Multivariate regression relationships between ocean conditions and early marine survival of coho salmon (Oncorhynchus kisutch)

Washington State hatcheries have released coded wire tagged coho salmon (On corhynchus kisutch) since the early 1970s and have recorded data on the num ber and ages of adult returns. From these data, we isolated marine survival from release to age 2 using a multinomial model incorporating the multivar iate structure of the age-at-return data. Only hatcheries on or near the co ast were used in the analysis in order to isolate marine effects. Using mod els to explore linear and curvilinear relationships, early marine survival was regressed against environmental covariates of sea surface temperature ( SST), coastal upwelling, and the date of spring transitions. With hatcherie s serving as replicates, curvilinear relationships were found between survi val and both June SST and the date of spring transition. Maximum survival o ccurred for a June SST of 13.45.C and for a spring transition date around A pril 2. The regression results support the idea of optimal environmental co nditions for coho salmon survival and may help fisheries managers better un derstand the dynamics of early marine survival of salmonids.