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Although marine protected areas (MPAs) are increasingly considered an essential part of the ecosystembased approach to management (EBM), most modelling studies of MPAs to date have been based on single-species models. Given the desire to rapidly establish MPAs under international and regional treaties and conventions, and the role MPAs play as part of EBM, it is desirable to extend analyses to encompass the wider ecological and socio-economic effects of MPA establishment. To this end, this report examines the predicted effects of selected existing and proposed MPAs on fisheries, biodiversity and ecosystem structure using Ecospace spatial ecosystem models developed for five different large-scale continental shelf regions: the Campeche Bank (Gulf of Mexico), East China Sea, North Sea, Northern Benguela Current (Namibia) and the Northern Gulf of California. Three MPAs were examined in each system. In some instances, the introduction of an MPA simultaneously led to fishery and ecosystem benefits. The introduction of the Inshore Closed Line and Summer Closure in the East China Sea led to increases in both total yield and average longevity of animals in the system (a proxy for size). However, there was no consistent response to MPA establishment. Only two of the eight fisheries MPAs established to enhance specific target species were predicted to lead to an increase in biomass and yield of the focal species. In some instances, establishing a fisheries MPA led to a reduction in both overall yield and focal species yield. The simulated MPAs had similarly mixed effects for biodiversity conservation. The combined Biosphere Reserve and Vaquita Conservation Refuge in the northern Gulf of California, established for protection of the vaquita (Phocoena sinus), led to a 46% increase in vaquita biomass over a 20-year period compared to an equivalent simulation run without the MPA. In this instance, the MPA was predicted to be successful in providing significant protection for the focal conservation species; however, this came at the cost of a 40% reduction in total yield. The examination of the effects of MPA establishment on biodiversity and ecosystem structure led to mixed results; for the indices measured, there is no direction of change in the values of the indices that can be consistently taken to indicate that the system was moving to a less impacted state. However, for the sake of this report, we assumed that the direction of change of the biodiversity or ecosystem metrics within an MPA, as a result of the MPA, was the ‘correct’ direction of change in each metric for that system. Comparison of the direction of change of the ecosystem and biodiversity metrics within an MPA and across the whole system indicated that the benefits that accrue within an MPA can come at the cost of a general decline in ecosystem structure and biodiversity averaged across the whole system when the effects of effort redistribution are accounted for. In addition to trade-offs between fishery and conservation concerns associated with MPAs, the simulations revealed that MPAs can lead to trade-offs between sectors within a fishery. In simulations that led to an increase in total yield, in no case did all sectors of the fishery benefit from the MPA, and in many instances, some sectors lost out as a result of the MPA. Conversely, where an MPA led to an overall reduction in yield, in no cases did all sectors of the fishery suffer, and in some instances, some sectors ben

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