Marine reserve design criteria and measures of success: Lessons learned from the Exuma Cays Land and Sea Park, Bahamas

Among the many potential benefits of no-take marine reserves, three importa nt postulated effects are (1) to supply biomass of harvestable individuals to fished areas through emigration; (2) to increase spawning-stock biomass, which subsequently magnifies larval recruitment; and (3) to restore more n atural size-frequency distributions of the protected populations, specifica lly to enhance the larger size classes, which may affect sex ratios and rep roductive output. The Exuma Gays Land and Sea Park (ECLSP), covering 442 km (2) in the central Bahamas, was established in 1958 and closed to fishing i n 1986, making it one of the first acid largest marine reserves or 'no-take ' zones in the western Atlantic. The ECLSP is ideally situated between smal l-scale developments in the northern and southern Exuma Gays and encompasse s a diversity of contiguous shallow-water habitats from the Great Bahama Ba nk to the eastern platform margin in Exuma Sound. Scientific investigations during the past decade have compared queen conch, spiny lobster, and group er resources in the ECLSP to those in adjacent fished areas and have demons trated greater species diversity, density, biomass, potential reproductive output, and larval densities for these species. The lack of historical data limits determination of whether closure to fishing has resulted in increas es in these attributes over time, but available data strongly support the c ontention that the ECLSP has significantly greater spawning-stock biomass o f various organisms because of protection from fishing. Although evidence i s strong that the ECLSP is an important source of larvae to adjacent areas in the Exuma Sound ecosystem, few data show adult emigration to fished area s. Some target species outside the reserve may have declined, and because t he ECLSP probably depends on larval transport from upcurrent areas, awarene ss is growing that this reserve will not be successful in isolation. Experi ences in the ECLSP suggest that marine reserves will be most successful if they contain contiguous habitats from bank to deeper shelf (>30 m) environm ents, minimize threats such as coastal development, and provide protection of unique features such as spawning aggregations.