Richard M. Starr1, Mark H. Carr2, Jennifer Caselle3, James A. Estes4,
Caroline Pomeroy2, Craig Syms2, David A. VenTresca5, Mary M. Yoklavich6
1University of California Sea Grant Extension Program
2University of California Santa Cruz
3University of California Santa Barbara
4U.S. Geological Survey
5California Department of Fish and Game
6National Marine Fisheries Service
Most evidence for the effects of marine reserves comes from tropical nearshore ecosystems. We attempted to evaluate the effects of marine reserves on temperate kelp forest systems by contrasting the population structure (density and size distribution) of 10 species of epibenthic fishes and several aspects of the associated ecosystems between three marine reserves and adjacent exploited areas in Central California. Densities of fishes were 12-35% greater within the reserves but this difference was not statistically significant. Habitat features explained only 4% of the variation in fish density and did not vary consistently between reserves and nonreserves.
The average length of rockfish (genus Sebastes) was significantly greater in 2 of the 3 reserve sites, as was the proportion of larger fish. Population density and size differences combined to produce substantially greater biomass and therefore reproductive potential per unit of area within the reserves. The magnitude of these effects seems to be influenced by the reserve's age. While our results demonstrate that current levels of fishing pressure influence kelp forest rockfish populations, differences between the reserves and adjacent non-reserves are surprisingly small. We discuss a number of reasons why the influences of fishing on kelp forest ecosystems may be greater, or at least different, than our findings indicate. Potentially confounding influences include the very small size of the reserves, effects of historical fishing, poaching, spillover effects on adult and larval populations from reserve to non-reserve habitats, and the possibility that catastrophic phase shifts induced by human disturbances have altered both reserve and non-reserve areas.