Forty-two tagged sperm whales released bubbles during 10- to 15-minute resting bouts, supporting the idea that the animals use bubble loss to avoid drifting up to the surface.
The Journal of Experimental Biology study says expanding lung gas makes resting whales more buoyant as they rise, and bubble release helps restore neutral buoyancy.
Whales resting closer to the surface averaged about 11 bubble releases, versus three or four for animals resting after dives of 200 meters or more, when compressed lung air reduces buoyancy.
The findings also suggest sperm whales can maintain fine vertical positioning even during probable sleep, though researchers say bubble release may also help with oxygen intake or carbon-dioxide removal.