POPULATION-GENETICS OF THE SANDBAR SHARK (CARCHARHINUS-PLUMBEUS) IN THE GULF-OF-MEXICO AND MID-ATLANTIC BIGHT

Allozyme electrophoresis and restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) were performed on sandbar sharks (Carcharhinus plumbeus) from coastal waters of Virginia, including th e Chesapeake Bay, and the Gulf of Mexico to test the hypothesis that i ndividuals from the two locations comprise a single gene pool. Both te chniques revealed a very low degree of genetic variability within the species (allozyme mean heterozygosity = 0.005, mean nucleotide sequenc e diversity = 0.036%). The small amount of genetic variation present a ppeared to be evenly distributed between sampling locations; and there fore, the null hypothesis of a single gene pool could,not be rejected (contingency chi(2) = 1.344, P > 0.5, chi-square significance of mtDNA haplotype distribution = 0.81). This conclusion is consistent with th e known life-history characteristics of the species, as well as the re sults of tagging studies.