Abstract
Obtaining accurate species-specific landings data is an essential step toward achieving sustainable shark fisheries. Globally distributed sharpnose sharks (genus Rhizoprionodon) exhibit life-history characteristics (rapid growth, early maturity, annual reproduction) that suggests that they could be fished in a sustainable manner assuming an investment in monitoring, assessment and careful management. However, obtaining species-specific landings data for sharpnose sharks is problematic because they are morphologically very similar to one another. Moreover, sharpnose sharks may also be confused with other small sharks (either small species or juveniles of large species) once they are processed (i.e., the head and fins are removed). Here we present a highly streamlined molecular genetics approach based on seven species-specific PCR primers in a multiplex format that can simultaneously discriminate body parts from the seven described sharpnose shark species commonly occurring in coastal fisheries worldwide. The species-specific primers are based on nucleotide sequence differences among species in the nuclear ribosomal internal transcribed spacer 2 locus (ITS2). This approach also distinguishes sharpnose sharks from a wide range of other sharks (52 species) and can therefore assist in the regulation of coastal shark fisheries around the world.
Highlights
Shark fisheries have intensified worldwide in response to increasing demand for shark products
The large dataset evaluated (166 reference samples) and the large interspecific genetic divergence found in the internal transcribed spacer 2 locus (ITS2) locus among all sharpnoses (Table 3) indicates that the possibility of false positive or false negative is remote
The ITS2 locus has been used for species identification owing to its consistent low intraspecific polymorphism and high interspecific variability even among closely related congeneric species [13,15]
Summary
Shark fisheries have intensified worldwide in response to increasing demand for shark products (fins, meat). Most shark landings are reported as an amalgam of species, in which products are sorted by broad taxonomic groups This problem is compounded by the fact that sharks are not usually sold as whole animals, but as carcasses or processed in the form of fillets, making it difficult to identify species of origin. The genus Rhizoprionodon is represented worldwide by seven species of small sharks [1] characterized by a relatively pointed snout, earning them the common name ‘‘sharpnose sharks’’: Rhizoprionodon porosus (Caribbean sharpnose shark), R. lalandei (Brazilian sharpnose shark), R. terranovae (Atlantic sharpnose shark), R. oligolinx (Grey sharpnose shark), R. taylori (Australian sharpnose shark), R. acutus (Milk shark) and R. longurio (Pacific sharpnose shark). Sharpnose sharks exhibit a conserved external morphology that makes them quite difficult to identify, even as whole animals
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