Scientists record a long-distance polar bear swim

Bear 20741 swam in waves of three to six feet. Durner knows of no other polar bear that has swam 426 miles.

"But really, what separates this bear besides the length of her swim was the detail of data that we were able to obtain from this animal," he said. The long swim, Durner said, demonstrates bears' fidelity for sea ice — or at least this bear's.

"Polar bears evolved to exploit the sea ice environment," he said. "Behaviorally, morphologically, they differ from their close relatives, brown bears. Those adaptations are for a sea ice environment . polar bears only occur where there's substantial sea ice during the course of the year because that's where they derive their sustenance."

Before 1995, even during the peak summer sea ice melt, polar bears could find remnant ice over the continental shelf, where seals thrive.

"If they decided to go swimming between ice and floes or between ice and land, they didn't have as far to go," he said. "They probably swam tens of kilometers instead of hundreds of kilometers like we're seeing with some of the bears now."

The second recapture wasn't the end of polar bear 20741. Researchers put another collar on the bear and tracked her until the collar stopped transmitting six months later. Durner hopes to see her again.

"I would be ecstatic," he said.

Her long-distance swim demonstrated a useful behavior but could compromise her ability to survive.

"They're mighty animals," he said, "but they're also vulnerable."