In August 2014, marine ecologist Sarah Fortune was trying to tag bowhead whales with transmitters so she could study their feeding habits in Canada’s Cumberland Sound, where many of the large sea mammals spend their summers.
But the whales kept swimming into a small, shallow bay with large boulders, where at least one removed a transmitter by rubbing against the rocks. “The whales were just rolling onto their sides, lifting their flippers out of the water, doing headstands, lifting their tails out of the water,” she said. The behaviour was puzzling.
Though she didn’t know it at the time, the mystery of the rock-rubbing whales dates back at least 170 years. Around 1845, whalers started calling bowheads “rock-nosed whales” after seeing them rub their heads on boulders. Several subsequent papers have also noted the behaviour, usually concluding the whales were using the rocks to rest.
But Fortune noticed that large pieces of skin were peeling off some of the whales. Perhaps, she thought, they were “using these rocks like humans using pumice stones, to get rid of calluses or dead skin.”
Fortune and a team of researchers published a paper in the journal PLOS One recently that seems to confirm her suspicions. Overhead footage of the whales taken by drones in 2016 — part of another study tracking the whales’ summer feeding habits — reveals that the animals are using the large rocks to rub dead skin off their bodies.
“Having the drones changed everything,” said Fortune, a marine ecologist at the University of British Columbia. “We could clearly see these whales clustered around these boulders taking turns sloughing off skins.”
Besides solving a centuries-old mystery, the findings confirm long-held suspicions about how bowhead whales molt.
Like humans, most whales, dolphins and porpoises are thought to shed skin and hair continuously, a little at a time, throughout the year. But certain cold-water whale species — belugas and narwhals — are believed to shed their skins during the summer, when they relocate to warmer places.
Biologists suspect the warmer water increases metabolic activity in the whales, speeding up the molting process and stimulating the growth of new hair and skin.
Until recently, little had been known about the molting habits of bowhead whales. Because they reside mostly in the Arctic, and take their summer vacations in more temperate waters, many biologists assumed they were among the whales who molted seasonally.
Fortune’s study, as well as a 2016 study published in a Russian journal, now help confirm those suspicions, and shed light on why the bowheads keep returning to their summer destination.
“It’s fascinating to understand that this habitat we’ve been studying, where we’ve seen whales for hundreds of years, is a multiuse area,” she said. “They’re coming here because they can feed but also to use warmer waters and these rocks to facilitate molting.”
Knowing why whales prefer a particular habitat will aid researchers as they seek to understand how global warming will affect marine creatures, said Fortune.
“There’s going to be a northern expansion in human activity,” she said. “So it’s important to know what the purpose is of the areas that the whales are occupying so we can manage human activities in that area.”The New York Times
>>Like humans, most whales, dolphins and porpoises are thought to shed skin and hair continuously, a little at a time, throughout the year. But certain cold-water whale species — belugas and narwhals — are believed to shed their skins during the summer, when they relocate to warmer places.
>>Biologists suspect the warmer water increases metabolic activity in the whales, speeding up the molting process and stimulating the growth of new hair and skin.
