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article imageHistoric Alaska heatwave is killing off thousands of salmon

By Karen Graham     Aug 18, 2019 in Environment
Juneau - Unusually warm temperatures across Alaska this summer has led to die-offs of unspawned chum, sockeye and pink salmon, with the warm waters acting as a "thermal block," basically a wall of heat salmon don’t swim past, delaying upriver migration.
From the Koyukuk River to the Kuskokwim, to Norton Sound, to Bristol Bay’s Igushik River, the heatwave has proved fatal to thousands of Alaska salmon, reports the Juneau Empire.
Alerted by locals about the die-offs, Stephanie Quinn-Davidson, director of the Yukon Inter-Tribal Fish Commission, took a group of scientists on an expedition along Alaska's Koyokuk River at the end of July. They counted 850 dead salmon on the expedition but estimated the number was likely 10 times higher.
“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.” Davidson attributes the deaths to heat stress.
Adult sockeye salmon encounter a waterfall on their way up river to spawn.
Adult sockeye salmon encounter a waterfall on their way up river to spawn.
Marvina Munch, U.S. Fish and Wildlife Service
The scientists examined many of the dead fish - looking for signs of lesions, parasites, and infections, but came up empty-handed. Nearly all the salmon they found had "beautiful eggs still inside them," she told CNN News.
Heatwave breaking records
Conservation organization Cook Inletkeeper put out a blog-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 River, the warm water created a thermal block that prevented the salmon from moving upstream. "Cook Inletkeeper has been tracking stream temperatures in non-glacial systems across the Cook Inlet watershed since 2002. But this is a first – we’ve never seen stream temperatures above 76 degrees Fahrenheit," wrote Mauger.
Mauger also points out that the warm temperatures are also affecting the salmon in various ways, depending on the stream. "Physiologically, the fish can't get oxygen moving through their bellies," Mauger said. In other places in the state, the salmon "didn't have the energy to spawn and died with healthy eggs in their bellies."
The most abundant salmon species in the watershed is sockeye salmon. The Bristol Bay watershed suppo...
The most abundant salmon species in the watershed is sockeye salmon. The Bristol Bay watershed supports the largest sockeye salmon fishery in the world, with approximately 46% of the average global abundance of wild sockeye salmon.
The bigger picture is bleak for salmon
Salmon populations are also under threat from over-fishing, particularly in southwestern Canada and northwestern Washington. Orca whales, which are themselves endangered, feed on salmon. There has been a steady decline in orca whale populations over the past several decades.
Last week, the Environmental Protection Agency (EPA) told staff scientists it would no longer oppose the Pebble mine project in Alaska that had the potential to devastate one of the world's most valuable wild salmon fisheries, just after President Trump met with Alaska's Gov. Mike Dunleavy.
However, there are a few bright clouds - "Salmon are very resilient. They've overcome a lot," said Mary Catharine Martin, a spokeswoman for the non-profit Salmon State. She is talking about Alaska's Bristol Bay, the largest sockeye salmon fishery in the world.
In 2016, commercial fishing celebrated the more than 2 billion salmon that have been harvested from the Bay’s waters. "That's very good," Martin said. "Salmon have sustained the way of life of the people of Alaska for thousands of years."
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