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For millennia, Indigenous people living in Alaska and Canada's Yukon territory have relied on Chinook salmon. The large, fatty fish provide essential nutrients for Arctic living and have influenced traditions and languages across generations.

But over the past three decades, many communities have been unable to fish Chinook amid a sharp salmon population decline.

The situation could worsen as climate change warms rivers in the Arctic, stunting salmon growth, according to a study in Scientific Reports led by the University of Colorado Boulder.

"The fish are really important for maintaining the culture and language of Indigenous communities," said Peyton Thomas, a research associate at the Institute of Arctic and Alpine Research.

In collaboration with locals on the ground, the team is now working to help communities prepare for the changes ahead.

Over the past two summers, Thomas and her team visited many Alaskan tribes to understand changes to the lands and communities.

"People pointed to not being able to teach their children the names of the fish or the practices of how to process them," Thomas said.

The silver lining: Some rivers in the area could remain suitable for young salmon, and a less popular fish species, Dolly Varden, might benefit from warming waters.

Melting North Pole

Over the past 50 years, the Arctic has warmed nearly than the global average. Climate change has melted sea ice, thawed frozen ground and eroded coastlines, reshaping the Arctic landscapes Indigenous peoples have called home for generations.

In Alaska, Indigenous community members told Thomas that these changes have disrupted many aspects of their life: In winter, they haven't been able to access neighboring villages, because the river connecting them didn't freeze. Thinning and fragmented sea ice has made travel and hunting harder and riskier, cutting off sources of food and income. The area has seen more frequent and intense extreme weather events like typhoons, further damaging already limited infrastructure.

Prior research has suggested that increased river temperatures can affect fish species adapted to cooler environments. Chinook salmon in the Arctic are a prime example. These fish spend their first one to two years in cold river water bulking up, before embarking on a journey of hundreds of thousands of miles to the ocean. There, they spend the next six years growing, to up to 100 pounds, before returning to the rivers to spawn.

In recent decades, river communities in Alaska have seen a major decline in the number of young and adult salmon in the water. estimated that Chinook salmon populations in the Yukon River, Alaska's largest, plummeted by more than 57% between 2003 and 2010.

When Thomas and team visited Indigenous tribes near the Alaska-Yukon border along the Yukon River, community members told them that they hadn't been able to fish Chinook in 30 years.

"The loss of fish, as well as the loss of access to fishing and foraging grounds, means people are relying more on buying food from the store, which is really expensive and doesn't meet their nutritional needs," Thomas said.

Two fishes, two tales

Working closely with Indigenous communities in Alaska, Thomas and her team set out to better predict how climate change would affect fish populations in the seven river basins spanning watersheds in Alaska and Yukon.

After talking to tribal members, the team focused on two species important for subsistence, Chinook salmon and Dolly Varden, a type of trout.

Using computer models, the team simulated how the region's climate and rivers might change by mid-century. They found that summer river temperatures could rise by 1.26 °C (2.27 °F) by mid-century compared to the average between 1990 and 2021.

When they combined these data with a fish growth model, they found that in the warmest future years, four out of seven river basins would experience water temperatures surging above what juvenile Chinook salmon can tolerate.

On the other hand, Dolly Varden thrive in slightly warmer water than Chinook salmon. The simulations suggested that these fish might nearly double their growth in many rivers.

"It is good news that not all species are going to decline under warming," Thomas said. "But communities have different preferences about fishing Dolly Varden. We're trying to show that maybe, in warm years, Dolly Varden could be an alternative."

The team also identified some rivers that may serve as refuges for Chinook. For example, the Aniak and Andreafsky rivers, both tributaries of the Yukon River in Alaska, are likely to remain suitable habitats. Protecting and restoring juvenile salmon in these rivers could bring the greatest benefit, Thomas said.

"We are hoping to provide communities with some applicable information, like when and where the water would be too warm for salmon, which could help them decide whether to reduce fishing," she said.

Uncertain future

This study comes just a year after Alaska and Canadian authorities agreed to pause Chinook salmon fishing, both commercial and subsistence, for seven years in a bid to allow their populations to recover.

The fishing ban only applies to Canadian-origin Chinook. Commercial fishing continues for the Alaska stock.

"Everything has an impact on fish populations. We need more studies to look into not just the environmental factors, but also how fishing activities play a role," Thomas said.

Wild Fish Conservancy, a nonprofit conservation group, has filed a petition with the National Oceanic and Atmospheric Administration (NOAA) to have Alaska Chinook salmon receive federal protection under the Endangered Species Act, which would ban commercial fishing of this species. The decision is still pending.

Meanwhile, Thomas plans to return to Alaska next year.

"The coolest part of this work is just being able to see how we're all trying to connect with each other," Thomas said. "We learned so much from history and people's daily lived experiences in these places. Everyone should be a part of all of this work, because we can't do it just by modeling."