Stock-specific Ocean Distribution and Migration of Chum Salmon in the Bering Sea and North Pacific Ocean

Chum salmon (Oncorhynchus keta) is a major pelagic fish species in the Bering Sea and North Pacific ecosystems. The stock-specific ocean distribution of chum salmon was estimated by genetic stock identification (GSI) and hatchery otolith marks. Fish were caught by 1-h trawls at 98 stations in the Bering Sea, North Pacific Ocean and Gulf of Alaska during the early summer (June/July) and late summer/early fall (August/September) of 2003. Tissue samples were collected from chum salmon (n = 3,980) and run for 20 allozyme loci to estimate the stock composition of mixtures. In addition, otoliths were collected from chum salmon (n = 4,424) and examined for mark patterns to determine hatchery origin. The GSI-estimates combined with catch data (CPUE) indicated that the ocean distribution patterns of immature chum salmon were different among eleven regional stocks. Japanese stocks were mainly distributed in the Bering Sea during summer and early fall. The distribution of Russian (primarily northern Russian) stocks was similar to that of Japanese chum salmon, but they also spread into the North Pacific Ocean. Northwest Alaska stocks including fall runs in the Yukon River were relatively abundant at the southern edge (50°N) of the Gulf of Alaska and eastern North Pacific Ocean. Alaska Peninsula/Kodiak Island stocks were widely distributed in the Bering Sea and North Pacific Ocean. The southeast Alaska (SEAK)/North British Columbia (BC) stocks were distributed throughout the northern Gulf of Alaska, the eastern North Pacific Ocean and the southern Bering Sea. The distribution of the South BC/Washington stocks was similar to that of the SEAK/North BC stocks, but extended into the central Bering Sea. The samples included otolith-marked chum salmon released from Alaska (n = 66), Canada (n = 3), Japan (n = 23) and Russia (n = 6). The recovery sites of marked fish were largely consistent with the marine distribution of those regional stocks estimated by GSI. The seasonal migration patterns of Japanese chum salmon in the Bering Sea were assessed from the best available information.