ROLE OF MARINE RESERVES IN RECRUITMENT TO REEF FISHERIES - A METAPOPULATION MODEL

While marine reserves can replenish local populations of reef fishes exploited by fishermen through enhanced survivorship of post-recruitment fishes, the manner in which reserves enhance larger-scale recruitment to fish stocks is poorly understood. We investigate a metapopulation model to see how marine reserves might help to conserve such populations and benefit fisheries. The model defines two kinds of patches: (i) those open to fishing and (ii) those maintained as reserves free from exploitation. Each patch may occur in one of two states according to whether or not it contains fishes recruited to the fishery. It is shown that reserves become highly beneficial as the local extinction rate caused by fishing becomes large because they provide a source of recruitment into fished-out patches. In such circumstances, the introduction of reserves meets the needs both of conservation and of sustainable exploitation of the fishery. The abundance of the exploitable population is maximized when half of all patches (reserves + exploited patches) are occupied by the stock. The sustainable yield is also maximized when half of all patches are occupied, assuming that yield is proportional to the local extinction rate. This result could provide a rule of thumb for fishery managers addressing the specific question of enhancing recruitment in heavily deleted stocks of certain reef fisheries. However, like other metapopulation models, the one here makes some important simplifying assumptions which would need to be addressed in the application of these results to specific fisheries.