King salmon backbone hangs in a smokehouse.

What happens when salmon don’t return? 

Regional warming in the Arctic is exacerbating the decline of Yukon River Chinook Salmon

By Nicole Pepper and Ellis Goud 

To Brooke Woods, fish is everything. Living just outside the Koyukon village of Rampart, Alaska – one of 50 small fishing communities along the Yukon River – her daily childhood routine involved waking up in the log cabin her family built, walking to school every day, and most importantly, going to fish camp right outside of her home. 

Fish camp is both a location and a tradition. During the summer, families travel to riverside camps to harvest and process fish for the long winters, as well as connect with community and large extended families. Here on the Yukon River, the camps line the banks of the world’s longest salmon migration. The river and its tributaries pass through countless Alaska Native communities across the region, providing a key location to fish throughout the summer.

“Growing up, salmon, fish camp, and family were such important parts of our livelihoods and kinship,” Woods says. “My mom’s siblings – she was one of eleven – would all come to Rampart from surrounding communities where they lived, including my grandma. And we would all go to fish camp, which is a really important place outside of our homes.”

Today, Woods is the Climate Adaptation Specialist at Woodwell Climate Research Center, where she integrates Indigenous Knowledge to shape equitable and science-backed policy in the Arctic. But now, she can’t fish for salmon in the river she grew up near. And neither can anyone else. 

Salmon as subsistence 

Last year, the Alaska Department of Fish and Game and Fisheries and Oceans Canada signed an agreement suspending the harvest of Chinook salmon for seven years – the length of their life cycle – in response to declining population numbers. A combination of mortality from bycatch and environmental factors from climate change has exacerbated their decline. 

Chinook salmon, also known as king salmon, are one of the main salmon species in the Yukon River. They are the largest, most nutritious, and most valued fish in Alaska Native culture. Over the past few years, their numbers across the state have fallen below the long-term average. Historically, 375,000 salmon passed through the Yukon River Drainage every year. Last year, there were only 65,000.

The ban on Chinook harvesting is devastating for Alaska Native communities because salmon, among other fish, make up a large part of their traditional diet. Rich in protein, omega-3 fatty acids, and essential vitamins, salmon has served as a primary food source for thousands of years. 

Subsistence provides food security in rural Alaska and is necessary for community health. Due to remoteness, short growing seasons, and high transportation costs of food, fresh produce is scarce.  Without access to salmon, Alaska Native communities often have to replace this crucial protein with expensive commercial foods that are lower in quality and nutrition.

Beyond nutritional and economic benefits, salmon is also a vital part of Alaska Native culture. Knowledge of salmon harvesting is passed down through generations, and the sharing and receiving of salmon is critical to preserving traditional ways of life. It is also a way for communities to connect with the land. 

“Salmon is such an important part of who we are as Indigenous people,” Woods explains. “I feel like I’m very strong in my culture because of salmon.”

But as salmon populations decline and harvesting halts, Alaska Native communities lose access to one of the most vital fish species in their diet and culture. 

“Our foods, they keep us well in so many different ways,” Woods says. “And when that’s taken away from you, it’s hard to find healthy ways to get through.”

The journey across the Yukon River 

Every June, Alaska Native communities wait in anticipation for the salmon to arrive. 

Yukon River Chinook salmon begin their lives in freshwater spawning grounds and spend up to a year growing into juveniles, also known as smolts. After going through smoltification, they migrate into the ocean and spend anywhere from one to six years maturing and growing into adults. When they are ready to reproduce, salmon migrate from the Bering Sea back to their spawning grounds across the Yukon River basin. 

As adult Chinook salmon make the journey upstream to spawn, some migrate as much as 2,000 miles. Starting in the summer, typically from June to September, the salmon pass through the Yukon in different groups called runs. 

To George Yaska, the Indigenous Knowledge Liaison for the U.S. Fish and Wildlife Service in Alaska, the summer season passes in phases of fish runs. Yaska grew up in Huslia and lived off of fish on the Koyukuk River, a tributary that flows downstream into the Yukon. 

“The very first salmon that show up are the fish that we want to start cutting,” Yaska says. “They’re the freshest, the strongest, the biggest, and the fattest.” 

Chinook and chum (dog) salmon migrate through the Yukon first, followed by coho (silver) salmon. While many people travel to the riverside to fish, Yaska says Alaska Native fishers only take what they need.

“If we did well early, we would stop [fishing],” Yaska says. “There were lots of people above us. The fish haven’t got to them yet, and we have to let them fish.”

But year after year, less and less salmon are passing through the Yukon. Growing up, Yaska’s family would take 40 to 50 fish to keep them fed through the winter. In the 90s, it was 10 to 20. And this year, it’s zero. 

Warming temperatures are killing salmon 

Science indicates that warming water temperatures are a major contributor to low salmon returns, NOAA Fisheries says. As climate change advances, rivers in higher latitudes, like the Yukon River, are warming nearly twice as fast as rivers in temperate areas. In recent years, Alaska has recorded multiple record-breaking heatwaves – including this summer. The state released its first heat advisory ever in June.

In outer regions around Fairbanks, temperatures above 75 degrees trigger a heat advisory. In the interior, it’s 85 degrees. In June, temperatures were expected to reach the mid-80s. 

While these temperatures may not appear dangerous, they can cause extreme ecological changes in the Arctic, including increased wildfires, permafrost thaw, soil erosion, and most important for salmon, ocean and stream warming. 

Increased water temperatures impact salmon health at every stage in their life, especially during their migration period. They become stressed in warmer water, forcing them to burn energy faster and swim slower. Salmon also become more susceptible to disease.

Daily maximum stream temperatures have risen over 10 degrees above the optimal spawning temperature of 5 degrees Celsius this summer. In July, Yukon River Drainage’s pilot station – the first station in the watershed that all salmon must pass through to migrate upstream – exceeded the critical temperature threshold of 64.4 degrees Fahrenheit (18 degrees Celsius) nine days in a row. Once a stream’s temperature passes this temperature limit, fish can lose their ability to function. 

In the Salcha Station, located in the middle of the Yukon River Drainage, daily maximum stream temperatures were higher than the maximum optimal spawning temperature of 55 degrees Fahrenheit (12.8 degrees Celsius) throughout the majority of the summer. The Salcha Station is historically one of the most abundant spawning grounds for Chinook salmon. 

The management crisis

Issues around commercial harvesting have also played a role in declining salmon runs in Alaska. In the mid-90s, the majority of Chinook salmon in the Yukon were overharvested by commercial fishermen several years in a row. In 1995, the first 10-mile stretch of the Yukon River after the Bering Sea (also known as Y-1) was the site of a large-scale overharvesting event. 

“Eight hundred commercial fishermen fished for 9 and a half or 10 and a half inch fish, which is huge,” Yaska says. “In a 24-hour opening, they caught 147,000 kings.”

Because there were so many taken at once, salmon have not been able to rebound to their initial population numbers.  

“Ever since then, the run has been demolished,” Yaska says. 

Bycatch at sea also poses a threat to salmon populations. Trawlers catching pollock, a common fish in the Bering Sea, are the main source of salmon bycatch. When salmon are unintentionally caught by large industrial trawlers, the fish often die from stress, injury, or suffocation. 

In 2011, the NPFMC implemented a Chinook salmon bycatch limit in response to unusually high bycatch numbers – including a peak of 122,000 caught in 2007. Amendment 91 designed a system to manage Chinook salmon bycatch in the Bering Sea pollock fishery by setting two caps on the number of salmon that could be incidentally caught, with a high limit of 60,000 and a low limit of 47,591 depending on the overall size of the salmon runs that year. 

Amendment 110, also called the Three-River Index, was developed shortly after Amendment 91 to further monitor and protect Chinook salmon populations. If the number of salmon returning to the Kuskokwim, Unalakleet, and Upper Yukon River systems is less than 250,000 fish, the cap is reduced to a high limit of 45,000 and a low limit of 33,318.

To measure bycatch, every pollock vessel in the Bering Sea must carry at least one certified observer to monitor, identify, and count salmon. Additionally, every vessel has an Electronic Monitoring system and cameras to record the vessel’s catch. 

But even with current management actions, salmon populations are still struggling. As stream temperatures increase, salmon are under possibly lethal conditions during the summer months of migration. Decreasing bycatch numbers in the Bering Sea before salmon migrate through the Yukon River gives the population the best chance of dealing with today’s climate stressors. 

“All the other issues that are now in play – temperatures, ocean conditions, ecosystem problems due to trawling out in the Bering Sea – all of those things are now having an impact when they didn’t before,” Yaska says. 

Taking community action

When fewer salmon return to the Yukon River, tribes, communities, and families suffer. As climate warming and bycatch decimate salmon populations, Alaska Native communities believe the best course of action towards salmon success is Indigenous-informed management practices, not banning subsistence. 

“Shutting down subsistence in rivers – shutting down tribes – is not the solution,” Woods says. “Tribes are not the reason we are seeing the salmon collapse. We have traditional values of only taking what you need.”

Woods has spent almost 10 years in the advocacy sphere, where she and Alaska Native community members have worked to uplift tribal sovereignty in governance and management. Although the work is exhausting, Woods has seen progress and solidarity across the region. 

“Tribes and Alaska Native organizations are exhausting all avenues to ensure that our salmon survive and that traditional practices, or subsistence, is provided,” Woods says. 

When Alaska Native community members are represented in government bodies like the Alaska Board of Fisheries, management practices can focus on encouraging representative and equitable decision making while protecting both salmon and subsistence. 

Yaska, who works with tribes on both the Yukon and Kuskokwim Rivers through the U.S. Fish and Wildlife Service, ensures the integration of Alaska Native knowledge into conservation efforts. By giving community members a seat at the table, their knowledge and way of life can be preserved. And as Alaska Native culture and tradition is protected, so are the salmon that communities rely on. 

“Because salmon have no voice, we have to try to speak for them,” Yaska says.

Trees play a crucial role in mitigating the effects of climate change by absorbing climate-warming carbon dioxide from the atmosphere. As temperatures climb and human activities release more and more carbon, managing and protecting trees has become essential to curbing global warming.

In 2021, partners at Woodwell Climate Research Center, Local Governments for Sustainability (ICLEI), and the World Resources Institute (WRI) launched a tool providing communities with fine-scale information about their trees to better manage and protect them. 

The Land Emissions and Removals Navigator (LEARN) tool is an interactive map and data analysis system that contains remote sensing and forest inventory data on tree cover, land use change, disturbances, and carbon stocks. Users – mostly county and municipal planners – can generate a custom estimate of carbon emissions and removals from trees for any area in the contiguous United States. 

“That’s the idea with the LEARN tool – it makes these complicated datasets readily accessible,” Dr. Rich Birdsey, Senior Scientist at Woodwell Climate and collaborator on LEARN, says. 

Easily accessible tree cover data gives community members the opportunity to take action at the local level. For example, a city planner might use LEARN to see if trees are gaining or losing cover in their city. If trees are losing cover, they can work with their municipal departments to increase the urban canopy. 

In the last year, scientists added the ability to identify mature and old-growth (MOG) forests to the tool. MOG forests are the later stages of forest development, where trees are larger and store more carbon than younger forests. They are also more resilient and adaptive in the face of disturbances and play a role in maintaining biodiversity by providing habitat for wildlife. This makes them a high priority for protection. 

In addition, users can now view the protection status of an area. Ranging from low to high, they describe what activities – like logging and mining – are allowed in the area. Users can draw connections between activities and carbon estimates, and hopefully, change local land management practices to better protect their trees. 

LEARN’s protection statuses include: 

“The assessment is more relevant now because the Department of Agriculture has proposed a rule that would relax forest protections, particularly with respect to roadless areas,” Birdsey says. 

In June, U.S. Secretary of Agriculture Brook Rollins announced that the U.S. Department of Agriculture is rescinding the 2001 Roadless Rule. The rule protected 58 million acres of roadless land within the National Forest System from construction and commercial logging. With no protections for roadless areas, logging and commercial uses of land will be allowed.

“Because of the large area currently designated as roadless, and the significant area of mature and old-growth forests within these areas, this is of great concern to the conservation community,” Birdsey says. 

Birdsey hopes that the LEARN tool can mobilize community members and land managers to take action. Whether it be working with local governments to protect MOG forests or connecting neighboring counties to each other, communities can collaborate to tackle climate change on a local level. 

“Since federal policies are opening up more public land to logging, it is becoming more important than ever for local communities to weigh in on forest management plans,”Birdsey says. 

In the northern ecosystems of the Alaskan boreal forest and tundra, wildfire is a natural – and even necessary – process. But as temperatures rapidly warm, wildfire frequency and severity in the state are breaking historical records.

Scientists at Woodwell Climate Research Center are studying the effects of these increased fires on the ecosystem. In a study published earlier this year, a research team led by Research Scientist Dr. Scott Zolkos examined the relationship between northern wildfires and one concerning byproduct of them: mercury pollution. 

Higher temperatures, more wildfires, more pollution

In the last 25 years, Alaska has experienced some of the worst fire seasons on record. One of the reasons behind this is that climate change is hitting the north harder than other regions. 

Northern latitudes, including the Arctic and boreal regions, are warming three to four times faster than the rest of the planet. As warmer temperatures melt snow earlier in the year and dry out soil and vegetation, the fire season lengthens and intensifies. According to Woodwell scientists, 2024 was the second-highest year for wildfire emissions north of the Arctic Circle. 

“It’s really sort of a new phenomenon, the level of burning we’re seeing in the tundra,” Dr. Brendan Rogers, Senior Scientist, says. 

Increasing fires means increasing air, water, and ecosystem pollution from the byproducts of burning vegetation and soils. Mercury is a toxic pollutant in wildfire smoke, but there is sparse research on mercury release from northern peatland wildfires which means scientists don’t yet have a great understanding of how increasing northern wildfire activity could counteract efforts to curtail human-caused mercury release. To understand these impacts, Zolkos and collaborators studied areas of the Yukon-Kuskokwim (YK) Delta in southwestern Alaska— a peatland environment that burned in 2015. The summer of 2015 made history as one of Alaska’s worst fire seasons, with over 5 million acres of land burned. 

The research team used peatland soil samples that were collected between 2016 and 2018 by undergraduate participants of The Polaris Project to measure mercury. They then used the new mercury data together with organic carbon and burn depth measurements from another recent study to develop models that predicted mercury emissions from the 2015 wildfires.

Measuring mercury release

Mercury continuously cycles through the environment in air, water and soil, often changing between liquid and gaseous forms. It enters the atmosphere as emissions from human activities like the burning of fossil fuels and natural processes like wildfires and volcanoes. High levels of mercury can accumulate in the ground when vegetation takes up mercury from the atmosphere, then decomposes and deposits it into the soil. In northern peatlands, mercury has been accumulating with organic matter for thousands of years. 

Mercury emissions occur when wildfire burns organic matter in soil and releases mercury that is bound to it back into the atmosphere. With increased temperatures and wildfire activity, the stabilization accumulation of mercury in the soil is threatened – and so is air quality. 

“There are huge mercury stores in northern peatlands,” Zolkos says. “If peatlands burn more, it could potentially offset global efforts to reduce human mercury release into the environment.” 

Zolkos and collaborators found that levels of mercury in peat in the YK Delta were similar to those in peatlands elsewhere in the north. Using an atmospheric chemical transport model developed by collaborators, the researchers also found that mercury deposition within 10 kilometers of wildfire sites was two times higher than normal, even though the majority of emissions from the fire traveled beyond Alaska.

With this information, Zolkos believes that increasing fire activity has the potential to unlock large amounts of soil-bound mercury in the North. The challenge now is figuring out exactly how much mercury is being released and where it ends up. 

As a step to understanding this, Zolkos is leading a pilot project to develop an atmospheric mercury monitoring network across wildfire-susceptible peatlands in Alaska and Canada. Twenty-six air samplers, which collect mercury molecules in the air, were deployed at seven sites in Arctic-boreal peatlands across Alaska and Canada during the summers of 2024 and 2025. After the 2025 summer season is complete, the samplers will be sent to a lab at Harvard University, where Zolkos will measure their mercury content.

“Our goal is to work with collaborators to deploy these simple and cost-effective samplers that capture mercury in the atmosphere,” Zolkos says. “And from that, we can back-calculate the concentration of mercury in the air to understand wildfire impacts.”

By studying trends, Zolkos can compare levels of mercury in the air in areas affected and not affected by wildfire. And with added contextual data, scientists can model how much mercury might have been released from the soil and vegetation by wildfire. 

Understanding wildfire impacts on air quality

In addition to containing mercury, wildfire smoke also emits particulate matter (PM2.5). PM2.5 refers to particles that are smaller than 2.5 micrometers in diameter – thirty times smaller than the average human hair. When breathed in, they can affect the heart and lungs and cause a variety of health problems, including aggravated asthma, decreased lung function, and increased respiratory symptoms. 

Together with collaborators from the Permafrost Pathways project, Zolkos is also collaborating with Alaska Native communities to install PurpleAir sensors, a system of particulate matter monitors, to support tribally-led wildfire air pollution monitoring. This project helps to address monitoring needs in Alaska, where nearly 90% of rural communities reached or exceeded unhealthy levels of PM2.5 at least once due to wildfire in the last two decades. 

“It’s a really great opportunity to work together with Alaskan Native communities and also to share knowledge, learn from them, and try and help them with any needs that they have for environmental monitoring,” Zolkos says. 

So far, particulate matter sensors have been deployed in Pond Inlet in Nunavut, Canada, Churchill in Manitoba, Canada, and Akiachak, Alaska. 

“The complex impacts of wildfire on Arctic and global communities is not something that can be solved by taking a measurement and seeing a number alone. These climate health impacts require a more holistic way of thinking and doing research” Dr. Sue Natali, Senior Scientist and lead of the Permafrost Pathways project, says. “What gives me hope is that the Western scientific community is now listening and hearing more from Indigenous partners to co-produce research to support climate resilient communities,”