Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


John E. Graves

Committee Member

John A. Musick


Molecular genetic techniques were used to elucidate genetic population structure in three species of sharks, the coastal sandbar shark (Carcharhinus plumbeus) and Atlantic sharpnose shark (Rhizoprionodon terraenovae), and the pelagic shortfin mako (Isurus oxyrinchus). Allozyme analysis and analysis of restriction fragment length polymorphisms (RFLP) of mitochondrial DNA (mtDNA) were used to test the null hypothesis that the mid-Atlantic Bight and the Gulf of Mexico sandbar sharks consist of a single gene pool. RFLP analysis of mtDNA was used to determine the pattern and level of genetic divergence in the sandbar shark between the western North Atlantic and the Eastern Indian Ocean, and within the entire species range of the cosmopolitan shortfin mako and the Atlantic sharpnose shark. No significant genetic divergence was detected in the sandbar shark between the mid-Atlantic Bight and Gulf of Mexico. Genetic variation was extremely low but homogeneously distributed. A significant degree of genetic divergence was detected between North Atlantic and Australian sandbar sharks. All Australian sandbar shark mtDNAs were fixed for alleles other than those detected in the North Atlantic. The hypothesis that the shortfin mako comprises a single panmictic population was rejected. The overall probability of drawing samples with such disparate allele frequencies from a single gene pool was &<&0.001. The only barrier to gene flow detected appeared to be the equatorial Atlantic. Samples from Brazil, Australia, and California were not significantly different from each other, however all three were significantly different from the North Atlantic sample. The shortfin mako exhibited a considerably higher level of genetic variation than the sandbar shark. The Atlantic sharpnose shark did not exhibit significant differences in allele frequency throughout its range. The level of genetic variation detected in mtDNA was intermediate to that of the sandbar shark and the shortfin mako.



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