Killer whales use kelp to massage and groom each other

Killer whales have been spotted doing something unexpected: using seaweed to massage one another.

Experts observed them breaking off pieces of kelp, placing it between themselves and another whale, and rolling it between their bodies. The behavior looks deliberate – and it’s something researchers had never seen before.

The discovery was made by scientists at the Center for Whale Research, working with the University of Exeter. They used high-quality drone footage to study southern resident killer whales in the Salish Sea, off the coast of Washington State.

What they saw was new: pairs of whales using kelp together in a way that might count as tool use – a first for marine mammals.

Whales shared seaweed

Killer whales have long been known to engage in “kelping,” a term used when they rub themselves with seaweed. But this new behavior goes further. The whales aren’t just grabbing kelp for themselves. They’re using it with each other – what the scientists are calling “allokelping.”

What makes this behavior stand out is how the kelp is used. Whales were seen selecting it, trimming it, and then coordinating with a partner to rub it between their bodies. That makes it more like tool-making than simple play.

“We were amazed when we first noticed this behavior,” said Dr. Michael Weiss of the Center for Whale Research.

Whales favor kin for “kelping”

The whales didn’t allokelp randomly. Most of the time, they did it with relatives – especially close maternal kin – or whales of similar age. The researchers think it may help strengthen social bonds or even benefit skin health.

“Bull kelp stalk is firm but flexible, like a filled garden hose, with a slippery outer surface. I suspect these features make it an ideal grooming tool,” said Weiss.

“What I find remarkable about this behavior is just how widespread it is in the population. Males and females of all life stages and from all three southern resident pods were seen using kelp in this way. All evidence points to it being an important part of their social lives.”

Allokelping was seen on two-thirds of the observation days. Based on the consistency, the researchers think it might be universal within the group.

Quality of drone footage

So why hadn’t anyone noticed it before? The quality of drone footage made all the difference.

“This population of whales has been formally studied for 50 years – the best-studied orcas on the planet – and yet major new discoveries can still be made,” said Rachel John, a graduate student studying animal behavior at the University of Exeter.

According to John, the researchers hadn’t noticed ‘allokelping’ before because the videos being collected from their previous aircraft weren’t of high enough quality, but the footage we’re getting now shows this behavior in great detail.

She recalled the moment they realized what they were seeing: “Drone cameras allow us to see things that were invisible to us from boats or the shore. I was watching one of those really close-up videos when I saw something that looked like a brown stick between two whales that were in contact with each other.”

Kelping behavior of killer whales

John said her team didn’t think much of this at first, but they had also noticed pairs of whales staying in contact with each other for long periods – several minutes at a time.

“We looked back at lots of videos and realized that rubbing kelp between their bodies wasn’t just a one-off thing – it was happening all the time,” she noted.

“Once we saw whales breaking off pieces of kelp intentionally, it became clear that this is not just play – this is something important in the social lives of the southern resident killer whales.”

The importance of touch

Professor Darren Croft, of the University of Exeter and the Center for Whale Research, thinks the answer lies in the importance of touch. “We know touch is really important,” he said. “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.”

This behavior may also play a role in skin health. Whales and dolphins use a variety of strategies to shed dead skin – and this could be yet another adaptation serving that purpose.

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

Scientists are now working to confirm these initial findings and investigate the social and skin health benefits of this behavior.

A population on the brink

As of July 2024, there were only 73 southern resident killer whales left. They don’t breed with other killer whale groups. That makes them a closed population – and a critically endangered one.

Their main food source is Chinook salmon, which is also declining. The salmon face pressure from overfishing, habitat destruction, climate change, and pollution. On top of that, whales have to deal with noise and chemical pollution from boats and industry.

Dr. Weiss warned that without significant change, the future of southern resident killer whales looks grim.

“Under the status quo, all of our projections indicate the population will continue to decline,” he said. “They are struggling to find enough of the large Chinook salmon needed to survive and successfully rear their young.

“We often think about biodiversity in terms of protecting the phenotypic variation we see in animal populations – such as differences in size, shape, and color. However, conserving cultural and behavioral variation may be just as important.”

Dr. Weiss added that allokelping is yet another piece of evidence of the southern residents’ uniqueness. If we lose them, he said, we lose so much more than 73 individual animals or a genetic lineage.

Vanishing kelp forests

The new findings also suggest that the future survival of southern resident killer whales may face an added threat: the decline of kelp forests they rely on for grooming tools. This decline is being driven by rising ocean temperatures linked to global warming.

Protecting the kelp forests where these whales craft their grooming tools could be vital to preserving their unique cultural behavior. It may also help ensure the long-term survival of the southern resident killer whale population.

The full study was published in the journal Current Biology.

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