When the beavers came to streams near the Alaskan village of Venetie, the fish disappeared. 

For generations, the Gwichʼin people of the tiny Arctic village depended on the bounty of white fish pulled from Martin Creek. 

“We don’t fish there anymore,” said tribal elder Eddie Frank. “The fish are gone. When the beavers came, they changed the creek.”

Over the last several decades, people in remote Alaska communities have observed an influx of beavers as the warming climate has fostered the growth and expansion of woody vegetation,  providing more forage and dam construction materials for the eager engineers. 

Recent studies have highlighted a vicious circle of expanding Arctic beaver populations and global warming. As climate change creates new habitats for beavers in the High North, their dams can cause more permafrost to thaw, releasing huge stores of greenhouse gases to further warm the atmosphere.

Scientists are trying to figure out the degree of permafrost thawing the toothy rodents’ dam-and-den building is causing and how fast those defrosted organic soils will degrade and release long-trapped carbon and methane.

But in addition to the implications for the planet’s atmosphere, the beavers are having impacts on the ground that are raising concerns in villages like Venetie about disappearing food sources, deteriorating water quality and increasingly difficult navigation of waterways.

“Stream by stream and floodplain by floodplain, beavers are transforming lowland tundra ecosystems,” said the 2021 Arctic Report Card released in December by the National Oceanic and Atmospheric Administration. 

In 2018, researchers using satellite imagery mapped 12,000 beaver ponds in Alaskan tundra, double the number observed 20 years earlier. Prior to the mid-1970s, residents of the Alaskan Arctic encountered few beaver ponds. Today the rodents and the waterworks they construct are a source of angst for Indigenous people and an increasing focus of Arctic science.

“The environmental changes caused by beavers are not always easy for people to live with,” according to a study prepared by the University of Alaska Fairbanks for the Selawik National Wildlife Refuge.

Biologists from the U.S. Geological Survey, the National Park Service, the U.S. Fish and Wildlife Service and the Alaska Department of Fish and Game have teamed with university research scientists from Alaska and the lower 48 states to try to grasp the cascading consequences of the spread of beavers and their ponds. 

But research that was just gathering momentum in 2018 stalled during  the pandemic, leaving most of the questions surrounding the beavers’ expansion of their territory and the consequences of their dams still largely unanswered.

Beavers and a Changing Landscape

“It’s not so much that we care about beavers,” said Ken Tape, an associate professor at the University of Alaska, Fairbanks’ Geophysical Institute and a leading researcher exploring beaver migration in the Arctic. “We care about how their engineering is having consequences in changing the landscape; how beaver ponds that are popping up in increasing numbers have consequences.”

The effects of beavers expanding their range illustrates how interlinked Arctic impacts have rippling consequences on  people, ecosystems and food sources, said Susan Georgette​, U.S. Fish & Wildlife Service ​manager of the Selawik National Wildlife Refuge.

“Beaver are not simply furry rodents moving their way across the Arctic, but one of the cogs in a complex mechanism shifting the landscape from the familiar Arctic we have known,” Georgette said. “Beavers are simultaneously the result of climate change and one of the factors amplifying climate change. Their impact does not occur in isolation.”

The dizzying acceleration of warming in the Arctic has transformed the region into a warmer, wetter and more diverse environment, she said. The beaver migration has become part of that intricate transition and foreshadows the Arctic becoming a much different place by the end of the century.

Scientists say there are several factors to explain why beavers are homesteading in Arctic regions where neither researchers nor Indigenous people have ever observed them in the past.

In the typically treeless tundra, warming temperatures have encouraged the increasing growth of vegetation, especially of shrubs that provide beavers with bark to eat and branches to build with. Higher temperatures also mean lakes and streams freeze solid for shorter periods of time or not at all, allowing beavers to continue their construction for longer portions of the year.

With temperatures in Alaska rising twice as fast as the rest of the globe, winter is freezing later and spring is arriving earlier, providing beaves with much longer seasons in which to forage and build. 

Under such favorable conditions, there’s little to stop their expansion. On the tundra, beavers have few natural predators and little competition for resources, though they are often trapped for their fur or removed as pests.

Warming Is Expanding the Habitats of Animals Large and Small

Beavers are just one of myriad creatures that are expanding their habitats in response to climate change.

In the Arctic, the same warming trend that has led beavers to extend their territories northward also has allowed moose and snowshoe hares to populate northern tundra regions. 

The increase in shrubs and earlier snowmelt has opened up regions hundreds of miles north of the animal’s historic home turf, according to a 2016 study.  

Shifts in animal habitat stimulated by climate change could have “profound” consequences across the globe, according to a 2017 report published in the journal Science.

 “Climate-driven changes in species distributions, or ‘range shifts,’ affect human well-being both directly (for example, through emerging diseases and changes in food supply) and indirectly, by degrading ecosystem health,” according to the report.

The report calls out the Arctic as an example of the peril, saying “changes in distributions of fish, wild reindeer, and caribou are impacting the food security, traditional knowledge systems, and endemic cosmologies of Indigenous societies.”

Climate change can influence the spread of insects as well, exposing humans to greater risk of vector-borne diseases. Increasing temperatures have led to the northward migration of several insect species, including mosquitos responsible for the spread of the Zika virus, dengue fever, chikungunya and malaria.

 Scientists believe two key disease-spreading mosquitoes—Aedes aegypti and Aedes albopictus—will significantly expand their global range, posing a threat to 49 percent of the world’s population by 2050.

Trickle Down Effects

Beavers have different effects on waterways depending on the number and size of the dams they build, and the surrounding habitat. The dams alter the hydrology of a stream by slowing the flow, storing and spreading water to create wetlands, raising the water table and lowering the oxygen content of the water. 

Fish can be especially threatened by the dams’ blockage of free-flowing streams, which can restrict access to spawning grounds, as well as lower oxygen levels and increase turbidity of the water. The disruption to the hydrology can encourage the proliferation of non-native species that compete with the traditional population of Dolly Varden trout, Arctic grayling and freshwater sculpin that are a primary food source for Indigenous people near many streams. The ponds that form behind the dams can increase water temperatures during winter, which may disadvantage some Arctic species by reducing spawning habitats and inhibiting fish egg incubation.

But researchers also see positive effects on native fish from the beavers’ work. 

Some ponds can create an environment conducive to a robust fish population, bolstering the food supply for native people in those areas. 

“Most of these ideas are still in the hypothesis stage,” Tape said. “But finding the answers is important to the people whose lives are so entwined with the environment.”

Alex Whiting, director of Environmental Programs for the native Village of Kotzebue, said the potential disruption dams pose to fish populations goes beyond eliminating a single, vital food source.

“It could have a devastating impact on the annual cycle of resources,” he said. “Fish play a large part in the food chain.”

If the fish disappear or the population declines steeply, that would have consequences not only for the wild food chain, he said, but also to trading, a cultural mainstay for indigenous people.

“If a family has a gunny sack of fish, they can take that and trade for something they need,” he said. “But if they don’t have that gunny sack, they can’t trade for what they need; maybe caribou meat.”

Human damming of wild rivers for water storage and power generation during the last century had similar consequences to those of the new beaver dams, he said. 

“Look at what happened to the fish when those dams went up,” Whiting said. “Spawning was disrupted. Fish were no longer able to freely grow in the places they thrived. So, the number of fish went down. That’s what is happening with the fish and the beavers. The beaver dams are disrupting the natural habitat of the fish just as the big dams did on rivers, and you can see from history what that does.”

Indigenous Traditions at Risk

Many fishing spots have sustained families for generations. As a young Inupiaq adult, Diana Ramoth, who’s 65 now and lives in Selawik, remembers her father taking her to a location where the abundance of fish could feed her family and other Inupiaq families. It was important for him to pass on to her generation this bountiful place, she said.

“He wanted to show me,” she said. “It was a small creek where the fishing was good for the family. It’s not there now. The beavers closed it. So it is lost to my family.”

To understand the scale of the impacts of beaver dams on the tundra and Indigenous people, individuals and organizations in Alaska, Canada and Eurasia have joined forces. The Arctic Beaver Observation Network, a coalition of scientists, tribal entities, local observers and agency land managers, formed in 2020 to confront the beaver issue.

Beavers moving northward in the Canadian Arctic are disrupting Arctic char, one of the main food sources for Nunavik communities scattered across the northern third of Quebec province, according to a 2021 report co-produced by Mikhaela Neelin, a master’s degree candidate at Montreal’s McGill University, and Nunavik land claims organizations.

The exploding beaver population, along with streams shrunken by drought and choked with debris from thawing permafrost, were among the primary worries of community members surveyed for the report, which included their observations of beavers moving into the Arctic and how that affected water quality and the availability of fish.

“You know when I was young, there were no beavers up here. None. You never heard of a beaver,” Kuujjuaq resident Johnny May said in the report.

“There’s a little creek going to Stewart Lake, we used to catch all kinds of speckled trout in the fall when the ice was thin, but over the years the beavers have built dams so there is no more fish in the creek.”

Recollections of Inuit, like May, and aerial surveys reveal the extent of the beavers’ impact in the Canadian Arctic. 

In an area along Ungava Bay, Neelin and her research colleagues searched more than 500 miles of lake shores, rivers and streams for beaver. They identified 46 lodges, 22 food caches, 33 dams and 8 partial dams. But the 2019 survey best highlighted the vast knowledge of the native people.

“The helicopter survey gave a snapshot in time, but the observations from Inuit hunters gave the broader picture of the expanding populations,” Neeling said.  

In Nunavik, Inuit fishers expressed fear that beaver dams could change the migration habits of the Arctic char, which is one of the most consumed foods among villagers, Neelin said. Beaver-built barriers can cause Arctic char to change the water passages they use during their brief migrations, making fishing grounds more difficult to find and catches less bountiful.

“For Inuit who have traditional ice fishing sites near to their communities, the absence of Arctic char may impact the food that they are able to provide for their families,” Neelin said. “If Arctic char decline and/or shift their overwintering habitat due to beaver presence, this could have important implications for Inuit food security.”

In addition to blocking waterways, the wetlands that expand behind the dams can collapse roads and trails, making it more challenging for indigenous people to reach traditional hunting grounds and berry fields that they have relied on for generations. Other studies have shown that losing access to traditional food sources harvested in the wild can lead to indigenous populations relying more on store-bought foods that are expensive and less nutritious.

“Moreover, Inuit knowledge passed down over generations guides harvesting practices and cultural identity is intrinsically connected to the Inuit food system,” she said. “Thus, the rapidly changing environment and changing distribution of harvested species impacts many facets of Inuit livelihood.”

To reduce the beavers’ impacts, regional wildlife managers have recommended removing the dams, hunting and trapping the animals and managing the vegetation that allows them to thrive.

“There is no one-size-fits-all solution, but to me, the ultimate goal is to support Inuit organizations in their decision-making for wildlife management, and to provide information and tools so that they can take steps towards climate change adaptation for themselves,” Neelin said. “We expect that beaver populations will continue to grow and expand, and it is important to continue studying the impacts of beavers on other species, rivers, and permafrost in the Arctic, since this is very new.”

Beaver Fevers

The rapid expansion of the beaver population also poses potential health threats to native villages.

Indigenous people in the Arctic have increasingly reported cases of giardia, a tiny waterborne parasite that causes serious intestinal illness. Scientists know beavers are hosts of the bug and their ponds provide an ideal breeding ground, but haven’t yet confirmed their connection to the outbreak of illnesses.

Beaver ponds also have been identified as a potential source of mercury, a highly toxic heavy metal that can be released by thawing permafrost, build up in fish and cause serious health problems in humans. Although the amount of mercury in fish taken from Arctic beaver ponds is below the danger level established by the Environmental Protection Agency, the potential effects on the health of native people who consume the fish is drawing increasing scrutiny from researchers.

“There are some really large changes that we need to understand,” said Michael Carey, a research fish biologist for the USGS Alaska Science Center and one of the scientists examining the rippling consequences of beaver ponds.