Recruitment and survival of Northeast Pacific Ocean fish stocks: temporal trends, covariation, and regime shifts

Two measures of productivity for fish stocks (recruitment and stock-recruit residuals) within two large marine ecosystems (Gulf of Alaska and eastern Bering Sea - Aleutian Islands) showed significant positive covariation within several groups of species and significant negative covariation between certain others. For example, stock-recruit residuals of gadids (Gadidae) in the Bering Sea were inversely related to those of shelf flatfishes (Pleuronectidae), suggesting that environmental forcing affects these groups in opposite ways. Salmon (Oncorhynchus spp.), Pacific herring (Clupea pallasii), and groundfish stocks each showed strong patterns of covariation within these taxonomic groups and within ecosystems, and both salmon and groundfish stocks showed positive covariation between the two ecosystems. However, we found little evidence of covariation between salmon and herring stocks or between these stocks and demersal stocks. Recruitment and stock-recruit residuals in individual stocks did not show a consistent response to known climatic regime shifts. However, combined indices of productivity across stocks showed decadal-scale variability (regime-like patterns), suggesting that both pelagic productivity (mostly salmon) and demersal productivity increased in response to the well-documented 1976-1977 climatic regime shift, whereas the 1988-1989 regime shift produced inconsistent or short-lived responses.