New study proposes to uncover where chinook salmon could be dying en route to Yukon

The state of Alaska is proposing new research to track dwindling chinook salmon numbers this spring, and it's possible the study could eventually extend into the Yukon. 

This week, members of the bilateral Yukon River Panel met in Anchorage, Alaska, to brainstorm ways to help the salmon, which undertake one of the longest salmon migrations in the world.

It's during this migration, though, that tens of thousands of salmon seem to go missing every year. In 2022, only about 11,000 chinook crossed into the Yukon. That number falls sharply below a minimum, internationally agreed-upon threshold of 42,500 fish, a number set more than a decade ago to ensure the salmon stock doesn't crash.

The research project is a bid to figure out where the salmon could be dying as they swim toward the Yukon.

Zachary Liller, a researcher with the Alaska Department of Fish and Game, said up to 500 salmon would be radio tagged near the Pilot Sonar Station, located near the mouth of the Yukon River. From there, tracking towers will be set up along the length of the river, up to the U.S.-Canadian border. The towers will be able to pinpoint the precise locations of the salmon. 

"The strategic approach here is to track the upriver success of those Canadian-origin fish to determine whether they are in fact making it to the border, and, if they're not, where they are having problems," Liller told the panel Wednesday.

Tissue samples will also be collected from the fish, he said.

"We'll be able to assign each of those tagged fish to a distinct stock of origin, so we'll know exactly which ones are Canadian fish and which ones are U.S. fish."

Could the research happen in the Yukon?

Steve Gotch, the Canadian chair of the Yukon River Panel, told CBC News it's a possibility. 

"Over the next five to six months, we will be in active discussions with the Alaska Department of Fish and Game around what opportunities exist in Canada," he said.

Ultimately, he said, Yukon First Nations have the last word. 

"They will need to be instrumental in determining whether or not we will seek to advance some directed efforts in the upper Yukon River watershed this season."

Two concurrent studies

Alaska scientists have been studying what role ichthyophonus — a parasite that can cause fatal disease among fish — plays in en-route chinook salmon deaths. The work will happen alongside the radio tagging research — that is, if it goes ahead.

Liller said there is tension between the two studies.

"There is unfortunately no way to confirm ichthyophonus disease without killing the fish," he said, "and obviously these tagged fish need to live."

"There's no way to pair [the studies] together, but the fact that they are co-occurring in the same place at the same time gives us a lot of power to combine information from those studies to draw reasonable conclusions about what might be happening and where it might be happening."

When scientists screen for ichthyophonus infections, they need to kill fish to study organs and flesh. In a move that drew criticism in the territory earlier this year, state researchers killed at least 452 salmon.

While ichthyophonus has been appearing in fish for some time, it has increasingly come under study by scientists due to the sheer number of infected salmon. 

Gotch, the panel chair, said the number now hovers around 40 per cent, whereas 25 years ago — when infections first started being documented in the territory — the number of infected salmon sat somewhere between 10 and 15 per cent. 

"In most cases, this microorganism doesn't cause significant harm to the fish. However, when fish with ichthyophonus are under extreme periods of stress, such as during their spawning migration, essentially their immune system starts to weaken and the infection can take over and result in premature death.

"There's been one year of study that has confirmed that infection rates are high, but at this point in time, we don't yet know if this is a leading factor causing the loss of fish when they are in river."