Extending full protection inside existing marine protected areas, or reducing fishing effort outside, can reconcile conservation and fisheries goals

Most fish stocks world-wide are fished at maximum sustainable yield (MSY) or overfished, as many fisheries management strategies have failed to achieve sustainable fishing. Identifying effective fisheries management strategies has now become urgent. Here, we developed a spatially explicit metapopulation model accounting for population connectivity in the north-western Mediterranean Sea, and parameterized it for three ecologically and economically important coastal fish species: the white seabream Diplodus sargus, the two-banded seabream Diplodus vulgaris and the dusky grouper Epinephelus marginatus. We used the model to assess how stock biomass and catches respond to changes in fishing mortality rate (F) and in the size of fully protected areas within the existing system of multiple-use marine protected areas (MPAs). For each species, we estimated MSY and the corresponding values of stock biomass (BMSY) and fishing mortality rate (FMSY), providing crucial reference points for the assessment of fisheries management. Diplodus sargus is currently in low overfishing, while D. vulgaris and E. marginatus are in high overfishing. Stock recovery to BMSY for the last two species requires a reduction of current F around 50%. This would guarantee an increase in both stock biomass (around 50% and 75% for D. vulgaris and E. marginatus respectively) and catch (around 15% and 30%) after a transient time of ~15–30 years. Alternatively, doubling the size of fully protected areas over fishable areas within the existing network of MPAs would lead to positive conservation effects for all three species without substantially affecting the overall productivity of the fishery and the total economic value of the catch. Synthesis and applications. We provide the first assessment of stock status for three coastal species in the north-western Mediterranean and evaluate the ecological and fisheries outcomes of different management strategies. Extending full protection inside existing multiple-use marine protected areas or reducing fishing effort outside can deliver both conservation and fisheries benefits.