Melting Sea Ice Forces Polar Bears to Travel Farther to Survive

Polar bears in the Beaufort Sea have been forced to travel outside their usual Arctic hunting grounds because of declining sea ice. Their increased, sprawling movement has contributed to a nearly 30% drop in their overall population.

Recent research has found that the bears’ home range was about 64% larger from 1999-2016 than it was in the decade-plus earlier from 1986-1998. Their home range is the amount of space the animals need for food and other resources required for survival and reproduction.

Polar bears (Ursus maritimus) depend on sea ice for hunting and fishing. They stalk seals on the ice, ambushing them when they surface to breathe at openings in the ice. But as the Arctic temperatures warm and sea ice melts, polar bears have to travel increasingly farther to find habitat.

For their research, scientists studied polar bears in the Beaufort Sea, an outlying sea of the Arctic Ocean, located north of Canada and Alaska.

“Our study was designed to quantify the impact of sea ice declines on polar bear home range size in the Southern Beaufort Sea,” lead author Anthony Pagano, a postdoctoral researcher in Washington State University’s School of the Environment, tells Treehugger.

“From our telemetry data, we knew anecdotally that bears were moving greater distances to remain on the summer sea ice than they had in the 1980s and 1990s. This study sought to quantify the extent of that change while also evaluating the effect of summer land use as an alternative movement strategy.”

The results were published in the journal Ecosphere.

Tracking Movement

Pagano and colleagues from the U.S. Geological Survey used satellite tracking data to study the movement patterns of female polar bears from 1986-2016. They found that polar bears have been forced to travel farther north of their usual hunting grounds on the continental shelf to remain on sea ice.

The continental shelf is the edge of the continent that is underneath the ocean. The shallow area contains lots of prey including fish and seals.

“Increased movements would result in increased energy expenditure relative to previous time periods. Additionally, displacement from their primary foraging habitat over the continental shelf may reduce polar bear access to seals,” Pagano explains.

Some polar bears travel to find sea ice for traditional hunting, while others move inland on the coast, looking for food like berries and carrion instead.

“While little data exists on polar bear feeding rates during the summer, one study that collected data in 2009 found polar bears on the sea ice in the fall in the Southern Beaufort Sea were primarily fasting, which suggests that these bears that are making these long distance movements to remain on the sea ice have little access to seals,” Pagano says.

“In contrast, bears that are using land during the summer were able to greatly reduce their home ranges, which suggests this movement strategy (land use) would be more energetically advantageous than remaining on and moving with the receding summer sea ice.”

Polar Bear Decline

Polar bears are categorized as vulnerable by the International Union for Conservation of Nature (IUCN) Red List of Endangered Species. According to the IUCN, there are approximately 26,000 polar bears in the world today.

Having to travel farther because of melting ice has had an impact on the number of bears that survive, researchers say.

“Polar bears in the Southern Beaufort Sea were documented to have declined approximately 30% in abundance between 2001 - 2010. This population was also documented to have declined in body condition during this time. Since these declines, abundance is estimated to have remained stable from 2010 - 2015."

Researchers plan to continue their work to follow how the bears are coping with the changes in their habitat.

Pagano says, “These results help illustrate the impact that changes in Arctic sea ice are having on polar bear movement patterns in the Southern Beaufort Sea and help for better predicting how polar bears in the Southern Beaufort Sea may respond to future declines in Arctic sea ice.”