Killer whales display rare behaviour using tools to groom each other

In the cool, kelp-rich waters of the Salish Sea — a stretch of ocean between British Columbia and Washington State — researchers surveying the critically endangered southern resident killer whales have witnessed something extraordinary.

The whales were fashioning short lengths of bull kelp stipe (a stem-like structure) from full stalks, placing the kelp between themselves and a companion, then rolling it between their bodies.

It’s a behaviour never before reported in marine mammals.

 “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… was incredibly exciting”, says Dr Michael Weiss, a whale behaviour expert from the Centre for Whale Research in Washington.

Tool use is rare among marine animals, and tool-assisted social grooming is even rarer. Though cetaceans have been observed casually draping kelp over themselves — a behaviour known as “kelping” — this newly described act goes further. The team dubbed it “allokelping”: kelping with a partner.

Southern resident killer whales are an isolated population of orcas that inhabit the coastal waters of the Pacific Northwest. Unlike some other ecotypes that hunt marine mammals, southern residents feed exclusively on fish — primarily Chinook salmon. They live in tight-knit family groups, passing down vocalisations and behaviours across generations. With fewer than 80 individuals remaining, they are classified as critically endangered.

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

The allokelping behaviour was observed across all social groups, sexes, and age classes. Whales were more likely to engage in these kelp-sharing sessions with close kin or similarly aged companions. Individuals with more sloughing or dead skin were also more frequently involved, hinting at a potential hygienic purpose.

“What I find most remarkable is that despite this apparently being a common behaviour — 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,” says Weiss. “To me, this demonstrates not just the power of new observation methods but also how much we still have to learn about these animals.” 

Whether this grooming tool use is exclusive to southern residents or occurs among other whale populations remains unknown. But the discovery adds a new dimension to our understanding of marine mammal intelligence and social culture.

“This finding highlights yet another way these whales’ society and culture is unique and the importance of recovering the southern resident killer whale population,” says Weiss. 

These findings are published in Current Biology.