WINNIPEG - Researchers say melting Arctic sea ice is enticing more killer whales to Nunavut waters where they are competing with Inuit hunters for food and threatening to replace polar bears as the North's top predators.

Scientists from the University of Manitoba interviewed hunters from 11 of the territory's communities about their observations on the habits of killer whales seen in the area. The findings are published in the online journal Aquatic Biosystems.

Lead author Steven Ferguson, who is with the Department of Fisheries and Oceans Freshwater Institute at the university, said the Inuit are seeing more killer whales. The powerful predators tend to avoid sea ice but that ice is disappearing.

Once in the Arctic, he said, killer whales have been seen to use a variety of hunting tactics to feast on belugas, seals and narwhals.

Sea ice often provides the only cover such mammals have to escape one of the Orcas. Seals can get out of the water onto the ice and other whales can manoeuvre into ice-packed areas where the killer whale's dorsal fin prevents it from following.

"If we lose that sea ice, they are now going to be out in the open water and don't have the kind of strategies to reduce the risk of a killer whale catching them and eating them," Ferguson said. "We just might see a lot of mortality in some of the more southerly areas."

He suggested the killer whales could be behind a massive transition within the whole Arctic ecosystem.

"This change of what animals live in the Arctic is likely going to happen with the warming but we didn't anticipate that...killer whales might be removing certain susceptible prey and maybe temperate species will move up to take their place."

Ferguson also suggests that while the population of other whales and seals is relatively healthy, killer whales could cause problems for the Inuit who will be increasingly competing against the giant mammals for food.

Inuit have long expressed concern about the apparent increase in killer whales. Sightings used to be rare — about six a year in western Hudson Bay — several decades ago. By 2000, that number had jumped to more than 30 annually.

Peter Ewins, director of species conservation at World Wildlife Fund Canada, saw a dozen killer whales during one outing near Churchill, Man., in August. Their influx into the North has been a steady trend, he said.

As the Arctic sea ice melts and threatens the home of polar bears, killer whales could very well replace the iconic mammal as the North's top predator, he said.

"When you take the ice away for longer and longer, then the killer whale just moves in and dominates."

Both people and Arctic animals will likely adapt to this new reality, but it's not going to be easy, Ewins said. Even a far-off presence of killer whales can drive animals away from traditional hunting spots, making it more difficult for the Inuit. New species may move in while others become more scarce.

"Some new mix of species is going to comprise the future food chain."

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