Designing a Dry Tortugas Ecological Reserve: How big is big enough? …to do what?

A review of the global experience with no-take marine reserves strongly suggests that they are important tools for marine conservation and fishery management, capable of providing benefits in the form of ecosystem protection, improved fishery yields, expanded understanding of marine systems, and improved nonconsumptive opportunities. The degree to which a reserve will provide certain benefits or achieve specific goals will vary with species, depending on life-history characteristics and various aspects of reserve design. The Florida Keys National Marine Sanctuary management plan created a network of no-take reserves encompassing just 0.5% of the sanctuary's total area but provided for the creation of a Dry Tortugas Ecological Reserve, an additional marine reserve in and adjacent to the Dry Tortugas region of the sanctuary. The existing reserves are small because they were intended to provide only limited fishery benefits, but additional fishery benefits are being considered among the objectives of a Dry Tortugas reserve. How big must such a reserve be to provide specific benefits, and how can one predict this size without having one? We use a simple model based on the percent of virgin biomass (%B₀) in fished and unfished areas to provide managers with a quick and easy way of estimating the reserve size required to meet specific management objectives. Analyses of %B₀ for populations in fished and reserve areas suggests that a Dry Tortugas reserve encompassing at least 30–40% of the region is required to elevate all stocks from current levels to overfishing-threshold %B₀ levels, but smaller reserves might be used to complement conventional fisheries-management practices as a buffer against some level of overfishing and insurance against complete stock collapse.