BioProject

Sharks and rays are some of the most threatened marine taxa due to the high demand for fin-related products in many Asian communities. More...

Sharks and rays are some of the most threatened marine taxa due to the high demand for fin-related products in many Asian communities. At least 25% of shark and ray species are considered to be threatened with extinction. In particular, the density of reef sharks in the Pacific has declined to 3 to 10% of pre-human levels. Elasmobranchs are thought to be sparse in highly urbanised and turbid environments such as the waters off Singapore. Low visibility coupled with the highly elusive behaviour of sharks and rays pose a challenge to diversity estimation and biomonitoring efforts as sightings are limited to chance encounters or from carcasses ensnared in nets. Here, we tested the utility of eDNA metabarcoding as applied on seawater samples to detect elasmobranch species in Singapore. With a total of 84 water samples collected from nine localities, we found 47 shark and ray molecular operational taxonomic units, of which 16 had species-level identities. When data were compared against historical collections and contemporary sightings, we found 143 overlapping records and two potentially new species records. The magnitude of local elasmobranch richness uncovered by eDNA is substantially greater than the seven species sighted over the last two decades. Our findings demonstrate that eDNA metabarcoding is effective in detecting shark and ray species despite the challenges posed by the physical environment, granting a more consistent approach to monitor these highly elusive and threatened species. Less...