| 英文摘要 |
This study is aiming to elucidate the CPUE trend and age composition of north Pacific albacore exploited by Taiwanese longline fisheries, 1995-2009. Following the increasing fishing efforts of Taiwanese longline fisheries operating in the north Pacific, the albacore CPUE declined drastically since year of 2000. It is aware that the catch statistics are a mixture of albacore-targeting and non-albacore-targeting fisheries. Unfortunately, it is almost impossible to distinguish one from another directly from the logbook report. In this study, based on a clustering analysis on the catch composition of Taiwanese longliners, the nominal catch statistics can be clearly categorized into two groups. Group 1 is characterized by higher albacore CPUE (averaging 28.52 fish/1000 hooks), smaller size of fish, operating in temperate waters with mainly 9-13 hooks per basket, whereas group 2 is characterized by lower albacore CPUE (averaging 0.19 fish/1000hooks), larger size of fish, operating in tropical waters with more than 14 hooks per basket. The grouping was further confirmed by discriminant analyses with only 3 % error count. Standardized albacore CPUE was then obtained by applying GLM procedure for the group 1 data. Based on Suda’s (1966) growth equation, a knife-edge-cutting method was also applied to Taiwanese albacore length measurement to estimate the age composition of North Pacific albacore exploited by Taiwanese. These results will be provided as a basis for the upcoming stock assessment of the north Pacific albacore by the ISC. |