Catch, effort and sampling strategies in the highly variable sardine fisheries around East Java, Indonesia

Abstract

Temporal and spatial patterns in the fishery for Sardinella spp. around East Java, Indonesia, were studied in an attempt to develop an efficient catch and effort sampling strategy for this highly variable fishery. The inter-annual and monthly variation in catch, effort and catch per unit of effort (cpue) are quantified and discussed, using official catch reports and reports from local village cooperatives. In 1993 the total catch of Sardinella spp. in East Java was 56 000 tonnes and the total effort was equivalent to 5000 units of purse seine. A maximum sustainable yield (MSY) of 40 000 tonnes of sardines is estimated, at an optimum effort of 3000 units of purse seine. The present study focuses on the purse seine fishery since this fishery accounts for more than 50% of all sardines landed in East Java. Purse seiners use lamps to attract fish and peak catches are landed around the new moon. Catches are smaller towards the full moon, when the fishery is inactive during a period of 10 days. Considerable differences exist between monthly catches from peak seasons and monthly catches from off-seasons. The fishery is further characterized by a relatively large amount of zero catches. A catch and effort data recording system (CEDRS) is developed based on the analysis of temporal variation in cpue and effort in the purse seine fishery for sardines. A purse seine fleet, with a variable size of 40 to 70 vessels, was sampled in Probolinggo harbour at the Madura Strait, during 4 to 6 days per month from March 1990 until March 1991. The overall mean effort of the fleet was 36.1 trips per day, of which on average 12.6 trips per day resulted in non-zero catches. The geometric mean cpue over the non-zero catches was 404 kg per trip. The proposed CEDRS has an accuracy of 30% for the estimated annual catch, 21% for the cpue and 9% for the effort (non-zero catches). A minimum required number of 4 sampling days per month is calculated for the temporally stratified CEDRS, with months used as strata within years, and lunar phases as strata within months. For this purpose, the lunar cycle is divided in three lunar phases, one around the full moon, one around half moon and one around the new moon. Within the proposed CEDRS, no sampling takes place in the lunar phase around full moon, when the fishery is inactive. The sample of 4 days per month is proportionally allocated over the other two lunar phases.