Fish mobility affects the distribution of commercially caught fish species in marine protected areas (MPAs) and fishing grounds (FGs). Previous theoretical findings predicted that highly mobile fish would benefit little if at all from protection in MPAs. However, these predictions conflict with empirical evidence showing that more mobile commercial fish respond at least as well to protection as less mobile commercial fish. We analyze two single species biased movement models and identify necessary and sufficient conditions for the models to agree with the qualitative observation that an increase in mobility corresponds to an increase in the relative abundance of the fish population in MPAs as compared to the population in FGs. This work was done with Dr. Thomann and Dr. DeLeenheer.