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

Two potential limitations must be considered when comparing these migration rates. First, it is possible that recreational fishing in the upper Banana River could have reduced the number of tags available to FM RI sampling activities outside the NTZ, leading to lower tag recovery rates from this area. However, several fish from the Banana River study area were recaptured on multiple occasions--a common occurrence in this region where fish are caught and released in fishing practices. Although there is some postrelease cryptic mortality associated with catch-and-release practices, these releases likely limited the effects of local fishing on our analyses. Second, our assumption that the migration patterns of recaptured fish represented the migration patterns of the overall population may not be valid if the respective length frequencies were not also equally represented. The use of multiple gear types and sampling strategies to collect fish for tagging increased the likelihood that the length frequencies of species in our collections represented the available population. Reported recapture length frequencies closely approximated the population length frequencies in our collections for red drum, black drum, and sheepshead but over-represented the frequency of larger individuals for common snook and spotted seatrout. Because red drum and black drum were the principal species that displayed multidirectional migration patterns, we considered the potential for size bias to be minimal in our comparisons of estimated ingress and egress rates.

Ultimately, a determination of the net result of these migration patterns, in terms of replenishment to or withdrawal from adjacent fisheries, would require accurate assessments of species population abundances that were beyond the scope of this study. If there are large enough differences in population densities across the NTZ boundary, either as a result of increased production inside the reserve or high fishing mortality outside, then the relatively low emigration rates that we observed could still result in a net export of exploitable individuals to fished populations in surrounding waters. In trammel-net collections from this same reserve during the late 1980's, Johnson et al. (1999) estimated that in the protected habitats, relative abundances of red drum populations were 6.3 times greater and of black drum were 12.8 times greater than the relative abundances of these populations in adjacent unprotected areas. More recent shoreline haul-seine data from 1997-2000 show that these abundances were only 1.8 times greater for red drum and 1.5 times greater for black drum (FMRI, unpubl. data). To what extent the difference in abundance estimates between these two temporally separate studies is related to fish movements, to stringent changes in management regulations that have occurred, or to the difference in sampling methods used is undetermined. However, if we consider the more recent population level differences between the NTZ and adjacent waters, then the emigration and immigration rates observed in the present study indicate that there is a potential for more substantial movements by these species towards protected habitats than away from them.