| 英文摘要 |
This study is aiming to elucidate the annual CPUE trend of North Pacific albacore, and also to analyze the annual fluctuation of its age composition based on Taiwanese longline catch statistics.
The Taiwanese longline fisheries operated in the North Pacific Ocean appeared to have two operation types. One clearly targeted on albacore while another one targeted on non-albacore species. Results of cluster analyses on the longline catch composition revealed that catches of the former fisheries were mainly comprised of albacore (more than 90%), while the latter fisheries rarely caught albacore (only 0.8%). These two fisheries could also be distinguished by their operations that the albacore-targeting fisheries applied only 9-13 hooks between two floats (per basket) in their daily operation while the non-albacore-targeting fisheries normally applied 14-20 hooks between two floats. The GLM model was then applied to the albacore-targeting CPUE to obtain standardized CPUE trend of the North Pacific Albacore. In comparison to the nominal CPUE trend, the standardized CPUE appeared to be higher and rather stable particularly after the year of 2000.The lower nominal CPUE after 2000 may reflect that only part of the increasing fishing effort after 2000 were targeting on albacore. The annual age composition of the albacore was also examined using knife-edge-cutting method based on length measurement data provided by the OFDC. Results show that before 2003 age groups of 3-5 year contributed most of the albacore catch, and in the year of 2003 and afterwards age groups of 4-6 year became the majority of albacore catch. It may also be partly explained by the increasing fishing effort of non-albacore-targeting fisheries which tended to catch slightly larger albacore if not any. |