Scientists have successfully developed a first-of-its-kind, portable, environmental DNA (eDNA) test to help find the world’s rarest turtle, the Swinhoe’s softshell turtle (Rafetus swinhoei), a species on the brink of extinction.
As of 2024, only two Swinhoe’s softshell turtles were known to exist: one captive male, which is over 100 years old, at the Suzhou Zoo in China, and one wild animal, whose sex is unknown, in Xuan Khanh Lake, Vietnam.
The only hope for the species’ long-term survival is to find additional animals, which have so far eluded detection by traditional survey methods, for captive-breeding programmes.
“Most eDNA testing is done in a laboratory setting, which requires samples to be collected, preserved and transported to a lab capable of testing for eDNA, and these labs are not always widely available,” says Dr. Tracie Seimon, Director of the WCS Zoological Health Program’s Molecular Laboratory and lead author of a recently published scientific paper in Environmental DNA.
“This new eDNA test kit is designed to be portable, very user-friendly and streamlined, and allows researchers or biologists will little molecular experience to be easily trained, so the test can be performed in the field.”
How does the eDNA test work?
Turtles shed their DNA into their environment through urine, faeces and skin cells, but DNA can degrade over time and be diluted in such large water bodies, presenting challenges for detection, especially when there are so few individuals left.
“Researchers first collect water samples at the lake, and then filter these samples on-site,” explains Seimon. “The eDNA is captured on filters and can be tested right away, with results in about one hour. The kit can be transported anywhere. This is the first time a portable qPCR (quantitative polymerase chain reaction) kit like this has been used successfully to detect such a rare animal and in such a large body of water.”
The search for Swinhoe’s softshell turtles
The breakthrough test was developed by the WCS Zoological Health Program based at the Bronx Zoo, WCS Vietnam, in partnership with the Asian Turtle Program of Indo-Myanmar Conservation (ATP-IMC), and the Central Institute for Natural Resources and Environmental Studies (CRES) in Vietnam.
The goal was to develop a portable eDNA water test to detect a known individual of Swinhoe’s softshell turtle, confirmed through a previous capture and regular photographs of the turtle in vast 3,000-acre Dong Mo Lake in the outskirts of Hanoi, Vietnam.
Now that the methodology has been validated, the search will be extended for Swinhoe’s softshell turtles in half a dozen large unexplored and understudied lakes, reservoirs and other large bodies of water in Vietnam where large softshell turtles have been recorded, but where no Swinhoe’s softshell turtles have been confirmed.
“Time is ticking," says Seimon. “Swinhoe’s softshell turtle is considered functionally extinct, meaning their population density is too low to reproduce naturally. Their future existence hinges on finding additional animals in other unexplored lakes that may still exist, both for protecting these animals and securing a captive breeding population.
The lakes where these animals live are huge, so searching for Swinhoe’s softshell turtle is like finding a needle in the haystack - you could think of eDNA as a tool that helps us find that needle. If an animal can be confirmed, then we know where to direct resources for conservation management, planning and protection, and eventually species-recovery.”
Previous artificial insemination attempts several years ago with a captive male and female at Suzhou Zoo, China were unsuccessful, and the female at the zoo died in 2019.
As well as helping in the race to stop Swinhoe’s softshell turtles’ going extinct, the new portable eDNA could be adapted to help find other elusive and threatened species.
“This new eDNA test is super-exciting because it can be applied to search for rare and endangered wildlife worldwide, including remote locations that lack power or standard laboratory infrastructure,” says Seimon.
"This type of eDNA test is being applied to search for the critically endangered saola, or Asian Unicorn, in the forests of the Annamite mountains in Laos. eDNA technology is continuing to push the boundaries of how it can be applied, from monitoring diseases in waste water to detecting rare species in remote forests, oceans, freshwater rivers, streams and even air. It’s a useful approach to add to our conservation toolbox for finding rare and threatened species, environmental monitoring and management of protected areas.”
Main image: Swinhoe’s softshell turtle (Rafetus swinhoei)/WCS
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