Interaction between Pacific Cod (Gadus macrocephalus) and Herring (Clupea harengus pallasi) in the Hecate Strait, British Columbia

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Abstract
Pacific cod (Gadus macrocephalus) and herring (Clupea harengus pallasi) in the Hecate Strait have shown fluctuations consistent with the hypothesis that herring recruitment rates are strongly influenced by cod predation. Regression analyses of herring juvenile survival, as measured by log recruits per herring spawner, on Pacific cod abundance indicate that the cod may cause a total instantaneous mortality rate averaging around 0.75∙yr−1 with each cod consuming several hundred herring. Somewhat lower estimates of herring consumption per cod were expected on the basis of stomach contents data, but the discrepancy may well be due to systematic underestimates of cod abundance. Cod recruitment rates are positively correlated with herring abundance, but it is impossible to determine from historical data whether this correlation reflects predator–prey interdependence or the impacts of older cod on their own offspring, since cod and herring abundances are inversely correlated. Peak cod abundances in northern British Columbia during the late 1950's may be partly responsible for the collapse of the herring reduction fishery of the 1960's, and management of the two species should be coordinated to reflect the possibility of similar events in the future.

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