As more killer whales move into the Arctic, at least one population of polar bears is learning how to make the best of no longer being at the top of the food chain.
Research presented at a scientific conference in Winnipeg this week suggests the bears are beginning to take advantage of the beached remains of an orca's favourite food - bowhead whales.
"It's still early days yet in this story," said Gregory Thiemann of York University in Toronto. "(But) we're seeing more consumption of bowheads by polar bears in Foxe Basin."
Inuit hunters say killer whales have long been seen - if rarely - in some parts of the Arctic, but Foxe Basin north of Hudson Bay hasn't been a spotting site because of heavy pack ice. That ice, however, is clearing and killer whales have moved in.
"Killer whales are now annually present in the region," says the report.
Bowhead whales are also present in large numbers. Up to 7,600 of them summer in the rich feeding grounds of northwestern Hudson Bay and northern Foxe Basin.
Yum, say killer whales, which love nothing more than bringing down a younger, smaller bowhead and feeding on its head and mouth. That creates a large, floating carcass which eventually drifts up on a shoreline.
Yum, say polar bears, which will basically eat anything they can, especially in summer, when an increasing lack of sea ice is making it harder and harder for the bears to find a perch from which to hunt seals.
"If there's a bowhead on shore, bears will find it," said Thiemann.
He and his colleagues tested fat tissue from 103 bears harvested by hunters from spots around Foxe Basin. They found 56 per cent of the bears in the northern part and about half the bears in nearby Hudson Strait had eaten bowhead.
Although bowheads are too big for bears to kill on their own, the bears have probably always feasted on whales that wash up after they die, said Thiemann. But those percentages sound pretty high for scavenging on natural mortality.
"It seems like a logical story," he said. "We don't have the full picture yet, but as orcas increase in Hudson Bay, you're going to have more predation on big whales and more big-whale carcasses for bears."
It's an example of how Arctic food webs are changing as the North undergoes some of the most drastic climate change on the globe.
"This is a complex system and a complex story," Thiemann said. "It's difficult to predict how some of these interactions are going to shift over time."
The bowhead bounty may help explain why Foxe Basin polar bear numbers have remained stable as sea ice declines.
"The increasing abundance of killer whales and bowhead whales in the region could be indirectly contributing to improved polar bear foraging success despite declining sea ice habitat," the study says.
That might work for a while, said Thiemann. But polar bears do need ice to hunt.
"A decline in habitat is ultimately going to lead to a decline in polar bears. What happens in the interim, how some of these food web processes shift as sea ice declines, is going to be the more complex part of the story."
