Spatial Patterns of Survival and Growth in Coho Salmon
and the Influence of the Ocean Environment
Current Status of Accomplishment or Milestone: The manuscript has been published, as: Hobday, A. J. and G. W. Boehlert. 2001. The role of nearshore ocean variation in spatial and temporal patterns in survival and size of coho salmon. Can. J. Fish. Aquat. Sci. 58 (10): 2021-2036.
Background: Interannual and decadal variability in ocean survival of salmon are well known, but the mechanisms through which environmental variability exerts its effects are poorly understood. Coho salmon represent a good species to study because they have a relatively simple life history, a broad geographic range, and respond to variations in ocean conditions.
Purpose of Activity/Goal of Project: Several studies have examined correlations of oceanographic conditions with the Oregon Production Index, which is a large-scale assessment of coho salmon ocean survival (based on hatchery releases) that averages over a very large spatial domain. In this study, a finer scale approach was taken both with environmental data and with data on hatchery-reared coho salmon. The latter came from individual releases (1973–1998) along the species’ entire North American range and were analyzed to provide information on survival and size to discern finer scale relationships.
Description of Accomplishment and Significant Results: Three geographic regions (north of Vancouver Island, Puget Sound and Strait of Georgia, and the outer coast south of the tip of Vancouver Island) showed coherent trends in survival and size of returning fish. Within each region, multivariate nonlinear models were used to relate coho survival and final size to spatially and temporally tailored environmental variables at time periods of release, jack return, and adult return. The most important environmental variable, as indicated by the highest amount of variance explained, was a calculated proxy for mixed-layer depth, followed by sea level. In all regions, survival and adult size were most influenced by environmental conditions at the release time. A shallow mixed layer was associated with increased survival and decreased size in all regions. Improved understanding of the relationship between environmental conditions and size and survival of coho salmon provides insight into production patterns in the coastal ocean.
Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): Historical research on salmonids has concentrated on the freshwater phase of the life history. Understanding the populations and implementing recovery plans will require improved understanding of how variability in the ocean contributes to variations in production and survival of salmon. This study addresses this problem.
Problems: None.
Key Contact: George Boehlert (831-648-8515; George.Boehlert@noaa.gov)