Orcas also ask their partner to scratch their backs.

BarcelonaThat orcas and other marine animals need to scratch is nothing new. It has been known for years that several species of orcas do what is known as kelp: Scrubbing seaweed with your head, fins, and body to remove parasites and keep your skin healthy.allokelping.

In a study published this Monday in the journal Current Biology have documented how orcas use kelp tools to scratch each other's backs (allokelping). A type of behavior that was completely unknown until now and that could mark a before and after in the study of the behavior of aquatic animals, since it is the first evidence that marine mammals make and use tools.

"We were stunned when we first detected this behavior," says CWR research director Michael Weiss. He and his team observed how, for eight of the twelve days of their research, a group of orcas from the Salish Sea, in the inland waters of Washington, USA, which has been studied for half a century, used pieces of algae to scratch each other.

The best-studied orcas on the planet

University of Exeter MA student in animal behaviour Rachel John details how, despite being "the best-studied orcas on the planet", theallokelping because the videos recorded from airplanes weren't of sufficient quality. Now, however, images they've recently managed to capture using drones "show this behavior in great detail."

Researchers have observed how orcas bite off the end of a kelp stalk to remove a piece and place it between themselves "and another companion" to rub and scratch each other. In addition, they have also observed how they use them to massage each other and that they also keep kelp wrapped around their bodies for extended periods. According to the researchers, who emphasize that this is a behavior seen in orcas of all ages, these movements "probably serve to strengthen social bonds" and to care for their skin.

"We know that orcas often make contact with other members of their pod – touching their bodies and fins – but using kelp in this way could enhance that experience," explains John, who insists that orcas and dolphins have several strategies to help remove dead skin, and this behavior could be another one.