Whitehorse Daily Star

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HANGING FOOD – A Northern Tutchone woman hangs chinook salmon in the smoke house at her fish camp on the Stewart River in the late 1980s.

Warming Yukon River adversely affecting salmon

While it’s hard to measure how much warmer water in the Yukon River is affecting chinook salmon returning to spawn, there is evidence to suggest it’s having an impact on stress.

By Chuck Tobin on May 22, 2020

While it’s hard to measure how much warmer water in the Yukon River is affecting chinook salmon returning to spawn, there is evidence to suggest it’s having an impact on stress.

Alaska scientist Vanessa von Biela has been researching heat stress on Yukon River chinook salmon.

It’s difficult to quantify the impact because the research is just not there yet, she said in an interview with the Star this week.

von Biela says there was a time when it was thought nature ensured salmon had everything they needed for the migration upriver to the spawning grounds, the only variable being the salmon fisheries along the way.

There are, she says, telling signs that heat stress may be a contributing factor to chinook mortality, particularly from last year, when the temperature of the Yukon River did reach above 21 C on occasions through mid-July.

Fish don’t maintain a constant body temperature like humans and other mammals, explains the scientist with the U.S. Geological Survey’s Alaska Science Centre in Anchorage.

Fish adjust to fluctuating water temperatures, though adjustments come with the cost of spending more of the energy reserves they depend on to reach the spawning grounds.

von Biela says it’s believed the optimal temperatures for Yukon River salmon are in the 15 C range.

They don’t know what the optimal temperature is for chinook salmon, but the research shows temperatures of 18 degrees or more begin stressing the chinook, forcing them to distribute more oxygen throughout the body while burning more reserves.

At a certain water temperature, von Biela says, the combination of higher oxygen demand in the fish’s body and lower oxygen in the water can act like a survival cliff, when there is just not enough O2 to go around.

“They can die really quickly….The brain and the body tissues are demanding way more oxygen than they can deliver.”

They don’t know where the cliff is for chinook, she says.

von Biela says with 15 years of scientifically reliable temperature records, there still need to be more data about spawning success to get a clearer understanding if temperatures are influencing that success.

The science community hasn’t been able to explain why the Yukon River chinook stocks have not recovered from their decline in the 1990s, says von Biela.

Heat stress, says the research scientist, is not an unknown.

One year it killed upward of 90 per cent of B.C.’s Fraser River sockeye run, she points out.

While it may be too early to connect any dots on the Yukon River, von Biela says, there is evidence to suggest water temperature is a factor affecting the survival rate of chinook.

Initial research shows some Pacific salmon are making it to the spawning beds, but are not releasing their eggs, while there is also evidence of mortality during the migration.

Since the 1990s, the temperature of the Yukon River has hit 18 degrees many times, she says.

von Biela says last year it went above 21, and for nearly all of July, the temperature was above 18.

Yukon River communities in Alaska were seeing carcasses of Pacific salmon last summer like they’ve never seen before, she says.

von Biela says ongoing research into female chinook reaching the spawning grounds but not depositing their eggs may some day establish a link between water temperatures and spawning success.

Reaching remote spawning grounds to cut open the carcasses of dead females to see if they’ve released their eggs is both costly and logistically challenging, she points out.

von Biela says communities on both sides of the border with easier access to spawning grounds can take it upon themselves to do their own research by examining the carcasses to see if eggs have been released.

It’s an opportunity to organize a group effort to continue the community research in years to come, she says.

von Biela says more information helps to create a better understanding of whether there is a relationship between water temperature and salmon mortality.

“It does take a fair amount of data to determine why are fish dying with eggs.”

von Biela says she is not a climatologist, and can’t say whether climate change is having an impact on river temperatures.

“I would not argue with somebody who made that conclusion, I will tell you that.”

The Joint Technical Committee of the international Yukon River Panel released its annual report detailing the Yukon River salmon run of the previous summer earlier this spring.

It estimates that last year, 219,624 chinook salmon – plus or minus 10 per cent – passed by the Pilot Station sonar located in Alaska upriver from the mouth. It was the second-largest return going back to 2006.

In the days of seemingly plenty – as recently as the 1990s – it was common for the total harvest of chinook on both sides of the border to approach 200,000 fish, according to records.

The Alaska commercial and subsistence fisheries would take the largest portion, by far, including a portion of Yukon-origin chinook bound for the Yukon, in accordance with the sharing agreement under the international treaty governing Yukon River salmon.

There has not been a commercial fishery for chinook on either side of the border for several years because of depleted stocks.

The subsistence fisheries on both sides have also been in a conservation mode in years of late, though the subsistence catch of chinook in Alaska in 2019 was estimated to be 48,379, according to the joint technical report.

It was the largest in years, and a reflection of the annual harvest in the ’90s. The five-year average for the Alaska catch up to 2018 was 20,480.

The Yukon’s aboriginal food fishery harvested an estimated 3,104 chinook in 2019 – 2,764 along the mainstream and 340 on the Porcupine River.

The Yukon harvest was on par with recent years.

The number of fish that made it to the spawning grounds is estimated at 42,052, or just below the minimum target of 42,500.

It was the first time since 2013 that the minimum escapement was not met, and well below the 10-year average escapement of 54,252.

There were 282 chinook that reached the Whitehorse fish ladder, the lowest return since 1988, when chinook raised at the Whitehorse Fish Hatchery began contributing to the run.

As a general rule of thumb, salmon managers in the past have assumed 50 per cent of the chinook that go by the Pilot Station sonar are of Yukon origin.

There have been runs where the estimated Yukon portion has been as low as 41 to 43 per cent.

Of the estimated 219,624 chinook that passed by Pilot Station last year, the joint technical report estimates there were 72,500 of Yukon origin – given the estimated spawning escapement of 42,052, the estimated Yukon First Nation harvest and the estimated catch of Yukon-origin fish in Alaska.

While the 72,500 falls short of being 50 per cent of 219,000, there are a few possible variables that need to be taken into consideration, says Steve Smith of the Department of Fisheries and Oceans office in Whitehorse.

Smith explained in an interview earlier this spring the pre-season forecast for the return of Yukon-origin chinook was 66,000 to 99,000.

He said there could be a few reasons why the return came in at the low end of the forecast and didn’t balance with the Pilot Station count of 219,624.

The Pilot Station estimate may have been off, he said.

Smith pointed out the run of abundant summer chum into Alaskan waters occurs at the same time as the chinook run, and it can be difficult for the sonar to separate the two fish.

Perhaps the total catch of Yukon-origin chinook by Alaska was under-estimated, Smith said.

There is a possibility chinook mortality was a factor during the migration upriver, he added.

Smith said it was a very low water year last year, and temperatures were warm.

Comments (15)

Up 3 Down 2

Elizabeth on May 28, 2020 at 11:28 am

The warm water temperatures were in Alaska, not the Yukon. Near the mouth of the Yukon River, water temperatures reach 21C but were above 18C for the majority of the Chinook migration (in this section of the river). When the Chinook reached our side of the border, the Yukon River was much cooler, which is why none of us saw those extreme temperatures.

If you are interested, there was a documented massive die off of summer chum on the Alaska side (Koyukuk) and reports of dead Chinook on our side with eggs still in them.

It is real.

Up 11 Down 1

iBrian on May 27, 2020 at 5:58 am

Over harvesting would be the key to the decline.
Anything else is fodder to fill applications for funding to try and deviate from the fact.
Salmon have not been respected, 10,000’s are harvested just for Dog mushing teams feed every year.

Up 12 Down 5

My Opinion on May 26, 2020 at 9:03 pm

A simple google search will show this to be impossible. Average High Temps can barely get to 70 let alone coupled with the average overnight lows in the mid 40's. How will this heat the river to temps in excess of that? Fake News.


I have an underwater thermometer on my boat. This time of year it is in the 40's at best and by late summer mid 50's. I have been keeping anglers notes for thirty years and it has not changed.
Maybe they were measuring temperature in an Oxbow and the data suited their narrative.

Up 11 Down 9

Jc on May 25, 2020 at 6:12 pm

One one lesser voice. You haven't lived in Newfoundland in the late 80s during the so called Cod crisis. I was. Somehow the scam has made its way to Yukon. I wonder if our Premier from Nova Scotia had anything to do with this one.

Up 20 Down 14

One One-Lesser-Voice on May 24, 2020 at 12:32 pm

More than a few deniers posting comments and reacting to comments.
Stick a thermometer in the water and see for yourselves how warm the Yukon River gets in July. Think about fish on a marathon non feeding migration having to take on the added stress of warm water.

I agree these fish have been fished down with large mesh sizes too much fishing and the best way to rebuild stocks is to have almost no fishing or pressure and let them rebuild themselves if they can.

If we really cared we would find a way to do the right thing.

Up 5 Down 9

Josey Wales on May 24, 2020 at 7:26 am

I know things smell fishy here, and in the context of nature and the natural world...
if I may chime in here with a uncharacteristic completely free of toxic political/societal commentary...a positive comment on recent image?

A image that if not inspired with the natural world and all its potential for aesthetic pleasure? The potential for you having deep seeded personal issues is exponentially increased.
All that bloviating to illustrate a photo on Fridays Star by Vince...nuts eh?

Galloping Grazers is a great shot deserving of a step outta "the zone"
...Be nice, Thank you Mother Nature & Vince (he too a by product of)!

Then...leave...full stop.

Up 21 Down 4

Greiko on May 23, 2020 at 9:13 pm

Ok, how can the Yukon River system get to 21 degrees when the ambient temperature rarely gets that high....it is not possible.

Up 41 Down 7

Groucho d'North on May 23, 2020 at 11:15 am

And here we have an also-ran excuse for the low numbers of salmon returning to their natal waters. I view these as distractions from the primary fact that too many fish are being harvested by too many people. If it doesn't stop soon, there will not be salmon in our grandchildren's future.

Up 24 Down 17

Unfeckingbelievable! on May 23, 2020 at 10:12 am

Really: 21 degrees Celsius? That’s not possible. The ‘expert’ must be a Liberal Party member with that kind of distortion of reality happening. I will be asking the Liberal Party to let me borrow their unicorn next week to get back and forth to work as my car is in the shop. Hopefully the Territorial Court Judges and the Department of Injustice are done with it. I know, I know, they are not supposed to be on the same unicorn together but hey - It is the YuCon where there is no halfway... And the Executive and the Judicial branches like to play all day where seldom is heard an ethical word and the lies are said loudly all day...

What does one have to do with the other?

A 21 degree Yukon River sounds like the kind of reasoning employed in a Yukon Court - It was not murder it was a consensual killing... The Crown failed to disprove the defence theory that the deceased asked the defendant to shoot his wallet as he threw it in the air... Therefore, I hereby give reason to this doubt although it be not reasonable!

La Carribe du Nords!

Up 37 Down 10

No 21C around here on May 23, 2020 at 9:55 am

I live on the Yukon River and never experienced 21C in the river last summer. I take the temperature because I love to swim, and it was 18C, maybe 19C at the highest, and that was right at the top of the water. Go down a foot or two and it's a lot colder. I think this article is blaming hot water when the truth is over fishing. Call me a 'denier' but the reality is, I'd have been swimming every day if it were 21C, and it wasn't. Anybody else out there taking temperatures last summer?

Up 9 Down 16

One One-Lesser-Voice on May 22, 2020 at 7:40 pm

Water temperatures in the Yukon River near Dawson City have often been in the 19 to 21 C range in mid to late July.

Up 15 Down 11

JC on May 22, 2020 at 7:15 pm

Not to worry. Give it time, the Salmon will adapt to the change in temperature. Just like everything else including humans. Start worrying about the nuclear war threat thats likely to happen soon.

Up 23 Down 11

Matthew on May 22, 2020 at 5:38 pm

Pretty sure there have been salmon in this river for 100,000+ years, they will be there for the next 100,000 too...

Up 31 Down 6

Gringo on May 22, 2020 at 3:20 pm

Wow a whole lotta “maybes “ “ands if and buts” In that piece. Perhaps she could tell us where the temp of the Yukon River got to 21c cause I know if nowhere on that river system that gets anywhere that warm.

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