Optimized Predator‐Prey and MPA Based Fishing Strategies for the Baltic Sea

ABSTRACT Marine protected areas (MPAs) have become the de‐facto mechanism for marine species conservation and management and the ecological benefits of no take zones (NTZs) are supported by an expanding scientific interest in their effectiveness. However, in the south‐western Baltic region there is a paucity of studies on the validity of MPAs, possibly due to the lack of enforcement. In this work we investigate the effects of nonconstant harvesting of a resource simultaneously under predation pressure. We use a functional response of the predator dependent Crowley‐Martin type in age‐structured state equations of a fixed time‐horizon optimal control problem, wherein a pre‐existing MPA may be encountered. Where available, only peer‐reviewed data and biomass stock levels are used for biological parameters in the state equations. Our results for the prey component of the model show that a moderate penalty exists that yields the same benefits as a fully closed reserve. However, taking into account the whole system we observe that an NTZ benefits the predator species too.