The effects of Marine Protected Areas on densities and movement patterns of rocky reef fish in Southern California

No-take Marine Protected Areas (MPAs) are relatively new tools to protect marine ecosystems from the detrimental effects of fishing, yet rigorous empirical studies of MPA effects are lacking. This dissertation contains three studies that address pressing questions asked by stakeholders, scientists, managers, and decision makers facing difficult choices between long-term ecosystem protection and possible socioeconomic hardships resulting from area closures (Scholz et al. 2004). The first study examined MPA effects by comparing fish populations inside five MPAs to similar harvested areas. I found large increases in density, size, biomass, and egg production for fishery-target species within MPAs. MPAs averaged 580% more legal-sized fish, the largest sizes existed only inside MPAs, and biomass was 1,000% higher. The degree of response to MPA protection was related to harvest level, with non-harvested species showing no consistent difference between MPAs and control sites. Because responses were consistent across five sites, MPAs in similar habitat in the Southern California Bight are likely to produce similar results. The second study investigated the predicted fishery benefit of spillover of harvestable fish from MPAs to adjacent waters. I tagged and followed movements of over 300 California sheephead ( Semicossyphus pulcher) inside and adjacent to a no-take MPA on Santa Catalina Island. Densities and dispersal rates (mechanisms driving spillover) were higher inside the MPA, and emigration out of the MPA was higher (0.67%) than immigration into it (0.59%). However, the low sample sizes suggest that results should be interpreted cautiously. I also found distinct groups of resident and dispersive sheephead, suggesting that the more mobile group at the Catalina MPA may meet a fishery goal of spillover, and the more resident group meets conservation goals. Finally, I examined an indirect MPA effect by investigating whether increased densities of predatory adult fish negatively impacted young prey conspecifics. Adult kelp bass (Paralabrax clathratus ) are the primary predator on young conspecifics at the Catalina site. I found that the increased adult densities inside the MPA negatively impacted kelp bass recruitment and densities of 1-2 year-olds. The strongest negative effects were among the youngest kelp bass inside the MPA. Overall, this dissertation helps fill important gaps in MPA science.