PREVIEW

In a fascinating discovery, scientists have documented killer whales biting off lengths of kelp and using them to groom each other. The behaviour, observed in drone footage, reveals a highly complex interaction, with the whales rolling the kelp between their bodies for prolonged periods, possibly to strengthen social bonds and promote skin health.

The footage was captured in the Salish Sea, an inland waterway between Washington State, USA, and Vancouver Island, British Columbia. This discovery is the result of a study led by the Center for Whale Research (CWR) in collaboration with the University of Exeter.

“We were amazed when we first noticed this behaviour,” said Dr Michael Weiss, research director at the CWR. “It’s unlike anything we’ve seen before in marine mammals.”

Known as “allokelping,” the practice involves two whales using kelp together, with one biting off the end of a stalk and positioning it between themselves and a partner. Unlike previous “kelping” behaviours – where whales move kelp with their heads, fins, and bodies, likely for play or to remove parasites – this new behaviour sees the kelp selected, trimmed, and manipulated by two whales, suggesting a deliberate use of tools for grooming.

Dr Weiss explained: “Bull kelp stalks are firm but flexible, like a filled garden hose, with a slippery outer surface. These features make it an ideal grooming tool.” He noted that this behaviour was seen across both males and females of all life stages, with individuals from all three pods of the southern resident population involved.

The CWR’s team observed this new behaviour across 8 out of 12 days included in the study, with a clear pattern emerging: whales most often paired up with close maternal relatives or individuals of a similar age. The fact that this was documented in such a well-studied population – the southern resident killer whales, which have been under observation for 50 years – is even more remarkable.

“This behaviour had gone unnoticed in the past simply because previous drone footage wasn’t clear enough,” said Rachel John, a Masters student studying animal behaviour at the University of Exeter. “With our new footage, we can now see this behaviour in greater detail.”

The purpose of allokelping remains uncertain, though there are several theories. Professor Darren Croft, an expert at the University of Exeter and executive director of CWR, pointed to the importance of touch in animal social relationships, particularly in primates. "We know that touch plays a significant role in moderating stress and building relationships, and using kelp in this way could enhance those social connections," he said. He also suggested the kelp’s antibacterial and anti-inflammatory properties could benefit the whales’ skin health.

Though other killer whale populations have been seen rubbing their bodies against smooth stone beaches, likely to slough off dead skin or parasites, the southern resident killer whales have not been observed engaging in this behaviour. The decline of kelp forests, exacerbated by climate change, adds another layer of concern to the survival of these whales. As kelp forests are critical for this behaviour, their loss could threaten the social and cultural fabric of this already endangered population.

With just 73 southern resident killer whales remaining, their population is critically low. These whales are heavily reliant on Chinook salmon, which has also seen sharp declines due to overfishing, habitat destruction, and climate change. Noise and pollution from human activity further complicate their survival.

Dr Weiss warned: “Unless significant changes are made, the outlook for southern resident killer whales is very bleak. We’re not seeing the birth rates needed to sustain the population, and unless we change course, we’ll continue to see their decline.”

As a result, conservation efforts are being ramped up, not just to protect the whales, but also their unique behaviours and the ecosystems that sustain them. Professor Croft stressed the importance of safeguarding the kelp forests, noting that their decline due to rising ocean temperatures could have devastating consequences for the whales’ future.

“We could be on the verge of losing not just a species, but an entire culture,” said Dr Weiss. “These whales don’t just represent a genetic lineage; they embody a complex society with deep cultural traditions. If we lose them, we lose something truly irreplaceable.”