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Fishery Bulletin 98(1) 



lar analyses (e.g. Vaughan-^) to manage the red drum 

 fishery. Knowledge of stock structure in red drum, 

 i.e. the geographic relation between spawning and 

 recruitment, is needed to facilitate the management 

 of this fishery. 



Molecular studies have been used to define appro- 

 priate geographic scales for monitoring and man- 

 aging exploited animal populations (Moritz, 1994), 

 including marine fishes (e.g. Bentzen et al., 1996; 

 Graves, 1996; Tringali and Bert, 1996). Although 

 several population genetic studies have been con- 

 ducted on red drum, the existing data are equivo- 

 cal. On the basis of significant differences in allele 

 frequencies at a single allozyme locus, Bohlmeyer 

 and Gold ( 1991) concluded that red drum are weakly 

 subdivided between the Atlantic Ocean (North Car- 

 olina and South Carolina) and the Gulf of Mexico. 

 However, data from other allozyme surveys (Ramsey 

 and Wakeman, 1987; Campton'*) did not permit the 

 rejection of the null hypothesis that red drum form a 

 single panmictic gene pool. In contrast, on the basis 

 of small but statistically significant differences in the 

 frequencies of several composite mitochondrial DNA 

 (mtDNA) haplotypes between red drum collected 

 from North Carolina and South Carolina waters and 

 red drum collected from the Gulf of Mexico, Gold and 

 Richardson (1991) and Gold et al. (1993, 1994) reas- 

 serted that red drum are weakly subdivided between 

 these regions, ostensibly along the south Florida 

 coast. In addition, Gold et al. (1993) reported a pat- 

 tern of mtDNA differentiation in Gulf red drum con- 

 sistent with the isolation by distance model (Wright, 

 1943) for samples ranging from Florida to Texas. 

 However, samples from a significant portion of the 

 species range, including locations near the putative 

 Atlantic-Gulf division (i.e. the eastern Florida sea- 

 board), were not assayed in any of the above studies. 

 An equally tenable but untested hjrpothesis is that 

 isolation by distance occurs over the entire range 

 of the species, perhaps in the absence of a genetic 

 break at a particular geographic location. 



Localized population subdivision in red drum has 

 also been postulated. From comparisons with sam- 

 ples from North Carolina and South Carolina waters 

 and samples from the Gulf of Mexico, Gold and Rich- 

 ardson (1994) proposed that red drum inhabiting 

 Mosquito Lagoon, Florida, form a genetically distinct 

 population. Red drum in Mosquito Lagoon report- 



edly have a life history uncharacteristic of other red 

 drum. Adults occupy this coastal lagoon throughout 

 the year and may complete their life cycle within 

 the lagoon (Johnson and Funicelli, 1991). Adult red 

 drum also occur throughout the year in other coastal 

 lagoons adjacent to Mosquito Lagoon (e.g. Banana, 

 Indian, and Halifax Rivers), but these have not been 

 surveyed genetically. Rather than forming a self-con- 

 tained population, red drum from Mosquito Lagoon 

 may belong to a larger subpopulation occupying Flor- 

 ida Atlantic waters. 



Owing to the perceived decline of red drum abun- 

 dance in the 1980s, state agencies in Alabama, Flor- 

 ida, South Carolina, and Texas studied the feasibility 

 of stock enhancement as a means of supplementing 

 wild populations. Hatcheries in Florida, South Caro- 

 lina, and Texas currently employ stocking on a large 

 scale (McEachron et al., 1995; FDEP"^). Hatchery 

 programs potentially affect the gene pools of indige- 

 nous red drum populations by way of an inappropri- 

 ate introduction of non-native individuals (Hindar et 

 al., 1991) and by hatchery-induced inbreeding effects 

 (Tringali and Bert, 1998). For example, because brood- 

 stocks for large-scale stock enhancement programs 

 along the Atlantic seaboard have been obtained from 

 Mosquito Lagoon and nearby estuaries (Halstead^), 

 there is a potential for artificial genetic exchange 

 between putatively separate gene pools (e.g. those of 

 Mosquito Lagoon and the Carolinas). 



State and regional fishery managers (Vaughan'^; 

 FDEP'') and hatchery managers (FDEPM have 

 adopted the stock structure scenario proposed by 

 Gold et al. (1993) and Gold and Richardson (1994) 

 in which red drum are divided into Gulf of Mexico 

 and Atlantic populations, and those fish in Mosquito 

 Lagoon comprise a unique, self-contained Atlantic 

 subpopulation. However, several important ques- 

 tions regarding the genetic structure of red drum 

 remain unanswered; each has serious implications 

 for fishery management and stock enhancement pro- 

 grams. First, are red drum populations in the Gulf 

 of Mexico and Atlantic really subdivided or do the 

 observed genetic differences solely reflect isolation 

 by distance over the range of the species? Second, if 

 a genetic break does exist somewhere between the 

 Gulf and the coast of the Carolinas, where is it? 



■* Vaughan, D. S. 1995. Statu.s of thi- ri-d drum stock on the Atlan- 

 tic coast: stock a.sse.ssment report for 1995. Southeast Fisheries 

 Science Center, Natl. Mar Fish. Serv., Beaufort, NC. 50 p. 



'' Campton, D. E. 1992. Gene flow estimation and population 

 structure of red drum iSciaenops ocellatiis) in Florida. Final 

 report, cooperative agreement no. 14-16-009-1522, National 

 Fisheries Research Center, U.S. Fish and Wildlife Serv.. Gaine.s- 

 ville, FL. 



' FDEP (Florida Department of Environmental Protection). 

 1993. A stock assessment of red drum iSciaein>ps ocellatiis) in 

 Florida. Florida Marine Research Inst., Dep. Natural Resources, 

 100 Eighth Ave. SE, St. Petersburg, FL, 24 p. 



•^ Halstead, B. 1997. Stock Enhancement Research Facility, 

 Florida Department of Environmental Protection, 14495 Harlee 

 Road, Port Manatee, FL 34221. Personal commun. 



' FDEP (Florida Department of Environmental Protection l. 

 1993. Marine fi.sh stock enhancement and hatchery executive sum- 

 mary. Report to the legislature. FDEP, St. Petersburg, FL, 17 p. 



