Climate-driven Change in Eating Habits Behind Drop in Mercury Accumulation for Polar Bears, Finds Study

Polar bears are consuming less harmful mercury in their diet not because there’s less of the toxin in the environment, but because climate change is altering the way the bears forage for food, new research has found.

Mother polar bear and cub on the Arctic Ocean.

Mother polar bear and cub on the Arctic Ocean. NASA

Hair samples taken from southern Beaufort Sea polar bears between 2004 and 2011 found mercury levels down about 13 percent per year among adults, according to a study in the journal Environmental Science & Technology.

After factoring in the animals’ body-mass indices and food sources, the scientists determined that the polar bears were accumulating less mercury because as sea ice diminishes with climate change they were consuming fewer ringed seals, which eat higher on the food chain and so accumulate more mercury. Instead, the bears were eating more of others species like bearded seals and bowhead whales, which eat zooplankton.

Study co-author and biologist Todd Atwood of Alaska Science Center said that about 20 percent of the area’s bears have moved inland to eat the carcasses of bowhead whales harvested by hunters. But that’s a limited resource, warned another researcher, and also brings hungry bears into more dangerous contact with local human populations.