An analysis of genetic population structure in red drum, Sciaenops ocellatus, based on mtDNA control region sequences

Genetic information pertaining to stock structure in red drum (Sciaenops oc ellatus) is equivocal, complicating attempts to develop sound fishery manag ement and stock enhancement plans. In this study, genetic stock structure w as examined by using mitochondrial DNA (mtDNA) control region sequences of 209 individual red drum from six locations in the Gulf of Mexico and five l ocations in the nearshore Atlantic Ocean off the southeastern United States . Eighty-one polymorphic sites within a 369 base-pair portion of the contro l region defined 134 different haplotypes which differed by up to 26 nucleo tide substitutions. Red drum showed high average within-sample haplotype (0 .98) and nucleotide (0.030) diversities. Sequence divergences between pairs of haplotypes ranged from 0.27% to 7.06% ((x) over bar=3.17%). Cluster ana lysis of haplotypes revealed very little phylogeographic structure among mt DNA lineages. However, a neighbor-joining tree based on nucleotide divergen ce between pairs of samples 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, constitute a self-c ontained, reproductively isolated population. Hierarchical analysis of mole cular variance supported the hypothesis that red drum are subdivided into t wo weakly diverged populations with a genetic transition in south Florida b etween Sarasota Bay and Mosquito Lagoon. This area forms a zone of differen tiation between two genetically semi-isolated populations between which the structuring of heterogeneity differs from that under the assumption of pan mixia. In addition, the analysis of molecular variance also indicated that red drum from Apalachicola Bay are genetically divergent from all other sam ples. The Atlantic and Gulf red drum populations are likely to respond inde pendently to harvest regulations; these fisheries should continue to be man aged separately. Additional subdivision of the Gulf stock between peninsula r Florida and the northern and western Gulf may also be warranted.