The plaice of the English Channel: spawning and migration

Abstract

The spawning of plaice in the English Channel was studied by means of plankton surveys carried out during the winters of 1970–71 and 1971–72. Spawning occurred over a wide area of the Channel between the Straits of Dover and 4°W. In 1970–71 the total egg production was at least 4.15 x 10¹² fertilized eggs and equalled the level of egg production in the Southern Bight of the North Sea. Between 75 and 85 % of the eggs were spawned in the eastern Channel.

Tagging experiments carried out on the spawning fish showed that approximately 56% of the Channel spawners migrated to the southern North Sea after spawning. The remainder stayed within the English Channel.

The number of female plaice which spawned in the Channel in 1970–71, as estimated from the results of the plankton surveys, the tagging experiments and fecundity data, was between 30.7 and 47.3 million fish.

The drift of the spawning products is discussed in relation to the known nursery areas for plaice. It is suggested that, under normal wind conditions, a high proportion of the Channel progeny would be swept through the Straits of Dover to nursery grounds in the Thames estuary and on the coasts of Belgium and the Netherlands.