Potential impacts of the restoration of coastal and estuarine nurseries on the stock dynamics of fisheries species

Coastal and estuarine (CE) areas are essential fish habitats; they act as nurseries for a large proportion of species of fisheries interest but face high levels of cumulative anthropogenic pressures. A comprehensive analysis of the impacts of CE nursery habitat degradation at the population scale for exploited fish species is still lacking. Our study aims to assess the effects of CE nursery habitat restoration for four species of main fisheries of interest in the Eastern English Channel (EEC): sole (Solea solea), plaice (Pleuronectes platessa), whiting (Merlangius merlangus) and seabass (Dicentrarchus labrax). A generic age- and stage-based population model representing the dynamics of exploited populations and integrating the dependence of recruitment on juvenile habitats was used. This model allowed us to evaluate the combined effect of nursery degradation and fishing pressure on stock dynamics. The model was parameterized for each of the four species based on stock assessment outputs in the EEC and literature and then used to simulate equilibrium states under different habitat restoration scenarios. These scenarios were built using previous estimates of both surface area loss and decrease in marine juvenile fish density in CE habitats facing anthropogenic pressures in the EEC. Surface area and quality restoration enhanced both biomass and sustainable catch levels for the four species in the EEC. The species with higher concentrations in shallow nursery areas were the most sensitive to habitat restoration. The response also depended on life history traits, i.e., species with lower resilience to fishing pressure (i.e., steepness) exhibited a stronger response to habitat quality scenarios.