Climatic effects filtered through the food web affect the dynamics of Arcto-Norwegian cod

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The world's largest cod stock, the Arcto-Norwegian cod (a.k.a. North-East Arctic cod), is heavily influenced by temperature in two ways: First, cod recruitment tends to be high when Barents Sea temperature in the spawning year is high. Secondly, there is a more indirect effect of climate via herring and capelin: Warm conditions increase the chance of high recruitment of Norwegian Spring-spawning herring; 1-2 year old herring eat 0-year old capelin; and cod cannibalism increases when the biomass of 1-4 year old capelin is low. While these relationships have been shown separately and for the later years, we develop and parameterize models for the effects of herring (via capelin) and temperature on cod recruitment at age 3, using data from 1973 until present. Using data on cod, herring and temperature back to 1921 to verify the model,we find a significant relationship between predictions and data back to the 1950s, but before this, the predicted time-series pattern is not observed in the data.