CATCH RATE FLUCTUATIONS OF SKIPJACK AND OTHER TUNA RESOURCES IN THE NORTHERN WATERS OF ACEH

The most dominant species ol'the ''large pelagic group" landed in Lampulo, Aceh, were skipjack, yellowfin tuna and small tuna. Thcse fish were caught by mini purse seine through fishing activities carried out on a dailv basis. Data analysis was based on landings recorded at Larnpulo l,'ishing Base, Banda Aceh. The data consistc'd of monthly catches ancl rllrmb€rr of trips covering bhe 1981-r-1995 period. Three distinct trencls of catch and ellbrt were observed within the period 198i)-1995. During the period 1985 1987. the increase in efTort was fbllowed by an increase in both catch and catch per unit effort (CPUE). In the period 1987-1990 the decrease in effort was followed by a decrease in both c:atch and CPUE. From this phenomenon it likely that the surplus production model for the maximum sustainable vield estimation could not be applied. ln the final period of 19901995. increase of effbrt resulted in an increase of catch but a slightlv decreased (IPUE. Based on the average of the 1 I vears rnonthly catch rate within the period lg851ggb, it could be concluded that the best fishing seas()n, as intlicated by the higher catch rate, occurred earlv in thc vr:ar from January-May.


INTRODUCTION
The "large pelagic r€lsorlrces" catagory of national fisheries statist,ir;s includes skip- jack, other large tunas (vellowfin, bigeye), shark, small tuna and Spanish mackerel.As a result of their oceanic migratory behaviour the tuna resources available in the western Indonesian waters are believed to be a small portion of the Indian Ocean tuna population.This resource has been erxploited and nran- aged by several countries rrround the Indian Ocean from the east coast of Africa, the south coast and southeast co:lst of Asia.Maurititrs.Seychelles, Maldive Islands and Austrerlia under the Indo-Pacific Tuna I)evelopment and Management Progrernrme (Ardill, 1994).
lt is important for stock assessment purposes that data should be collected from the coun- tries along their migratory path.
Various attempts have been made to assess these valuzrble resources.The poten- tials of' skipjack and other large tuna re- sources in lndonesian waters were esti- mated to be 15,300 tonnes and 32,000 tonnes respectively (Uktolseja et al., 1gg1).I{ow- ever, according to Venema (1996) there has been a consensus antong tuna specialists that at this stage of knowledge of these resources nobody t:an make reasonable predictions of the true potential.Historical trends from the easbern Indian Ocean suggest that the long linc {ishery for tuna is mature and large ' Researcher of the Ilese:rlclr lnstit.utefbl Maline l,'ishelics..fakarta inr:rettses in 1tt'odut't.ionr:trtrnot bc expecled.
Catch rate fluctuations could also be used to analyze inter-specific interactions occttrr- ing in a resource community.The most common interaction in a dynamic commttnity can be found in the form of a predator-prey relationship and/or food competition (Larkin et a1.,1984).Based on tabttlated 1991-1995   catch rate data it is apparent that an inter- specific interaction occurred between skipjack and small tunas.This is shown by the high catch rates of skipjack being minored by the low catch rate of small tunas and vice versa (Figure 3).The catch rate of larger tuna is similar to the pattern of the catch rate of skipjack.Interaction between species are complex.Yesaki (1994) reported that juvenile kawakawa (Eu,thynnus affinis'l were found in the stomachs of skipjack and yellowlin.Roger (1994) suggested that surface tuna in the poor feeding areas form small schools swimming rapidly in search of richer areas, and feed on what they meet.In richer areas they form large schools feeding heavily on concentrations of prey lish, such as anchovies (lloger, 1994).What kind of interaction occurred between skipjack and small tuna in this area is still unknown.-tNio€oNN#(o61 @$ t\Nt\@iiicD O t\ @ rr.. -l OJ tn @ O Cn cO cO @ ca li^-i rO Or tO N O) 6I i tO C <fi rO 6l C\ 6l oo co o) i ca or rr) N @ trci   burras (it'r u,4' of the total tuna nrade up the remaining 3"/o of the conrbincd total catch (Table 3) During the 1991-1995 period the percent- age of skipjack in the small purse seine catches and other large tuna ranged between 47.2 and 57.7"/,:, and between 1.9 and 4.0 ,,/u, and snrall tuna between {0.[J and l-r7.1,2r.

Status of Exploitation
The large pelagic fish yropulations ltrndecl at Lampnlo are believed to be perrt of' the Indian Ocean stock.Asscsstttent of't,hc st.ocl< to obtain a conrpt'ehettsir,'t: ficttr lc ot' tlrt' resource should incot'portttc data {i'ont ttciglrbouring countries along tlre fishes' ntigrtttorv path.
The trend of annttal <':rtr:h ratc's bt-'tween the period 1981-r-199i-r was ulntost flat wiLl-r rr slight decrease in 199ir.'l'his was probably due to the high exploitation level in .|995 which produced a low t:zrtt'h rate of onlSr I-rl2 kg/day/ boat within ttrat 1ru'iod.'l'lris inrplies that the level of exploitation ol' skipjar:k, otlrer large tuna and small tuna resourt:t,'s in the northern watcrs of Ar:eh htrs probatrl.yreached full exploitatior.r.Additional etfort in ternrs of an increzrsing nunrber of'l'ishing boat is therefore not reconrnlended.As fishing operations are now cotrcerrtrated very close inshclre, nroves to cover nrot'c offshore wnters need to be encouraeed.

6( 21
Within tlrat period, relatively high nrontlrly cutch r:rtes occurred in the earl.1'period of the year, covering January, F'ebruary, April and May.