Mapping distribution patterns of skipjack tuna during January-May in the Makassar Strait

Abstract

Skipjack tuna is an important fishery species, targeted by purse seine and handline fisheries in Makassar Strait. Fish distribution patterns are markedly influenced by several underlying oceanographic factors. This study aimed to assess the relationship between skipjack CPUE and some oceanographic variables, and map out the distribution pattern of this fish in the study area during January-May 2018. To meet these objectives, we combined satellite data of sea surface temperature (SST) and chlorophyll-a concentration (chl-a) with catch data. We used generalized additive models (GAMs) to explore skipjack abundance in relation to the oceanographic conditions and we employed the gravity centre of fishing ground movements to map the fish distribution pattern. Results indicate that SST and chl-a significantly influenced skipjack tuna CPUE. The fish schools were mostly located in the eastern Makassar Strait. In January skipjack schools were initially in Majene offshore waters and moved to Mamuju waters in February. The skipjack schools returned to the border area between Polman and Majene waters in March and then made a continuous migratory journey to the south-western areas of Barru and Pare-pare offshore waters in April. In May, the skipjack tuna returned to concentrate in southern areas of Majene waters. We proposed that the fish schools followed a clock-wise distribution movement pattern where the habitat displacements may have a link with the dynamic ranges of preferred oceanographic conditions (habitat hotspots). It is likely that these areas provide good feeding opportunities for skipjack tuna.