Modelling larval dispersal of Pecten maximus in the English Channel: a tool for the spatial management of the stocks

The great scallop Pecten maximus supports one of the most important and valuable commercial fisheries around the British Isles and in the northwest of France, but the resource is mainly managed at the scale of each local fishing ground through a combination of European, national and local measures. To analyse the larval dispersal pathways and connectivity patterns among fishing grounds of the great scallop in the Celtic Sea and the English Channel, a particle tracking model was developed. The model combined a 3D physical circulation model that simulated currents and temperature fields and a scallop larval submodel that took into account a temperature-dependent planktonic larval duration and an active vertical swimming behaviour. Due to the lack of stock assessment at the regional scale, the location of the main fishing grounds was established by combining different sources (e.g. grey literature, unpublished scientific surveys, vessel monitoring data, fishermen) while the spawning biomass of each stock was estimated from landings data. Results indicated that each local stock could not be considered as a single independent management unit and that all stocks except that of the Bay of Brest were connected to neighbouring stocks, suggesting that the management should be defined in a metapopulation context. Three major groups of strongly interconnected stocks including two or three stocks exhibiting high retention and self-recruitment rates and some peripheral stocks with a low self-recruitment rate were defined: the North Brittany and Channel Islands, the eastern English Channel, and the SW of England. Our results were discussed in terms of the definition of management units in comparison with genetic and phenotypic data, and in terms of resource management in a transnational context.