The arctic is home to a growing number of whales as sub-arctic species are expanding their territory into newly ice-free arctic waters, researchers report. Researchers at the University of Washington have participated in a study using underwater microphones to track the whales by their sounds as they move through the narrow passage of the Bering Straight between Alaska and Russia. Three years of recordings reveal more detections of both arctic and sub-arctic whales traveling through the 58-mile narrow choke point as seasonal sea-ice coverage is in an ongoing decline with climate change, the university reported Wednesday. Arctic beluga and bowhead whales have been detected migrating seasonally through the region from the arctic south to spend winter in the Bering Sea, the researchers said, while large numbers of sub-arctic humpback, fin and killer whales are traveling north through the Bering Strait to feed in the biologically rich Chukchi Sea. "It's not particularly surprising to those of us who work up in the Arctic," UW oceanographer Kate Stafford said. "The arctic seas are changing. We are seeing and hearing more species, farther north, more often. And that's a trend that is going to continue." "These animals are expanding their range," she said. "They're taking advantage of regions in seasons that they may not have previously."