Scientists track sharks by sampling seawater

Scientists from Salford University have shown that traces of DNA in the sea can be used to monitor shark populations.

Current methods of baiting, hooking and filming sharks, rays and other large fish are invasive and costly and require teams of scientists spending much time at sea.

The new study published in Scientific Reports shows that a sample of seawater can provide the identifiable tracks of numerous species of shark.

“Water contains minute fragments of the skin, excretions, blood of animals that have swum through there,” explains Stefano Mariani, professor of conservation genetics at the University of Salford.

“It’s just like when detectives do a forensic search of a crime scene, and can locate tissues and cells that contain the DNA of the suspects”

Almost half of all known shark species are classified as ‘data deficient’, in part, because of the expense and complexity of finding the animals in the first place.

“The beauty of our method is that we can get a picture of shark diversity without the need for chasing, baiting and hooking them – so it is a lot faster for conservation scientists and less traumatic for the animals,” added Judith Bakker, the lead author of the study.

Grey SharkGrey Shark by Tim Nicholson

The team, which included scientists from Europe and the Americas, took water samples in four sites in the Caribbean and three in the Pacific Coral Sea. The team recovered significantly more shark DNA sequences in areas less affected by people. Remote localities such as the Chesterfield atolls in New Caledonia and protected areas such as Bimini, Bahamas show both the highest number of species and most individuals. The less remote and non-protected locations, however, show lower values for both diversity and abundance.

Bakker said: “To be able to glean so much information about these charismatic predators by simply sampling a few litres of water is truly astonishing.”

“Sharks are vulnerable to overfishing, often have slow growth rate and low fecundity, and therefore are a flagship species in marine conservation.”

Work still needs to be done though to accurately resolve identification of closely related species and improve the DNA reference database.

Oceanic ecosystems are increasingly impacted worldwide. Marine predators like sharks are under often unsustainable fishing pressure. These fish are key species in virtually all marine food webs and have long been in conflict with human societies, due to their perceived competition with fishers or risk to humans. Owing to their relatively slow growth rate and low fecundity, they are also particularly vulnerable to overfishing. Only recently have sharks become the focus of conservation initiatives, as the importance of these charismatic animals for the maintenance and resilience of healthy ecosystems is now widely acknowledged.

Further Reading

Environmental DNA reveals tropical shark diversity in contrasting levels of anthropogenic impact, Bakker et al, Scientific Reports 7, Article number: 16886 (2017) doi:10.1038/s41598-017-17150-2

The article was originally published by Scuba Travel