The DNA found in sea turtle poop could be scientists’ newest monitoring tool

Tracking the signal of environmental DNA, or eDNA, can be used to track animals themselves.

By Katie Valentine

Sea turtle poop may not sound like the most scientifically interesting subject. But it could turn out to be a useful tool in monitoring populations of sea turtle species, according to results from a recent pilot study from NOAA researchers.

That’s because the poop of sea turtles — and every other animal — holds DNA that contains bits of information about the animal. When animals shed skin, urinate, or defecate, DNA is released into the environment around them. Tracking the signal of this environmental DNA, or eDNA, can be used to track the animals themselves. Analysis of eDNA can be done more quickly, easily and inexpensively than traditional scientific sampling methods, which often involve physically capturing animals. 

“eDNA is tissue-free,” said Kelly Goodwin, a microbiologist at NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML). “So instead of having to take a biopsy or a tissue sample, or physically capture the animal, the idea is that you can just use seawater to figure out where animals live.” 

eDNA is being tested as a way to monitor the populations of a variety of marine animals, including whales, porpoises and fish. Compared to fish and marine mammals, which have more skin surface area to shed eDNA, sea turtles have large shells, which made scientists unsure whether their eDNA signals would be too weak to detect in their seawater habitats.

To find out, Goodwin and a team of researchers, led by Peter Dutton from NOAA’s Southwest Fisheries Science Center, set up an experiment in the San Diego Bay. Kirsten Harper, a postdoctoral associate working with Goodwin and Dutton, looked at whether eDNA samples from endangered green sea turtles would match up against visual sightings. Dutton’s team set up a traditional sampling technique — net capture — in which sea turtles swim into large nets and are brought to shore for data collection, then released.* Harper took samples of seawater in the places they captured sea turtles, to see whether turtle eDNA could be detected from the water sample. As part of the study, Harper also took samples from a turtle exhibit, comparing seawater taken near turtles to areas without turtles. Overall, the study showed that eDNA could be detected from sea turtles and the signal was consistent with visual sightings.

“The data are encouraging that eDNA could be used for monitoring these turtles,” Goodwin said. “With continued development, we should be able to look at the eDNA signal and tell you where the animals frequent and track whether their habitat usage is changing.”

That’s important, because knowing where green sea turtles are means being able to accurately advise Naval, commercial and recreational boating operations the areas that should be avoided so as to not pose a risk to the turtle, whose populations are listed as threatened or endangered — depending on their location — under the Endangered Species Act. 

There’s still work that needs to be done to optimize the technique, including tweaking the eDNA testing method so that scientists can detect green sea turtles even when there’s only very small amounts of eDNA in the water. But using eDNA is a promising technique that could save scientists time, money and manpower when compared to traditional sampling, and also make for a less invasive sampling experience for the turtles.

For more information on NOAA scientists’ use of eDNA to study marine animals, check out this story from NOAA Fisheries. It explores how eDNA is being used to monitor harbor porpoises, which are extremely difficult to monitor using traditional biological sampling methods. 

*NMFS Research Permit #18238