PULLMAN, Wash. – In recent years, polar bears in the Beaufort Sea have been forced to travel well outside their traditional arctic hunting grounds, which has contributed to a nearly 30% decline in their population.
The bears’ home range, or the amount of space they need for food and other resources, was 64% larger from 1999 to 2016 than it was from 1986 to 1998, according to a study recently published in the journal Ecosphere.
“If they have to travel further, these bears use more energy, which can threaten their very survival,” said Anthony Pagano, a postdoctoral fellow at Washington State University’s School of the Environment and lead author of the study. “If we are to preserve the habitat of these amazing mammals, we need to focus on the root of the problem, which is slowing global climate change.”
For the study, Pagano and colleagues from the US Geological Survey used satellite tracking data to analyze the movement patterns of female polar bears from 1986 to 2016 in the Beaufort Sea region north of Alaska.
Their work over the past two decades has shown that polar bears must travel further north of their traditional hunting grounds on the continental shelf in order to stay on their receding sea ice habitat.
Extending approximately 100 miles north of Alaska and Canada, the continental shelf is a shallow water habitat that is rich in fish for the bear’s favorite prey, seals.
In early summer, when seals are weaning their young and are most vulnerable to attack, polar bears often double their body weight from eating the fatty meat.
Anthony Pagano
The researchers’ data show that the sea ice over the continental shelf is receding earlier and further; The bears are evicted from this primary foraging habitat and travel further north into deeper waters where there are fewer seals to hunt for.
“The combined effects of having to keep moving north with the ice in the summer and then retreating in the fall and winter when the ice freezes takes a huge toll,” Pagano said. “Our work underscores the worrying effects of the decline in sea ice on polar bear movement patterns.”
Another interesting result of the study is that around 20% of the polar bear population in the Beaufort Sea completely forego their traditional sea ice hunting areas in summer and autumn. These bears migrate inland along the coast of Alaska and Canada in search of food such as carrion, berries and sometimes even Greenland whale carcasses that are left on the shore by indigenous people who hunt the large aquatic mammals.
“Sometimes there are 50 to 100 polar bears that gather around these whale carcasses and compete with each other for food,” said Pagano. “As more bears land, I suspect there will be much more competition for these food resources and we will likely see further decline in abundance and survival.”
In the future, Pagano and his colleagues at the USGS plan to conduct further studies of polar bears migrating inland to get a better idea of how they are coping with their new terrestrial habitat.
He said the best thing people can do to conserve the southern Beaufort Sea’s roughly 800 remaining polar bears is to focus on curbing global carbon emissions, which are the main cause of Arctic sea ice decline.
Recent modeling has shown that if regulations are put in place to reduce these emissions to avoid global warming of more than 2 ° C (3.6 ° F), it could dramatically slow the decline in polar bear habitat in the Arctic, which in turn would help these animals survive.
“Meeting a polar bear while flying over the Arctic in a helicopter is a surreal experience,” said Pagano. “They are incredibly massive and impressive. It is amazing to see this animal so uniquely adapted to this harsh arctic environment. They are worth the effort it takes to maintain them. ”
