The biodiversity benefits of marine protected areas in well-regulated fisheries

There is long-running debate concerning the conservation benefits of marine protected areas (MPAs) in seascapes that are already 'well-regulated' by other forms of fisheries management. Resolving this issue is particularly important given recent calls for expanding MPA coverage. Here, we adapt an influential model from agriculture - the land sparing/sharing framework - to an archetypal managed trawl fishery to determine how catches can be obtained at least cost to biodiversity in such seascapes. This new sea sparing/sharing framework fixes catch across scenarios so that fishing effort displacement is not overlooked. We find that a sparing strategy combining MPAs with fishing effort regulation is best for biodiversity when avoiding the local extinction of sensitive species is a priority. However, if there are no sensitive species, or if biodiversity is instead measured in a way that emphasises species abundances, then a sharing strategy relying on fishing effort regulation alone instead prevails. Extending these findings globally to 'well-regulated' crustacean trawl fisheries, we find that & AP;72% may benefit from no-trawl MPAs (& AP;57-100% depending on the methodology chosen). However, these MPAs could also necessitate increased fishing effort if catches are to be maintained. Our framework thus suggests that whether MPAs increase biodiversity in a well-regulated seascape depends heavily on the presence of highly sensitive species there, as well as conservation and management priorities.

Automated summary

There is ongoing discussion about the effectiveness of marine protected areas (MPAs) in well-regulated seascapes with other forms of fisheries management. This study adapts a model from agriculture to determine how to achieve catches at minimum cost to biodiversity in managed trawl fisheries. The results show that a combination of MPAs and fishing effort regulation is best for biodiversity when avoiding local extinction of sensitive species is a priority. However, if there are no sensitive species or if biodiversity is measured in terms of species abundances, then relying solely on fishing effort regulation is more effective. Evaluating the findings globally, it is estimated that over 72% of well-regulated crustacean trawl fisheries could benefit from no-trawl MPAs, although such MPAs may require increased fishing effort to maintain catches.