Recent Changes in the North Sea Plaice Fishery

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Abstract
In the period between the wars, the North Sea plaice stock was one of the classical examples of an overfished stock. Since the second world war the catches have been well above the inter-war average, reaching the record level of some 110,000 tons — twice the inter-war average — in 1964. The catch-per-unit-effort has also been high. These changes agree very closely with earlier predictions of the effect of rational management. A reduction of about 40% in total fishing effort (calculated in English steam trawler units) has coincided with a corresponding decrease in the total mortality. A change in the distribution of English fishing from grounds where small fish predominate to grounds where small fish are scarce has caused an increase in the average size and age at first capture of about 5 cm or 1·2 years respectively. Of the factors that are not directly related to fishing the total number of recruits has not changed, though a larger proportion now comes from the eastern, German Bight, spawning group. There has probably been some increase in growth rate, but not sufficient to account for the observed increase in average size of the individual fish in the landings. It is therefore clearly demonstrated that most of the observed increase of some 40,000 tons in the average annual landings of North Sea plaice is largely due to the two basic elements of rational fishing: less total fishing, and better protection of the small fish. However, these changes in fishing have been fortuitous, and not the result of a deliberate policy of management. They may be reversed in the future, unless steps are now taken to prevent this.

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