Marine survival and distribution patterns of two Puget Sound hatchery populations of coho (Oncorhynchus kisutch) and chinook (Oncorhynchus tshawytscha) salmon

To better understand the factors associated with mortality of chinook (Oncorhynchus tshawytscha) and coho (Oncorhynchus kisutch) salmon, we examined data from two nearby hatcheries in Puget Sound, Washington, USA for salmon released from 1969 to 1998. The chinook salmon smolts released from the University of Washington (UW) hatchery were larger than those from Soos Creek hatchery (12.93 g versus 5.17 g) and had higher survival rates (2.21% versus 0.77%), and the Soos Creek coho salmon were larger than UW coho (25.25 g versus 12.60 g) and had higher survival rates (7.15% versus 4.27%), but in neither hatchery nor species did size explain the variation in survival among years. The two populations of each species shared very similar marine distributions, as inferred from patterns of coded wire tag recoveries from fisheries. The correlations in survival rates were significant in all cases, but strongest for UW salmon of both species (r = 0.70), followed by chinook from the two sites (r = 0.49), then coho from the two sites (r = 0.40) and lowest for coho and chinook from Soos Creek (r = 0.35). These results are consistent with the hypothesis that the period shortly after release affects survival because both populations of chinook salmon and the UW coho were released in May whereas Soos Creek coho salmon were released in April. Analysis of environmental variables indicated some correlations consistent with other investigations (chiefly negative correlations with sea surface temperature in the first summer at sea) but there were also inconsistencies (e.g., correlations at one hatchery or for one species but not the other). Taken together, the results highlight the higher survival rates of coho than chinook salmon, the negligible effect of body size on interannual variation in survival, and the variation in survival between populations from nearby sites.