Projected Impacts of Ocean Warming on the Potential Fishing Zone of Eastern Little Tuna (Euthynnus affinis) in the Java Sea

In this research, the impact of ocean warming was examined on sea surface temperature (SST) in the habitats of eastern little tuna in the Java Sea, following the IPCC's projected temperature rise scenarios of 1, 2, and 4°C. Satellite-derived SST, chlorophyll-a, salinity, and the eastern little tuna catch data from 2016 to 2020 were analyzed. SST preference for E. affinis was determined from the histogram of CPUE against SST. The highest average catch per unit effort (CPUE) occurred during the northwest monsoon season (December to February) and the first transitional season (March to May), with 85 and 72kg/ trip, respectively. The locations with SST of 29- 30°C appeared to be the most productive fishing areas, i.e. CPUE of 80kg/ trip.  Shifting in the locations of potential fishing areas was identified from the SST at the current condition and each of the three scenarios of projected temperature rises. Optimal habitat projections for eastern little tuna fluctuate between the northwest and first transitional seasons due to the projected SST rises. During the northwest season, a 1°C temperature increase maintains a potential habitat in the Java Sea, particularly in February, but it disappears with temperatures’ increase of 2 and 4°C. Conversely, during the first transitional season, potential habitats appear only in January with a 1°C rise and are not present under the 2 and 4°C increase scenarios. The fish concentration is expected to move closer to Java's coastal waters while seasonal factors may drive the fish westward.