Interaction between fish and fishing vessels in the Javanese purse seine fishery

Abstract

The purse-seincrs of the Java Sea use light and fish aggrcgating devices (FAD) to concentrate and catch small pclagic fish (L)ecupteru.r sp., Amblygaster sirm, Sardinella gihhosa). This sets a question about the intcraction between fish and fishing vessels. Relevant estimates of fishing mortality and fishing effort require an understanding of this interaction. To gain information on this relationship, acoustic surveys were performed on the fishing grounds and the present paper analyses these data. Using acoustic surveys, the fish density was measured and the number of schools was counted pcr sca surface unit. The fishing vessels were located by radar. Acoustic data were stratilied into two groups, one where fishing vessels were present and the other where they were not. This stratification was tested for by resampling the data. Day and night sampled data were analysed in each strata separately. Variograms were computed to characterise spatial structure both for the fish and the purse-seiners. Contingency tables between number of schools and fish density were computcd to characterise the relation between biomass and schools for the day and the night when seiners are absent or present. At night, in the absence of purse-seiners, the number of schools increase and fish rise from the bottom. In areas where purse-seiners are present this natural phenornenon is stronger. It also changes the spatial structure both of the fish density and the school abundance. The spatial structure of the vessels is similar to that of the fish density. The fishermen seem to be able to detect by day fish concentrations which will bc fished later by night.

Can fishermen allocate their fishing effort in space and time on the basis of their catch rates? An example from Spermonde Archipelago, SW Sulawesi, Indonesia

“…Therefore, their selection of remote locations cannot be explained by what is found for other gears. The high variance in catch rates seems characteristic for this gear (Dudley & Tampubolon 1986) and could partly be explained by the competition phenomenon described for purse seine units off Java, Indonesia (Poitier, Petitgas & Petit 1997). Several boats cooperate in search of fish concentrations, yet compete for space to operate their gear at the selected location.…”

A tool for site prioritisation of marine protected areas under data poor conditions

“…Catch, net revenue þ ( À ) [55], [56], [57], [58], [59], [60], [61], [62], [41], [63], [64], [54] [43], [65], [66], [67], [40], [64], [42] ii. Distance À (þ ) [68], [69], [40], [11] iii.…”

Reconstructing historical trends of small pelagic fish in the Java Sea using standardized commercial trip based catch per unit of effort

“…Particularly, the Java Sea is one of Indonesia's most productive areas for commercial fisheries of small pelagic species (Sujastani, 1978;Widodo, 1988;Nurhakim, 1995) and purse seines have been the most popular fishing gear to harvest small pelagic fish species in this area since decades. Such a fishery has existed in the Java Sea since the 1970s and several improvements on auxiliary fishing gears were developed in connection with the expansion of fishing grounds (Atmaja, 2002;Potier et al, 1997). In most parts of the Java Sea, in which the medium and large Purse seine fleets operate, the shallow sea floor consists of a vast sand and mud bank ranging from 50 to 70 m in depth (Wyrtki, 1961;Durand and Petit, 1995).…”