Catch and standardized CPUE of the blue shark by Taiwanese small-scale longline fishery in the North Pacific Ocean.

Abstract

This study estimated the blue shark catch and abundance index of the small-scale Taiwanese longline fishery from 2001 to 2010. Almost all sharks caught by these fleets landed in Nanfanao, Chengkung and Tungkang fishing ports located at eastern and southwestern Taiwan. The landing data indicated that the shark landings of offshore fisheries were dominated by blue sharks of 62.2%, followed by shortfin mako shark, bigeye thresher shark, scalloped hammerhead shark and pelagic thresher shark, respectively. According to daily sale records, all the blue sharks landings at Chengkung were considered as whole fish, and 89.5% of blue sharks landed at Nanfanao were frozen and processed. The conversion factor between fresh and frozen landing of blue shark at Tungkang was assumed to equal to Nanfanao. The processed weight only occupied 41.08% with whole body (20.11% – 56.11%, n=59). After converting frozen landing into catch, estimated annual catch of blue sharks by Taiwanese small-scale longline fisheries ranged from 8847 mt to 16081 mt, with an average of 12314 mt in 2001-2010. Fishing efforts were the estimated from fishing days of each trip and numbers of hook per day. The fishing days of each trip of Taiwanese small-scale longline vessels in Nanfanao and Chengkung were estimated by record of vessels departure and arrival time. The standardized CPUE of blue shark ranged from 20.75 (kg/1000 hooks) to 63.57 (kg/1000 hooks) from 2001 to 2003, and increased to 40.63 (kg/1000 hooks) to 64.67 (kg/1000 hooks) from 2005-2010.