Despite their large size, whales are swift, sleek swimmers that can move through the water at high speeds. But over time, a whale can be slowed down by animals that are a mere fraction of its size: barnacles.
These small, sticky crustaceans attach to whales’ skin and hitch a ride to filter more of the ocean’s nutrient-rich waters. If the barnacles get too big, they can actually cause drag that slows the whale down or requires it to work harder to swim at the same speed.
But the humpback whales migrating through the Pacific Ocean off Australia’s Gold Coast have devised a clever solution to this problem, according to a new paper published this spring in the Journal of Marine Science and Engineering. Scientists caught the animals on video rolling around on the sandy ocean floor to exfoliate their skin and scratch off the hitchhikers before they get out of control.
The footage comes from suction-cup sensors stuck to three whales between August 2021 and October 2022. The sensors, which are equipped with high-definition cameras and other data-gathering tools, captured five total humpbacks rolling in the sand—and even showed their dead skin coming off in the water. Opportunistic fish swooped in to munch on the floating skin, as well as eat it right off the whales’ bodies.
It’s possible that some of the whales were rubbing on the sand to remove the attached sensors, the scientists write. However, the footage showed whales both with and without the sensors exhibiting the behavior, and the creatures did not appear to be targeting the sensors with their rolling. That led scientists to conclude exfoliation was likely the main goal.
“They were doing these bizarre rolls, going fully on their back and on their side,” says study co-author Olaf Meynecke, a marine ecologist at Griffith University in Australia, to the Australian Associated Press. The motion seems to target barnacles, which “start very small,” he adds to the publication. “But once they become bigger, they are very hard to remove for the whale.”
Whales do have some luck ridding themselves of barnacles and dead skin while breaching, or jumping forcefully out of the water and crashing back down. However, this behavior can’t totally get the job done, Meynecke says in a statement. Plus, whales need to regularly remove dead or excess skin to help keep the bacterial communities that live on their bodies healthy and appropriately sized.
The idea of whale exfoliation is nothing new. As early as 1845, whalers reported seeing bowhead whales rub their heads on rocks. Past studies have also explored this behavior—researchers in 2017 captured drone footage showing bowhead whales “clustered around … boulders taking turns sloughing off skins,” as marine ecologist Sarah Fortune, a co-author of that study but not the current one, told the New York Times’ Douglas Quenqua. A 2016 study also documented bowhead whale molting to help “maintain the optimal skin thickness.”
Notably, the humpbacks in the new study appeared to return to roughly the same spot for their spa time—a region situated about six miles off the shoreline of the Gold Coast’s Main Beach, where the sea floor was roughly 130 to 165 feet below the surface. It may have been an ideal spot for sloughing off dead skin because it has a mix of rubble and sand, the researchers write in the paper.
And the whales weren’t just rubbing their bodies along the ocean floor for purely practical purposes. The videos also suggest the practice was a social activity. Two of the five whales not only rolled together, but also swam alongside one another for a few hours. To that end, the researchers suggest that future studies should consider the social bonding implications of rolling.
“The behavior was either following courtship, competition or other forms of socializing,” Meynecke says in the statement.