Fish harvesting, marine reserves, and distribution of individuals over space

Abstract

We analysed exploitation of populations that are partly protected in a marine harvest refuge to prevent their over-harvesting in the remaining unprotected area. We carried out our analysis by introducing the model of ideal free distribution to the population renewal process. In the model, individuals in the target population are distributed so that per capita resource availability becomes matched in the harvested and non-harvested areas. We show that the yield from the harvest effort is strongly affected by the fraction of area protected from harvesting. The harvest effort maximising the yield depends on the relative size of the protected area. Maximum yield is independent of the size of the protected area unless the fraction is > 0.56. If this value is exceeded, annual yield declines rapidly with increasing protected fraction. However, our major - and somewhat surprising - finding is that protected areas can be established without any loss to commercial harvesting if harvesting follows reproduction and population densities are balanced between harvesting seasons according to resource availability.