Environmental DNA offers scientists a look at salmon’s past and future

salmon migrating, seen at the Katmai National Park, Alaska
With refinements to eDNA tracking methods, researchers can now collect data about what fish were present in an area up to two days after the fish have left the area.

By Meredith Redick, KCAW – Sitka

Scientists have many ways to track fish populations – but they usually require seeing the fish. Now, researchers at the National Oceanic and Atmospheric Administration are refining a method to collect data about what fish were present in an area – up to two days after those fish have moved on.

Diana Baetscher is a research geneticist at NOAA’s Alaska Fisheries Science Center in Juneau.  She said that when fish swim, they shed scales, slime, and other tiny fragments into the water. Those fragments contain DNA – and they can provide a breadcrumb trail for scientists looking to learn about fish populations.

“eDNA is environmental DNA,” Baetscher said. “It’s sort of a really simple concept. At its heart, it’s the fact that all organisms shed DNA or genetic material into the environment, and that can be water or air or soil.”

Baetscher said collecting environmental DNA, or eDNA, is less time-intensive than some other methods. Scientists can scoop up seawater and test it to get a picture of what species of fish have recently passed through.

“eDNA has sort of grown as this way of trying to shortcut some of the amount of time that goes into those other ways of counting fish,” she said.

Baetscher is the author of a paper published on March 12 that will help scientists better interpret the data in those scoops of seawater. She says that while the signs can stay in the water for up to 48 hours after fish leave an area, that signal might be affected by factors such as tide and water temperature.

“So you know, if you have a really strong current downstream of a whole bunch of fish, do you see that signal changing because the current is changing, or the wind is changing, or the tide is changing? So, you know, we actually need to study the movement of the eDNA separate from the fish to be able to then use that to understand something about fish.”

Baetscher looked to net pens full of hatchery chum salmon in Juneau’s Amalga Harbor for a dense, consistent source of eDNA. She found that the signal left by the chum salmon was strongest at the water’s surface, and it disappeared faster during outgoing tides. Baetscher said this study was just one step towards making eDNA a more useful tool. In the meantime, eDNA is already being used to expand where scientists can track fish – like for Arctic fish communities under sea ice.

salmon dna alaska
A figure from the March 12 paper shows that eDNA signs get weaker with distance from the net pens, and that the effect is stronger during an outgoing tide.

“Another that we’re really excited about is looking at changing species distributions in the subarctic and the Arctic,” she said. “What do those fish communities look like, and how much are they changing year over year and throughout a calendar year?”

Baetscher hopes the data collected by filtering water under the sea ice will give researchers a snapshot of fish communities that they otherwise would be unable to access.

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