November 26, 2025
Counting salmon is a breeze with airborne eDNA
A male Coho salmon, featuring the characteristic hooked nose, returns to spawn from the Oregon Coast.NOAA Fisheries
During the annual salmon run last fall, University of Washington researchers pulled salmon DNA out of thin air and used it to estimate the number of fish that passed through the adjacent river. Aden Yincheong Ip, a UW research scientist of marine and environmental affairs, began formulating the driving hypothesis for the study while hiking on the Olympic Peninsula.
“I saw the fish jumping and the water splashing and I started thinking — could we recover their genetic material from the air?,” he said.
The researchers placed air filters at several sites on Issaquah Creek, near the Issaquah Salmon Hatchery in Washington. To their amazement, the filters captured Coho salmon DNA, even 10 to 12 feet from the river. Scientists collect environmental DNA, or eDNA, to identify species living in or passing through an area, but few have attempted to track aquatic species by sampling air.
This study, published Nov. 26 in Scientific Reports, shows that eDNA can move between air and water — a possibility scientists hadn’t accounted for even though aquatic animal DNA sometimes appears in airborne study data.
The researchers then merged air and water eDNA with the hatchery’s visual counts in a model to track how salmon numbers rose and fell during the fall migration. Although the amount of salmon DNA in the air was 25,000 times less than what was observed in the water, its concentration still varied with observed migratory trends.
“This work is at the edge of what is possible with eDNA,” said senior author Ryan Kelly, a UW professor of marine and environmental affairs and director of the eDNA Collaborative. “It pushes the boundaries way further than I thought we could.”
Researchers have streamlined the process of sampling eDNA over the past decade. Water and air are reservoirs for discarded bits of skin, hair and other DNA-rich detritus. Like a footprint, eDNA flags the presence of a species nearby.
After hatching, young salmon migrate to the ocean for one to several years before returning to the same stream to spawn. They leap and thrash near the surface of the water, likely shedding eDNA in the process. Every year, as the fish pass through migratory bottlenecks, people count them to gauge population health, set catch limits and monitor rehabilitation efforts.
This map shows migration patterns for specific salmon populations along the West Coast. The data comes from NOAA Fisheries and the arrows point toward the freshwater streams, like Issaquah Creek, where salmon originate and return to spawn.NOAA Climate.gov
Ip began to wonder about remote monitoring efforts while watching the fish wiggle upstream. eDNA has become a valuable tool for tracking endangered and invasive species. He developed an experiment to test the air for salmon DNA in conjunction with colleagues at the UW.
“This is Aden’s baby,” said Kelly. “He arrived saying ‘I know you can get eDNA from the water, but I want to do something nobody has done before.’”
Researchers placed filters 10 to 12 feet from the stream and left them out for 24 hours on six different days between August and October, testing four filter types each time. Three were vertical filters and the fourth was an open 2-liter tub of deionized water to capture settling particles.
A Coho salmon leaps out of the water toward the researcher’s filters, visible on the ladder at the top of the image. Aden Yincheong Ip
In the lab, they washed eDNA from the filter and measured its concentration with a Coho salmon-specific tag to a DNA amplification method called polymerase chain reaction. They referenced air and water eDNA concentration and visual counts to track population changes, assuming that each method has its own margin of error, and the true number of fish is unknown.
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.”
There are still a number of variables to account for, such as rain, wind, humidity and temperature, that the researchers plan to continue exploring in future studies.
“Right now, we’re pushing the boundaries of possibility,” Kelly said. “Eventually, we will develop the technique, as we have for waterborne eDNA, into something that can help guide management and policy.”
For more information, contact Aden Yincheong Ip at adenip@uw.edu
Co-authors include Gledis Guri, a UW postdoctoral researcher in the School of Marine and Environmental Affairs and Elizabeth Andruszkiewicz Allan, chief scientist at the eDNA collaborative in the School of Marine and Environmental Affairs at UW.
This research was funded by the David and Lucile Packard Foundation and Oceankind.
Tag(s): Aden Yincheong Ip • College of the Environment • eDNA Collaborative • Ryan Kelly • School of Marine and Environmental Affairs