Bull. Jpn. Soc. Fish. Oceanogr. 73(2), Page 98-104, 2010   Transitions in purse seine fishing in the southwestern Sea of Japan after the second half of the 1980s Tsuyoshi Shimura1†, Shinya Masuda1, Ryosuke Uji1, Jun Yamamoto2 and Yasunori Sakurai3 1 Tottori Prefectural Fisheries Experimental Station, 107 Takenouchidanchi, Sakaiminato, Tottori 684-0046, Japan. 2 Field Science Center for Northern Biosphere, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611, Japan. 3 Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido 041-8611, Japan. † e-mail: simura-tu@pref.tottori.jp The southwestern Sea of Japan, from Tsushima Island to the Oki Islands, is one of the major fishing grounds in the Tsushima Warm Current region of the Sea of Japan. In this area, four species of pelagic fish (Japanese anchovy, Engraulis japonicus, chub mackerel, Scomber japonicus, horse mackerel, Trachurus japonicus and Japanese sardine, Sardinops melanostictus) are mainly caught by purse seine fishing; however, little is known about the long-term variation of purse seine fishing after the 1980s regime shift. The purpose of the present study is to clarify the inter-annual fluctuations of the catch per unit effort (CPUE), the main fishing season and main fishing grounds of four species of pelagic fish caught by purse seine fishing in this area. The abundance and distributional changes in four species of pelagic fish were examined using the catch data of the four species caught by two purse seine fishing vessels in Tottori Pref. from 1985 to 2005. In the 1980s, sardine CPUE increased and main fishing grounds were formed in the continental shelf; however, the main sardine fishing grounds were expanded to offshore regions around the continental shelf in the 1990s. This shift was affected by higher sea surface temperature and stronger volume transport of the Tsushima Warm Current. The CPUE of sardines decreased rapidly after 1997, while the CPUE of anchovies in spring and horse mackerel in all seasons increased on the continental shelf around the Oki Islands. Monitoring of the ocean environment and purse seine fishing trends may become important for adaptive management for the small pelagic fishes in the southwestern Sea of Japan. Key words: CPUE, fishing grounds, purse seine, small pelagic fish, southwestern Sea of Japan, Tsushima Warm Current