Low genetic diversity and population structure of the narrownose shark (Mustelus schmitti)

The narrownose smooth-hound shark Mustelus schmitti is a coastal species endemic to the Southwest Atlantic Ocean. As this species is an important fishery resource, there is interest in knowing its genetic population structure. In this study, we used mitochondrial cytochrome b gene sequences to examine the genetic structure of the narrownose smooth-hound populations within the Río de la Plata and its Maritime Front in the SW Atlantic Ocean. We found no evidence for genetic structure in the analyzed samples. Low levels of pairwise ΦST values indicated high connectivity and suggested genetic homogeneity at this geographic range. Additionally, notably low nucleotide and haplotype diversities found in this species could indicate that M. schmitti experienced a population bottleneck, recent expansion or selection. The results presented here indicate that M. schmitti exists as a single demographic unit in the Río de la Plata and its Maritime Front. The low genetic diversity values found in the present study, together with the low resilience to exploitation of this species, raise considerable concern over the conservation status of M. schmitti.