Do static and dynamic marine protected areas that restrict pelagic fishing achieve ecological objectives?

There has been a recent proliferation of large-scale marine protected areas (MPAs) containing pelagic habitats. These contribute substantially towards meeting the area-based goal of Aichi Biodiversity Target 11 and contribute to managing pelagic ecosystem pressures, including fishing. We assessed theoretical and empirical evidence on whether static and dynamic spatial management of pelagic fisheries have achieved ecological objectives. Exceptionally few studies have assessed ecological responses to MPAs that constrain pelagic fisheries, leaving substantial uncertainty over their efficacy. Assessments have provided a limited basis for causal inferences, and have not evaluated whether other management tools would be more effective. Pelagic MPAs have relatively high promise to mitigate fisheries bycatch of species of conservation concern at temporally and spatially predictable hotspots and, for some species, to protect habitats important for critical life history stages. MPAs have limited capacity to contribute to maintaining absolute biomass levels of pelagic stocks and populations near targets and above limits because MPAs would need to be extensive to account for broad and temporally and spatially variable distributions, and be designed to account for catch risk outside of the MPA, including from displaced fishing effort and fishing-the-line. For non-overexploited stocks, which is the status for most target pelagic species and their prey, there would likely be little response in absolute stock biomass to an MPA. Reducing fishing mortality of prey species might not affect the biomass of their pelagic predators because prey species experience light fishing pressure and because there may be a weak correlation between the absolute abundance of forage fish and their predators. There is a limited basis for predicting the effects of MPAs on fisheries-induced evolution (FIE) in pelagic species. We describe how pelagic MPAs could be designed to achieve five ecological objectives while avoiding causing cross-taxa conflicts and exacerbating FIE. To fill substantial gaps in knowledge, we prescribe counterfactual-based modeling of time series data of standardized catch records to infer causation in assessments of ecological responses to pelagic MPAs.