Population Genetics and Phylogeography of Blacktip Shark

    The blacktip shark (Carcharhinus limbatus) is found along tropical and subtropical coastlines throughout the Atlantic, Pacific, and Indian Oceans.  Like many large sharks, blacktip sharks utilize coastal nursery areas, chiefly shallow bays and barrier island lagoons, as a location where young sharks find appropriate food and more importantly avoid predation by larger sharks.  Along the Atlantic coast of North America, the blacktip shark is the most important species in commercial longline fisheries and is also an important recreational species.  Ph.D. student Devon Keeney and Ed Heist at SIUC are working in collaboration with Drs. Robert Hueter and Michelle Heupel of Mote Marine Laboratory on a National Science Foundation funded study of blacktip shark population genetics and phylogeography.  Neonate and young-of-the year blacktip sharks have been collected from continental nursery grounds from the waters of South Carolina, Florida, Texas, Mexico, and Belize.  Additional specimens of blacktip shark have been collected from Australia, Hawaii, and Africa.   If female blacktip sharks are returning to natal nursery areas we would expect to see significant differences in mtDNA haplotype frequencies among nurseries, analogous to the mtDNA haplotype frequency differences seen among sea turtle nesting beaches.  If both males and females are segregation prior to mating, we would also expect to see differences in bi-parentally inherited nuclear microsatellite loci, analogous to what is seen among salmon stocks that ascend different tributaries for spawning.

Ph.D. student Devon Keeney (left) and Dr. Ed Heist tag a neonate blacktip shark in Laguna Yalahau, Mexico.

Current results indicate significant differences in mtDNA haplotype frequencies in blacktip sharks collected from continental nursery areas.  These data indicate that blacktip shark females deliver their pups to the same region in which they were pupped.  However a lack of differences among three nurseries from the west coast of Florida separated by 100 to 250 hundred kilometers indicate that there is considerable straying among specific nurseries.  Small but significant differences in nuclear DNA microsatellite loci indicate that stock structure exists for males as well, however the much greater degree of differentiation at mitochondrial vs. nuclear markers is indicative of a higher degree of male-mediated gene flow.

Frequencies of mtDNA haplotypes from continental nurseries.

    The very different degrees of signal in the maternally-inherited mtDNA data and the biparentally inherited nuclear microsatellites suggest that females exhibit a greater degree of fidelity than males.  This is similar to recent findings in the great white shark by Pardini et al. (2002).  Higher degrees of female fidelity is perhaps not surprising given that mating and parturition (birth) in blacktip sharks take place nine to twelve months apart.  Thus males need never return to their natal nursery area but females do so presumably to increase the likelihood that their offspring survive.

More Blacktip Shark Information :

• NOAA/NMFS Fact Sheet
• Florida Museum of Natural History
• Alabama Dept. of Conservation and Natural Resources

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation

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URL: http://www.science.siu.edu/zoology/heist/research/blacktip.htm
Last updated: 18-April-07 / EJH