A new study led by Griffith University in Australia has found that, on their return journey south to cooler waters, humpback whales frequently use sandy, shallow bay areas to roll over in the sandy substrate in order to remove dead skin cells.
The experts used suction cap tags to track migrating whales between August and October 2021. These so-called CATS tags are fitted with integrated high-definition video, a VHG transmitter for retrieval, a magnesium release system, a hydrophone, several magnetometers, as well as temperature, light, pressure, and GPS sensors.
Data collected from the tags revealed that whales often performed full and side rolls at depths of up to 49 meters on the seafloor that was lined with fine sand or rubble.
“On all occasions of sand rolling, the whales were observed on video to be slowly moving forward with their head first into the sand followed by rolling to one side or a full roll,” said study lead author Jan-Olaf Meynecke, a marine biologist at Griffith.
“During the different deployments, the sand rolling was observed in the context of socializing. The behavior was either following courtship, competition, or other forms of socializing. So we believe that the whales exfoliate using the sand to assist with moulting and removal of ectoparasites such as barnacle and specifically select areas suitable for this behavior.”
Since in tropical and subtropical waters, barnacles – sticky, tiny crustaceans related to crabs, shrimps, and lobsters – attach to humpback whales in their early life stages, whales need to remove them frequently to avoid excessive growth leading to drag and energy loss. Moreover, whales also host a diversity of skin bacteria which, if they grow in large numbers, pose significant threats for open wounds. Thus, removing excess skin is essential for maintaining a healthy bacterial skin community.
Finally, the observations revealed that the skin falling off during whales’ cleaning procedure was consumed by fish such as the juvenile silver trevally, suggesting that, besides helping whales maintain their health, this behavior can also provide important ecosystem services.
The study is published in the Journal of Marine Science and Engineering.