Humans aren't the only species using seaweed in their skin-care routines.
Last year, American researchers spotted pairs of southern resident killer whales rubbing each other with kelp.
鈥淲e found that killer whales were using segments of bull kelp as a grooming tool,鈥� said Michael Weiss, the research director at the Center for Whale Research (CWR) 鈥� a Washington-based organization dedicated to the study of southern resident killer whales.
For 12 days, the organization flew a new, high-powered drone above the Salish Sea, which recorded 30 instances of orcas plucking kelp stalks using their teeth and lips, before wedging the strands between themselves and a partner.
鈥淔rom there, they ... manoeuvre it back and forth and make these big S-shaped postures to get the right spot,鈥� Weiss said.
These interactions, which the researchers documented in a paper published in the Massachusetts-based journal Current Biology on Monday, were more prevalent among close relatives and orcas similar in age, and lasted anywhere from one to 15 minutes. The routine also occurred across all age and sex classes and in the whales' three major pods.
While the experts aren鈥檛 sure why orcas engage in this behaviour, they have a few predictions.
鈥淲e think it probably has a role as a social interaction to cement ... relationships,鈥� Weiss said. 鈥淭he other thing we found was that whales with greater coverage of dead skin ... were more likely to do the behaviour, which indicates it might have a role either to help remove dead skin or maybe it treats discomfort and itchiness that comes with dead skin.鈥�
According to the CWR, this is the first known case of wild marine mammals making tools out of objects from their environment.
鈥淪ocial grooming is really prevalent in social animals,鈥� said the research director. 鈥淏ut what鈥檚 unique here is the use of a tool 鈥� of an external object 鈥� to do that behaviour. That's quite rare, and it's really only been reported consistently in a few species of primate.鈥�
Weiss also thinks this behaviour says a lot about the social behaviour of southern residents.
鈥淭hey struggle to find enough food to survive and to reproduce, and yet they're still spending all of this time and effort on an elaborate social interaction,鈥� he said. 鈥淚 think [it] really emphasizes how key those relationships are for their health and well-being.鈥�
Only 74 of these whales remain, according to the federal government, and the research director says this new discovery could help protect the endangered species.
鈥淭he fact that these whales have unique behaviours ... emphasizes how unique they are and how worthy of conservation and care they are,鈥� Weiss said.
As for the future of this research, the CWR hopes to explore more about the hygenic functions of these behaviours, in addition to the social aspect of the routine.
鈥淲e also want to look ... at how rates of this behaviour between individuals might predict changes in their social relationships,鈥� Weiss said. 鈥淒o whales that kelp together end up hunting together or sharing food, or doing these crucial survival behaviours? That's going to take more analysis and more data.鈥�
