Contrasting Early Marine Ecology of Chinook Salmon and Coho Salmon in Southeast Alaska: Insight into Factors Affecting Marine Survival

To identify processes potentially contributing to the differential marine survival rates of Chinook salmon Oncorhynchus tshawytscha and coho salmon O. kisutch originating from Southeast Alaska, we compared the early marine ecology of the two species during the critical first summer in marine waters. We predicted that the higher survival rates for coho salmon relative to Chinook salmon were related to the larger size, faster growth, or different habitat or species associations of coho salmon. Our size and growth expectations were largely substantiated: juvenile coho salmon were larger than juvenile Chinook salmon and had faster length-based growth, although weight-based growth rates were similar. The most obvious difference was in their distributions. Juvenile coho salmon overlapped spatially and temporally with abundant juvenile pink salmon O. gorbuscha and chum salmon O. keta, whereas juvenile Chinook salmon were geographically separated from other salmonids. This suggests that coho salmon benefited from a predation buffer that did not extend to Chinook salmon. Our results indicate that factors influencing marine survival of juvenile Chinook salmon and coho salmon in Southeast Alaska are attributable to species-specific differences in their early marine distribution patterns and species interactions.