Killer whales may use kelp brushes to slough off rough skin
Salish Sea orcas could be the first marine mammals known to manufacture their own tool
Two killer whales in the Salish Sea rub a kelp stalk (brown) between their bodies.
Center for Whale Research, NMFS NOAA Permit 27038
A brush with kelp may help some killer whales clean up nicely.
A group of killer whales (Orcinus orca ater) residing in the Salish Sea off the coast of British Columbia and Washington tear short stalks of bull kelp (Nereocystis luetkeana) with their teeth and use the pieces to groom one another, researchers report June 23 in Current Biology. The behavior may represent the first toolmaking observed in a marine mammal and the first among wildlife that benefits two individuals at the same time.
The killer whales’ grooming habit was among the first things Michael Weiss and colleagues saw using a new drone with “really intense” zoom to observe the animals. The team, which has watched over the Salish Sea whales since 2018, initially thought the behavior might be a one-off observation. “But once we knew what to look for, we started seeing it over and over and over again, multiple times a day,” says Weiss, a behavioral ecologist at the Center for Whale Research in Friday Harbor, Wash.
High-resolution aerial footage taken in the spring and summer of 2024 showed that killer whales fashion their tools by biting kelp and jerking their heads. The seaweed’s large, buoyant bulb and fingerlike fronds provide resistance that helps whales break off a piece. The whales then flip the stalk onto their snouts and press it onto another whale, rolling the piece between their bodies.
Close relatives and similarly aged peers often partnered up to use the kelp tools, hinting that the behavior may strengthen social bonds. Individuals with more dead skin also seemed to participate more frequently than others, suggesting the kelp serves as an aquatic brush.
Other marine mammals also use tools. Dolphins, for example, can use coral or sea sponges as tools to groom or eat. If confirmed, the Salish Sea’s killer whales would be the first marine mammals known to manufacture a tool. The team plans to observe the whales over a period of several years to investigate whether the whales mainly use kelp tools to exfoliate dead skin and whether the behavior helps them form bonds.
It’s unclear if other groups of killer whales have similar grooming behaviors. Killer whales are among “the most well-studied marine mammals on the planet,” Weiss says. Yet, in a lot of ways, “we’re still just scratching the surface of all of the different aspects of their lives.”
