Changes in North Sea gadoid stocks

Abstract

Abundance and biomass of the major gadoid species in the North Sea have undergone large changes in the present century. During the gadoid outburst of the 1960s and 1970s, cod, haddock, whiting, and Norway pout produced some of the largest (as well as some of the smallest) year classes on record. Food requirements of the enhanced populations may have been some three to four times as large as current and previous levels. Although growth rates of cod did not change, there is evidence that food for juvenile haddock, and possibly whiting, was in short supply during the periods of maximum population density. The environmental factors that led to this increase in reproductive success have not been identified. Indices of recruitment for the whole North Sea, as provided by VPA, represent the pooled contributions of separate spawning units and may not be the most appropriate data to use when modelling the relationship between stock, recruitment, and environmental variables. Analysis of historical data indicates that recent levels of spawning-stock biomass of cod and haddock are close to their historic minima and fishing mortality rates are at (cod) or near (haddock) an historic maximum. Measures to reduce fishing mortality and improve exploitation patterns should be given the highest priority.