Research Reveals Sperm Whales Use Bubble Release for Vertical Sleep Buoyancy Control

Discovery of Unique Sleep Mechanism

Researchers from the University of St Andrews and Université de Neuchâtel have identified the method sperm whales use to sleep in a vertical position just under the ocean surface. This unique sleeping posture is believed to buffer them from surface waves and conserve energy by avoiding deep dives for rest.

Buoyancy Regulation Through Bubble Release

The study, published in the Journal of Experimental Biology, reveals that resting sperm whales release gas bubbles to control their buoyancy. Sperm whales are naturally positively buoyant due to spermaceti oil in their heads. As breath-hold divers, their lung gases expand while resting, and bubble release counteracts this expansion, allowing them to achieve neutral buoyancy and remain submerged.

Data Collection and Simulation

Data was collected using small tags attached with suction cups to sperm whales off the Norwegian coast, recording sound and 3D movements. Clear bubble sounds were detected, and movement data was used to create a simulation modeling tissue density, drag, and gas volumes. This simulation confirmed that bubble release reduces positive buoyancy, enabling submerged rest.

Implications for Whale Physiology

The results also indicate that sperm whales begin resting dives with less diving gas volume compared to deep foraging dives. Professor Patrick Miller noted that this demonstrates exquisite buoyancy control, even while the whales are thought to be asleep. Researchers suggest that bubble release might also be linked to the off-gassing of excess CO2 or N2 from tissues, potentially impacting metabolic gas exchange.