Multidirectional movements of sportfish species between an estuarine no-take zone and surrounding waters of the Indian River Lagoon, Florida

Fishery Bulletin, July, 2004 by Derek M. Tremain, Christopher W. Harnden, Douglas H. Adams

Abstract--We examined movement patterns of sportfish that were tagged in the northern Indian River Lagoon, Florida, between 1990 and 1999 to assess the degree of fish exchange between an estuarine no-take zone (NTZ) and surrounding waters. The tagged fish were from seven species: red drum (Sciaenops ocellatus); black drum (Pogonias cromis); sheepshead (Archosargus probatocephalus); common snook (Centropomus undecimalis); spotted seatrout (Cynoscion nebulosus); bull shark (Carcharhinus leucas); and crevalle jack (Caranx hippos). A total of 403 tagged fish were recaptured during the study period, including 65 individuals that emigrated from the NTZ and 16 individuals that immigrated into the NTZ from surrounding waters of the lagoon. Migration distances between the original tagging location and the sites where emigrating fish were recaptured were from 0 to 150 km, and these migration distances appeared to be influenced by the proximity of the NTZ to spawning areas or other habitats that are important to specific life-history stages of individual species, Fish that immigrated into the NTZ moved distances ranging from approximately 10 to 75 km. Recapture rates for sportfish species that migrated across the NTZ boundary suggested that more individuals may move into the protected habitats than move out. These data demonstrated that although this estuarine no-take reserve can protect species from fishing, it may also serve to extract exploitable individuals from surrounding fisheries; therefore, if the no-take reserve does function to replenish surrounding fisheries, then increased egg production and larva] export may be more important mechanisms of replenishment than the spillover of excess adults from the reserve into fishable areas.

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Fishery reserves or no-take sanctuaries, defined as areas where all fishing activities are prohibited, are increasingly proposed as an additional measure to traditional fishery management practices for protecting fish populations from overexploitation (PDT, 1990; Bohnsack and Ault, 1996). The American Fisheries Society recently issued a policy statement on the protection of marine fish stocks at risk of extinction and supported the development of large marine reserves to protect and rebuild vulnerable populations (Musick et al., 2000). Although reserves have been established primarily in reef or coastal marine habitats, the potential to apply similar management strategies in estuarine systems may also be possible (Johnson et al., 1999; Roberts et al., 2001).

Reserves in estuarine areas may help protect exploitable fishery species. Increases in species' sizes and densities within these reserves may also enhance adjacent fisheries by two separate mechanisms. Johnson et al. (1999) found that an existing estuarine no-take sanctuary on Florida's central east coast protected populations of larger, spawning-age sportfish species. As a result, they suggested that protection of populations in no-take sanctuaries could also lead to the replenishment of surrounding fisheries through increased egg production, larval export, and juvenile recruitment. Additionally, mark-recapture data have demonstrated that large juvenile and adult fishes emigrate from estuarine protected areas to surrounding waters (Bryant et al., 1989; Funicelli et al., 1989; Johnson et al., 1999; Roberts et al., 2001; Stevens and Sulak, 2001) and these data have been used to suggest that spillover of excess adult fish from estuarine reserve areas can directly supplement nearby fisheries. Roberts et al. (2001) concluded that the abundance of International Game Fish Association based on line-class-record catches in the vicinity of the estuarine no-take sanctuary on Florida's east coast resulted indirectly from protection and spillover of large adults to outlying waters.

It has also been suggested that reserves protect areas of undisturbed habitat (PDT, 1990), either by design or through cessation of destructive practices, and reserves are commonly established in areas of pristine, productive, or otherwise important habitats required by the species being protected (e.g., Russ, 1985). Furthermore, studies have shown that protecting fishery species can indirectly change the overall community structure (Cole and Keuskamp, 1998) and, under certain circumstances, can increase primary and secondary productivity (Sala and Zabala, 1996; Babcock et al., 1999). The influence of habitat quality on fish movements in relation to protected areas has not been investigated; however, reserve habitats that offer potential advantages in the form of improved habitat quality (Chapman and Kramer, 1999) or increased food and habitat availability could be expected to attract, or at least retain, individuals that immigrate to the reserves from surrounding unprotected habitats. Reserve areas that attract and retain exploitable individuals from surrounding habitats at higher rates than they replenish the surrounding habitats could be considered to be sinks in terms of their ability to directly supplement adjacent fisheries through spillover of exploitable-size individuals. Fish emigration from reserve habitats and the replenishment of nearby fisheries is a commonly predicted benefit of harvest reserves (see reviews in Roberts and Polunin, 1991, and Rowley, 1994). However, there are currently no studies that simultaneously examine emigration and immigration in relation to estuarine reserves or that document the extent to which reserve areas may also function to withdraw individuals from surrounding fisheries. Without an assessment of net exchange, the interpretation of reserve benefits with respect to replenishment cannot be properly evaluated.