Fig. 1. Offshore, coastal and freshwater sampling locations where chum salmon were collected. (A) Sampling locations for immature and maturing chum salmon in the Gulf of Alaska, the central Bering Sea and the NW Pacific Ocean. In summer, chum salmon were caught in the Bering Sea along and near 180° longitude during cruises of the RV Wakatake-maru in 2001–2003, and at locations in the NW Pacific Ocean at 154°59'E during the cruise of the RV Hokusei-maru in 2001 (circles). In autumn, fish were caught in the central Bering Sea during cruises of the RV Kaiyo-maru in September 2001–2003 (open squares). In winter, chum salmon were caught at stations in the Gulf of Alaska during cruises of the RV Kaiyo-maru in February 2006 (filled squares). (B) Sampling locations for pre-spawning chum salmon in September–October, 2001–2003 in SW and FW in Hokkaido, Japan. a: Esashi on the NE coast; b,c: Ishikari Bay; d: Ishikari River estuary; e: midway between the coast and the hatchery; f: fish wheel located 4 km downstream from the hatchery; and g: the hatchery at the Chitose Field Station.