The role of coastal ocean variation in spatial and temporal patterns in survival and size of coho salmon (Oncorhynchus kisutch)

Interannual and decadal variability in ocean survival of salmon are well kn own, but the mechanisms through which environmental variability exerts its effects are poorly understood. Data on hatchery-reared coho salmon (Oncorhy nchus kisutch) from individual releases (1973-1998) along the species' enti re North American range were analyzed to provide information on survival an d size. Three geographic regions (north of Vancouver Island, Puget Sound an d Strait of Georgia, and the outer coast south of the tip of Vancouver Isla nd) showed coherent trends in survival and size of returning fish. Within e ach region, multivariate nonlinear models were used to relate coho survival and final size to spatially and temporally tailored environmental variable s at time periods of release, jack return, and adult return. The most impor tant environmental variable, as indicated by the highest amount of variance explained, was a calculated proxy for mixed-layer depth, followed by sea l evel. In all regions, survival and adult size were most influenced by envir onmental conditions at the release time. A shallow mixed layer was associat ed with increased survival and decreased size in all regions. Improved unde rstanding of the relationship between environmental conditions and size and survival of coho salmon provides insight into production patterns in the c oastal ocean.