By Yereth Rosen
ANCHORAGE, Alaska, Feb 25 (Reuters) – As sea heat waves have helped wipe out some of Alaska’s legendary salmon migrations in recent years, authorities have resorted to sending food expeditions from emergency to affected communities, while scientists warn that the industry’s traditional harvest days could be numbered.
Salmon all but disappeared from the Yukon River’s 2,000-mile (3,200 km) run last year as record high temperatures led to fish piling up dead in streams and rivers before they could spawn. A study published Feb. 15 in the journal Fisheries details more than 100 salmon deaths at freshwater sites around Alaska.
These losses meant that, even though temperatures were milder in 2021, Yukon River salmon runs remained so anemic that Alaska and Canada were forced to halt their salmon harvest to ensure enough fish survive to reproduce for another year.
“Alaska is notorious for salmon and cold,” said Vanessa von Biela, a US Geological Survey research biologist and lead author of the 2019 death study. Now, “we basically have the issues known for a long time at lower latitudes”.
The collapse of Yukon River salmon harvests has dealt financial blows to commercial fishers and Indigenous communities, who traditionally stock fish as a year-round staple.
Commercially, salmon fishermen on the river only earned a total of $51,480 for their 2020 harvest, before the harvest was canceled in 2021. By comparison, they earned $2.5 million in 2019 and $4.67 million in 2018.
Last month, the U.S. Commerce Secretary declared a two-year Yukon River fishing disaster, making federal relief funds available.
The state sent emergency fish shipments last year from the most plentiful salmon in Bristol Bay and elsewhere.
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Scientists have mainly blamed ocean warming, with a series of heat waves in the Bering Sea and North Pacific Ocean from 2014 to 2019 affecting salmon living in the sea before they return to spawning grounds.
Although the heat waves have passed, their effects have not gone away, said fisheries scientist Katie Howard of the Alaska Department of Fish and Game. “We still see the residual effects,” she told a state legislative committee in Anchorage earlier this month.
Climate change may also affect salmon diets, with young salmon being able to feed on nutrient-poor foods like jellyfish, as the warmer waters of the Bering Sea drive out the more nutritious zooplankton that fish normally eat.
“In my opinion, the salmon are starving because of climate change,” said Brooke Woods, chair of the Yukon River Intertribal Fish Commission of the Athabascan village of Rampart.
But the impact on freshwater habitats is also increasingly studied.
From previous research conducted by von Biela on the rivers, streams, and lakes where salmon spend their early and late life stages, the team found that Chinook salmon exhibit heat stress at temperatures above 18 degrees Celsius ( 64.4 degrees Fahrenheit) and began to die above 20°C.
In the past, water temperatures from Alaska to the Yukon ranged between 12°C and 16°C, with upstream Canadian monitoring sites measuring even colder waters. But in 2019, temperatures on the Alaskan side were above 18C for 44 straight days, according to the February study.
The impact of warming can be mitigated by climate-induced runoff from glaciers, which feeds colder water into rivers and streams.
Scientists expect salmon to gradually move to new areas in Alaska, with profound effects for people who depend on the fish for their livelihoods, food and culture.
“The salmon will find a way,” von Biela said. “But it’s going to be difficult for communities that are in places where there may be no salmon left.”
(Reporting by Yereth Rosen; Editing by Lisa Shumaker)