地方公庁船によるマグロ延縄資源調査の推移と混獲モニタリングとしての特徴

摘要

地方公庁船によるマグロ延縄資源調査における操業実態およびサメ類，海鳥類，海亀類の混獲状況を1992－2005年について取りまとめた。公庁船調査はハワイ周辺海域に操業が集中する傾向があり，そのなかでも1－8月は南側，9－12月は北側で操業が行われた。本調査はサメ類に関する情報源となり得ることが示されたが，海鳥・海亀に関しては必ずしも混獲実態を反映しない操業状況であった。%Biological information on tunas, billfishes and other non-target species has been collected in the pelagic longline survey conducted by the Japanese training and research vessels (JTRV). We analyzed the changes of fishing practices and spacio-temporal distribution of fishing efforts by the JTRV survey from 1992 to 2005, and discussed the effectiveness of the survey as a monitoring tool for non-target species. Fishing gear configuration did not change drastically during the period. Fishing efforts concentrated in the area around the Hawaiian Islands, and the high density zone of fishing efforts were shifted seasonally between the south (from January to August) and the north sides (from September to December) of the islands. Very few fishing operations were conducted in April, August and December, because cruise schedule of training vessels were related to the school terms. Data obtained from the JTRV survey provided substantial information on pelagic shark and non-target teleost fish in the Central and North Pacific. Contrastingly, the survey provided little information on seabirds and sea turtles: incidental catch of seabirds and sea turtles occurred very infrequently because habitats of these animals scarcely overlapped with season, area and gear depth of the JTRV fishing operations. The low incidence of seabirds and sea turtles suggests a possibility in which incidental catch of these animals in longline fishery may be controlled to a low level with the modification of fishing operations. The JTRV survey information should be important for the further analysis on fishing resources and marine ecosystems in response to global climate changes.