Environmental DNA reveals beaver presence

A small vial of water collected two kilometers downstream is enough to reveal the presence of beavers in a waterway.  

“It’s pretty promising that they are very easy to detect,” said Jesse Burgher, a PhD candidate at Washington State University Vancouver.

The Washington Department of Fish and Wildlife had been translocating beavers around the state, either for conservation reasons to boost numbers in some regions or to remove problem beavers in others. But they didn’t have a good way of tracking whether beavers stayed in the places where they were translocated. VHF tracking devices attached to their tails didn’t stay on for very long, so they didn’t give a great picture of where translocated beavers were going.

In a study published recently in Animal Conservation, Burgher and his colleagues turned to environmental DNA—or eDNA—techniques, to track the presence and absence of creatures in the wild.

Environmental DNA, which wildlife researchers are using in an increasing number of situations, involves taking environmental samples from soil, water or even air in some cases. Researchers then analyze these samples in the lab using DNA detection methods to determine the presence of the species they are looking for.

Can eDNA analysis find beavers?

In this case, the team used water to sample for the presence of 10 beavers that they released, split between 2020, 2021 and 2022. Before releasing VHF-tagged beavers in Gifford Pinchot National Forest and Mt. Baker-Snoqualmie National Forest in the Washington state Cascades near Leavenworth, the researchers first took water samples downstream from the planned release sites to make sure there weren’t any beavers there already.

They sampled the water again the day after each release, the following week, and after a month at various distances from the release site, up to 2 kilometers away. They continued to take samples for two subsequent months after the first month, as well.

In almost all cases, the researchers were able to detect beavers in the water samples the day after they were released. Regardless of the time and distance from the release site, they detected beaver presence 93% of the time. “[Environmental DNA] was fairly reliable at detecting them if they were upstream,” Burgher said.

Given the 93% detectability by one sample alone, Burgher said that with two water samples within 3 kilometers, he would be confident that the method would be accurate for detecting beavers.

This method would be useful for a landscape-scale inventory of beaver occupancy in a region, he added.

The team also found that the quantity of DNA in samples reduced in a fairly predictable, linear fashion the further away they were taken. In the future, Burgher said this means wildlife managers might be able to use the technique to determine how far a beaver is upstream just by using a water sample.

But even the beavers that left the release sites, as revealed by the VHF tracking data, were still detectable months later. “More work is needed to understand how long beaver eDNA signals remain detectable after animals leave a stream,” Burgher said.