Salmon have been dying en mass in Alaska this summer before they can spawn, and scientists are attributing it to heat stress .
The hoards of dead salmon found floating in the Alaskan rivers in July drew scientists to investigate the die-off later in the month. Director of the Yukon Inter-Tribal Fish Commission Stephanie Quinn-Davidson took a group of scientists to the Koyokuk River, according to CNN.
There, the scientists arrived at a minimum count of 850 dead, unspawned salmon in Alaska's Koyokuk River– which NPR reports as the site with the largest of the current die-offs.
"A river that is usually teeming with life felt like a tomb," University of Alaska Fairbanks fisheries professor Peter Westley told NPR.
This 1991 photo provided by the Alaska Department of Fish and Game shows spawning pink salmon in Anan Creek, near Wrangell, Alaska. (ADF&G via AP)
Five different types of salmon visit Alaska's rivers: the chum, sockeye, king, silver and pink salmon, all of which prefer to dwell in colder waters. The type of salmon mostly mentioned by the scientists was chum salmon.
Pacific salmon typically die after spawning, either providing food for other animals or providing nutrients for the stream, according to the U.S. Geological Survey. However, when scientists cut the dead fish open, they found in most of them with "beautiful eggs still inside them," Quinn-Davidson told CNN.
Scientists looked for signs of parasites, lesions, tumors or other infections but found none.
"I think there's strong evidence to suggest that fish are dying because of heat stress," Dr. Vanessa von Biela, who studies the effects of temperature on Yukon salmon, told NPR.
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Parts of Alaska are currently experiencing drought as well – one that Alaskan Department of Fishing and Game Biologist Stormy Haught told AccuWeather was "a longer drought than we usually see."
The U.S. Drought Monitor shows Anchorage and surrounding areas in the middle of an extreme drought, and the majority of the southern part of the state at least abnormally dry.
"Streams are warm," Haught said. "Streams are low or really non-existent, and we’re having a hard time getting pink salmon into the streams to meet our escapement goals."
Escapement numbers play a role in determining fishing quotas and are set by the Board of Fisheries. With the struggle to meet these goals, there is concern about how it might affect the future population and wildlife that depends on the salmon for food.
"“These are two-year fish," Haught said. "Fish spawned in 2019 will come back in 2021, and so there is a concern that this is a very poor, what we call, brood year. That can have effects for 2021."
Pacific salmon begin their trek upstream to spawn typically during the months of June and July, journeying from cool ocean waters to rivers with temperatures that are more easily influenced by daily temperatures.
On Aug. 15, the National Ocean and Atmospheric Administration (NOAA) declared July 2019 the hottest month on record for the planet and noted Alaska specifically had its warmest July since statewide records began back in 1925.
NOAA declared July 2019 as the hottest month on record. As scientists believe salmon die-offs are the result of heat stress, Alaska has had its warmest July since the statewide records began in 1925. (NOAA)
"The hot weather observed over the month of July in Alaska could not have come at a worse time for these migrating salmon," AccuWeather Meteorologist Brandon Buckingham said. "Once the salmon begin the trek upstream, there is no turning back no matter the water conditions."
While it may take a few months for ocean water temperatures to warm up, Buckingham explains that rivers and streams can change in temperature much faster than oceans.
"Rivers and streams will always heat up and cool down faster than ocean temperatures, solely due to the depth and amount of volume," Buckingham said.
Within the first two weeks of July, Alaska had reached stifling temperatures, and several cities had set new heat records. The scientists had gone out onto the river toward the end of that month. While this time frame wouldn't be enough to raise ocean water temperatures, it was sufficient to raise the river water temperatures according to Buckingham.
"The time frame over those few weeks in July is crucial for salmon. This heat wave hit at a very unfortunate time for these migrating fish," Buckingham said.
Cook Inletkeeper's Science Director Sue Mauger and her team had published a study in 2016 which covered how climate change would affect temperatures in Alaska's streams. They created models showing both moderate and pessimistic projections.
"2019 exceeded the value we expected for the worst-case scenario in 2069," Mauger told CNN.
As can be expected, fish that prefer cold water don't do well in warm water.
"Salmon generally thrive when water temperatures hover in the low to mid-50s during spawning season," Buckingham said. "Early in the season, it is not uncommon for salmon to head upriver when the water temperatures are near 70."
According to the National Wildlife Federation, the ideal water temperature for king, or chinook, salmon ranges from 55 to 64 degrees Fahrenheit, and massive fish kills have happened at or above 71.6 F.
With heat wave after heat wave baking Alaska, water temperatures near Bethel broke into the 70s in early July, according to KYUK.
The Cook Inletkeeper, which tracks real-time temperatures of rivers in Alaska, recorded that stream temperatures on July 7 had topped at 81.7 F in the Deshka River.
"The July heat wave will have serious impacts," Buckingham said. "Even though temperatures weren't much higher than average, the variance of water temperatures in July is much less, normally, so five degrees above average can be a serious issue."
There have been no reports of king salmon die-offs so far this summer, according to NPR. The Cook InletKeeper notes that warm waters can block their migration, including that from July 1 to July 9, only 13 king salmon had passed the Deshka weir based on data from the Alaska Department of Fish and Game.
"We've been tracking stream temperatures in non-glacial systems across the Cook Inlet watershed since 2002," Mauger said. "But this is a first – we've never seen stream temperatures above 76 degrees Fahrenheit."
Normally, snowmelt helps keep Alaskan rivers cool. However, the snowmelt this year was the fourth earliest on record, according to the Associated Press.
"If the snowmelt was one of the earliest on record, that will generally cause rivers to run lower [due to] the lack of melting water, and they will warm up faster," Buckingham said.
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