GEOGRAPHICAL DISTRIBUTION AND STATUS OF SCADS POPUIATION IN THE WATERS OF THE SOUTHERN PART OF THE SUNDA SHELF

The scads population have long been exploited in ldonesia. Exploitation to the ofishore water started when purse seine was introduced in 1970. The exploitation extends eashalards to the Macassar Stait and northwards to the southern part of the South China Sea. The scads (Decafrerus russe//r) and (Decaf,erus macrosomaltorm the bulk of the catch. Norv the scads are exploited in the whole Java Sea. tne siuOy describes the geogiaphic repartition of the scads populations, the evolution of the landings linked to the exteniion of the fishini grodtos, and the reproductive biology of these species. Analysis was canied out from commercial landings of tire seiners. D. macrosoma, an oceanic species where the landings increaed a lot when the fishing giounOs extended east'wards and dominant from October to Aprii. D.russetlii, a neritic species, which form 6e-bulk of the catch since the exploitation started. lt inhabits the fishing grounds off the North coct of Java to Masalembo lsland and the southern part of Sotrth China Sea. For the two species tfrere is a West-Eat tend in the size. The application of surplus production model revealed significant indications that the level of exploitation alread slighly exceeded maximum sustainable yield and since 1992, the catch of scads exceed sustainable yield curve. KEYII/ORDS: geography, scads distribution, status, Sunda Shelf


INTRODUCTION
Since 1970, the development of the exploitation of small pelagic resources in the Sunda Self waters is strongly linked to the introduction and fast booming of the prrse seiner fleets.After the trawl banned in 1980, these fleets became the sole semi industrial exploitation in these waters.Numerous trawlers were transformed to purse seiners.In 1982J1983, the fleets extended their fishing ground towards the eastern part of the Java Sea and the southern part of the South China Sea.This extension was made easier by the introduc'tion of bigger vessels (80-100 GT).In 1986/1987, fishing tactic changed, light reptaced fish aggregating device (FAD) (rumpon) as the main attraction of fish (Atmaja & Sadhotomo, 1985; potier &  Sadhotomo, 1995a), and in 1987 fteets setiled in West Kalimantan, based at Pontianak then expanded to Pemangkat in 1990.At least four species of scads are found in lndonesian waters, i.e., Decapterus kunoides, D. macarellus, D. russellii, and D. macrosoma.ln the southern part of the Sunda Shelf, the last two species are the main components of small pelagic resources in the area.They represent up to 60% of the catch (potier & Sadhotomo, 1995a).Before the introduction of the purse seiners, D. russdlii was commonly caught by danish seine fishery (Potier & Sadhotomo, 1995b).In the South China Sea, the results of survey show the existence of share scads by Indonesian and Thailand around the Natuna groups (Midai island) (Sujastani & Amin, 1978).Hardenberg (1938) gave a hypothesis on the distribution of scads populations D. russelliiin the Java Sea.According to this arFhor, three populations inhabrts the Jara Sea waters, the first population entering the Java Sea from Flores Sea during the South-East monsoon; the two other populations coming from the West during the North-West monsoon.Among these two populations, the Indian Ocean one enters the Java Sea through the Sunda Strait, the South China Sea one through the Karimata Strait.part of the East population is resident in the Java Sea and its spawning grounds are close to the Bawean lsland.
The present study describes the repartition of the main characteristics of scads populations found in the southern part of Sunda Shelf through the analysis of the scads landings by purse seine net, and their status.

MATERIALS AND METHODS
Data of length frequency were colleded from the commercial catch of purse seiners based in Pekalongan (Central Java) and pemangkat (West Kalimantan) landing places during period of 1996-1999.
Catch and effort data of purse seiners came from Pekalongan and Juana Landing Place during periods of 19762004.This data collection was part of the research activities of Research Institute for Marine Fisheries and Java Sea Pelagic Fishery Assessment Project.
Length frequency data were obtained through daily sampling.Sampling procedure is explained in potier & Sadhotomo (1991) and presented in Appendix 1.
Sampling of the catch must be carried out on board the purse seiner before the fish is sorted by commercial category and by size for sale.In every landing place, two systematically taken from the vessel and the fish hold.
-1, Research lnstitute-for Marine Fisheries, Ministry of Marine Afiairs and Fbheries Muara Baru, Jakarta ' xesearch center for CaPture Fisheries, Ministry of Marine Afiairs and Fisheries.Jakarta Vessel selection: Only the vessels disembarking the fresh fish were taken as samples, if those are more than five vessels coming from the same fishing zones, other wise only one sample to be taken, and the secpnd samde would be the second order if the vessel is coming from another fishing zones.lf the number of landings of the same zone are less than five, only one sample taken in a day.Fish hold selection, the procedure is the same as for vessels.One basket is taken by fish hold then fish is sorted by species, and counted.For each species, 50 fish are measured, if the number is less all individuals are measured.Total of 1,400 samdes were measured, they cover all fishing grounds of the purse seine fishery from the southern part of South China Sea to Makassar Strait.
The purse seine fishery exploits nine fishing grounds.Based on the results of the hierarchic clarification performed by Potier (1998), they were grouped in four areas, namely southern part of South China Sea, Central part of the Java Sea (North of Central Java-Karimunjawa lslands), eastern part of Java Sea (Bawean, Masalembo, Kangean, and   Matasiri lslands) and western part of Makassar Strait (Samber gelap, Lumu-lumu, Lari-Larian lslands).
Repartition by weight of the scads catch in each fishing area was calculated ffom the ratio in weight of each species in the samples.The average length of fish caught was derived from cumulative frequency distribution.
The estimation of the current status of scads fish resources in the Sunda Shelf was based on the existing data from the development of purse seine fishery during 1976-2004.The status of scads was estimated by applying surplus production model (Schaefer model).This model assumes a linier relationship between the catch per unit etfort (CPUE) and effort (Gulland, 1%1 in Fauzi 1999)

Spatlo Temporal Distribution
In fisheries statistics, landings of various scads species are recorded as one entry.In fac't, significant variations exist between the two species according time of the year and fishirg zones.The landings of D. macrosoma are high in the eastern part of Java Sea and the Makassar Strait.D. russe/li dominates in the western part of the Java Sea and the South China Sea (Figure 1).
Comparing the monthly landings of the two species in the different regions of the Sunda Shelf, it shors two situations: in the southern part of the South China Sea and the western part of the Java Sea, landings of D.
russellii are highly dominant along the year.In the eastern part of Java Sea and Makassar Strait, that   species dominates the landings from May to September, and D. macrosoma forming the bulk of the catch from October to April.Then, the extension of fishing grounds toryards the East increased the share ol D. macrosorna in the landings of the purse seine fishery (Figure 2).

Average Sizes of Fish
In the landings, individuals of the two species range from 5 to 25 cm.However, most of the catch (97o/o for D. macrosoma, 91o/o for D. russellii) consists of fish measuring between 10 cm and 18 cm (Fl).
The cumulative curves of the size distribution calculated for each region show that the average size increases from the west to the east of the region (Figure 3) Semilar were also reported in the previous studies (Dwiponggo, 1987; Widodo, 1988; Sadhotomo  & Potier, 1995; Potier, 1998).
The study of the matn modes confirms the results found with geographic repartition of the average size.The smallest modes are found in the west part of the region and the largest ones in the east.Even, small   individuals disappear from the distributions in the east where the largest ones remain alone.In east region, landings oI D. macrosorna, consist in one mode only.
In every region D. russellii landings have more modes than D. macrosoma (Figure 4a). Figure 4b showed that average of size was not decreased.lt is a possible that the fisher tends to search and to choose fishing ground where was consisted of large size, they take a narrow range of species and size through choice of fishing ground by seasonal.
the fishing strategy.Together with increase in number of large fishing vessels, there was a simultaneous increase in engine capacity of vessels.There was general decrease in the number of vessels with engines less than 120 HP, while vessels with 180-320 HP engines showed an increase since 1990, and the most of fishing tac'tic has used spotlight (Atmaja,   2002).These, in total, increased fishing efficiency per unit effort.
The scads (D. russellii and D. macrosoma\ ol genus Decapterus dominated the pelagic fish landings on the Sunda Shelf.Decapferus as single genus contributed 51o/o of pelagic fish landings.The catch of pelagic fish and scads showed a declining trend, while fishing days tend to increase (Figure 5).

St*rs of Scads FisherY
Purse seine fleet was introduced in Indonesia in 1970, in which north coast of central Java were playing an innovation role of the effective gear on small pelagic fish exploitation.Historical data on the fishery showed that the development of the exploitation of small pelagic resources became offshore, extending their fishing ground toward the eastern part of the Java Sea to the Makassar Strait, is related to dynamic of its fishery which represented through larger fish hold capacity, enlargement of the fishing areas, and rapid changes of 10 t5 20 Forh length {cm) Catch-etfort data in the periods between 1990 to 2004, where the most of fishing tactic used spotlight' were used to estimate the current status of scads fish resources in the Sunda Shelf.The application of surplus production (Schaefe/s model) revealed significant indications that the level of exploitation slightly exceeded maximum sustainable yield, and sinie-1992, the catch of scads exceed sustainable yield curve (Figure 6).

DISCUSSION
Some authors have already discussed the exploitation of the scads resources in the Sunda Shelf (Sadhotomo ef a/., 1983;Widodo, 1988Widodo, , 1989bWidodo, , 1991: :  Potier, 1998; Atmaja 1999).They found that the exploitation was conducted for the most part on immature fish.The bulk of the landings are constituted of fish which are sexually uncletermrned.ln terms of stock dynamics, it is of great importance.Widodo   (1989a) suggests that the increases in the exploitation rate will lead to the recruitment overfishing, the size at first capture (Lc) being higher than the size at first maturity (Lm).Other such as Potier (1998) suggests that the exploitation should be made on a small part of the stocks which extend far beyond the limits of the exploitation area.
In the Sunda Shelf, small pelagics are very sensitive to the environmental changes.As a result of the monsoon, the hydrology varies a lot along the year.
The salinity is the main factor regulating the distribution of these populations.From our study, D. russe//ii is a resident species of the Java Sea and shows a neritic behaviour, D. macrosoma is a more oceanic species and enters the Java Sea during the South-East monsoon when prevailing conditions are optimal.
These different behaviors are in agreement with the work of Potier & Sadhotomo (1995a) on the small pelagic of the Java Sea. and other oceanic species.The exploitation is now made on more complex species and less dependent on one species (D. russellii), as previously caried out.
From genetics studies, it seems that D. russe/f7 has a wide repartition in the Sunda Self (Perrin, 1998).D.   macrosoma should not be presented some difference.The exploitation of the purse seiners seems to be done on two populations: South China Sea, and the eastern one which extends from the Java Sea to Macassar Strait reachirg the northern part of Sulawesi (Arnaud,   1998).
Like most Indonesian fisheries, the Java Sea fisheries may be characterized as de facfo open access with no restrictions on fishing effort.Free competition occurs among large-scale and small scale fishers.Increasing numbers and sizes of fishing gear and boats, as well as extension of operations into new fishing grounds, have resulted in biological and economic over-exploitation.Over-exploitation, as indicated by the catch of pelagic fish and scads showed a declining trend, while fishing days tend to Relationship between CPUE and effort (left) and Overlapping Sustainable yield curve (Schaefe/s production model) and catch-effort during periods 197&2004.AE = 1,5 -810-oc E R2 = 0,7 increase.lt means that fisher have to stay a longer times at sea for searching fish schooling or they should be oriented on the successful of their trip.Substitution fleet as responds to diminution of stock pelagic fish, some purse seiner vessels turn to denish seine for demersal fishing (the demersal resources of the Java Sea have recovered during twenty year of the trawl ban and now reoresent an underutilized resource).These indicated that purse seine fishery has decreased in CPUE and profit per vessel.Since 2002, the increase in landings ol leather jacket (A/esferus monocerosl when peak season of scads also signal the unhealthy status of the pelagic fishery.
The pelagic fishery recourses including the scads resources are over-exploited on Sunda Shelf, thus stringent management measure should be formulated and enforced to ensure sustainability.At least access restriction to the fishery for new vessels and the matter of controlling fishing tactic, especially amount of spotlight.

CONCLUSION
The species of scads form the bulk of the purse seiners landings.They have a big economic input on the fisheries of the northern coast of the Java lsland.
Since the fisheries extended eastward, the percentage of D. macrosoma increases in the landings.
Ncmradays, there is a balance among the species in the catch of purse seiners.Most of the catch consists of immature individuals.Such practice can endanger the stocks sustainability.However, as the exploitation is conducted on more complex species, where some populations are exploited on part of the stock only, the system has a strong resilience.
The management of pelagic fisheries should focus on the interaction of the large-scale and small scale fishers.The proposals for the scads management should as far as possible adopt an integrated approach to incorporate biological, environmental and socio- economtc asDects. Figure1

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ndonesi an Flshen'es Research Joum d Vd. 1 the exploitation towards eastern part of the Java Sea increased the landings of D. m*rosoma