TREND IN TUNA LANDINGS BY THE LONGLINE FISHERY OPERATING OUT ON BENOA , BALI

The number of longline vessels operabing out of Port of Benoa, Bali has increased steadily since 1986. However, this increase has been more rapid since 1994, and in 1996 there were 528 vessels registered in the port. Tuna exports peaked at 16,?00 tonnes in 1993 bui have since declined, despite the larger number of vessels in the fishery in 1996. (,)f the total landings, there was an increase in bhe proportion of bigeye Luna (Thun'nus obesus) during this period. from 25% in 1993 to 4lo/o in 1996. Southern bluefin tuna (Thunnus maccoyii) remained a small component ofthe fishery, ranging from 4,1 to 5% ofthe total landings oftuna and billfish. The catcl rate ofsouthern bluefin tuna (SBT) declined slightly, although ihe high seasonality ofthe caich (reflecling the spawning season of this species) may obscure small trend. The catch rate of bigeye tuna varied without trend, except for a possible small increase during the last six month of 1996. Yellowfin tuna (Tft.unnu,s albacares) catch raies cleclined steadily over ihe period of molitoring. This declining catch rat.e is due partly to an increase in the t:rrgeting of bigeye ul' the expense of yellowfin.


INTRODUCTION
Collaborative research between Common'   wealth Scientific and Industrial Research Organization (CSIRO) Marine Research, Hobart, and the Research lnstitute of Marine Fisheries, Jakarta, was initialed in September, 1992 to   monitor southern bluefin tuna caught by the longline fishery, operating out of Benoa.Southern bluclin tunit is a by catch ol't,his lishcry, which represent a significant proportion of the global catch for the species.Southern bluefin tuna is considered to be over'exploited (Anonim, 1994;  Caton e, ol., 1990).This fishery operates on their spawning ground, and catches mature southern bluefin tuna that have migrated from southern waters to spawn (Farley & Davis, 1997).The fishery Iandings consist mainly of yellowfin and bigeve tuna, which are intented for export to Japan as fresh sashimi quality tuna @avis et al., 1995).
Landings have been monitored continuously since 1992, providing a useful time series of catch and biological data for this fishery.In this paper, we report on changes in the spawning component of the southern bluefin tuna population as well as changes in the fishery from l99ll to 1996' MATERIALS AND METHODS

Catch Monitoring
We have attempted to record ll0% of longline landings at the Port of Benoa.This means that l,ho amounl, of samllling int:rcitsctl as l'hc lishcrv developed.Total landings processed at P'f Perikanan Samodra Besar (PSB) have been monitored since 1992, while the landings of three companies processing at PT Sari Segara Utama (SSU), have been monitored since December l9{}:J' ln 1996, lantlings at, ftrur companies prtxxlssing at PT Banclar Nelayan were also monitored.At each processing facility, the number and weight by species of all tuna processed for both export and domestic use was recorded.Individual dre$lred weights (gilled, gutted and de{inned) of southern bluefin tuna (SBT) were recorded at PSB. and   individual dressed weights and most lengths of SBT were recorded at SSU and Bandar Nelayan.On average, l4S landings representing;30% of the longline fishery were monitored each month.') Researchers of CSIR() Division of Marine Research, Hobart, Tasmania, Australia ") Researchers ofthe Research Institute for Marine Fisheries, Jakarta

Methods of Estimated Landing
To provide monthly estimates of total landings in Bali, the monitored landings were multipliecl by the reciprocal value of their export market share, except for landings by the PSB fishing companv.This was because the company targeted bigeye tuna, and the species composition of their landings was not representative of the whole Benoa-based longline fishery (Davis et ol., 1996).The PSti data were later included after the other landings were extrapolated to the whole Bali catch.The market share was estimated from the proportion of export monitored, to the total export permits issued for tuna and billfish by the Laboratory Quality Oontrol and Fish lnspection Section of the Provincial Fisheries Service of Bali.

RESULTS AND DISCUSSION
Trend in Longline Vessels Using the

Port of Benoa
Longline vessel registrations obtained from the Benoa I'ort Authoritv for the years lg86 to the resent indicate a steady increase in vessel using the port (Figure l).In 1994 a number ofTaiwanese vessel left Benoa and operated out of Bitung, North Sulawesi.This was in response to new regulations restricting the use of Benoa to vessel owned by lndonesian companies, resulting in a temporarv reduction in the number of vessels using the port.600 400 IFR ,lournal Vol. V No,1, 1999 However, in 1995, many of these boats returned to Benoa as joint venture boats.renamecl and flying the Indonesian flag.This has resulted in a marked increase in the number of boats trom 242in 1994 to 472in 1995.and 528 in 1996.

Tuna Export
The increase in longliners using the [\lrt of Benoa was due to the development of tresh tuna export to Japan in 1998, which was made possible by the proximity of an international airport.Tuna and billfish export rose rapidly between 1988 and l99il due to the increase in number of longliners using the port @igure 1).Export peaked in 190;l at 16,700 tonnes, and but decreased in 1994 when many boats left tire port.Export remained below 12,000 tonnes in 1994 and did not increase in lg95 despite the influx of boats back to the port late in that year.Export in 1096 increased to l4,l'rl-rl'r tonnes when 528 vessels used the port, but, this was well short of the 16,700 tonnes eqtorted in 199i1when there were onlv 291 vessels.

Species Composition of Landings
Yellowfin tuna has been the dominant, component of the fishery throughout four years (Figure 2).The two largest monthly landings of yellowfin were 1,934 tonnes in February 199:l and 1,956 tonnes in April 1995.The lowest monthlv 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996   Year   Number of longline vessels (squares) registered at the Port of Flenoa, and exporl, rt{' tuna and billfish (circles) from Bali.l)ata supplied by Benoa Port Authority and DGF Provincial Fisheries Service of Bali, respectively.landing was 412 tonnes in June 1994.The yellowfin tuna catch appears highly variable.It does not follow any seasonal pattern, and generally is declining with time.This decline has been partly compensated for by an increase in landings of bigeye tuna over the same period.
Bigeye tuna eomprised the second largest component of the longline catch.The largest landing of 1,220 tonnes of big eye occured in February, 199:1.This level was not exeeeded until 1,230 tonnes was caught in March 1996.Landing, again, did not appear to follow a seasonal pattern.
Generally, the peaks and troughs in landing match those of yellofin tuna.There has been an increase in landing over time.This was seen more clearly in catches by year in 199:1, bigeye accounted for Since 1993, when the annual catch was 1,20b tonnes (Iable 1), landings remained below 1,000 tonnes until 1996, when it peaked at l,i3?i3 tonnes.
The increase in southern bluefin landings in 1996 was expected because of anticipated increase in effort due to the influx of vessel into the Port of Benoa trrward,s the endof lgg5 @avis erol., lgg6).
However, southern bluefin still remains a small component of the fishery, ranging fro m 4. I tn E.1o/o of the total landings of tuna and biMish.
The total landing of tuna in 1996 was 2b,08ll tonnes caught by 528 longline vessels operating out of the Port of Benoa.This was onlv a little IFR Journal Vol.V No.I.1999 higher than the 28,567 tonnes landed in ll)9lJ when there were onlv 291 vessels using the port.The porthas grown considerably in terms of wharf area, processing plants and infrastructure.However.congestion in the port, and slow turn-around of vessels, has probably reduced the effective fishing time of each vessel.Only moderate inerease in effort will occur in the future.

Trend in Catch Bates
Catch per unit of effort OPUE) is expressed as the number of tuna landed per vessel fishing day.Some landing were excluded because the number of fishing days was not known, and there were insufficient dat,a to caleulate OPLIE befirre f)ecember l99il.As well, the landings bv [,SFJ fishing company that targeted bigeye were not included.Fishing days appeared kl be a fairly stable indicator of effort over this period, altough there hadbeen a gradual increase in the average number of hooks ller set each year (lable 2), resulting in a l0% increase over the three years.
(IPUE for southern bluefin, bigeye and vellow- fin tuna were plotted by month from December 199i1 to July 1996 (Figure i)).Southern bluefin showed high seasonality in CPUE, reflecting the protracted spawning season each year.the period, and there had been a small but consistent increase in CPI-IE during the last six month of 1996.
Yellowfin OPUE did not show seasonal variability, but nevertheless declined over the sampling period.These trends could be caused by changes in abundance, either driven environment or through fishing, or perhaps by changes in fi,shing methods to target bigeye.

Trend in Targeting
The relative proportions of southern bluefin, bigeye, and yellowfin in landings suggested widely differing fishing practices by individual longliners.
The bigeye targeting index (proportion of bigeye to bigeye and yellowfin) varied from near zero to almost one (Figure 4).PSB vessels targeted bigeye, anrl most of their landings have a bigeye targeting index greater than 0.9.This was achieved largely by deeper longline sets (Davis el   ol., l99l'r).In l99il, PSB was the only company targeting and catching mainly bigeye.However, since then a number of other companies have ben successful incatching bigeye, and there has been a trend away from catches dominated by yellowfin towards mixed catches or catches dominated by bigeye.
This appears to influence the catch of southern bluefin (Figure 4).Where the targeting was achieved by deeper sets (such as those by the PSB fishing company), southern bluefin comprise less than Zoh of the catch.However, at intermediate indices of bigeve targeting, some vessels were catching particularly high proportion of southern bluefin (up to 130%).This trend is more marked in 1996 than in previous years.It is not known what fishing/targeting practices are involved in attaining these high catch rates for southern bluefin but, unlike the PSB fishing company, they probablv do not rely on deeper long line sets.Sueh fishing practices may be of concern if measures need to be taken to conserve the spawning stock of southern bluefin tuna.

Trend in Export
Tuna is graded into export and non-export quality at the processing factories.The proportion of southern bluefin graded as export quality has declined over the years of l99ll to 1996 (Figure 5).The proportion of yellowfin and bigeye graded as export quality has also decreased slightly.
These changes may be due to more critical grading for export.It may also be because fish are ofpoorer quality.The rapid increase in vessels in the Port IFR Journal VoI.V No.l.1999 of Benoa may have streched the captrcity of the port infrastructure to support frequent lanclings and rapid processing of fish of resulting in prxtrer fish quality.Consistent with increased congestion in the port, there is a trend for fishing boats tn trans-ship catehes and be re-supplied with fuel, bait and ice by carrier boats, thus reducing the number of port visits.
Some albacore were exported when monitoring started in 1992 (Figure 5), but none has been exported from company monitored since September 199;1.A very small proportion of billfish is exported.

Size Composition of SBT in Monitored Landings
Weight-frequency histograms for southern bluefin had been plotted by year fcrr the years of 1993 to 1996 (Figure 6), and length-frequency histograms for the years of 1994 to 1996 (Fieure  7).Lengths measured in 199;l were not ineluded because of problems detected in the length measurement (Davis et al., 1996).
There have been no major changes in weight distribution over the four years.However.vari- ation in condition might have confounded detection of trends between years.The 100-l l0 ke classes had beeen well represented in all years and were the major elasses in 1996.
The length frequency distributions of southern bluefin differed between years.In 1991-r, there was a greater proportion of southern bluefin larger than 180 em than in the previous year.The 1996 length distributions were more similar to those of 1994 than 1995.There was a slight increase in the proportion of southern bluefin smaller than 165 cm in 1996 compared to previous year.It is not known whether this is due to an increase in recruitment of smaller fish.An inr:rense in recruitment of smaller fish is expected if the reduction in catch quotas, introduced in 1984.
have had the desirecl effect and enabled more fish to survive to maturity.However.given our current understanding of mean age at first maturity, and the presence of strong cnhorts from the 1985-89 year classes (Gunn e.t al., 1996), an increase in recruitment to the spawning grounds is expected in four years.Further monitoring of the spawning population is needed to determine whether this is the case.

CONCLUSIONS
The number of longline vessels operating out of the Port of Renoa reached a historical hish of Nonmil\ J.H. Farle.y, and D. Le 528 in 1996.The amount of tuna exported from Bali in 1996 was 14,500 tonnes, which is less than the 16,700 tonnes exported in 199;l when there were only 291 vessels using the port.The poor export perforlnance in relation to the large number of vessels operating in 1996 can be attributed to limitations of the port to service so many vessels and to process the catches.Further expansion of tha fleet will depentl on the development, of new port lacilities.
'l'here has been a shift in the species caught in fishery.from mainly yellowfin tuna in 1993 and 1994 io equal amounts of yellowfin and bigeve tuna in 1996.It is not known to what extend the 56 percentage of bluefin in yearly tuntr landings of individual longliners plottetl agitints the bigeye targering index (bigeve/bigeye + yelkrwfin).Only those vessels lantling more than 10 tonnes of tuna in each year are included.
changes in species caught is due to shifting targeiing practiees, or changes in abundance of yellowfin and bigeye tuna.Southern bluelin tuna remained a small component of the fishery in 1996.but was a significant part (lil%) of the global cateh for this species.
24.7o/o of landings and this figure increased to 41.4% in 1996, almost as large as the yellowfin component (Iabel 1).ln contrast, southern bluefin tuna landings fluctuate predictably around the spawning season which peaks from January to March @arley & f)avis, 1997).The largest monthly catch of southern bluefin (428 tonnes) was caught in February, lggB.

Table 1 .
The seasona-l nature of the fishery made it difficult to detect small changes in abundance.The average mon thly ( ) PUE for the spawning p eriod (Sep tember Estimate total and proportion (%) of tuna anrl billfish in longline landings at