Long-term changes in growth and population abundance of sole in the North Sea from 1940 to the present

Sole stocks in the North Sea have shown a threefold variation in abundance over the past 50 years, largely as a result of fishing activity and variability in recruitment. Natural fluctuations in abundance have also occurred as a result of severe winter mortality as in 1962/1963 when the spawning stock biomass was reduced by more than half. Analysis of historical growth changes provides a means of assessing the causes of these variations in abundance. Changes in growth of female sole since the early 1940s were examined using back-calculated length increments from otoliths. Growth was lowest in the decade following the war and increased during the 1960s at a time of declining stock size. Growth of individual year classes appeared to be affected by the reduction in stock abundance in 1963. The extent to which these changes are related to eutrophication, beam trawl activity and density-dependent factors are discussed.