Sperm Whales blow bubbles to achieve restful, vertical sleep

Researchers from the University of St Andrews and Université de Neuchâtel have discovered that sperm whales release gas bubbles to regulate their buoyancy and sleep vertically just below the ocean surface, according to a study published Wednesday in the Journal of Experimental Biology. The findings explain how the whales maintain their unique resting position without drifting upward. Sperm whales are naturally positively buoyant due to large amounts of spermaceti oil in their heads. As breath-hold divers, gas in their lungs expands as they drift up, and releasing bubbles counteracts this expansion to achieve neutral buoyancy. Scientists collected data using suction-cup tags attached to sperm whales off the Norwegian coast. The tags recorded sound and three-dimensional movement, capturing clear bubble sounds. A simulation based on tissue density, drag, and gas volumes confirmed that bubble release reduces positive buoyancy, enabling the whales to remain submerged while resting. Professor Patrick Miller from the Sea Mammal Research Unit at the University of St Andrews said the study confirms sperm whales exquisitely control their buoyancy by releasing gases to remain submerged with near-neutral buoyancy just below the sea surface. The authors suspect the behavior may also relate to off-gassing excess carbon dioxide or nitrogen from tissues into the lungs.