Cross Correlations Between Reconstructed Ocean Abundances of Bristol Bay and British Columbia Sockeye Salmon (Oncorhynchus nerka)

Abstract

Anecdotal reports of a tendency for British Columbia sockeye salmon (Oncorhynchus nerka) to be low when Bristol Bay, Alaska, returns are high prompted a reconstruction of minimum abundances of sockeye resident in the Gulf of Alaska each year from the early 1950s to mid-1970s. This backwards reconstruction using Fry's virtual population analysis was done by using catch, escapement, and age structure data for each area in British Columbia and Bristol Bay. Use of more sophisticated backwards reconstruction methods was precluded by lack of age-specific annual survival rates by stock. Ocean abundances of British Columbia and Bristol Bay sockeye show significant autocorrelations at periods consistent with the cyclic dominant patterns of their largest stocks. Cross correlations at lag 0 between ocean abundances of various ages of fish from these two regions show one case of a significant inverse relation in abundances. In addition, there are significant cross correlations between British Columbia and Bristol Bay ocean abundances at various time lags, showing that cycles in their abundances are out of synchrony. This lack of synchrony persisted longer than would be expected from cyclic dominance patterns and age at maturity of British Columbia and Bristol Bay sockeye, and several alternative explanations of this asynchrony are discussed.