The North Sea Herring: being the report of the North Sea Working Group to the Herring Committee of ICES

Since 1955, catches of herring in the Southern Bight of the North Sea have declined. Consequently, the biology of the North Sea herring stocks has been examined thoroughly to find the causes of decline. It has been.known for a long time (Johansen, 1924) that there was more than one main stock of autumnspawning herring in the North Sea. The herring spawn off the Scottish north-east coast in August and September, in the region around the Dogger Bank in September and October, and in the Straits of Dover and the eastern English Channel in November and December. The differences in spawning time and spawning area might in themselves be considered enough to provide evidence of distinctness. However, it is also clear that herring from all three spawning groups mix on the feeding grounds between the Dogger Bank and the Shetland Islands. 

A major problem facing the biologists was the identity of stocks. Therefore, in assessing the causes of the decline in the southern North Sea fisheries, the following major problems arose: (1) the identity of stocks and (2) the rate of mixing of fish of the different spawning groups in the feeding fisheries, so that fishing effort could be properly segregated to the different herring stocks. Only when these problems would be solved could good estimates of fishing mortality be made, and then estimates of natural mortality. Hence a rather complex procedure was needed to investigate the causes of failure.

During the 1950s a number of natural changes pattern of r-ecruitment and in stock quantity. As in the distribution of fisheries have taken place. work of elucidating the causes difficult.

The terms of reference for the Working Group were:

That, in view of the serious state of many of the North Sea herring fisheries, a Working Group should be set up to meet for 6 days in Copenhagen at a suitable date, to make a detailed appraisal of all existing data on stock separation and identity for the North Sea herring populations and on the effects of fishing on these herring stocks. The findings should be reported to the Herring Committee at its annual meeting in 1961. All countries with herring fisheries in the North Sea should be invited to send participants to the meeting. Dr. D. H. Cushing has been nominated as Convenor for this Group. 

The North Sea Herring Working Group met in Copenhagen {24-30 April 1961), Hamburg {30 April-5 May 1962), Copenhagen {30 September 1962) and Ijmuiden {28-29 March 1963).

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