FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

Sunfishes (Molidae) comprise the largest bony fishes inhabiting the epipelagic to mesopelagic realms in tropical and temperate ocean regions. Sunfishes are principally bycatch species captured by longline, harpoon, drift net, and set net fisheries in eastern Taiwan. To fill in some of the necessary gaps in the knowledge of sunfishes for local fisheries management, we investigated variability in species composition, abundance, size composition, and the possible correlations of these phenomena with sea surface temperature (SST) in eastern Taiwan. Fishery data regarding sunfishes was collected from Shingang fish market, Taitung, from January 2016 to October 2017, and from the set-net complex, Hualien, from January 2003 to December 2011. The species comprised Masturus lanceolatus (80%) followed by Mola spp. (20%). The species abundance, average standard length, and size composition exhibited seasonal variability, with the abundance reaching a peak in winter when the SST was low. Small, immature individuals first appeared in winter, and then the number of fish caught decreased sharply in summer while the proportions of the largest individuals were highest in summer. The catch number of Masturus lanceolatus was highest in winter and late spring/early summer, and it was caught mainly at water temperatures above 20 °C. Variability in the catch data, a proxy of population dynamics, appeared to be closely associated with water temperature, the life history traits of the fish, and their migratory behavior.