t r o n microstoma was t h e l e a s t a b u n d a n t o f t h e s e 3 s p e c i e s i n t h e f r i n g i n g r e e f . I n t h i s c a s e , o n l y t h e monthly r o t e n o n e s a m p l i n g d a t a c o l l e c t e d i n t h e n e i g h b o u r i n g f r i n g i n g r e e f o f P a p e t o a i was s t u d i e d .

The g r o w t h o f t h e s e f i s h was s t u d i e d w i t h P e t e r s e n ' s method ( 1 8 9 6 ) . I n 1 9 8 2 , P a u l y j u s t i f i e d t h e p o s s i b i l i t y of u s i n g t h i s method i n t h e c a s e o f s m a l l t r o p i c a l f i s h . D i f f e r e n t growth models were a d j u s t e d t o t h e d a t a of l e n g t h f r e q u e n c y ( l i n e a r , l o g a r i t h m , power, e x p o n e n t i a l , Von B e r t a l a n f f y and Gompertz). The growth c u r v e adopted was t h a t of t h e minimum Sum o f S q u a r e D e v i a t i o n (SSD) between t h e e x p e r i m e n t a l and c a l c u l a t e d p o i n t s . I e s t i m a t e d t h e d u r a t i o n o f l a r v a l l i f e by m e a s u r i n g t h e l a p s o f t i m e between t h e g r e a t e s t spawning e p i s o d e and t h e f i r s t s e t t l e m e n t o f p o s t l a r v a e . I n d o i n g s o , I assumed t h a t l a r v a e o r i g i n a t i n g from spawnings a t Moorea ended up by s e t t l i n g t h e r e o r t h a t m a j o r spawning e p i s o d e s o c c u r e d e l s e w h e r e i n f r e n c h P o l y n e s i a a t t h e same time.

To o b t a i n a n e v a l u a t i o n o f t h e b i o l o g i c a l p r o d u c t i v i t y of e a c h p o p u l a t i o n t h e e q u a t i o n s of R i c k e r (1946) and A l l e n (1950) were used:

P = g E w i t h P = B i o l o g i c a l p r o d u c t i o n

a

-

g = I n s t a n t growth c o e f f i c i e n t B = Mean biomass between 2 l e n g t h s

RESULTS dlDD DISCUSSI(EJ

FEEDING HABITS

Maito a r e d i u r n a l f e e d e r s (Fig.2). O t h e r s f e a t u r e s o f t h e i r f e e d i n g h a b i t s a r e :

11

I t empties i t s stomach i n l e s s t h a n two h o u r s and i t s i n t e s t i n e i n l e s s t h a n f o u r hours. 21 I t s t a y s a t t h e f o o t of p a t c h r e e f s a t n i g h t b u t wakes up a t 5 a.m. and b e g i n s f e e d i n g a t 7 a.m.. Between 5 a.m. and 7 a.m. i n d i v i d u a l s e s t a b l i s h a f e e d i n g t e r r i t o r y . 31 80% o f stomach c o n t e n t s were i n o r g a n i c m a t e r i a l s i n g e s t e d i n c i d e n t a l l y d u r i n g f e e d i n g . T h i s m a t e r i a l i s r e d i s t r i b u t e d o n t h e r e e f w h i l e t h e f i s h s w i m s . 41 20% o f stomach c o n t e n t s were o r g a n i c m a t e r i a l s . 70% o f t h i s was r e p r e s e n t e d by d i a t o m s and u n i d e n t i f i e d o r g a n i c m a t t e r , 29% were cyanophycae ( C a l o t h r i x and Lyngbia) and o n l y 1% were macroalgae.

S t e g a s t e s n i g r i c a n s was a l s o d i u r n a l l y a c t i v e , w i t h two f e e d i n g p e r i o d s e a c h day: 1 0 a.m. t o noon and 4 p.m. t o 6 p.m. A t o t i were omnivorous w i t h a high tendency t o b e i n g h e r b i v o r o u s ( T a b l e 1 ) . P a y r i (1982) h a s found t h a t t h e a l g a l t u r f p r o t e c t e d by S t e g a s t e s n i p r i c a n s i s composed of t h r e e p a r t s .

11

F i l a m e n t s of c o l o n i a l b l u e - g r e e n a l g a e ( N o d u l a r i a , Lyngbia, ~ y c r o s ~ s t i s ) and microphytobenthos ( < 5mm). 2/

Brown a l g a e ( ~ ~ h a c e l a r i a , E c t o c a r p u s , G i f f o r d i a ) and r e d a l g a e (Wurdemania, H e r p o s i p h o n i a , ~ a n i a ) ( 5 - l ~ m m ) and 3

/

Ceramiales ( P o l y s i p h o n i a and Lophosiphonia (10-25mm). However, o n l y p a r t s 2 and 3 a r e a c t i v i l l y e a t e n (Lobel 1980, P a y r i 1982).

Araoe i s a c a r n i v o r e t h a t i s most a c t i v e between 5 p.m. and 7 p.m. C r u s t a c e a n s , m a i n l y C h l o r o d i e l l a b a r b a t a r e p r e s e n t e d 75% o f t h e stomach c o n t e n t s ( T a b l e 2 ) . With i n c r e a s i n g a g e , t h e f i s h e a t s a d e c r e a s i n g number of amphipods and isopods.

REPRODUCTION

There i s no s e x u a l dimorphism i n t h e e x t e r n a l morphology o f Maito. Spawning o f t h i s s p e c i e s was observed and d e s c r i b e d by R a n d a l l ( 1 9 6 1 ) , Bagnis (1970) and Robertson (1983). I observed spawning o n t h e i n n e r s l o p e o f t h e b a r r i e r r e e f i n Moorea i n October 1982, one day a f t e r t h e f u l l moon, a t noon. Together w i t h d a t a o n t h e gonadosomic i n d e x ( F i g . 3 ) , I concluded t h a t a t Moorea d u r i n g 1 9 8 2 , t h i s s p e c i e s was mature between October and F e b r u a r y w i t h a n i n t e n s e spawning p e r i o d d u r i n g November- December. The new body f a t a s s o c i a t e d w i t h t h e gonads ( F i s h e l s o n & a l . , 1985) was found i n a l l of t h e 1 545 f i s h examined.

S e x u a l dimorphism i s a l s o m a t u r i t y o c c u r e d between October s e a s o n s a t t h e b e g i n n i n g , and Yamamoto (1979) found t h a t s e x u a l I s l a n d s was o b t a i n e d a t an age c o u p l e s , t h e eggs a r e demersal.

a b s e n t i n S t e g a s t e s n i g r i c a n s . Sexual and A p r i l w i t h two l o n g spawning a t t h e end, of t h i s p e r i o d ( F i g . 3).

m a t u r i t y o f A t o t i i n t h e Ryukyus of two. S t e g a s t e s n i g r i c a n s spawns i n

T h e r e i s l i t t l e i n f o r m a t i o n a b o u t r e p r o d u c t i o n i n H o l o c e n t r i d a e ( T h r e s h e r , 1 9 8 6 ) . The d a t a o n GSI show t h a t S a r g o c e n t r o n microstoma spawns from December t o J a n u a r y ( F i g , 3 ) . T h i s spawning s e a s o n ( i e summer) seems t o b e t h e same f o r t h e H o l o c e n t r i d a e i n t h e C a r i b b e a n (Munro e t a l , , 1973; W y a t t , 1976).

STOCK AND BIOMASS

A mean biomass of 25g.m-2 f o r C t e n o c h a e t u s s t r i a t u s was found d u r i n g s p r i n g and summer ( f r o m September t o arch) and a mean biomass o f 1 5 g.m'2 from A p r i l t o August, e x c e p t i n J u n e

able

3 ) . I t s h o u l d b e n o t e d , however, t h a t t h e biomass of t h i s s p e c i e s i s n o t e x p e c t e d t o b e c o n s t a n t a c r o s s m i c r o h a b i t a t s w i t h i n t h e l a g o o n a t Moorea.

M a i t o c h a n g e l o c a t i o n s o n t h e r e e f a t d i f f e r e n t s t a g e s o f i t s development, S m a l l f i s h a r e found c l o s e t o t h e beach and t h e n mean l e n g t h i n c r e a s e s towards t h e r e e f ( G a l z i n , 1985). Moreover M a i t o a r e a l w a y s more a b u n d a n t , b u t h a v e a lower mean w e i g h t on t h e f r i n g i n g r e e f t h a n on t h e b a r r i e r r e e f .

The mean biomass o b t a i n e d w i t h t h e t h r e e methods t h a t were u s e d t o c e n s u s t h e S t e g a s t e s n i g r i c a n s , v a r i e d between 5 8 and 9 7 g.m-2 ( T a b l e 4 ) - The l o w e s t b i o m a s s was o b t a i n e d by d i v i n g c o u n t s . T h i s c a n b e e x p l a i n e d by t h e d i f f i c u l t y I had i n c o u n t i n g t h e j u v e n i l e s h o l d i n g i n s i d e c o r a l f o r m a t i o n s . Biomass of t h i s s p e c i e s was g r e a t e s t a t t h e edge o f t h e f r i n g i n g r e e f a d j a c e n t t o t h e c h a n n e l . I n t h i s a r e a , I c o u n t e d a mean o f 1 2 individuals.m'2 w i t h a maximum o f biomass o f 1 5 1 g.m-2. Is seems t h a t t h e p o p u l a t i o n of S t e g a s t e s n i g r i c a n s is r e l a t i v e l y s t a b l e . Between 1976 and 1 9 8 3 , t h e r e w e r e no s i g n i f i c a n t c h a n g e s i n t h e abundance of t h i s s p e c i e s on t h e f r i n g i n g r e e f ( G a l z i n , 1986b).

F o r S a r g o c e n t r o n m j c r o s t o m a , t h e n o c t u r n a l s p e c i e s , maximum abundance ( 0 . 1 6 ind.m'L) was found o n t h e b a r r i e r r e e f a t dusk ( 6 p.m. ). During t h e 1 5 months, t h e mean biomass was 3.5 g.m-2 w i t h a r a n g e between 0.9 and 9 . 5 g.m-2. The maximum d e n s i t y and biomass was found d u r i n g w i n t e r ( ~ ~ r i l t o August).

GROWTH AND BIOLOGICAL PRODUCTIVITY

The m a j o r spawning e p i s o d e of M a i t o was r e c o r d e d o n t h e 1 8 t h o f O c t o b e r 1982 i n s i d e t h e c h a n n e l o f T i a h u r a . The f i r s t j u v e n i l e s ( t o t a l l e n g t h of 3 5 m ) were s e e n on 2 6 t h December 1982. T h i s g i v e s a l a r v a l l i f e o f 70 d a y s which i s q u i t e s i m i l a r t o t h a t of 75 d a y s f o r A c a n t h u r u s t r i o s t e g u s

andal all,

1961) and 8 4 d a y s f o r t h e Naso o f t h e G r e a t B a r r i e r Reef ( B r o t h e r s & a l . , 1 9 8 3 ) . The b e s t growth c u r v e s _- (SSD = 0.63) were o b t a i n e d w i t h t h e Von B e r t a l a n f f y e q u a t i o n ( F i g u r e 4 , T a b l e 5 ) . B i o l o g i c a l p r o d u c t i v i t y was c a l c u l a t e d from t h e r o t e n o n e s a m p l i n g d a t a o b t a i n e d d u r i n g t h e y e a r . The mean p r o d u c t i v i t y f o r C t e n o c h a e t u s - s t r i a t u s i n t h e f r i n g i n g r e e f of Moorea was e s t i m a t e d t o b e 1 6 . 1 g.m'L. year'i, r a n g e 8

-

32 g..m'2.year-1(~able 5 ) .

The two spawning p e r i o d s gave r i s e t o two main p e r i o d s o f l a r v a l s e t t l e m e n t f o r A t o t i . The same o b s e r v a t i o n was made by Yamamoto (1979) i n Japan. The b e s t growth c u r v e s (SSD = 0.52) was o b t a i n e d w i t h t h e Gompertz e q u a t i o n ( F i g u r e 4 , T a b l e 5 ) . J u v e n i l e S t e g a s t e s n i g r i c a n s s e t t l e d on t h e f r i n g i n g r e e f o f Moorea one month a f t e r spawning. The f i r s t spawning t o o k p l a c e i n A p r i l w i t h s e t t l e m e n t of j u v e n i l e s i n May, and t h e second spawning occured i n October w i t h s e t t l e m e n t o f j u v e n i l e s i n November. My o b s e r v a t i o n s a r e i n l i n e with t h o s e of B r o t h e r s & a l . (1983). They found t h a t 1 4 pomacentrids from t h e G r e a t B a r r i e r Reef had l a r v a l l i v e s of between 2 1 and 24 days.

The mean b i o l o g i c a l p r o d u c t i v i t y observed f o r t h i s s p e c i e s was 55.6 .m-2.year'1 ( T a b l e 5 ) .

The p r e s e n t o b s e r v a t i o n s i n d i c a t e t h a t Araoe h a s a l a r v a l l i f e of 6 0 days w i t h spawning i n December and s e t t l e m e n t o f j u v e n i l e s i n F e b r u a r y a t a minimum s i z e o f 25 mm. The b e s t growth c u r v e s (SSD = 0.54) were o b t a i n e d w i t h t h e Von B e r t a l a n f f y e q u a t i o n ( ~ i ~ u r e 4 , T a b l e 5 ) . The mean b i o l o g i c a l p r o d u c t i v i t y of S a r g o c e n t r o n microstoma was e s t i m a t e d t o be 2.6 g.m'2.year'1(~able 5 ) .

FISHERIES YIELD

The t h r e e s p e c i e s t h a t were s t u d i e d made up 64% of t h e t o t a l number o f f i s h e s and 74% o f t o t a l f i s h biomass on t h e f r i n g i n g r e e f ( G a l z i n , 1985). T o g e t h e r t h e s e 3 s p e c i e s have a b i o l o g i c a l p r o d u c t i v i t y o f 74 g.m-2 year-1 and a biomass of 103 g.m-2. A s i m p l e e x t r a p o l a t i o n g i v e s a biomass f o r t h e t o t a l f i s h community o f 140

-

²

g.m

.

T h i s biomass i s s i m i l a r t o t h a t found i n o t h e r c o r a l r e e f a r e a s ( T a b l e 6 ) . For example Goldman & T a l b o t (1976) thought t h a t 200 g.m-2 was t h e maximum biomass t h a t a c o r a l r e e f c o u l d produce. Biomass from n a t u r a l c o r a l r e e f s , however, a r e lower t h a n t h o s e from a r t i f i c i a l r e e f s , which can r e a c h 1 500 t o 1 700 g.m-2 ( R u s s e l , 1975; R a n d a l l , 1963).

U s i n g t h e e m p i r i c a l e q u a t i o n given by Gulland (1983) I e s t i m a t e d t h e maximum s u s t a i n a b l e f i s h e r i e s y i e l d f o r t h e f r i n g i n g r e e f of Moorea a s :

YMAX = X ( Y + M E ) G u l l a n d , 1983

w i t h : YMAX = G r e a t e s t p o s s i b l e y i e l d G u l l a n d , 1983 X = A r b i t r a r y f a c t o r s e t a t 0 . 3 Gu 1-land

,

1983 Y = C u r r e n t annual c a t c h = 1 0 ~ . k m ' ~ Munro, 1987

5

⁼ Mean biomass

w i t h a l s o :

F = F i s h i n g m o r t a l i t y =

Y / B -

Munro, 1987 Z = T o t a l m o r t a l i t y = M

+

^{F = P/B} Munro, 1987 P = B i o l o g i c a l p r o d u c t i o n

w i t h my d a t a :

t h e n :

YMM = 0.3 (10 +(0.63 X 1 0 3 . 4 ) ) = 23

T h i s r e s u l t i s i n agreement w i t h t h o s e o b t a i n e d from o t h e r c o r a l r e e f s i n t h e I n d o - P a c i f i c p r o v i n c e (Table 7).

CONCLUSION

I have demonstrated i n t h i s p a p e r t h a t t h e e s t i m a t e d y i e l d of f i s h e s from a f r i n g i n g r e e f i n French P o l y n e s i a , based on t h e p o p u l a t i o n dynamics of t h r e e dominant s p e c i e s , i s s i m i l a r t o t h a t r e c o r d e d from o t h e r c o r a l r e e f s . T h i s e s t i m a t e of 23 ~ . K m - ~ . ~ e a r - l i s l i k e l y t o be lower t h a n t h e a c t u a l v a l u e , however, because i t i s based o n t h e b i o l o g i c a l p r o d u c t i o n of s p e c i e s t h a t c o n s t i t u t e d o n l y 74% o f t o t a l biomass. F u r t h e r r e s e a r c h i s needed t o confirm t h a t e s t i m a t e s of t o t a l y i e l d based o n dominant s p e c i e s r e p r e s e n t t h e a c t u a l y i e l d . T h i s w i l l b e h a r d t o a c h i e v e i n French P o l y n e s i a because most T a h i t i a n s f i s h i n a s u b s i s t a n c e manner and s o c o l l e c t i o n of f i s h e r i e s s t a t i s t i c s i s i m p r a c t i c a l . The o n l y p l a c e where i t may be p r a c t i c a l t o make s u c h a comparison i s Tikehau A t o l l . T h e r e , t h e t o t a l c a t c h from t h e a t o l l i s marketed i n Papeete. I encourage v e r i f i c a t i o n of my method a t t h e e a r l i e s t o p p o r t u n i t y b e c a u s e , i f i t p r o v e s r e l i a b l e , i t may be t h e s i m p l e s t way t o e s t i m a t e t h e f i s h e r i e s p r o d u c t i o n of c o r a l r e e f s s u b j e c t t o s u b s i s t e n c e and a r t e s e n a l f i s h e r i e s .

ACKNOWLEDGEMENTS

I thank M.Amat and J . B e l l who provided comments on e a r l i e r d r a f t s of t h e m a n u s c r i p t . T h i s s t u d y was s u p p o r t e d by t h e C e n t r e N a t i o n a l de l a Recherche S c i e n t i f i q u e ( C N R S ~ R C P 806).

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Observations on a coastal fish Dahlak archipelago, Red Sea. Sea Fiah Rea.Stn.Haifa Bull. ,49: 15-31.

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Ecologie des poissons r6cifaux de PolynCsie

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Important characteristics of the coral reefs of French Polynesia. 13th Annual Conference Australian Society for fish Biology Darwin:

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-

Interannual variability in Coral Reef Fish

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Moorea i s l a n d , S o c i e t y a r c h i p e l a g o . i n : B.DELESALLE, R.GALZIN, B-SALVAT ( ~ d s . ) Proc. 5 t h I n t e r n . C o r a l Reef C o n g r e s s , T a h i t i 27 May- 1 J u n e 1 9 8 5 , Vol.1 French P o l y n e s i a n C o r a l R e e f s : 73-102.

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E v a l u a t i o n v i s u e l l e d e s peuplements e t p o p u l a t i o n s de p o i s s o n s : a t h o d e s e t problkmes. Rev. Ecol.

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.

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The spawning

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-

O b s e r v a t i o n s on t h e spawning of s u r g e o n f i s h e s ( A c a n t h u r i d a e ) i n t h e S o c i e t y i s l a n d s . Copeia,2:237-238.

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-

An a n a l y s i s of t h e f i s h p o p u l a t i o n s of a r t i f i c i a l and n a t u r a l r e e f s i n t h e V i r g i n i s l a n d s . Carib.J.Sci. , 3 ( 1 )

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YAMAMOTO T..1979- Distribution and abundance of Eu~omacentrus

nigricans

~ a c e ~ & d e ) ( ~ i s c e s - ~ o m a c e n t r i d a e )

in the Ryukyu

islands. Seeoko Mar.Sci-Lab.Tech.Rep.,6:3-32.

TABLE

1

: Q u a l i t a t i v e study o f t h e stomach c o n t e n t s o f S t e g a s t e s n i g r i c a n s .

Algae

---

Sponges

---

Polychaeta

---

Galatheidae

F i s h eggs

---

Others

8 Hours

.---r---

Weight o f Weight

Prey %

mg. 10-1

.---

7 99 5 4 . 1

.---

TABLE 2 : Q u a l i t a t i v e study of t h e stomach c o n t e n t s of Sargocentron micros toma f i s h e d on the northwestern f r i n g i n g r e e f o f Moorea

i s l a n d .

Number o f Number

Prey 70

, - - -

Weight of prey

( g ) .---

0.127

.---

0.274

TABLE 3 : Mean w e i g h t , abundance and biomass of Ctenochaetus s t r i a t u s i n s i d e a 100 m 2 quadrat of the f r i n g i n g r e e f of Tiahura a t Moorea.

---

Fringing r e e f

---

Mean Weight

---

Number of f i s h measured

---

Number o f f i s h counted Biomass (g.m-2>

---

DEC.

12

---

MARCH 03

TABLE 4 : Four different ways of estimating the biomass of Stegastes nigricans in the fringing reef of Moorea.

--- ---

Lrect

1

^Diving

tim mat ion o b s e r v a t i o

---

Without tagging l d i r e c t

tim mat ion

---

-

From August 82 t o July 1983

---

From August t o September 1975

March 1976

---

June 1976

---

1

J u l y 1976 With

tagging

, - - -

Edge of the f r i n g i n g reef near the channe

a t 240 m from the beach

, - - -

Middle o f the f r i n g i n g reef

a t 170 m from the beach

.---

Diving

100 Counts

--- ---

BAILEY

550 (1951)

.---

40 SCHUMACHER

.---

e t

40 ESCHMEYER

---

(1943)

---

2 0

I --- --- --- --- ---

July 1983

1

⁷⁰

^{lD:l2:: [}

¹⁴⁴

^[

^{2 . 1}

^]

⁸³

1

--- --- --- ---. --- --- ---.-.--

Ctenochaetus striatus Stegastes nigricans (Quoy et Gaimard, 1824) (Lacephde. 1803)

Tahitian name Maito Atoti

Feeding habits Diurnal herbivore 'grazer) Diurnal omnivore 3.lgdry food day-' 0.39g dry food day-'

Gonad development 5 months 7 months

from October to February from October to April Spawning peaks One in November-December Two in October and April

Eggs Planctonic Demersal

Length range of fish in mn 42 to 246 10 to 156

Weight range of fish in g 1.12 to 257.79 0.02 to 97.07

- ~ -- -~

]Length-weight relation ship

I _

n . n l l ,,3.10

I

Growth equation (cm) Growth equation (g)

Biomass range in g.m -2

14.0 to 33.6 29.0 to 231.3

Biological production (P)

16.1 55.6

in g.m-2.year-1

Production range in g.m-2.year-1

1

8.2 to 32.0 21.0 to 167.0

P/B

I

^0.69

1

^0.72

Sargocentron microstoma Giinther.1859

Araoe

Nocturnal carnivore 6 months

from October to March One in December-January Benthic

63 to 183 3.6 to 84.7

5 years

TOTAL FOR

43.7 to 279.1

TABLE 5

-

Summary of the principal r e s u l t s obtained on the population dynamic and the biology of three dominant f i s h of the northwestern fringing reef of Moorea i s l a n d .

16

TABLE

6 : I c h t y o l o g i c a l b i o m a s s o b t a i n e d i n d i f f e r e n t c o r a l reef areas.

---

CLARK & a l . ( 1 9 6 2 )

--- - ---

RANDALL ( 1963

---

GOLDMAN &

TALBOT ( 1 9 7 6 )

.---

HAWAII ENEWETAK

A t 0 1 1

.---

BERMUDA

.---

RED SEA

.---

V I R G I N ISLANDS

---

D I V I N G COUNTS

---

D I V I N G COUNTS and ROTENONE STATIONS

---

D I V I N G COUNTS

---

D I V I N G COUNTS and ROTENONE STATIONS

---

ROTENONE STATIONS

---

EXPLOSIVES

---

D I V I N G COUNTS and EXPLOSIVES

---

D I V I N G COUNTS TAGGING ROTENONE STATIONS

---

REEF AREA

FRINGING REEF

---

REEF FLAT

---

PATCH REEF

---

FRINGING REEF

---

FRINGING REEF

---

OUTER REEF

---

OUTER REEF

---

FRINGING REEF

'ET BIOMASS (g.m-2)

17 TABLE 7 : Coastal tropical water fisheries yield in the Indo-Pacific area.

---

AUTHORS

---

HILL (1978)

---

COUNTRY, AREA

, - - -

COASTAL FISHERIES SAMOA

, - - -

CORAL REEFS PHILIPPINES

. - - -

CORAL REEFS AMERICAN SAMOA

, - - -

CORAL REEFS FRENCH POLYNES IA

, - - -

---

RESULTS (~.~m'~.~ear'l)

...

FISHERIES STATISTICS

...

FISHERIES STATISTICS

...

FISHERIES STATISTICS

...

POPULATION DYNAMICS

Figure 1

-

The a e r i a l view shows the northwestern part o f t h e i s l a n d o f Moorea w i t h t h e l o c a t i o n o f t h e study s i t e on the f r i n g i n g r e e f .

Bmpt iness Index

Bumber of individuals

I

I I 1 1 1 I I I I 1 1 1 I I

1 3 5 6 7 9 11 13 15 17 18 19 21 23 Hours

Figure 2

-

24 hours changes f o r the abundance and emptiness index o f Ctenochaetus s t r i a t u s f i s h e d on t h e f r i n g i n g r e e f o f Moorea i s land.

o- -

-0 emptiness index f o r stomach s t u d i e s ... emptiness index f o r i n t e s t i n e s t u d i e s

-

number o f i n d i v i d u a l s .

G o n a d o s o m a t i c 1. Ctenochaetus striatus i n d i c e s

2 0- - - -0 Sargouen tron microstoma

1 2 3

A

1.2-

1. 0-

0. 8 -

0. 6 -

0 . 4 -

0.2-

-

i

Figure 3

-

Seasonal changes for the GSI of the three species fished o n the North fringing reef of Moorea island.

L e n g t h n c m

C t e n o c h a e t u s s t r i a t u s L. max.

Saargocen t r o n o l i c r o ~ t o m = ~ / "

/.L, max. 18.3 o m

/

\./.

/ ; -

A:---

A t o t , i A r a o e M a i t o

Figure 4

-

Comparative length of growth curves f o r the three s p e c i e s s t u d i e d on the North f r i n g i n g r e e f of Moorea i s l a n d .