The role of marine reserves in optimal harvesting when fishing damages habitat

Background/Question/Methods   Analyses of spatial fishery models have established (at least in theory) that in order to maximize sustainable profit it may be necessary to permanently close areas to fishing.  In these cases, the conservation benefits that accrue within marine reserves are not necessarily in conflict with profit maximization. A limitation of this result is that the models used to derive it ignore one potentially important side-effect of harvesting: the habitat damage caused by intensive fishing. We have constructed and analyzed a spatially explicit bioeconomic model that incorporates detrimental habitat effects. In our model, fishing effort not only reduces the standing stock, but also diminishes fish reproductive rates and/or increases natural mortality. In our analysis, we take the viewpoint of a sole owner with jurisdiction over the entire habitat.  The owner distributes fishing effort to maximize profits – that is, to balance revenue from catch biomass with the cost of fishing. We assume that sustainable profit is the goal, and thus we calculate this effort distribution at equilibrium.

Results/Conclusions   Our analyses reveal that marine reserves may emerge as part of an economically optimal fishery management strategy when we account for the habitat effects of fishing.  The number of reserves, their size and their placement depend sensitively upon the magnitude and parameterization of the habitat effect.  In some cases (for example, when fishing costs are high) reserves only become economically viable when a habitat effect is introduced. Our results show that the biology of a particular fish species (i.e. its birth, survival, and dispersal rates), the mechanisms through which fishing effort affects that biology, and the costs of fishing all interact to determine the economic efficiency of marine reserves.