Trophic mechanisms underlying bentho-demersal community recovery in the north-east Atlantic

1. Bottom trawling is considered one of the greatest and most widespread causes of anthropogenic change in shelf seas, with major and prolonged impacts in areas with a long history of exploitation by fisheries such as the North Atlantic. Here, signs of recovery following the enforcement of regulations are increasingly being reported. 2. We examined the extent to which biological diversity and functionality are restored when fishing pressure is reduced by evaluating changes in species biomass and that of the main functional groups present in the continental platform, as obtained from systematic survey (IBTS) results. Moreover, we examined how this recovery is mirrored in the trophic organization of the affected communities by assessing variations in link density and strength of the main consumer species and investigating whether variations in species richness were paralleled by changes in network properties. Finally, we investigated whether reductions in fishing pressure (fishing mortality) were correlated with the abovementioned variations in community and trophic structure of the bentho-demersal assemblages. 3. Our results corroborate the apparent recovery of North Atlantic fishing stocks and further substantiate the improved welfare of the bentho-demersal assemblages of the Southern Bay of Biscay. Specifically, we found an increase in species richness and in the abundance of most functional groups, especially those more closely related to the benthos, following the reduction in fishing mortality. Increases in overall species richness were paralleled by an increase in the number of links and a reduction in mean interaction strength connecting the main consumer species with their prey items. This is in accordance with ecological theory and could explain the mechanism by which bentho-demersal assemblages restructure their trophic network towards more stable organizations. 4. Synthesis and applications. Detecting patterns of recovery or change to alternative stable states following stress release is essential to unravel the effects of perturbations and to design effective management strategies. Our study shows that trophic network properties provide a convincing tool to evaluate and perceive recovery patterns. The trends shown in our study appear to be related with the decline in fishing mortality resulting from the enforcement of fisheries regulations in the area. They substantiate the efficiency of these regulations as a guarantee for an ecosystem approach to fisheries management and advocate their enforcement at a wider level as a convincing measure to preserve the sustainability of marine resources and their welfare.