Effects of El Niño-Southern Oscillation events on catches of Bigeye Tuna (Thunnus obesus) in the eastern Indian Ocean off Java.

The effects of El Niño-Southern Oscillation events on catches of Bigeye Tuna (Thunnus obesus) in the eastern Indian Ocean (EIO) off Java were evaluated through the use of remotely sensed environmental data (sea-surface-height anomaly ISSHA], sea-surface temperature [SST], and chlorophyll-a concentration), and Bigeye Tuna catch data. Analyses were conducted for the period of 1997-2000, which included the 1997-98 El Nino and 1999-2000 La Nina events. The empirical orthogonal function (EOF) was applied to examine oceano- graphic parameters quantitatively. The relationship of those parameters to variations in catch distribution of Bigeye Tuna was explored with a generalized additive model (GAM). The mean hook rate was 0.67 during El Niño and 0.44 during La Nina, and catches were high where SSHA ranged from -21 to 5 cm, SST ranged from 24°C to 27.5°C, and chlorophyll-a concentrations ranged from 0.04 to 0.16 mg m-3. The EOF analysis confirmed that the 1997-98 El Niño affected oceanographic conditions in the EIO off Java. The GAM results indicated that SST was better than the other environmental factors (SSHA and chlorophyll-a concentration) as an oceanographic predictor of Bigeye Tuna catches in the region. According to the GAM predictions, the highest probabilities (70-80%) for Bigeye Tuna catch in 1997-2000 occurred during oceanographic conditions during the 1997-98 El Niño event. [ABSTRACT FROM AUTHOR]