| 英文摘要 |
??In this study the vertebra of blue shark, Prionace glauca which collected from Atlantic Ocean by observers were used for age determination, and the catch data which collected by observers from distant waters tuna longline fishery between 2004 and 2006 were also analyzed. A total of 72 specimens (42 male; 26 female; 4 unsexed) were collected and the vertebra were sectioned after it were cleaned and paraffin embedded. Growth band were counted on the X-ray films. Numbers of growth band for the oldest specimen was counted to be 15. Index of average percentage error (IAPE) was 3.9%。The best fitted growth equation was demonstrated to be the von Bertalanffy growth equation (VBGE) after AIC (Akaike’s information criterior) comparison. The parameters for VBGE were ＝388.5cm TL、k=0.10、t0=-1.46. 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 Atlantic Ocean from 2002-2006 were analyzed firstly. According to shark catch rate, five areas namely, A (5oN-15oS), B (15oS-50oS, west to 20oW), C (15oS-50oS, 20oW-20oE), D (5oN-20oN) and E (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 Atlantic Ocean. The shark bycatch in tropical area (areas A and D), is higher than that in temperate area (areas B, C, and E). Shark bycatch in weight ranged from 1601 tons (1984) to 12872 tons (1996) in South Atlantic Ocean, and ranged from 196 tons (1989) to 3066 tons (1994) in North Atlantic Ocean. Blue shark bycatch in weight peaked in 1996 of 11628 tons in South Atlantic Ocean and 1994 of 2684 tons in North Atlantic Ocean. Fin rate of blue shark is 5.3% in Atlantic Ocean. The results in this study are preliminary and further investigation is needed. |