eDNA: A hands-off science for species detection

The Suquamish Tribe is using environmental DNA (eDNA) to figure out which fish are using the Doe Kag Wats watershed, including small tributaries, wetlands and an extensive estuary system.

Off-channel habitat, such as wetlands or side channels where fish find refuge, tends to be overlooked when surveyed for specific species; eDNA can help tell who’s been there, said Debbie Kay, the tribe’s forest ecologist.

To get eDNA, a water sample is collected in a syringe or pump and passed through a filter that retains DNA. The filter is then sent to a lab for analysis. The results can show a variety of species present without having to handle the fish, making it less intrusive and more effective than electroshocking, which has been a common way to survey off-channel habitat, said Alison O’Sullivan, the tribe’s ecosystem recovery program manager.

Electroshocking sends a low-grade electrical current through the water, temporarily stunning and inhibiting movement of targeted fish and allowing biologists to count and observe species as they float to the surface. Unfortunately, this method also can be damaging to smaller fish and other animals and plants living in that environment, O’Sullivan said.

The tribe’s field biologists are sampling 30 locations within Doe Kag Wats every three months between November 2023 and August 2025.

“Doe Kag Wats is considered a culturally important site to the tribe and if we can understand the distribution of the species here, especially rare species, that supports improving the tribal cultural understanding of the area,” Kay said.

Doe Kag Wats is the largest relatively undisturbed coastal wetland in Washington state, according to the Washington State National Heritage Program.

The tribe owns nearly all the wetlands and streams in this watershed area. It has been minimally disturbed by human-made structures such as culverts and houses, so the tribe can sample the whole system, from the estuary to most headwaters of contributing streams. It has been minimally disturbed by human development and the tribe can sample the whole system.

A goal for the eDNA project is to determine habitat characterizations for each of the sampling locations, such as water temperature, stream size and gradient, and canopy coverage, “to get an idea of what streams look like at different times of year as we get hits for different species,” Kay said. “The idea is if we have habitat characterizations X, Y and Z for a certain spot, then we should be finding species A, B and C species here.”

The work also helps the tribe advocate for better protections for fish that use off-channel habitat, O’Sullivan said.

“We need data to support our positions about what fish need when evaluating and helping rewrite environmental codes and rules,” she said.

Suquamish field biologist Hanna Brush takes a water sample from the Doe Kag Wats estuary. Photo and story by Tiffany Royal