127 



Abstract.— Genetic information per- 

 taining to stock structure in red drum 

 ISciaenops ocellatus) is equivocal, com- 

 plicating attempts to develop sound 

 fishery management and stock enhance- 

 ment plans. In this study, genetic stock 

 structure was examined by using mito- 

 chondrial DNA(mtDNA) control region 

 sequences of 209 individual red drum 

 from six locations in the Gulf of Mexico 

 and five locations in the nearshore 

 Atlantic Ocean off the southeastern 

 United States. Eighty-one polymorphic 

 sites within a 369 base-pair portion 

 of the control region defined 134 dif- 

 ferent haplotypes which differed by 

 up to 26 nucleotide substitutions. Red 

 drum showed high average within-sam- 

 ple haplotype (0.98) and nucleotide 

 (0.030) diversities. Sequence diver- 

 gences between pairs of haplotypes 

 ranged from 0.27'7, to 7.06% (J=3.17% ). 

 Cluster analysis of haplotypes revealed 

 very little phylogeographic structure 

 among mtDNA lineages. However, a 

 neighbor-joining tree based on nucleo- 

 tide divergence between pairs of sam- 

 ples showed cohesion among Atlantic 

 samples and, to a lesser degree, among 

 Gulf samples. In contrast to a prior 

 study, we found no evidence that red 

 drum in Mosquito Lagoon, Florida, con- 

 stitute a self-contained, reproductively 

 isolated population. Hierarchical anal- 

 ysis of molecular variance supported 

 the hypothesis that red drum are subdi- 

 vided into two weakly diverged popula- 

 tions with a genetic transition in south 

 Florida between Sarasota Bay and Mos- 

 quito Lagoon. This area forms a zone 

 of differentiation between two geneti- 

 cally semi-isolated populations between 

 which the structuring of heterogeneity 

 differs from that under the assump- 

 tion of panmixia. In addition, the analy- 

 sis of molecular variance also indicated 

 that red drum from Apalachicola Bay 

 are genetically divergent from all other 

 samples. The Atlantic and Gulf red 

 drum populations are likely to respond 

 independently to harvest regulations; 

 these fisheries should continue to be 

 managed separately. Additional subdi- 

 vision of the Gulf stock between pen- 

 insular Florida and the northern and 

 western Gulf may also be warranted. 



An analysis of genetic population structure 

 in red drum, Sciaenops ocellatus, based on 

 mtDNA control region sequences 



Seifu Seyoum 

 Michael D. Tringali 

 Theresa M. Bert 



Department of Environmental Protection 



Florida Marine Research Institute 



100 Eighth Avenue SE 



St. Petersburg, Florida 33701-5095 



E-mail address (for 5 Seyoum, contact autfior) Seyoum_S'a'epic7dep state fl us 



Doug McElroy 



Department of Biology 

 Western Kentucky University 

 Bowling Green, Kentucky 42101 



Rod Stokes 



Department of Marine Science 



University of South Florida 



140 7th Avenue S, 



St. Petersburg, Flonda 33701-5095 



Manuscript accepted 5 March 1999. 

 Fish. Bull. 98:127-138 (2000). 



Red drum (Sciaenops ocellatus) is 

 a pelagic marine fish that is dis- 

 tributed over a large geographic 

 range that extends throughout the 

 northern Gulf of Mexico and along 

 the Atlantic coast of the southeast- 

 ern United States to Cape Cod, 

 Massachusetts (Ross et al., 1983). 

 Juveniles grow rapidly in estuarine 

 nurseries and reach reproductive 

 maturity by age 4. At this age they 

 join large schools of highly dispers- 

 ing adults and for the remainder 

 of their approximately 35-year life 

 span (Murphy and Taylor, 1990), 

 maintain a pelagic existence except 

 to spawn during annual congrega- 

 tions at the mouths of bays and 

 estuaries. The census size of the 

 breeding population in the Gulf of 

 Mexico has been estimated to be 

 greater than 7 million individuals 

 (Nichols^ ). Abundance in the Atlan- 

 tic is thought to be of a similar mag- 

 nitude (Gold et al., 1993). 



Red drum supports highly valu- 

 able commercial and recreational 



fisheries throughout its range 

 (Mercer, 1984). Fishing pressure 

 is directed principally on subadult 

 year classes (ages 2-4). A high rate 

 of annual mortality among some 

 cohorts (Murphy and Taylor, 1990) 

 and an overall decline in abundance 

 and recruitment during the 1980s 

 (Goodyear^) have led to concerns 

 regarding the status of red drum 

 spawning stocks. Because there have 

 been no prolonged offshore fisheries 

 for adult red drum, biological and 

 fishery-dependent data pertaining 

 to their spawning stocks have been 

 limited. Therefore, fishery managers 

 have had to rely principally on vir- 

 tual population analysis and simi- 



' Nichols, S. 1988. An estimate of the size 

 of the red drum spawning stock using mark/ 

 recapture. Southeast Fisheries Center, 

 Natl. Mar. Fish. Serv., Pascagoula, MS. 



- Goodyear, C. P. 1989. Status of the red 

 drum stocks of the Gulf of Mexico. Report 

 for 1989. Contract no. CRD 88/89-14. 

 Coastal Resources Div, Miami Laboratory, 

 Southeast Fisheries Center, Natl. Mar. 

 Fish. Serv., Miami, FL. 



