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

Previous modelling of areas closed to fishing (marine reserves) has general ly employed non-dynamic models and has not included biological factors such as stock-recruitment and weight-fecundity relations. These models predicte d that a marine reserve would result in a decrease in fishery yield, an inc rease in spawning biomass and that movements of fish across the reserve bou ndaries could reduce its benefits. We utilised an age-structured model base d on an Atlantic cod population that included more realistic reproductive f actors. We compared a Reserve regime that contained a reserve with a No-res erve regime in which the usual fishery management tools were used. As explo itation rate increased, the relative recruitment and spawners biomass decre ased in the No-reserve regime. Larger reserves resulted in more robust recr uitment 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 fe male spawners was maintained at a higher level in the Reserve regime and he nce the yield did not collapse. Faster rate of movement of fish decreased t hese advantages, but the higher spawners biomass and level of recruitment s till provided advantages for the Reserve regime. Moreover, even for highly mobile fish, our model suggests that a fish stock protected with a marine r eserve would be more resilient to exploitation than when managed without. H owever, a model realistic spatially and temporally would be necessary to as sess the usefulness of marine reserves to prevent overexploitation of migra ting fish. (C) 1999 Elsevier Science B.V. All rights reserved.