Strong genetic isolation despite wide distribution in a commercially exploited coastal shark

The common smoothhound, Mustelus mustelus, is an epibenthic species targeted by fisheries around the world driven by the increasing demand for shark products. Given the wide-spread occurrence of this species and corresponding lack of molecular data in many areas of said distribution, baseline molecular assessments of this commercially important shark may contribute to finer-scale analyses in areas in which this species is targeted. Therefore, population genetic analyses were conducted along the East Atlantic, from the Mediterranean Sea to the south-east coast of Africa, using microsatellite markers and the mitochondrial control region (mtCR). Overall, M. mustelus displayed low to moderate genetic diversity, with the Mediterranean populations appearing to exhibit the lowest mitochondrial diversity, and the west African populations displaying the lowest nuclear diversity. Microsatellite analysis indicated strong genetic differentiation between the three regions, with finer-scale population structure in each region, without correlation between genetic and geographical distance. For the mtCR sequences, a total of 18 haplotypes were identified, with a high degree of divergence discernable between the regions, largely in accordance with the microsatellite data. The study documents a remarkable level of population isolation across a vast area, suggesting little or no present-day connectivity among extant populations. The findings may serve as an essential baseline for global population management and commercial traceability of this threatened shark.