The orcas’ spa
14 June 2025
The Southern Resident Orcas are a group of orcas living in the Salish Sea, in the north-western Pacific Ocean, between the United States and Canada, off the coasts of Washington State and British Columbia.
They are considered a distinct population and are at risk of extinction. Among these orcas, scientists have observed a behaviour known as allogrooming — mutual body cleaning — involving the creation and use of actual tools designed for this purpose. The orcas set up their spas in forests of giant kelp, as documented by spy-drone footage captured by a British–American research team. The study was published just a few days ago in the journal Current Biology. The researchers coined the term allokelping to describe this newly observed behaviour: the orcas gather and modify pieces of giant kelp, specifically Nereocystis luetkeana, also known as bull kelp, to use together with a grooming partner. The orcas carefully tear off pieces of kelp from entire stalks, using their teeth and body movements to create short, manageable segments. Once they have a piece, the orca places it over its snout and approaches its partner. This marks the beginning of the mutual contact phase, during which both animals hold the kelp fragment between their bodies, rolling it over their skin in slow, coordinated movements to keep it from falling. But what’s the purpose of allokelping? One leading hypothesis is that it serves in skin care. Researchers have observed that this behaviour is more frequent among orcas showing visible signs of skin moulting — a natural process in which the animal sheds layers of dead skin. In this case, the kelp would act as a natural “brush”, helping remove flakes of epidermis. This interpretation is supported by similar behaviours seen in other orca populations, such as those in Alaska and British Columbia, where orcas rub themselves against smooth pebbles on beaches, presumably to achieve an exfoliating effect. The Southern Resident Orcas are considered endangered, and the loss of bull kelp forests due to ocean warming and acidification could jeopardise these orcas’ ability to continue practising allokelping. And that would be more than just an ethological curiosity: it’s a tangible demonstration of intelligence, cooperation, and cultural transmission in a great marine mammal.
