The relationship between spawning stock and recruitment for Atlantic cod stocks

Abstract

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.