Genetic insight into tiger sharks (Galeocerdo cuvier) and whiprays (Brevitrygon sp.) in Sri Lanka.

Marine predators often function as sentinel species, the first organisms to be impacted when a habitat is disturbed, and directly contribute to ecosystem health by maintaining physical connections between distal habitats. Elasmobranch fishes (sharks and rays) are common predators in most aquatic systems, but over the past 50 years, elasmobranch abundance has dropped > 70% from overfishing and climate change. Further, many populations throughout the world are known to be Data Deficient, confounding management decisions. To remedy this, we investigated patterns of genetic structure and diversity in two elasmobranchs from Sri Lanka, the tiger shark Galeocerdo cuvier, and the whipray Brevitrygon sp., using the mitochondrial genes ND2 and CO1. Our results showed low diversity and high connectivity in G. cuvier, with several haplotypes shared between sharks in Sri Lanka and other ocean basins. For Brevitrygon sp., our analyses confirmed this species to be Brevitrygon imbricata, but with additional genetic diversity not previously found in this species. Taken together, these results indicate that elasmobranchs sampled from the fish markets of Sri Lanka are connected by gene flow to populations in other regions, suggesting that they may resist depletion better than more-isolated groups.