Southern California MPAs Benefit Targeted Fish Species

Photo © Sean C. Figueroa

Photo © Sean C. Figueroa

When you think about southern California, palm trees, sandy beaches and that pesky LA traffic probably comes to mind. But if you enjoy fishing or diving, the waters of southern California call to mind majestic kelp forests filled with fish, crabs, and curious sea lions. As part of the statewide MPA network, MPAs now dot the waters offshore of southern California. In the fall of 1997 and 1998, a group of scientists set out to determine just how well the fishes that inhabit these temperate rocky reefs were responding to protection within 5 no-take southern California MPAs: 3 on the Catalina Islands and 2 on the nearby mainland.

Using SCUBA, these researchers counted the number and estimated the size of the fish they encountered during several months of underwater surveys, ultimately identifying 28 species and recording data on over 80,000 individuals. They used this information to determine the density, biomass (the total amount of fish by weight) and fecundity (the number of potential offspring) at multiple locations inside these MPAs as well as in nearby fished waters.

These reserves are greatly benefiting fish, particularly those highly prized by southern California fishers. Inside the reserves, the most popular targeted species were much higher in abundance. In addition, the largest individuals were only found inside of reserves. With larger and more fish inside the reserve, the biomass or total amount of targeted fish was more than two-thirds greater inside the reserves. Kelp bass, a popular species, was almost 10 times higher inside the reserve, and legal-sized biomass was over 27 times higher. These findings suggest that the protected areas are providing a safe haven for fish to reach maturity, translating into higher reproductive output. The reproductive potential inside the reserves was much higher than outside for most target species, suggesting that protected stocks inside the reserves could re-seed exploited stocks outside the reserves through the export of young fishes.
Understanding the impact of these reserves on targeted species is important, but the scientists also wanted to see how reserves affect associated species that aren’t directly targeted by fishers. The responses of these non-targeted species were mixed, and the positive effects on biomass and fecundity were nowhere near as high as those for targeted species. While southern California reserves provide important benefits for targeted species such as kelp bass, barred sand bass, and sheepshead, they provide fewer benefits for non-targeted species.

For more information: Tretault, I. and R. F. Ambrose. 2007. Marine reserves enhance targeted but not untargeted fishes in multiple no-take MPAs. Ecological Applications 17(8): 2251-2267.