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Everyone enjoys a good scratch. For a bowhead whale stretching up to 20 meters long and weighing as much as 75 tonnes in Canada’s Arctic, the question is what to do about it. The unexpected solution lies within the shallow and relatively warm waters of Cumberland Sound, off southeastern Baffin Island in Nunavut.
That’s where bowheads from the Eastern Canada-West Greenland population gather in late summer to rub themselves on large rocks just below the water’s surface.
“It’s like a day spa for the whales,” explains Sarah Fortune, a doctoral candidate at the University of British Columbia who led the research. “Think of it as using a pumice stone to get a callus off your foot, using the physical environment to help exfoliate the skin.”
In 2014, Fortune accompanied Fisheries and Oceans Canada scientists to research the diet and feeding behavior of bowheads in the rich habitat of Cumberland Sound. “Whales were at the surface, rolling over, doing headstands, tails out of the water, occasionally making loud vocalizations. We’d never seen this before,” she says.
The research team returned in August 2016 for further investigation—this time with a drone—and gathered conclusive evidence of what they had suspected: the whales were rubbing against rocks in water less than 10 meters deep as a way of removing dead skin.
Of the 81 whales the scientists observed, all were molting. About 40 percent showed signs of rock rubbing, including linear, light-colored markings on their bodies from the friction.
The findings provide a scientific answer to a mystery that dates back to at least the mid-1800s, when European whalers nicknamed the animals rock-nose whales, due to their close proximity to the rocks. More recently, Inuit who observed similar behavior in nearby Clyde River theorized the whales were using the rocks for resting.
“What we all had in common is that we had a limited view of whales and their environment until we sent up the drone,” Fortune says. “Then we had a complete picture of what was going on.”
Elsewhere in the Arctic, beluga whales rub themselves on nearshore mud and gravel in Cunningham Inlet. And in British Columbia, killer whales frequent particular “rubbing beaches,” such as one in Robson Bight in Johnstone Strait.
Scientists suspect that bowheads shed their skin annually as a way to avoid continuing damage from the sun, to rid themselves of algae and parasites, and to help with thermoregulation. Bowheads have more blubber than any other marine mammal, at up to 50 centimeters thick. They also seem to cool themselves in shallow water, opening their mouths to allow seawater to flow over their tongues and palates.
There are about 6,700 whales left in the Eastern Canada-West Greenland population of bowheads, and the population is rated special concern by the Committee on the Status of Endangered Wildlife in Canada.
Research into rock rubbing and feeding behavior in Cumberland Sound is helping to define habitat that may be critical to the long-term survival of the species.