| 英文摘要 |
In this study, vertebrae from 318 blue sharks, Prionace glauca (151 males, 110-310 cm; 92 females, 100-293 cm, 73 sex unknown individuals, 171-325 cm) caught in central and southern Atlantic Ocean between December 2006 and 2008 were used for age determination. Every vertebra was sectioned after it was cleaned and embedded. Growth rings were read and counted on X-radiographs. The most growth rings could be counted to be 15. Growth rings were formed once per year based on edge analysis. Parameters of von Bertalanffy growth equation for male and female were significant different via maximum likelihood ratio test (X2=22.73, P＜0.05), and were estimated to be L=318.8 m TL, k=0.154 year-1, t0=-2.316 years for male, and L=306.2 m TL, k=0.218 year-1, t0=-0.006 years for female, respectively. Observers’ data analysis including operation area, fishing effort, species composition, shark by-catch species composition, catch per unit effort by species, seasonal variation of CPUE in blue shark from Atlantic Ocean were presented. For the purpose of analyze the CPUE trend of blue shark, the observers’ records of Taiwanese tuna longline fishing vessels operating in the Pacific Ocean from 2002-2007 were analyzed firstly. According to shark catch rate, four areas namely, A (0o-20oS), B (south of 20oS), C (0o-20oN), and D (north of 20oN), were categorized. The shark catch data reported by observers were used to adjust the historical shark catch in Task I and to estimate blue shark and mako shark catches for Taiwanese longline fishery in the Pacific Ocean. The shark bycatch in tropical area (areas A and C), is higher than that in temperate area (areas B and D). Shark bycatch in weight was estimated about 10 thousand tons between 2001 and 2008 in Pacific Ocean. Total of 15 shark species caught from Pacific Ocean were measured total fins weight and body weight. The highest fin rate was estimated to be 9.85% for Carcharhinus albimarginatus, and the lowest fin rate was estimated to be 4.40% for Alopias pelagicus, respectively. The results in this study are preliminary and further investigation is needed. |