Southern resident killer whales in the Salish Sea have been documented deliberately biting off pieces of bull kelp and using the modified stalks to groom one another, according to research published in Current Biology on 23 June 2025. The behaviour, captured by high-resolution drones, represents the first recorded instance of a marine mammal manufacturing and using a tool. Footage taken during the spring and summer of 2024 shows one whale severing a short kelp stalk with its teeth, positioning the seaweed between its body and a partner, and then rolling in tandem to rub off dead skin. Researchers logged about 30 such episodes—termed “allokelping”—over eight days. Whales with more flaking skin and closely related or similarly aged pairs engaged in the practice most often, suggesting the activity serves both hygiene and social bonding functions. Tool use is known in several aquatic species, but previously recorded cases involved picking up unaltered objects. The study notes that the southern residents actively reshape kelp into exfoliating brushes, distinguishing their behaviour from that of dolphins that carry sponges or otters that crack shells with stones. With the Salish Sea population reduced to roughly 73 individuals, scientists say the discovery highlights the cultural complexity that could be lost if conservation efforts fail. The team from the Center for Whale Research and the University of Exeter plans longer-term monitoring to determine how widespread and durable the kelp-brushing tradition is within this endangered group.