FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

In order to understand the spatial and temporal distribution of larval bullet tuna (genus: Auxis) in the waters around Taiwan, 11 cruises to 62 sampling stations were conducted from 2007 through 2009 to collect larval fish and measure various environmental factors. A total of 909 larvae were collected using an ORI net. The abundance of Auxis larvae showed seasonal variations. In the spring, Auxis larvae were found in the Taiwan Strait and northeastern waters, and the average abundance was 32 ind./1000 m3. In the summer, the average abundance was 39 ind./1000 m3, and the Auxis larvae were widely distributed, ranging from the northeastern waters to the southwestern waters off Taiwan and also being observed in eastern waters in coastal regions. Principal components analysis showed that the levels of chlorophyll-a, zooplankton and Auxis larvae were high in areas with lower water temperatures during spring. During the summer, the levels of nutrients, chlorophyll-a, zooplankton and Auxis larvae were also high in areas with lower water temperature. Correlation analysis also showed that the abundance of Auxis larvae was negatively correlated with water temperature in spring and summer. In conclusion, the distinctive distribution of Auxis larvae in the spring and summer was profoundly influenced by the environmental factors, and autumn and winter were not the breeding season for the fish.