Arctic ice melts in the Chukchi Sea are the suspected cause of the bears swimming toward either land or more remote icebergs, The New York Times reported Saturday. Such sightings were rare until 2004 but have grown more common as polar bears hunt for seals.

"It's not unusual for bears to be swimming," said Susanne Miller, a biologist with the Fish and Wildlife Service, "but depending on their condition and how much time they're spending in the water, this could be problematic. It's going to cost them more energy to swim through water than travel on land."

Eight of the 10 bears seen in an aerial survey were within 15 miles of shore. Others were 35 and 50 miles from shore.

"There were some years when some bears may have had to swim as far as 100 miles," Steven C. Amstrup, the senior polar bear scientist with the U.S. Geological Survey in Anchorage, wrote in an e-mail message. "Now the ice is much farther offshore, more consistently and for longer."