MOVEMENT OF SOLE (SOLEA-SOLEA) IN THE BAY OF BISCAY - COASTAL ENVIRONMENT AND SPAWNING MIGRATION

During the studies on sole recruitment in the Bay of Biscay, transport process attracted considerable attention and led to important researc h on migration and dispersal. The last step to complete the study of t he spatial component of the Life cycle of sole in the northern part of the Bay of Biscay is the offshore migration of young adults towards t he spawning grounds. The present study deals with this pre-spawning mi gration. The main question concerns the kind of linkage between nurser ies and spawning grounds. The principal results are based on extensive tagging experiments carried out in autumn 1992 in two distinct nurser y grounds, Bay of Vilaine and Pertuis (4620 soles of 2-group and older ). One year later (January 1994) catches of tagged individuals reached 18.1% and 11.9% of the initial samples, respectively. From September to February a 50-km net displacement of the centre of the population w as observed towards the offshore deeper area. A small. trend to move o nshore appeared in spring. In parallel with these net movements indivi duals were dispersed around the centre of gravity of the population. T his dispersion was higher in a direction parallel to the coast. Indivi duals from different nurseries were mixed over the same spawning areas of the Bay of Biscay, and some individuals were also captured in and close to the English Channel. Changes in distribution were in phase wi th environmental changes and some elements concerning topographic pref erences also appeared. Some evidence for orientation was observed but random dispersal seemed more important. No particular link between a g iven nursery and a spawning ground in the vicinity appeared. This obse rvation suggests that the behaviour of the Bay of Biscay sole stock co nsidered as a whole, depends on the dynamics of individual nurseries a nd on the rate of exchanges between nurseries.