To graduate student Sarah Fortune, the rocky crags off Baffin Island were just part of its stark beauty. Then, she saw a group of eight bowhead whales rubbing their bodies against the large boulders. Using aerial drones to watch the whales, she saw that they were using the rocks to help remove loose, dead skin.
“It was like a bowhead whale day spa,” she says.
It’s the first time scientists have documented this behavior in bowhead whales (Balaena mysticetus), Fortune reports Wednesday in the journal PLoS ONE.
“This is really exciting. I’ve heard about this in beluga whales and orcas, but never in bowheads,” says Paul Anderson, a research scientist at Mystic Aquarium who was not involved in the study.
Scratch My Back
Fortune, a Ph.D. candidate at the University of British Columbia, didn’t set out to identify pumice stones for bowheads. Instead, she wanted to see how climate change affected their feeding behaviors. To track the whales in the frigid Arctic waters separating Baffin Island and Greenland, she placed sticky tags on the whales’ backs. When a tag’s signal died suddenly on the second whale she tracked, Fortune chalked it up to a malfunction.
But then she noticed the group of whales rubbing against boulders strewn around Cumberland Sound. A closer look revealed large patches of loose, dead skin all over their bodies.
The whales, Fortune realized, were shedding the top layer of dead skin, a process known as molting. What’s more, they were using the rocks to exfoliate. A sample of the water revealed few of the zooplankton that make up the entirety of the bowhead whale diet, which meant they were in Cumberland Sound specifically to use the rocks to assist molting.
In the summer of 2016, Fortune returned to Cumberland Sound, this time armed with aerial drones to monitor the whales’ behavior without disturbing them. Her footage revealed that all 81 whales in the area had signs of sloughing skin, and for 40 percent of them it covered at least two-thirds of their body.
Anderson had previously documented the same process in beluga whales (Delphinapterus leucas), which also make their home in the Canadian Arctic. Unlike bowheads, belugas will travel hundreds of miles to reach their “day spa” on the Cunningham Inlet along Somerset Island, to the northwest of Baffin.
“They do what we call the 'caterpillar,' moving in close to shore and rubbing against rocks. The warm fresh water flowing into the inlet helps to soften and hydrate their skin,” Anderson says.
Shed That Skin
Whales aren’t the only animals that molt: Insects and reptiles shed their outer covering of skin in order to grow. Birds and many mammals also undergo an analogous process, and Anderson says the same glands are responsible for molting in birds and other mammals, including whales.
Fortune hypothesizes that molting may help remove parasites such as whale lice and diatoms or to remove sun-damaged skin, both of which can harm whales’ health. The relatively warm waters in Cumberland Sound may make it easier for the whales to shed their skin.
Anderson believes the process may also help improve what’s known as hydrodynamic efficiency, a measure of how much effort it takes to move in the water. Gouges from rocks, other whales, and even ships can all roughen the skin and slow whales down.
No word yet on whether the whales have found a good spot to get a facial or a seaweed wrap.