The great (Sphyrna mokarran) and smooth hammerhead (S. zygaena) sharks are globally distributed species of significant conservation concern because they have high bycatch rates and high value fins. The great hammerhead has been assessed as endangered and the smooth hammerhead as Lower Risk / Near Threatened by the IUCN Redlist. There is no information on the population structure of either species to inform management and conservation efforts. We report on an ongoing assessment of the global population structure of both species using nuclear microsatellite markers and complete mitochondrial control region (mtCR) sequences (approximately 1098 nucleotides) from 78 great and 85 smooth hammerheads. Great hammerhead samples analyzed thus far included 59 North Atlantic and 6 Indo-Pacific individuals. Smooth hammerhead samples analyzed included 14 Atlantic, 23 North Pacific, 28 Southeast Pacific and 19 Indo-Pacific individuals. Analyses of the great hammerhead mtCR revealed strong geographical subdivision into two distinct evolutionary lineages with little exchange of haplotypes between the lineages (FST 0.704, P< 0.005) and little to no detectable genetic structure within either lineage. Smooth hammerhead mtCR revealed strong geographical subdivision into four separate populations with no evidence of gene flow between the populations (FST= 0.802, P< 0.00000) and little to no detectable genetic structure within the populations. Analyses of microsatellite loci from both species are currently underway. Despite the modest regional distribution of samples analyzed thus far, the data suggest that genetic population subdivision in these species may be extensive, making it likely that proper management will require a multi-regional approach.
Available at: http://works.bepress.com/mahmood-shivji/64/