Size structure of gray snapper (Lutjanus griseus) within a mangrove 'no-take' sanctuary

The establishment of marine reserves has been offered as an important fishery-management tool to complement the more traditional methods of size and bag limits, gear restrictions, closed seasons, and limitations on the number of fishers. In several parts of the world, 'no-take' zones, areas where fishing is forbidden, have been shown to benefit exploited populations, critical habitats, and community structure (see studies listed in NRC, 1999). Because fishing and bycatch mortality are all but eliminated in no-take areas, fish within these zones should live longer, grow larger, and be more fecund than those in fished areas (PDT, 1990; Bohnsack, 1993). Despite these expected benefits, the creation of marine protected areas in U.S. waters is relatively new, and where they have been established, they have been small in scale (Ogden, 1997; Murray et al., 1999). Consequently, there are few examples of no-take zones in the U.S. that can be used to evaluate their true benefits for exploited marine species. While the scientific community has largely embraced the use of marine reserves in fisheries management, detractors, mostly sport fishermen, continue to point to the lack of evidence that expected benefits will actually materialize (Law, 1996; Parrish, 1999; Lydecker, 2000; Wickstrom, 2000a,b). Size-distribution data can be a useful tool to assess the effectiveness of no-take reserves. The shape of length-frequency distributions is a result of recruitment, growth, mortality, and sampling (MacDonald, 1987). If sampling bias is comparable, a species' length-frequency distribution from different areas can yield important biological information specific to a given location. Since fishing mortality is selective towards larger fish and will be greater in fished areas than no-take zones, areas free of fishing mortality would be expected to contain more large individuals. Here, we report length-frequency patterns observed from an ongoing study designed to examine fish utilization of red mangrove (Rhizophora mangle) shorelines in southeastern Florida. In this effort, differences in the size structure of gray snapper (Lutjanus griseus), a species that is considered overexploited in this region (Ault et al., 1998), were revealed between an area closed to fishing and in surrounding waters open to recreational fishing.