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On the scaly trail of Yukon's chinook salmon

When you gaze across the waters of the Yukon River, you probably don't think about the mass of fishy mucus, urine and feces roiling beneath its surface. From now on, though, you might. Sorry.

When you gaze across the waters of the Yukon River, you probably don’t think about the mass of fishy mucus, urine and feces roiling beneath its surface.

From now on, though, you might. Sorry.

That rather unpleasant set of secretions is the key to a new technology that could help scientists learn more about the Yukon’s chinook salmon, without touching them at all.

The technology is called eDNA. That “e” stands for “environmental,” not “electronic.”

It’s a simple concept, really. Any organism in a body of water leaves behind a residue that’s full of DNA. For a fish, that might mean scales or, yes, mucus. For a human, it might be skin cells.

“It comes from any part of an individual,” said Denise Gordon, a Yukon College student who helped present the Yukon’s first salmon eDNA study at a public session at the college on Wednesday. “So if you were to fall into the Yukon River, by the time you get out, your eDNA is all over the water.”

That eDNA typically floats around in the water for up to three weeks. So to identify whether a species like chinook salmon is present in a river, scientists just need to collect a single water sample and send it to a lab for analysis.

If the technology works here, it could allow fisheries biologists to quickly test whether chinook salmon are present in streams and lakes all along the Yukon River - without even having to see them.

This past summer, the Yukon Research Centre partnered with environmental consulting company Hemmera to test eDNA technology using chinook salmon in the Yukon for the first time.

The researchers collected samples from three main locations: the Teslin River, the Nisutlin River and Kusawa Lake. Salmon populations in the two rivers are very well-known, so the results from those sites will be compared with what scientists already know to make sure the technology works.

But less is known about whether chinook salmon visit the various tributaries of Kusawa Lake. The researchers are hoping their samples will reveal new information about salmon in that area.

Michael Muller, a project director with Hemmera, said the eDNA technique is quick and easy compared with traditional salmon inventories like one that was conducted in the Yukon in 1997-98.

“The way it was done was you had a couple of fisheries (biologists) walking up the stream looking for salmon,” he said. “What would have taken them weeks, we did in a day.”

And there are other benefits to eDNA as well.

“The biggest advantage is that you don’t have to be able to handle the fish to see if they’re in the area,” said Gordon. “So this potentially will reduce a lot of stress to the fish.”

Taking this hands-off approach also reduces the risk of transferring diseases or contaminants from one stream to another. And it means that people without much specialized knowledge can do the bulk of the work.

“We’re excited because it has the potential to be very cost-effective,” said Muller. “We’re excited because it’s not invasive - we’re taking a water sample. And we’re quite excited by the levels of accuracy that we’re hoping to record.”

Some of the samples collected this summer will also be tested for DNA from bull trout, a species at risk in the Yukon. Muller said eDNA is especially useful for locating rare species like bull trout that can be hard to find.

“It’s an extraordinary tool at looking for needles in haystacks.”

But eDNA has limitations, too. At the moment, it can only be used to tell if a species is present or absent in a body of water. It doesn’t tell scientists how many fish are present, exactly when they were present, or whether they’re spawning.

Dennis Zimmermann, executive director of the Yukon Salmon Sub-Committee, had questions about how useful the tool will be for chinook management.

“What management problem does it solve?” he asked. “How are we going to be able to manage these fish so that we can meet escapement on both sides of the border? And how are we going to rebuild the stocks or put more eggs in the gravel?”

Zimmermann said eDNA could be very helpful in the Yukon if it could be used to distinguish between different chinook salmon stocks, like those from the Teslin River or the Pelly River.

“Right now, you could be putting a lot of pressure on a particular stock. We don’t know. Because in the middle river, where it’s being fished, you don’t know if you’re taking out a Teslin fish, or you’re taking out a Pelly fish,” he explained. “Any stock-specific information is useful.”

But Muller said he thinks it would be “very difficult” to get that degree of precision using eDNA.

Zimmermann said he wants to be sure management priorities are driving this eDNA research. “I want to make sure it’s being utilized to solve a problem, as opposed to just creating more data.”

Bruce Bennett, coordinator of the Yukon Conservation Data Centre, also cautioned that eDNA is better at telling whether a species is absent than whether it’s present. Bennett was involved with the Yukon’s first eDNA study earlier this year, which targeted frogs and toads.

He pointed out that a bear could carry a salmon upriver and eat it in the river, which would spread its DNA around an area where there might not be any live fish.

“Salmon DNA can get upriver in all sorts of different ways,” he explained.

Still, he said eDNA has lots of practical implications, even with those limitations. It can show how a species’ range is changing over time. It can also be used to study whether a human barrier, like a highway or a culvert, is blocking fish.

“I think it’s hugely useful for all sorts of things,” he said. “It’s really exciting.”

The Yukon Research Centre and Hemmera hope to receive the results from their water samples in the spring of 2016. Then they’ll know if all that fishy mucus could actually be a fishy gold mine.

Contact Maura Forrest at