In the cool, clear waters of the North Pacific, killer whales engage in unusual behavior. They glide beneath the surface with long ribbons of kelp clutched in their teeth. They approach a pod mate, nestle closeby, and begin to gently rub the kelp between their bodies. This isn’t play. It’s not hunting. It’s something else entirely — something we thought only a few animals could do.

The killer whales are using a kind of marine loofah to exfoliate.

Rubbing the kelp between their bodies is a form of mutual grooming, and quite possibly, the first documented tool use for social grooming in marine mammals. The discovery, detailed in Current Biology, all started with a serendipitous flight.

Exfoliating killer whales

It all started when Michael Weiss from the Centre for Whale Research in Washington was looking at some drone footage. In one of the clips, Weiss noticed something extraordinary. The orcas were grabbing the stalks of kelp plants with their teeth. They then swam to use the drag created to break off a short length of the stem. They’d then gently maneuver the stem onto their nose, rolling it back and forth on another orca.

It was unlikely anything ever observed before.

The orcas seems to like this behavior, and the researchers decided to study it in more detail.

The behavior was observed repeatedly in a small, critically endangered group of 73 orcas known as the Southern Resident killer whales. These whales live year-round in the Salish Sea — a stretch of coastal waters between Washington State and British Columbia.

Over the course of several months in 2024, researchers captured 30 separate episodes of what they now call “allokelping.” An orca would detach a two-foot-long stipe — the rubbery, stem-like part of a bull kelp — and use it to rub another whale. Often, the whales would press the kelp between their bodies and gently roll it back and forth, much like friends sharing a back massage.

“Let’s call it a kelp massage,” explained Prof Darren Croft from the University of Exeter and the Center for Whale Research in Washington State, for the BBC. “They’re using the kelp to rub between themselves.”

At first, scientists thought it might be a playful act. After all, orcas have long been known to drape kelp over their fins and foreheads—a behavior informally known as “kelping.” They also wear salmon as hats, sometimes (yes, really). But this was different. All age groups were doing it. And notably, it seemed to involve careful selection, manipulation, and shared intention which are hallmarks of tool use.

Why does it matter if whales are using tools

Tool use in animals is rare — and even rarer in the ocean. On land, chimpanzees fish for termites with sticks while orangutans use a number of different tools. Non-primates do it too, to an extent. Crows shape twigs into hooks and elephants scratch themselves with branches. But marine mammals have fewer examples, possibly due to the challenge of grasping objects in water or researchers simply not seeing what’s happening below the waves.

Or perhaps, it’s just because we’re not looking as much. If it weren’t for drones, we would have never noticed that killer whales do this. And drones are a relatively recent addition to the scientific toolkit.

If it is indeed complex tool usage, it’s a hallmark of advanced intelligence, something shared only by humans and a select few species on Earth. The fact that they do it in water is all the more remarkable.

Monika Wieland Shields, director of the Orca Behavior Institute, called the findings “amazing,” though she cautioned that the sample size is still small.

“Thus far, there is still a pretty small sample size of allokelping, but if, as the authors suggest, this behavior relates to social skin care, it’s probably been ubiquitous for some time,” she said. “This research demonstrates the new behavioral, cultural and social insights that can come from relatively new techniques like drone observation.”

A sign of culture?

It’s not clear if this is a universal orca behavior — it could be a cultural trait unique to the Southern Residents. Like regional dialects in birdsong or traveling strategies passed down in elephant families, cultural traditions in whales are increasingly recognized as part of their social complexity.

Now that researchers know what to look for, they’re looking for this type of behavior in other populations as well.

But the joy of this discovery is already shadowed by urgent concern. The Southern Resident killer whales are critically endangered. Their numbers have declined due to pollution, noise, and above all, the steep drop in their main food source: chinook salmon.

The kelp forests they use may also be at risk. Bull kelp thrives in cold waters, but as ocean temperatures rise due to climate change, large swaths of kelp are dying off in the Pacific Northwest.

These whales carry within them centuries of culture and adaptation, and quite likely, many advanced behaviors we haven’t yet learned about.

The findings have been published in the journal Current Biology, external,