A new study led by a University of Alaska Fairbanks scientist finds that narwhals are staying active and close to shore to avoid killer whales entering areas with declining sea ice cover in Canada’s eastern Arctic.
The study, published in late February in Proceedings of the National Academy of Sciences, marked the first time scientists simultaneously tracked both predator and prey marine mammals to understand their interaction.
Researchers found that when killer whales were anywhere within about 60 miles, narwhals avoided them by staying close to shore in shallower water. The narwhals also tended to make longer, faster movements. As soon as killer whales left the area, the narwhals moved offshore to deeper water and decreased their movement.
An average adult narwhal weighs about 2,100 pounds, while the average male killer whale weighs about 8,000 pounds.
“The mere presence of killer whales in a system can cause relatively large and persistent changes in behavior and space use in prey species,” wrote Greg Breed, an assistant professor at the UAF Institute of Arctic Biology, who conducted the study with Cory Matthews of the University of Manitoba and Steven Ferguson of Fisheries and Oceans Canada. The trio tracked a family group of killer whales simultaneously with seven narwhals in Baffin Island’s Admiralty Inlet for several weeks in the summer of 2009.
Narwhals live deep in the Arctic pack ice. Until recently this kept them safe from killer whales for most of the year, the study noted. Killer whales prey on narwhals and many other marine mammals. They have become increasingly common in the Arctic, where they were previously largely blocked by sea ice.
Degraded sea ice now allows the killer whales earlier access to the Arctic in areas where they historically ranged and new access to many areas where they had never been present before, such as Canada’s Hudson Bay.
If narwhals change their behavior in response to killer whales, they could feed less, experience more stress, expend more energy or raise fewer young, the study found. Other effects could cascade through Arctic ecosystems, and there are implications for wildlife management as well.
“Researchers and managers using tracking data to infer preferred habitat need to carefully consider how predators affect space use,” Breed said. “Preferred habitat might instead represent a refuge from predators” and not necessarily the best places for foraging, resting, or caring for young.
