In 2014, Sarah Fortune set out to study the feeding patterns of bowhead whales in the Canadian Arctic. Along the way, the PhD student with the University of British Columbia’s Marine Mammal Research Unit made a surprising discovery: namely, that the whales appear to return to Nunavut’s Cumberland Sound each summer not just to feed, but to exfoliate.
Fortune and her fellow researchers observed the whales rubbing their bodies against large rocks in a shallow fiord — previously undocumented behaviour that appears to help the whales slough off dead skin, along with any accumulated micro-algae and parasites. It’s now thought that this moulting process happens at least once per year and may help the exceptionally long-lived whales maintain a healthy appearance and improve skin function by stimulating the growth of new tissue.
“Think of it as humans adding a fresh coat of paint to their homes to improve the appearance,” Fortune explains.
The discovery of the whales’ rock-rubbing behaviour happened by accident on what Fortune now laughingly describes as one of her “most stressful” days in the field. In her quest to understand why the Eastern Canada-West Greenland population of bowheads seemed particularly interested in a shallow fiord within Cumberland Sound called Kingnait Fiord, Fortune attached non-invasive archival tags to the whales to track their underwater movements.
On the day of the discovery, one of the tags suddenly stopped pinging the researchers’ hydrophone. “I started panicking a little bit, like any PhD student who’s trying to get their data,” says Fortune. “But then we ended up drifting into a shallow bay with large boulders.”
The captain of the boat spotted the tag floating, damaged, on the surface. Fortune guessed that the whale had rubbed it off on a boulder, but it wasn't until the following day, when the team tracked a group of whales back to the rocky area, that she realized the significance of the behaviour.
“As we sat and watched, we noticed at least six other whales displaying really peculiar behaviour not consistent with feeding activity: flippers out of the water, rolling around, displaying their flukes. They seemed more like social behaviours.”
A water sample confirmed Fortune’s suspicions: there was no prey present.
Based on the whales’ skin condition — all of them had a mottled appearance, with large patches of light grey and peeling skin — the researchers surmised that the whales were moulting, and using the rocks to rub off the dead matter. Moreover, the presence of an old whaling station at the mouth of Kingnait Fiord suggested to Fortune that the whales have been returning to this spot regularly for a very long time.
In August 2016, the team returned to Kingnait Fiord with VDOS Global LLC, a drone photography company, and captured video footage and stills of the whales, including a clip showing their rock-rubbing behaviour:
The next phase of the research will be to document individual whales over multiple seasons to see how their skin condition changes between seasons. “We want to home in on when moulting occurs,” says Fortune. “From our data, it appears the summer is an important time for moulting, but we want to see if it’s also maybe happening in spring and fall.”
She adds that understanding how the whales are using Cumberland Sound and its fiords will play an important role in their conservation. Currently, the Eastern Canada-West Greenland bowhead population is assessed as being of special concern by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC), but with ice-free Arctic summers a growing probability due to climate change, the whales could face new threats from increased shipping activity on their seasonal migration routes.
“To mitigate harm, we need to know where the whales are going, when and why,” Fortune explains. “We now know Cumberland Sound is a multi-use habitat for these whales — not just for food, but moulting and rock-rubbing. That could be used to help with critical habitat designation in the future.”