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These whales use boulders for a good back scratch

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Ahhh, that’s the spot

This bowhead whale was caught scratching against a rock.
Video: Sarah Fortune et al., 2017.

Just like we use pumice stones to scrape dead skin off cracked heels during pedicures, bowhead whales may be using boulders at the bottom of the ocean to exfoliate, new research says. Identifying these scratching stones could be key to keeping human activity from disturbing these massive creatures.

In the summer of 2014, a team of researchers spotted a handful of odd-looking bowhead whales in a bay off the northeastern coast of Canada. These Arctic marine mammals average 50 to 60 feet long, and are powerful enough to break through ice. But this group looked splotchy, with patches of light gray and loose skin decorating their dark gray backs. And they kept rolling on their sides and backs and lifting their flippers out of the water. Apparently, they were in the bay for a good scratching, according to a study published today in the journal PLOS ONE.

Sloughing off dead skin and hair and regrowing them anew is called molting. Most whales, dolphins, and porpoises molt year-round — kind of like we do. But Arctic species like belugas are thought to molt all at once when they visit warmer waters during the summer. Bowhead whales have similar skin to belugas, and have been spotted molting in Russia’s Okhotsk sea. Graduate student Sarah Fortune at the University of British Columbia didn’t know if this specific population of bowhead whales in eastern Canada were regular exfoliators, too.

So two years later, the researchers went back to the same spot — this time, with a DJI Phantom 3 Professional drone. The team flew the drone to snap aerial pictures and videos of 83 whales. (The water was clear enough for them to see what the whales were doing at the bottom of the shallow bay.)

Almost all of them had splotchy skin. Many spent their time alternating between resting or rubbing their chins, heads, backs, and sides against the boulders in the bay. One whale was caught spending what was probably a blissful eight minutes scraping itself against a boulder. “We saw very clearly that the whales were taking turns rubbing their bodies on these rocks,” Fortune says. The whales bumped up against each other, too.

Fortune hopes that her research will be the starting point for identifying other bays around the world where bowhead whales turn for a good scratch. That way people can steer clear of them and let the whales do what they need to. The exfoliation ritual, in fact, might be more important than it seems. The whales may need to shrug off skin infested by parasites like whale lice or gunked up by plankton that might make it harder to regulate their body temperatures. The whales might also be getting rid of sun-damaged skin that would otherwise accumulate over lives more than 200 years long.

Or, just maybe, they do it because scraping off peeling skin feels so good.