Whale sharks are shedding their DNA into the seawater and leaving a trail of genetic clues in their wake, according to new research by The University of Western Australia.

The research, published in Molecular Ecology Resources, found that even the smallest genetic signs in the seawater could help track individual whale sharks and monitor populations.

Despite their large size, whale sharks are notoriously challenging to track. But like all marine species, whale sharks shed their unique DNA codes into the ocean – known as environmental DNA or ‘eDNA’ – via skin, faeces, blood, mucus, sperm and other biological material. 

The researchers from the UWA Oceans Institute and the Australian Institute of Marine Science (AIMS) collected this eDNA by visiting known whale shark ‘hot spots’ at Ningaloo Reef, where the team swam behind whale sharks and filled small bottles with seawater.

The team then analysed the seawater samples through a process called eDNA haplotyping. Lead author and PhD student Laurence Dugal from UWA’s Oceans Institute said while environmental DNA (eDNA) had been used in the past to monitor the presence of certain species, the new method used eDNA to answer an entirely different question. 

“Our new method has taken this incredible leap to detect the genetic signature of individual whale sharks just by analysing the seawater,” Ms Dugal said. 

“We have moved beyond species detection and into the realm of population genetics – we’ve opened a new door in what is possible with eDNA.” 

To confirm the signature of each shark the team also collected tissues samples of 28 whale sharks and compared the results. 

“The results were incredibly accurate – the tissue biopsies successfully matched, with high accuracy, to all the individual whale shark’s eDNA,” Ms Dugal said. 

“Up until now, we have only been able to get DNA samples through tissue biopsies, which is logistically difficult, expensive to collect and require invasive sampling techniques.” 

Dr Luke Thomas from the UWA Oceans Institute and AIMS said the research could go beyond whale sharks and be applied to other species at risk. 

“This new method is faster, cheaper, highly accurate, easier to scale up and minimally invasive,” Dr Thomas said. “It has the potential to radically change the way we monitor and track megafauna species. 

“It could also help answer global population-level questions for other megafauna, such as sharks, rays, marine turtles or dugongs.” 

This study was in collaboration with AIMS, UWA Oceans Institute, Curtin University, and a leading eDNA research lab at Aarhus University, Denmark. 

This study was supported by Santos as part of the company's commitment to better understanding Western Australia's marine environment.