Marine mammal and seabird population changes have contrasting but limited impacts on fisheries catches in the North Sea

Marine mammals and seabirds are high trophic level consumers that impact community dynamics. In the southern North Sea and eastern English Channel, the abundance of marine mammal species has markedly increased since 1990, while seabird abundance has remained stable since the early 2000s. To evaluate the interaction between top predators and fisheries, we developed an ecosystem model (1990–2014) that incorporated changes in predator abundances, fishing mortalities, and fishing effort. As marine mammal populations increased, predation mortality on commercial fish species increased. However, reductions in fishing mortality were the dominant driver of the overall change in total mortality for most commercial stocks. Seabirds had minimal impacts on commercial species, regardless of population trends. Resource overlap was higher among fishing fleets than between fisheries and top predators, suggesting inter-fleet competition, rather than predator foraging, drives competition. Although marine mammal impacts on fish stocks were evident, the overall effects of top predator increases on fisheries were limited, indicating that the restoration of marine mammal populations is not incompatible with optimized fisheries yields when viewed at the ecosystem scale.