Coho eDNA Measurable In The Air Along Seattle-area Salmon Stream

Anybody who’s ever been around a Northwest stream in fall can tell when the salmon are in just by the stench of washed-up, decomposing fish, but a new study shows that the presence of genetic material from ones still swimming upstream to the spawning grounds is detectable in the air as well.

Being able to measure airborne environmental DNA, or eDNA, may offer fishery biologists another way to quantify relatively how many salmon (and what species) are in the water at a given time – think streams without dams, weirs, fish ladders and other counting stations, or that require close monitoring to stop or start seasons.

The novel idea wafted into the mind of University of Washington student Aden Yincheong Ip last fall as he watched salmon surfacing on the Olympic Peninsula and wondered if the air also contained traces of their passage.

So Ip and three other researchers at UW’s School of Marine and Environmental Affairs set up four different kinds of sampling stations on the banks of Issaquah Creek between Lake Sammamish and the state salmon hatchery during the 2024 fall coho run and then compared what they collected in the devices over a six-week period to in-water eDNA samplers and the hatchery escapement report posted by WDFW.

Though the amount of salmon genetic material in the air was 25,000 times lower than what turned up in the water, they found it also corresponded pretty well to the runs’ dips, bumps and general trends as shown in both waterborne eDNA testing and WDFW’s escapement reports.

Their findings were recently published in Scientific Reports and are the subject of a UW press release out today. The release states:

“The airborne eDNA concentration fluctuated with the visual counts reported by the hatchery, suggesting that this could become a useful tool for tracking salmon populations. The strategy is more remote-friendly than other methods because it does not require electricity.

“’This technique quantitatively links air, water and fish,” Ip said. “Airborne eDNA doesn’t give us a headcount, but it does tell us where salmon are and what their relative abundance is in different streams.’”

Fellow study author Ryan Kelly said the work is “at the edge of what is possible with eDNA” and “pushes the boundaries way further than I thought we could.”

UW reported that the land-based stations were able to pick up salmon eDNA as far as 12 feet from the creek.

Per the paper, polytetrafluoroethylene, or PTFE, filters “produced the most consistent quantifications, with lower variance,” and they’re also “generally unaffected by rain.”

Ip, Kelly and the other two authors concluded their work “offers a transferable framework for other regions and study systems, while recognizing that replication across seasons, sites, and taxa will be needed to assess broad applicability.” UW stated they plan to look at variables such as precipitation, wind, temperature and humidity.

Funding for their study came from the David and Lucile Packard Foundation.

Previously, eDNA has been used to sample for invasive northern pike at Lake Roosevelt as well as a lake on San Juan Island where they were illegally released. Now it appears there are airborne applications.

Granted, Issaquah Creek is far smaller than, say, the Snohomish, Skykomish and other important Westside salmon rivers, but being able to monitor along their banks for fish is an intriguing development.