| 英文摘要 |
In order to gain a better knowledge of abundance index for the north Pacific albacore exploited by Taiwanese longliners, the generalized linear model (GLM) was applied to the daily logbook records of albacore-targeting fleets, which were defined based on their fishing activities and resultant catch compositions. In the GLM analyses, several sub-area segregations were adopted, and results showed that 2 sub-areas divided by 25oN Lat. can explain the highest proportion of variance either for the model or for the area factor itself. The GLM results revealed that the standardized CPUE fluctuated within a rather small range, suggesting that the north Pacific albacore population is currently under a reasonable exploitation, particularly since 2001.In this study, we also investigate the age compositions of north Pacific albacore based on length frequency data, given by OFDC, and growth equation reported by Wells et al. (2013). In the period 1995-2002, the albacore catch of Taiwanese longliners were mainly contributed by fish of age 2-4. Since 2003, significant proportion of the albacore catch was comprised of age 4-6 groups. Seasonal differences in the geographical distributions between age groups were observed. The CPUE gravity centers of albacore at age 5 and younger remained in the waters north of 25o N Lat. throughout the year, while those of fish older than 5 years tended to move down to the subtropical and tropical waters in June and July. Based on the monthly distribution of CPUE gravity center, those of fish older than 7 years likely move counter clockwise in the central north Pacific Ocean in the period of September-March. |
