Population characteristics and environmental interactions of the king scallop fishery in the English Channel

Scallops are currently the 3rd most valuable species in UK fisheries, with a first sale value of over £60 million per annum. Scallops are a non-quota species and landings have more than doubled in the last eight years. Forty percent of king scallop (Pecten maximus) landings into the UK originate from the English Channel. Despite the economic importance of this fishery there has never been a full stock assessment of scallops in English waters and there is a general paucity of scientific data for stocks in the English Channel. Existing management measures are not aligned with the biological structure of the stock, or based on robust science. The aims of the study were to provide data to assess the sustainability of the king scallop fishery through identifying the maximum spatial extent and distribution of fishing effort in the English Channel and defining scallop population structure by the degree of larval connectivity between spatially segregated scallop beds. The environmental impacts of the dredge fishery were investigated through quantifying bycatch and the impact of the dredge fishery on the habitats and communities present across scallop fishing grounds. The activity and spatial extent of the inshore and offshore scallop fleets indicated that although scallop fishing has occurred across a large proportion of the English Channel, fishing behaviour is sporadic and is concentrated in areas that are characterised by consistent scallop abundance. Economic and legislative drivers have altered historical fishing patterns in recent years. The patchiness of fishing behaviour, coupled with the nomadic nature of the fleet suggest that closure of areas that are infrequently fished could provide ecosystem benefits and potential benefits for the wider fishery while having minimal impact on fleet behaviour. Despite the well documented environmental impacts of scallop dredges, it is important to understand the environmental context in which fishing occurs as well as the predicted recovery timescales for benthic communities. Within the context of the English Channel king scallop fishery, species diversity and benthic community composition are constrained primarily by natural physical disturbance. It was not possible to detect community level response to a gradient of scallop fishing intensity against a background of environmental forcing. This could be due to historical fishing activity (40+ years) that may have changed the community to a stable altered state that continues to reflect the background environmental gradient across the English Channel. Bycatch in the English Channel was low compared to other towed mobile fishing gears and compared to other scallop dredge fisheries in the UK. Bycatch composition varied over local and broad spatial scales. The fishery affected a limited number of bycatch species of ecological importance and low biomass of such species were present, indicating that the population impacts of the dredge fishery on these species are likely to be minimal. Discards of commercial species also varied significantly with location and were higher in the eastern English Channel. Three reproductively distinct populations of scallops have been identified in the English Channel, indicating the largest appropriate management units. Large scale oceanographic currents maintain larval connectivity across much of the English side of the Channel; however complex hydrodynamic processes within Falmouth Bay suggest that larval dispersal is prevented at localised spatial scales in this location. The population in the Baie de Seine is reproductively isolated from the eastern English Channel, however larvae may disperse west, to the Baie St Brieuc and southern Cornwall, via residual currents. Improving the management, sustainability and public perception of the English Channel king scallop dredge fishery is a priority for the UK scallop industry. This thesis addresses fundamental gaps in the scientific data to inform future management and the sustainable exploitation of the fishery.