Population genetic research on the Spadenose shark, Scoliodon laticaudus (Chondrichthyes, Carcharhinidae), reveals the presence of two significantly differentiated clades along the Indian coast

Globally, many of the Elasmobranch species are threatened with extinction due to their vulnerable life history traits, habitat alterations, overexploitation, and climate change. The Spadenose shark, Scoliodon laticaudus Müller & Henle, 1838 , is an amphidromous coastal shark that exhibits placental viviparity. The latest IUCN Red List of Threatened species classified S . laticaudus as near threatened (NT) indicating its vulnerability to overfishing. We investigated the genetic population structure of S . laticaudus along the Indian coast using mitochondrial cytochrome C Oxidase 1 (COI), control region, and NADH dehydrogenase subunit 2 (NADH2) markers. Significant genetic differentiation was detected between the east and west coasts of India with the occurrence of two major haplotypes, one dominant along the east coast, and the other along the west coast when analyzed using all the 3 markers. The NADH2 sequences of the predominant haplotype from the west coast recorded 100% identity with sequences of S . laticaudus deposited in NCBI, GenBank. On the contrary, the predominant haplotype from the east coast recorded 100% identity with sequences of Scoliodon cf. laticaudus deposited in NCBI, GenBank. The divergence values of 2% and 3.7% between these haplotypes in the COI and NADH2 genes, respectively, indicate that they can be considered distinct species. Divergence between populations and speciation indicates restricted mixing and gene flow due to the limited dispersal capacity of nearshore elasmobranchs. Natal philopatry, selection on mitochondrial genes due to differential habitat characteristics, and environmental differences between the east and west coasts of India can also be considered as reasons for restricted gene flow and genetic differentiation. Based on the results of the present study, S . laticaudus and the putative S. cf. laticaudus can be managed separately along the Indian coast. A comprehensive investigation based on morphological and molecular information is also warranted to resurrect S. cf. laticaudus as a new species. Besides, restrictions on the fishery and the use of bycatch reduction devices in trawls can be undertaken to conserve this species from further depletion and possible extinction in the future.