An age-structured model showing the benefits of marine reserves in controlling overexploitation

Abstract

Previous modelling of areas closed to fishing (marine reserves) has generally employed non-dynamic models and has not included biological factors such as stock–recruitment and weight–fecundity relations. These models predicted that a marine reserve would result in a decrease in fishery yield, an increase in spawning biomass and that movements of fish across the reserve boundaries could reduce its benefits. We utilised an age-structured model based on an Atlantic cod population that included more realistic reproductive factors. We compared a Reserve regime that contained a reserve with a No-reserve regime in which the usual fishery management tools were used. As exploitation rate increased, the relative recruitment and spawners biomass decreased in the No-reserve regime. Larger reserves resulted in more robust recruitment and biomass of spawners. At low exploitation rates, marine reserves resulted in smaller yields. However, when the exploitation rate was larger than the rate which gives the maximum sustainable yield, the biomass of female spawners was maintained at a higher level in the Reserve regime and hence the yield did not collapse. Faster rate of movement of fish decreased these advantages, but the higher spawners biomass and level of recruitment still provided advantages for the Reserve regime. Moreover, even for highly mobile fish, our model suggests that a fish stock protected with a marine reserve would be more resilient to exploitation than when managed without. However, a model realistic spatially and temporally would be necessary to assess the usefulness of marine reserves to prevent overexploitation of migrating fish.