Print PageMarine protected areas (MPAs) are promoted as a tool to protect overfished stocks and increase fishery yields. Previous models suggested that adult mobility modified effects of MPAs by reducing densities of fish inside reserves but increasing yields (i.e., increasing densities outside of MPAs). Empirical studies contradicted this prediction: as mobility increased, the relative density of fishes inside MPAs (relative to outside) increased. We hypothesized that this disparity between theoretical and empirical results was the result of differential movement of fish inside vs. outside the MPA. We therefore developed a model with unequal and discontinuous diffusion, and analyzed its steady state and stability. We determined the Abundance in the Fishing Grounds, the Yield, the Total Abundance and the Log Ratio at steady-state and examined their response to adult mobility (while keeping the relative inequity in the diffusion constant).
Results/Conclusions
Abundance in the Fishing Grounds and Yield increased, while Total Abundance and Log-Ratio decreased, as mobility increased. These results were all qualitatively consistent with previous models assuming uniform diffusivity. Thus, the mismatch between empirical and theoretical results must result from other processes or other forms of differential movement.
