The increasing population of whales in addition to the ships that float through the Bering Strait is concerning scientists for a growing risk of a collision in the narrow waterway.

Kate Stafford, an oceanographer with the University of Washington Applied Physics Laboratory, said in a press release certain types of whales migrate to spend their winters in the Bering Sea. Using underwater microphones, the team detected a large amount of Arctic beluga and bowhead whales, as well as sub-Arctic humpback, fin and killer whales.

"It's not particularly surprising to those of us who work up in the Arctic," Stafford said in the release. "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."

Stafford recorded the whales in the Bering Sea from the summer and early winter of 2009 to 2012. The humpback, fin and killer whales were heard into late fall.

"These animals are expanding their range," Stafford said. "They're taking advantage of regions in seasons that they may not have previously."

The Bering Strait was once a land bridge that connected Russia to North America but is now a waterway merely 58 miles wide and 160 miles deep. The narrow waterway is a cause for concern as boats could easily collide with a whale as they pass through.

"The Arctic areas are changing," Stafford said. "They are becoming more friendly to sub-Arctic species, and we don't know how that will impact Arctic whales. Will they be competitors for food? Will they be competitors for habitat? Will they be competitors for acoustic space, for instance these humpbacks yapping all the time in the same frequency band that bowheads use to communicate? We just don't know."

The research team will likely next uncover why the whale populations are rising, as it could be overpopulation, widened ranges or both. Either way, Stafford proposed boats passing through the Bering Strait could slow down and create less motor noise or likelihood of a collision.

"The question is," said Stafford, "are these whale populations recovering and so they're reoccupying former habitat, or are they actually invading the Arctic because they can, because there is less seasonal sea ice?"