FISHERIES RESEARCH INSTITUTE,MOA,TAIWAN

The dolphinfish (Coryphaena hippurus) is a highly migratory, epipelagic fish found worldwide in tropical, subtropical, and temperate waters. In East Asia, the dolphinfish is an important species for commercial and recreational fisheries in multiple countries. It is also an important catch resource for coastal and offshore fisheries in Taiwan during the main fishing seasons of April-June (summer) and October-December (winter). In this study, the length-frequency and sex ratio of dolphinfish were analyzed based on 88,902 samples (54,717 female; 34,185 male) measured in Shingkang fish market from 2003 to 2018. The catch compositions and fishing grounds of the dolphinfish longline fishery were also explored based on the catch records collected from sampling vessels from 2012 to 2018. The body sizes of dolphinfish caught in summer were larger than those caught in autumn and winter. The sex ratio analysis indicated that the proportion of females in the sample was higher at 0.62. The proportion of males, however, becomes higher than females with increasing body length which correlates. About 75% of the longline vessels targeting dolphinfish operated off Shingkang from January to March. The longline vessels tended to operate in southeastern areas from April to June and returned to areas offshore from Shingkang from July to September. Then, the vessels moved northward to Hualien from October to December. There were significant differences in the length and sex ratio of the catches in the two seasons, with the length of the catch in summer being significantly greater than that in winter. The winter catch mainly consisted fishes that recently joined the group in November and December, and the proportion of females caught was significantly higher than that in summer. According to the catch compositions, more than 50 species were recorded in the total catch, and the proportion of dolphinfish was 81.1% while that of the bycatch was 18.9%, indicating that the dolphinfish longline fishery is efficient at avoiding bycatch.