December 1, 2025 — 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.”