Across‐Species Comparisons of Spatial Scales of Environmental Effects on Survival Rates of Northeast Pacific Salmon

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Abstract
We estimated the spatial scales of covariation in indices of spawner‐to‐recruit survival rates among 116 wild stocks of pink salmonOncorhynchus gorbuscha, chum salmonO. keta, and sockeye salmonO. nerka. These data spanned roughly four decades and represented stocks from 15 geographical regions in Washington, British Columbia, and Alaska. For comparisons between pink and chum salmon, we found positive covariation in survival rates within regions and between certain adjacent regions (e.g., correlations between 0.3 and 0.7) but little covariation between stocks of distant regions (separated by 1,000 km or more). Our results indicate that, on average, shared environmental effects accounted for at least 36% of the variation in survival rates of nearby pink and chum salmon stocks but only 18% for stocks separated by about 500 km. By comparing these between‐species patterns with within‐species patterns, we conclude that differences in the geographical overlap of fish during the freshwater and early marine life stages are much more important in determining the magnitude of shared environmental effects on the survival rates of these two species than are differences in their life history strategies. In contrast, patterns of covariation were weaker for between‐species comparisons involving sockeye salmon, especially for sockeye salmon stocks from Washington and British Columbia, which were mainly Fraser River stocks. By comparing between‐species correlations for northern sockeye salmon at two different time lags corresponding to processes operating during the early freshwater life stage and the early marine life stage, we found evidence that covariation in spawner‐to‐recruit survival rates was due largely to processes operating in the early marine life stage. Collectively, our results and those of previous studies show that the dominant effects of environmental processes on the survival rates of these three salmon species occur at local and regional scales rather than at larger, ocean‐basin scales.
Funding Information
  • Natural Sciences and Engineering Research Council of Canada