Effects of marine protected areas on overfished fishing stocks

The lack of population recovery in collapsed fisheries stocks after fishing bans has been observed in various fishing grounds and species. One of the plausible reasons for this phenomenon is the existence of multiple stable states: Ones the population size of a fisheries resource goes below a critical point, the resource converges to a smaller population state and stays around the state. We investigate recovery effects of marine protected areas on a depleted fishing stock using mathematical model. We consider two fishing policy: (i) Fishing efforts (such as the number of vessels) concentrate as narrowing the fishing ground due to the creation of the MPA; (ii) Fishing efforts in the fishing ground remain the same as before the establishment of the MPA. Our results suggest that a minimum fraction of the MPA in the concerned space could exist to reverse the depression, below which the stock shows no, if any, small recovery. Moreover, the fishing policy (ii) shows better results than that of (i) in our ecological analysis. We conclude that, in multiple stable environments, collapsed fisheries resources could recover by introducing a sufficient fraction of MPAs and managing fishing efforts correctly.