Genetic structure and congeneric range overlap among sharpnose sharks (genus Rhizoprionodon) in the Northwest Atlantic Ocean

Abstract

Sharpnose sharks (genus Rhizoprionodon) experience extensive fishing pressure throughout their ranges in the Atlantic Ocean. As such, it is important to understand the degree to which intraspecific populations interact across a spatial gradient. The Atlantic sharpnose shark (Rhizoprionodon terraenovae) and Caribbean sharpnose shark (Rhizoprionodon porosus) share a similar appearance and spatial presence within the Gulf of Mexico, though until recently only R. terraenovae was observed north of the Bahamas. We assessed the population structure of R. terraenovae using the mitochondrial control region (650 bp). Our results indicate significant genetic structure (FST = 0.049, P < 0.001; ΦST = 0.017, P = 0.008) between the Gulf of Mexico and the rest of the Atlantic. In addition, we observed R. porosus outside their known range, in South Carolina, Virginia, and northern Florida. Given the overlapping range with R. terraenovae, we assessed the potential for congeneric hybridization with the addition of the nuclear ribosomal internal transcribed spacer 2 gene (1260 bp). Results designate these specimens to be true R. porosus specimens, indicating the need for reevaluation of this species’ range.