New research from the University of St Andrews and Université de Neuchâtel shows how sperm whales can sleep in a unique vertical position just beneath the ocean surface. The only whale known to rest vertically, sperm whales may use this position to stay protected from surface waves while avoiding the energy of deeper dives. In a paper published on 23rd July in the *Journal of Experimental Biology*, scientists discovered that whales release gas bubbles while resting, regulating buoyancy and keeping them below the surface.

Because sperm whales are naturally positively buoyant due to spermaceti oil, the bubbles counteract expanding lung gas as the animal drifts upward, achieving neutral buoyancy. Tags attached with suction cups off the Norwegian coast recorded bubble sounds and 3‑D movement, allowing researchers to model tissue density, drag, and gas volumes. The simulation confirmed that bubble release reduces positive buoyancy and lets whales stay submerged during rest.

Results also indicate whales begin resting dives with less diving gas than deep foraging dives. Professor Patrick Miller noted that the fine‑scale buoyancy adjustments occur even while the whales are asleep, a capability alien to terrestrial mammals. The authors suggest bubble release may also relate to off‑gassing metabolic CO2 or N2, hinting at broader implications for metabolic gas exchange.