The relationship between spawning stock and recruitment for Atlantic cod stocks
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The relationship between spawning stock biomass and recruitment in Atlantic cod stocks is investigated by ranking the SSB values according to size and applying a moving average of ten points. The resulting averages are plotted against the average recruitment produced by the respective SSBs. The plot in most cases resembles a Beverton and Holt or Ricker type of relationship, showing substantial reduction in mean recruitment at low levels of SSB even though the relationship is not forced towards the origin. Applying a moving average of ten years to the time series of data shows how SSB and recruitment relationships have developed. For some stocks the apparent relationship might be explained by medium- or long-term variation in the recruitment caused by environmental conditions. Considering all the available data, there is nevertheless substantial evidence of reduced recruitment at low levels of SSB for the cod.