Winter Distribution and Trophic Status of Pacific Salmon in the North Pacific Ocean Under Changing Climate

Winter is believed to be a crucial period for marine salmon survival, but little biological data exists to support this hypothesis. In mid February 2006, a winter research cruise was conducted to examine the spatial distribution and biological status of chum and pink salmon in the western North Pacific Ocean and central Gulf of Alaska. The aims of the present paper are to estimate stock-specific distribution and trophic condition of winter salmon and assess impacts of climate changes on their distribution and survivals. Chum salmon were caught at 7 stations (48-54ºN, 145ºW) in the central Gulf of Alaska. Sea surface temperature (SST) of their winter habitat was around 5ºC between 51 and 54ºN, and increased to 6 or 7ºC between 48 and 50ºN, which was apparently lower than that of the summer habitat (8-12ºC). Ocean age 2 and 3 fish were dominant, and young fish (ocean age 1) were distributed in the southern water. Microsatellite stock identification confirmed various chum salmon stocks of Asian and North American origins intermingled in the Gulf of Alaska during winter. North American stocks were dominant in the northern water, and Asian (Japanese and Russian) stocks were dominant in the southern water. These results suggest that their preferable water temperature may be different among regional stocks or age groups.

To estimate trophic conditions of winter chum and pink salmon, we compared their muscle lipid contents in the western North Pacific Ocean and central Gulf of Alaska. The total lipid content of ocean age-1 chum salmon was much lower than that of older (ocean age 2-5) fish, suggesting critical conditions of young fish during winter. The total lipid contents of chum and pink salmon were significantly lower in the Gulf of Alaska than in the western North Pacific Ocean. The average SST in the western North Pacific and Gulf of Alaska was 4.7 and 6.3ºC for ocean age 1 chum salmon, 3.4 and 5.8ºC for older chum salmon, and 5.0 and 5.9ºC for pink salmon, respectively. The present results suggest that thermal regimes derived from climate change may affect the distribution, trophic status and survivals of overwintering salmon.