Unspawned male and female chum salmon along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

Unspawned male and female chum salmon along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

Warm waters across Alaska cause salmon die-offs

  • By Mary Catharine Martin For the Juneau Empire
  • Thursday, August 22, 2019 6:44pm
  • NewsAlaska Outdoors

From the Koyukuk River, to the Kuskokwim, to Norton Sound, to Bristol Bay’s Igushik River, unusually warm temperatures across Alaska this summer led to die-offs of unspawned chum, sockeye and pink salmon. Warm waters also sometimes this summer acted as a “thermal block” — essentially a wall of heat salmon don’t swim past, delaying upriver migration.

Stephanie Quinn Davidson, the Director of the Yukon Inter-Tribal Fish Commission, took a team of scientists along 200 miles of the Koyukuk River to investigate a die-off of chum salmon at the end of July. The team counted 850 dead, unspawned chum — and that, she said, was a minimum count.

“We were boating, going about 35 or 40 miles per hour, and we know we missed a lot,” she said. “On a boat going by relatively fast, we were probably getting at most half the fish and at the least about ten percent of the fish.”

Dead, unspawned chum salmon line the banks of the Koyukuk River after a warm water event during Alaska’s unusually warm temperatures this July. (Courtesy photo | Stephanie Quinn-Davidson)

Dead, unspawned chum salmon line the banks of the Koyukuk River after a warm water event during Alaska’s unusually warm temperatures this July. (Courtesy photo | Stephanie Quinn-Davidson)

Locals to the area said this same thing happened four or five years, ago, she said, but not to the scale it did this year.

She attributes the deaths to heat stress.

“We cut open the fish, looked for any size of disease, infections, parasites. … By all indications, these fish looked healthy,” she said. “They didn’t have any marks on them, or any sign of disease or stress otherwise. And the die off event coincides with the week of heat we had.”

The total run was more than 1.4 million chum, she said, with some arriving before the warm weather event.

“We definitely had chum salmon spawn,” she said. “And have chum salmon continue to make it to spawning grounds. There are salmon that made it through. Hopefully they’ll pass those genes on that allowed them to persist.”

A dead female chum salmon, her eggs unlaid, along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

A dead female chum salmon, her eggs unlaid, along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

In the Kuskokwim, according to KYUK, there was a die-off of salmon having “heart attacks” due to the warmer than usual water along the ocean.

In Norton Sound, large numbers of pink salmon were observed dead before spawning, according to KNOM.

Conservation organization Cook Inletkeeper put out a release July 10 noting that on July 7, stream temperatures on the Deshka were 81.7 degrees Fahrenheit — more than five degrees above the previous highest-recorded temperature in that location, according to science director Sue Mauger. In the Deshka, the warm water created a thermal block that prevented the salmon from moving upstream.

Mauger said she and others are in the middle of an intensive five-year temperature survey on the Deshka to figure out the location of the river’s cold waters, which could serve as refuges during climate change.

“We have so many different types of systems (in Alaska) with different hydrologies,” Mauger said. “Some are fed by glaciers, some by snowpack, some by groundwater… and the joy of salmon is how diverse their life histories are, to capitalize on all that different habitat… but when you’re hitting temperatures in the 80 degrees, there’s no doubt fish are in high stress, and if they’re surviving they must be hitting cold water refugia.”

A dead unspawned female chum salmon along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

A dead unspawned female chum salmon along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

Even Bristol Bay, which experienced its second highest harvest of sockeye salmon ever, at 43.1 million, experienced at least one die-off.

Nushagak/Togiak Area Management Biologist Timothy Sands said there was a large die-off of sockeye on the Igushik River. After hearing reports, he received a video from a boater around July 20 of dead, unspawned sockeye lining the banks of the river.

He has seen a thermal block in that river prevent salmon from migrating upstream before, in 2016.

That’s what the problem was this year, he said. “They couldn’t go upriver because it was too warm and the water didn’t contain enough oxygen, so they died,” he said. “The warmer the water gets, the less dissolved oxygen is in the water.”

University of Washington Professor of Aquatic and Fisheries Sciences Daniel Schindler noted that in addition to warm water containing less oxygen, it increases salmon’s metabolisms and need for oxygen, creating a “double whammy.”

Scientists examine dead chum salmon found unspawned along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

Scientists examine dead chum salmon found unspawned along the Koyukuk River this July. (Courtesy photo | Stephanie Quinn-Davidson)

Juneau-based research scientist for the University of Montana Chris Sergeant co-wrote a paper on warm, crowded, low waters’ effect on salmon. In essence, warm, low water plus large populations of salmon can lead salmon to suffocate. Climate change will lead this kind of thing to happen more frequently, Sergeant said, especially in snow-fed systems like the Igushik.

Bristol Bay experienced an early spring, Sands said, so though there was “a fair bit of snowpack,” that snowpack melted early, meaning it wasn’t there to cool the river in June.

The Igushik was also particularly affected because of its geography, Sands said.

“I’ve described it as a long pond,” he said. “The tide goes more than halfway up the river to the lake. It’s very slow-flowing, very muddy. When it was really sunny out, it just heats up that river faster.”

Though Sands doesn’t have estimates of the actual number of fish that died, based on the setnetter catch rate he said between 200,000 and 300,000 were in the river during the warm water event that killed the salmon there. A small amount of fish — he estimates between 500 and 700 — made it up to the spawning grounds during the thermal block, but most of the escapement goal was met from fish that swam upriver afterwards.

The die-offs “are happening around the state and seems to have coincided with that week of really warm, warm temperatures,” Quinn-Davidson said.

Contact

Are you aware of warm waters affecting salmon where you live? SalmonState — and fisheries scientists — would like to hear about it. Email information and/or photos to mc@salmonstate.org.


• Mary Catharine Martin is the communications director of SalmonState, a nonprofit initiative that works to ensure Alaska remains a place wild salmon thrive.


More in News

Michael Penn / Juneau Empire File
The Aurora Borealis glows over the Mendenhall Glacier in 2014.
Aurora Forecast

Forecasts from the University of Alaska Fairbanks’ Geophysical Institute for the week of March. 19

State Sen. Bert Stedman, center, co-chair of the Senate Finance Committee, presides over a committee hearing Thursday. The committee on Monday approved an $8.4 million fast-track supplemental budget to address staff shortages in processing food stamps, public defenders and legal advocates for vulnerable residents. (AP Photo/Becky Bohrer)
Bill with funds to address food stamps backlog goes to governor

Legislature gives near-unanimous approval to hiring extra staff to fix months-long backlog

Hoonah’s Masters Bracket team poses for a group photo on Saturday after being crowned this year’s champs for the M bracket in the Gold Medal Basketball Tournament at JDHS. (Ben Hohenstatt / Juneau Empire)
Hoonah crowned Gold Medal Masters Bracket champs

Hoonah’s Albert Hinchman named MVP.

President Joe Biden speaks during an event in the East Room of the White House in Washington, Thursday, March 23, 2023, celebrating the 13th anniversary of the Affordable Care Act. Recent moves by President Joe Biden to pressure TikTok over its Chinese ownership and approve oil drilling in an untapped area of Alaska are testing the loyalty of young voters, a group that’s been largely in his corner. (AP Photo/Susan Walsh, File)
Biden’s moves on Willow, TikTok test young voters

A potential TikTok ban and the Alaska drilling could weigh down reelection bid.

Students dance their way toward exiting the Juneau-Douglas High School: Yadaa.at Kalé gymnasium near the end of a performance held before a Gold Medal Basketball Tournament game between Juneau and Hydaburg. (Ben Hohenstatt / Juneau Empire)
Over $2,500 raised for Tlingit language and culture program during Gold Medal performance

A flurry of regionwide generosity generated the funds in a matter of minutes.

Legislative fiscal analysts Alexei Painter, right, and Conor Bell explain the state’s financial outlook during the next decade to the Senate Finance Committee on Friday. (Mark Sabbatini / Juneau Empire)
Legislators eye oil and sales taxes due to fiscal woes

Bills to collect more from North Slope producers, enact new sales taxes get hearings next week.

The FBI Anchorage Field Office is seeking information about this man in relation to a Wednesday bank robbery in Anchorage, the agency announced Thursday afternoon. Anyone with information regarding the bank robbery can contact the FBI Anchorage Field Office at 907-276-4441 or tips.fbi.gov. Tips can be submitted anonymously.  (FBI)
FBI seeks info in Anchorage bank robbery

The robbery took place at 1:24 p.m. on Wednesday.

Kevin Maier
Sustainable Alaska: Climate stories, climate futures

The UAS Sustainability Committee is hosting a series of public events in April…

Reps. Tom McKay, R-Anchorage, and Andi Story, D-Juneau, offering competing amendments to a bill increasing the per-student funding formula for public schools by $1,250 during a House Education Committee meeting Wednesday morning. McKay’s proposal to lower the increase to $150 was defeated. Story’s proposal to implement an increase during the next two years was approved, after her proposed amounts totalling about $1,500 were reduced to $800.
Battle lines for education funding boost get clearer

$800 increase over two years OKd by House committee, Senate proposing $1,348 two-year increase

Most Read