Polar bears are walking on an ever-faster 'treadmill' of ice

June 8, 2017, 8:11 a.m.
polar bear walking on sea ice
Photo: Mario_Hoppmann/Shutterstock

Sea ice is important to polar bears. Studies have shown that when ice is lost, they have to travel longer distances to find stable ground, which can be a serious threat to their survival.

But it's not just the traveling; it's the surface they're walking on. A new study has found that increased westward ice drift in the Beaufort and Chukchi seas near Alaska requires polar bears to spend more energy walking eastward on what researchers call a faster-moving "treadmill" of sea ice.

The study, led by the U.S. Geological Survey (USGS) and the University of Wyoming, is said to be the first assessment of the consequences of changing sea drift rates for polar bears.

"Increased sea ice drift rates likely exacerbate the physiological stress due to reduced foraging opportunity already experienced by many polar bears in the warming Arctic, adding yet another 'straw to the camel's back,'" George Durner, research ecologist with the USGS and lead author of the report, said in a statement.

For the study, researchers studied data from radio-tracking collars worn by adult female polar bears in the Beaufort and Chukchi seas, along with sea ice drift data from the National Snow and Ice Data Center. The data consisted of more than 77,000 bear locations matched with the ice drift measures from those areas. The information was collected from 1987-98 and 1999-2013.

In the study, which was published in the journal Global Change Biology, the researchers estimated that a polar bear must catch and eat one to three extra seals each year to make up for the additional energy expended by living on the faster-drifting ice. The extra energy spent goes hand in hand with early ice melt in the spring and more expansive ice melt in summer, which makes hunting seals more difficult.

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