Inclusion of South American samples reveals new population structuring of the blacktip shark (Carcharhinus limbatus) in the western Atlantic.

Carcharhinus limbatus has a cosmopolitan distribution and marked genetic structuring, mainly because of its philopatric behavior. However, analysis of this structuring has not previously included South American populations. In the present study, we analyzed a sample of adult individuals collected on the northern coast of Brazil and compared the sequences of the mitochondrial control region with those of populations already genotyped. Relatively high haplotype diversity (12 haplotypes, genetic diversity of 0.796) was observed, similar to that in other populations but with a much larger number of private alleles. In contrast to populations studied previously, which were represented by neonates, the pronounced allelic variability found in the South American individuals may have resulted from migrations from other populations in the region that have yet to be genotyped. This population was also genetically distinct from the other Atlantic populations (F(st) > 0.8), probably because of female philopatry, and apparently separated from the northwestern Atlantic group 1.39 million years ago. These findings indicate that the C. limbatus population from northern Brazil is genetically distinct from all other populations and should be considered as a different management unit for the protection of stocks.