A proposal to recover fish stocks: a meta-population, size-differentiated model coupled with currents

Around 70% of fish stocks worldwide are overfished. In European waters, this overfishing has forced EU authorities to drastically reduce fishing effort in European Mediterranean waters and to make changes in fishing gear (e.g. larger mesh sizes, or flying trawl doors). However, the new regulations do not mention the creation of marine reserves as one of the mandatory measures. According to our studies and the scientific literature, the design of a well-designed network of no-take marine reserves is an essential tool for stock recovery, the very measure on which the European Commission places the least emphasis. In order to establish marine protected areas, the ocean currents at a regional scale are a key element that allows us to understand how the planktonic stages drift between spawning to recruitment areas. We take into account a geodesic approach based on satellite observations and also combined with regional high-resolution 3D oceanographic circulation models.

We show that a well-designed network of marine reserves, taking into account variables such as the size of the protected area (which will depend on the target species or species), the spatial design of the network (based on the role of currents as a mechanism for dispersal of larval stages), the biology of the target species, among others. We address the optimisation of stock recovery through a meta-population, spatially-explicit and size-differentiated approach (important when quantifying the reproductive capacity of a population). Sub-stocks within the meta-stock would be connected by Lagrangian advection and current simulations using a combination of Ocean Parcels (https://oceanparcels.org/) and the IBI-MFC model freely available on Copernicus (https://marine.copernicus.eu/about/producers/ibi-mfc). This approach would allow the optimisation of the design of a ‘no take’ space network and help to recover the populations of exploited marine species in a faster and more efficient way.