When your home is billions of gallons of saltwater, you’ve got to get a little creative with your skin care regimes. Bowhead whales, for example, have incorporated giant, underwater boulders into their annual grooming.
All animals lose their skin cells to make room for new ones, and animals with hair or fur (including us) shed. Some animals, though, take the skin renewal process a step further, and remove huge chunks of their skin at once in a process called molting. New drone footage shows that includes bowhead whales.
Researchers based in Canada and the US watched 81 whales swimming in the shallows of Cumberland Sound, a bay off the coast of the chilly northeastern edge of Canada. They found that whales rub up against large boulders to scrape off their old skin to make room, presumably, for new skin better suited for the summer like belugas and narwhals. They published their findings in PLOS One on Nov. 22.
For years, perplexed human observers had seen bowhead whales get frisky with large rocks in shallow water. Back in 1845, some whalers even called them rock-nosed whales because they brushed up against them so much, although no one had any idea why. In more recent observations, marine biologists assumed the whales were just taking a break from swimming—which is also a bit odd, considering whales could presumably just float if they needed to rest.
Fortune initially started studying bowheads to learn more about their eating habits. When she and her team were out looking for whales to tag, they noticed two peculiar things: First, the whales kept rolling over rocks (video) and sticking their fins out of the shallow water, and chunks of their old skin kept flaking off. Fortune thought that these two phenomena were not coincidental. Perhaps the whales were actually using the rocks like a big natural loofa during the molting process.
Drone observations taken in August 2014 and August 2016 strengthened the link between scrubbing behavior and making room for new skin. “Having the drones changed everything,” Sarah Fortune, a marine ecologist at the University of British Columbia and lead author of the paper, told the New York Times (paywall). “We could clearly see these whales clustered around these boulders taking turns sloughing off skins.”
They found that the vast majority of the 81 bowhead whales included in the study showed signs of losing huge chunks of their skin over time. About 40% were caught in the act of rock-rubbing, and most of had patches of new skin all over their bodies (one whale in particular appeared to have almost all new skin). All of that signified molting, not just shedding.
The bowhead whale now joins the narwhal and beluga whales, seals, and sea lions in the group of sea mammals confirmed to molt. Scientists know these other sea mammals molt specifically to grow a “summer skin.” It’s not yet clear if that’s the case for bowhead whales; if it turns out they rub on rocks year-round, it could just be a routine part of grooming.
Fortune told the Times it’s important to study these sorts of whale behaviors as global warming makes the northern corners of the Earth more accessible to humans. If tourism disrupts the areas where bowhead whales exfoliate, who knows how these creatures will make room for their new layers of skin?