The common sole -Solea solea- is one of the most harvested flatfish population in the Eastern English Channel -EEC; ICES area VIId-. In the EEC, this population is currently assessed and managed as a homogeneous single stock. However, some ecological clues indicate that a metapopulation structure formed by a set of three loosely connected subpopulations associated with local coastal nurseries areas cannot be ruled out. Results show that key estimates of population dynamics parameters, stock assessment and management reference points are highly sensitive to the hypotheses made on the spatial structure.

A Bayesian integrated life-cycle model was developed to explore the sensitivity of population dynamics and stock assessment to the level of connectivity in the metapopulation structure, by considering a gradient of connectivity between: -i the current ICES hypothesis where all coastal nurseries contribute to one single homogeneous well mixed population and -ii a metapopulation structure with three loosely connected subpopulations and their associated coastal nurseries. While assessment obtained when hypothesizing a single spatially homogeneous population indicates catches near MSY, considering a metapopulation structure with three subpopulations revealed contrasted status, with two subpopulations being exploited above MSY and one below MSY.

A preliminary analysis of existing mark-recapture data supports the idea of a low connectivity within the EEC. We analyzed an extensive mark-recapture dataset of more than 40,000 fish tagged by CEFAS in the English Channel and the North Sea  between 1955 and 2007 to evaluate the connectivity induced by the movement of adults fish between the three potential subpopulations in the EEC, and with nearby areas. Results revealed very low connectivity between subpopulations in the EEC, and low movement of fish between the EEC and the North Sea.

Ongoing development within the SMAC project include additional tag-recapture experiments and the development of a tag-integrated life cycle model designed to simultaneously estimate fish connectivity, populations dynamics and stock assessment. Preliminary results on simulated data reveal that a moderate number of recaptured fish should provide enough information, in both quality and quantity, to reliably estimate metapopulation dynamics, and assess the consequence of the metapopulation structure on stock assessment.