Spillover from marine reserves related to mechanisms of population regulation

Spillover of fish from marine reserves to adjacent harvested waters may be mediated by density-independent movement, density-dependent movement, or both. If dispersal is by random movement, populations within the reserve must be regulated by density-dependent population growth (DDG). Density-dependent movement (DDM) can also regulate the population if accelerated emigration from a reserve to the surrounding fishing grounds leads to substantially increased mortality. Using spatially explicit models, we show that stock per unit area is bounded for DDG and increases with size for DDM. With DDG, spillover rate per unit area of reserve is maximized with reserves around 50% larger in linear dimension than the minimum size for population persistence. With DDM, spillover per unit area of reserve increases with reserve size. The results highlight the need for the mechanism of population regulation to be incorporated into theoretical and empirical investigations of marine reserve ecology.