Killer Whales Fashion Tools from Kelp and Use Them for Grooming

In a paper published this month in the journal Current Biology, marine researchers report evidence of the widespread manufacture and use of grooming tools in a population of killer whales (Orcinus orca ater) living in the Salish Sea, part of the Pacific Ocean between British Columbia and Washington.

Allokelping in southern resident killer whales (Orcinus orca ater). Image credit: Weiss et al., doi: 10.1016/j.cub.2025.04.021.

“We found that southern resident killer whales regularly use lengths of bull kelp during social interactions, apparently as a tool to groom one another,” said Dr. Michael Weis, a researcher at the Center for Whale Research.

“To find that the whales were not just using but also manufacturing tools, and that these objects were being used in a way never before reported in marine mammals, was incredibly exciting.”

Dr. Weiss and his colleagues discovered this unexpected whale activity while conducting aerial observations of southern resident killer whales, which are a critically endangered whale population with fewer than 80 individuals left found in the Pacific Northwest.

They have been monitoring the whales since 2018 to learn more about their foraging and social behavior.

“While there are other killer whales around the world, the southern residents represent a genetically, ecologically, and culturally distinct population,” Dr. Weiss said.

Through the high-resolution footage collected by their aircraft, the researchers found that the whales created tools by breaking off the ends of bull kelp stalks.

They then pressed pieces of kelp against a partner and rolled the kelp between their bodies for long periods of time.

The scientists observed this behavior in whales across all social groups, both sexes, and all age classes.

They found that whales were more likely to groom closely related whales or similarly aged partners.

They also saw some evidence that whales with more molting or dead skin were more likely to engage in grooming, suggesting it may have a hygienic function.

“What I find most remarkable is that despite this apparently being a common behavior — we see it most days we fly our drone over these whales — it hadn’t yet been discovered in this population despite nearly 50 years of dedicated observation,” Dr. Weiss said.

“To me, this demonstrates not just the power of new observation methods but also how much we still have to learn about these animals.”

“This population of whales has been formally studied for 50 years and yet major new discoveries can still be made,” said Rachel John, a student at the University of Exeter.

“We hadn’t noticed ‘allokelping’ (i.e. kelping with another whale) before because the videos being collected from our previous aircraft weren’t of high enough quality, but the footage we’re getting now shows this behavior in great detail.”

It remains unclear whether this grooming behavior is entirely unique to this population or more widespread among other whale populations and species.

Regardless, the discovery opens new avenues for understanding tool use in marine mammals and demonstrates that tools can be used in a wide array of contexts.

“We know touch is really important,” said Professor Darren Croft, a researcher at the University of Exeter and executive director of the Center for Whale Research.

“In primates — including humans — touch moderates stress and helps to build relationships.”

“We know killer whales often make contact with other members of their group — touching with their bodies and fins — but using kelp like this might enhance this experience.”

“It might also be important for skin health. Whales and dolphins have a variety of strategies to help them slough dead skin, and this may be yet another adaptation for this purpose.”

“Brown algae like bull kelp also have antibacterial and anti-inflammatory properties that may provide further benefits to the whales.”

“We’re now working on more research to confirm these initial findings and investigate the social and skin health benefits of this behavior.”

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Michael N. Weiss et al. 2025. Manufacture and use of allogrooming tools by wild killer whales. Current Biology 35 (12): R599-R600; doi: 10.1016/j.cub.2025.04.021