Temporal stability and spatial divergence of mitochondrial DNA haplotype frequencies in red drum (Sciaenops ocellatus) from coastal regions of the western Atlantic Ocean and Gulf of Mexico

Restriction-site variation in mitochondrial (mt) DNA was assayed among 1675 red drum (Sciaenops ocellatus Linnaeus) sampled from 20 localities along t he southeastern coast of the USA (western Atlantic) and the Gulf of Mexico (Gulf). Up to four consecutive year-classes (cohorts) were sampled at most localities. Nucleotide-sequence divergence among 170 mtDNA haplotypes ident ified ranged tin percentage) from 0.184 to 1.913, with a mean (+/-SD) of 0. 887 +/- 0.300. Comparisons of mtDNA haplotype frequencies across year-class es within localities were non-significant, indicating temporal stability of breeding components within localities. Significant heterogeneity in mtDNA haplotype frequencies was found across all localities, between (pooled) sam ples from the western Atlantic and the Gulf, and among geographically space d, regional groupings in the Gulf. Genetic divergence between subpopulation s of red drum in the western Atlantic and Gulf follows a pattern exhibited in other marine fishes, and probably stems from physical (historical enviro nmental heterogeneity, absence of suitable habitat, and current patterns) a nd, perhaps, behavioral factors. Genetic differences among red drum in the Gulf appear to be due largely to an isolation-by-distance effect that is at tributable to behavioral factors. The latter may include female philopatry to natal bays or estuaries, limited offshore (coastwise) movement of female s relative to their natal bay or estuary, or both. Genetic divergence among red drum in the Gulf occurs despite high gene flow (estimated as the numbe r of genetic effective migrants in an island mode). Conservation and manage ment of red drum should be based on the premise that strategies for a given bay or estuary will impact geographically proximal bays or estuaries more than distal ones. Trajectories of correlograms in spatial autocorrelation a nalysis suggest a geographic neighborhood size, relative to genetic migrati on of red drum from a bay or estuary, of roughly 500 to 600 km.