Polar Bears Spend An Extra Month on Land Annually as Sea Ice Declines, Study Finds

As ice-free summers in the Arctic's Baffin Bay grow longer each decade, bears are losing a foothold on their habitat.

In Baffin Bay, polar bears walk between countries. For Ursus maritimus, literally the “bears of the sea,” the sea ice that covers much of the North Atlantic and Arctic oceans is a bridge — between Greenland and the islands of the Canadian Arctic, and between a food scarce summer and the bounty of prey on the frozen ocean. For much of the year, polar bears use the sea ice as a platform to hunt ringed seals and bearded seals. In the spring, after seals have their pups, prey is more abundant. Hunting polar bears aim to find enough to sustain them through a summer fast, when the ice melts and they take refuge on land.

photo of polar bear
An extra month spent on land each year means an extra month of forced fasting for polar bears, with implications for nutrition and reproduction. Photo by Se Mo.

But sea ice decline disrupts the balance polar bears have struck between land and ice. In a recent study published in Ecological Applications, an international team of scientists looked at over two decades of data to decipher that polar bears spend on average a month longer each year on land than they used to. As the Arctic continues to warm, melting sea ice cuts their springtime hunt earlier each year, impacting both nutrition and reproduction.

“These early behavioral and physiological [effects] of climate change — like bears spending time on land and off the sea ice, and bears being in poor condition — are early indicators of what we expect to be demographic effects, or reduced survival,” says Kristin Laidre, lead author on the study and an Arctic ecologist at the University of Washington. “These are the first indicators for these polar bear subpopulations that there’s something wrong.”

Between 2009 and 2013, Laidre and a team of scientists from Canada, the United States, Greenland, and Norway tracked a subpopulation of Baffin Bay’s roughly 2,800 polar bears on the pack ice of Baffin Bay using radio collars. They then compared this data with historic data collected from 1991 to 1997. The changes they noticed reflected a rapidly changing landscape.

The Arctic is warming twice as fast as the rest of the world. According to NASA and the National Snow and Ice Data Center, sea ice in the Arctic has declined by an average of almost 13 percent each decade since 1979. In many areas across the region, like Baffin Bay and the Bering Sea, the ice pack is breaking up earlier and reforming later in the year. In 1991, when the data in Laidre’s study begins, Arctic sea ice covered 2.5 million square miles at its September minimum. Last year, the ice measured 1.6 million square miles.

It goes without saying that forced fasting an extra month can have significant effects on polar bear health. As Laidre and her team tracked polar bears on the ice, they assessed the health of these bears by sedating them to analyze their body condition. They also evaluated the size of these bears’ litters and compared this data with sea ice availability from the current and previous year.

The results showed that longer summers on land led directly to both malnourishment and fewer cubs, putting future survival at risk.

This is far from the first study finding that climate change impacts polar bears. In fact, polar bears — which are listed as vulnerable on the International Union for the Conservation of Nature Red List — have been called the “poster child” of climate change. As Megan Owen and Ronald Swaisgood from the San Diego Zoo explained in a 2008 commentary in the journal Biodiversity, the “lonely Polar Bear isolated on a small iceberg floating out to see, implicitly on a course to extinction” became a widely used symbol to drive media and political attention towards climate change. Author Jon Mooellam called polar bears “the celebrities of the wildlife world.”

Of course, it seems that you can draw any species’ name out of a hat to represent how climate change and other human impacts devastate wildlife populations. In Baffin Bay alone, which sits along the fabled Northwest Passage, polar bears aren’t the sole victims. Sea ice decline directly impacts other ice-dependent predators like walruses and narwhals, while increased shipping traffic during longer ice-free summers brings its own suite of challenges that impact seals, belugas, and other marine mammals by disrupting the food chain. This climate-change induced disruption also affects human communities. Subsistence hunters depend on the ice pack and its marine mammals.

According to Laidre, polar bears are a harbinger for the future. They show how landscapes are changing, and how those changes affect species, from the charismatic megafauna to microbes. “[This study] adds to the growing body of evidence that sea ice loss has direct effects on top predators and cascade effects through the ecosystem,” she says.

Whether or not polar bears represent the best canary in the coal mine of the climate crisis (and some would argue that heat waves, wildfires, and floods might serve as more resonant symbols), Ursus maritimus still steps onto a precarious icescape — a changing Arctic representing an altered planet.

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