BEHAVIOR, TRANSPORT AND RECRUITMENT OF BAY OF BISCAY SOLE (SOLEA-SOLEA) - LABORATORY AND FIELD STUDIES

This article is a comparison and a synthesis of laboratory and field studies focused on the influence of larval and early juvenile behaviour on the recruitment mechanisms of sole in the northern part of the Bay of Biscay. Laboratory studies concerned the individual behaviour of larvae and juveniles, in particular, changes in swimming activity controlled by endogenous factors and also reactions to light, current, pressure and feeding conditions. Experiments were performed in different types of tanks fitted with special devices to vary light, pressure and current. Specific methods using visual observations and an infra-red converter as well as actographic techniques with infra-red barriers were utilized. The relative contribution of endogenous and external factors on swimming activity and orientation vary during ontogenesis. Field studies concern a time series of fine-scale vertical distribution of larval stages. Endogenous rhythms and Light seem to play an important role in the control of diel vertical migration from early larval stages, whereas semi-diurnal and tidal behaviour could develop mainly after metamorphosis. A simulation is used for the study of the interactions between individual behaviour and tidal currents. Based on laboratory and field observations we propose and discuss a hypothesis of transport and migration. In the Bay of Biscay, such a hypothesis involves diffusion processes enhanced by active behaviour.