Role of a Military Restricted Area in Protection of Fish and Invertebrate Communities at San Clemente Island, California

Michael Esgro, California State University, Monterey Bay


"De facto" marine protected areas (DFMPAs) are regions of the ocean that are not formal marine protected areas (MPAs), but experience limited human impact nonetheless. Although DFMPAs are widespread globally, their potential contributions to marine conservation have not been well studied. In 2012 and 2013, we conducted remotely operated vehicle (ROV) surveys of deepwater (40—200 m) marine communities at a military DFMPA and a fished control site at San Clemente Island, the southernmost of the Channel Islands in the Southern California Bight. We used data extracted from ROV imagery to compare density and biomass of ecologically and economically important focal species between sites, as well as species richness, Shannon-Weaver diversity, and fish community dissimilarity between sites. At the individual species level, DFMPA presence was found to be a significant predictor of increased California Sheephead (Semicossyphus pulcher) abundance, increased California Sheephead biomass, and increased Ocean Whitefish (Caulolatilus princeps) biomass. At the community level, however, DFMPA presence was not found to be a significant predictor of increased species richness or increased Shannon- Weaver diversity, and fish communities were not found to be significantly dissimilar between sites. Our results likely represent the beginning of a trend toward more “pristine” ecological conditions at the DFMPA site, and suggest that DFMPAs can provide conservation benefits similar to those of MPAs. This concept has far-reaching implications for marine spatial planning efforts in California and beyond.