https://www.cbc.ca/news/indigenous/alaska-salmon-heat-deaths-1.5256288
[images and video in online article]
Heat stress that killed thousands of salmon in Alaska is a sign of
things to come, scientist warns
Experts blame heat wave in July for deaths of chum salmon along the
Koyukuk River
Rhiannon Johnson · CBC News · Posted: Aug 24, 2019
Scientists believe heat stress killed thousands of salmon in an Alaskan
river last month.
From July 7 to 11, communities along the Koyukuk River experienced
sustained air temperatures of over 30 C, well above the seasonal average
highs of less than 20 C.
Shortly after the heat wave, locals began reporting an unusual number of
dead chum salmon washing up on the banks of the river.
Lisa Bifelt is Athabascan and lives in the village of Huslia in interior
Alaska, almost 600 kilometres northwest of Anchorage on the Koyukuk
River. She grew up on the land and relies on subsistence hunting to
support her family.
"You'd see dead fish now and then, but I don't ever remember seeing this
many," she said.
She said she saw a post on Facebook from the Yukon River Inter-Tribal
Fish Commission asking for volunteers in the villages of Allakaket,
Alatna, Hughes, Huslia, Koyukuk and Nulato to survey and take photos of
the dead chum salmon. The villages are all along the Koyukuk River
except for Nulato, which is slightly south, just past where the Koyukuk
meets the Yukon River.
"There was a lot when we actually stopped and started counting them,"
Bifelt said.
"All of them had the eggs still perfectly in the sack, not even loose or
anything."
Finding salmon dead before they have spawned is unusual.
Survey by volunteers
Chum salmon are one of the largest species of salmon, second only to
chinook salmon. They hatch in freshwater streams and rivers then migrate
out to the Pacific Ocean to feed and grow before returning to the same
freshwater streams to spawn, then eventually die.
According to the National Oceanic and Atmospheric Administration's
fisheries department, there were hundreds of stocks of chum salmon in
Alaska in 2018, and while some stocks were below target population
levels, none were listed under the Endangered Species Act.
Bifelt reported her findings to Stephanie Quinn-Davidson, a former
fisheries biologist and director of the Yukon River Inter-Tribal Fish
Commission, which advocates for stronger tribal representation in
management decisions when it comes to fisheries.
Quinn-Davidson determined the results of the volunteers' surveys were
sufficiently alarming to send a team of scientists more than 300
kilometres by boat from Hughes to Huslia to investigate
She said when the team began travelling downriver from Hughes, they
almost immediately began seeing dead salmon. The fish were examined for
tumours, lesions, infections, parasites, worms — anything that would
indicate disease.
"Based on our observations, these salmon were perfectly healthy," she said.
"Every single salmon we observed had not yet spawned."
She said they tried to rule out as many causes as possible. Since the
die-off coincided with a heat wave, the team determined heat stress was
the culprit.
She said when salmon enter a river to travel to their spawning grounds,
they stop feeding. They only have their built-up fat stores as energy.
When fish are exposed to warmer temperatures, their metabolism increases
and they go through their energy stores much faster. The salmon that
died didn't have enough energy to make it to their spawning grounds and
their hearts failed, she said.
The team recorded 850 dead fish, but they estimate the actual number of
casualties could be up to 10 times higher.
No impact on overall population
Quinn-Davidson said dead salmon were also reported in mid-July to the
south on the Kuskokwim River and in Bristol Bay.
Many chum salmon made it to their spawning grounds this year and it's
not expected the deaths will have a drastic impact on the overall
population. But there are concerns that if heat waves become more
common, so will salmon die-offs.
Athabascan communities on the river fish for multiple species for
sustenance but worry that a decrease in chum will upset the natural cycle.
Ricko DeWilde, an Athabascan from Huslia who is on the National
Geographic television show Life Below Zero, isn't convinced heat is to
blame for the salmon deaths.
DeWilde said he started noticing dead salmon while boating from
Fairbanks to Huslia in mid-July.
"When I got to Huslia I talked to some elders and they said, 'Yes,
that's weird. That shouldn't happen. That's never happened before.'"
He said animals weren't feeding on the fish, which concerned him because
his community relies on fish and other animals for food.
Scientists investigating the deaths also observed that the fish did not
appear to have been eaten, but noted that most animals would prefer not
to eat something that was rotting.
DeWilde said he's not totally convinced the cause of death was heat
because the scientists didn't take samples of the fish to be examined in
a lab.
The scientists said the purpose of their investigation was to document,
not to take samples.
DeWilde believes it's worth exploring whether bacteria from the ocean or
radiation from the nuclear accident in Fukushima, Japan, in 2011, could
be affecting the salmon.
'It will happen again'
The die-off appeared to only affect chum salmon, not other fish species,
which raised concern and confusion among local communities.
Peter Westley, an assistant professor of fisheries at the University of
Alaska Fairbanks, said migrating fish face different challenges than
local fish, and species have different levels of heat tolerance.
He also said people shouldn't be surprised if it happens again.
The circumpolar world, including Alaska, is on the forefront of climate
change, Westley said, and "all predictions are that events like this are
going to become more frequent and more severe."
"We need to be ready to respond on the ground when this happens again in
the future," he said. "And it will happen again."
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