Sperm whales have been found to release bubbles of gas as a mechanism to regulate their buoyancy during sleep, according to a recent study published in the Journal of Experimental Biology. This discovery sheds light on how these deep-diving mammals maintain a vertical position underwater while resting.

Sperm whales are naturally positively buoyant due to the large amounts of spermaceti oil in their heads, which makes controlling their position in the water column essential. Researchers from the University of St Andrews, collaborating with the University of Neuchâtel in Switzerland, demonstrated that the whales emit bubbles to counteract the expanding gases in their lungs as they slowly ascend during their resting periods. This release of bubbles enables the animals to achieve neutral buoyancy, preventing them from drifting to the surface or becoming horizontal.

The study involved attaching suction-cup tags to 42 sperm whales, which recorded movement and acoustic data. Of those, 17 whales were observed while resting near the ocean surface, typically within nine meters of depth and in pods of five or six individuals. Analysis of the recordings captured distinct bubble sounds coinciding with the animals’ movements. Using this data, the researchers developed a simulation model incorporating factors such as tissue density, water drag, and internal gas volumes. The simulation confirmed that the controlled bubble release serves to reduce positive buoyancy, stabilizing the whales’ vertical posture during sleep.

This behavior likely provides practical benefits, enabling sperm whales to rest effectively without being affected by surface wave action while avoiding the energy costs associated with diving to greater depths. Sperm whale naps are brief, typically lasting 15 minutes or less.

Among cetaceans, only grey and bowhead whales have previously been documented to regulate buoyancy through bubble release, mainly during dives. Other marine mammals, such as humpback whales and Antarctic fur seals, also produce bubbles, but primarily for foraging or during ascent, respectively, rather than for buoyancy control.

The findings offer new insight into the unique adaptations sperm whales have evolved to manage the challenges of resting in their aquatic environment, highlighting sophisticated behavioral and physiological mechanisms that support their survival.