Fishing effort displacement drives ecosystem impacts within and beyond marine protected areas

Abstract

Anthropogenic pressures associated with fishing activities, although highly regulated, are deleterious to the natural functioning of marine ecosystems. The establishment of Marine Protected Areas (MPAs) is often used as a strategy to alleviate pressures faced by vulnerable species and habitats. Current approaches overlook the interconnectedness of species in the wider ecosystem context, governed by food web dynamic processes. There is a growing recognition of the importance of adopting Ecosystem-Based Fisheries Management (EBFM) strategies to ensure the resilience and sustainability of marine ecosystems. Our research utilises a North Sea food web model to test MPA designations in the context of potential changes to the distribution of bottom trawl fishing effort. We investigate three different fishing scenarios and consider, not only the impacts on target species, but also the effects that emerge from food web dynamic interactions at the ecosystem level. Our findings show that reducing bottom trawl fishing effort generally leads to increased biomass and greater typical length, particularly inside and adjacent to MPAs. Impacts extend beyond just target species with indirect effects observed for pelagic species, driven by cascading food web interactions. Protected, Endangered, and Threatened (PET) species responses to MPA implementation are limited but remain positive. From a fisheries perspective, total catch is maximised when fishing effort is proportionally redistributed across active fishing grounds rather than concentrated at MPA boundaries. At the ecosystem level, reduced fishing effort is associated with an increase in community mean mature trophic level and a flattening of the size-spectra slope. Collectively, our findings highlight that while fishing effort management can deliver ecological benefits, spatial closures alone may be insufficient if effort is merely redistributed rather than reduced.