Full Breakdown
Sperm Whales Use Bubble Bursts to Maintain Neutral Buoyancy While Resting
7/25/2026, 11:07:19 AM
Core Discovery
On July 23, researchers from the University of St Andrews and the Université de Neuchâtel published a paper in *Journal of Experimental Biology* showing that sperm whales (Physeter macrocephalus) release gas bubbles during short, vertical resting bouts to counteract their natural positive buoyancy. By expelling bubbles, the whales achieve near-neutral buoyancy and remain just below the surface without drifting upward.
Background & Context
Sperm whales are the largest toothed mammals and must surface for air consciously. Because continuous breathing is impossible during sleep, they are thought to employ unihemispheric sleep—alternating brain hemispheres—allowing vigilance while resting. Uniquely among whales, they adopt a vertical posture with heads upward, positioning themselves a few metres below the surface to avoid wave action while staying close enough to breathe.
Data & Statistics
- Tag deployments: 42 individuals were fitted with suction-cup tags off Norway’s Lofoten Islands.
- Resting duration: Bouts typically last 10–15 minutes.
- Bubble release frequency: Whales resting near the surface emitted about 11 bubble releases per bout, whereas those ascending from depths greater than 100 m produced only 3–4 releases.
- Depth effects: Deeper resting dives (>100 m) required fewer bubbles because higher water pressure compresses lung gas, reducing buoyancy.
Official Statements & Responses
The study’s authors explain that as breath-hold divers, sperm whales experience gradual lung-gas expansion while drifting upward. The simulation based on tag-recorded depth, sound, and 3-D movement confirmed that bubble emission reduces net positive buoyancy, allowing the whales to stay submerged during rest. The researchers also note that bubble releases may aid metabolic gas exchange, potentially off-gassing excess CO2 or N2 from tissues.
Verbatim Quote
“This study confirms that Sperm Whales exquisitely control their buoyancy by releasing gases to remain submerged with near-neutral buoyancy just below the sea surface. It is particularly fascinating they are able to make these fine-scale adjustments while they are thought to be asleep, a challenge totally alien to terrestrial mammals like us humans.” — Sea Mammal Research Unit, at the University of St Andrews
Why It Matters
Understanding this buoyancy-control mechanism clarifies how sperm whales can rest safely in a dynamic marine environment. It also provides insight into cetacean sleep physiology, a field limited by the difficulty of measuring brain activity in large, free-ranging whales. The findings suggest that fine-scale environmental awareness persists even during presumed sleep, challenging assumptions about marine mammal consciousness.
Conflicting Reports & Gaps
- Consciousness of bubble release: Researchers acknowledge they cannot yet determine whether the behavior is a conscious adjustment or an automatic physiological response.
- Alternative functions: While buoyancy regulation is supported by the data, the authors caution that bubble emission might also relate to oxygen uptake or carbon-dioxide removal, a hypothesis not yet tested.
- Direct brain measurements: No electroencephalogram (EEG) data exist for sleeping sperm whales, so the classification of these periods as “sleep” versus “rest” remains provisional.
What’s Next
Future work aims to capture neural activity during resting bouts and to explore the metabolic implications of bubble release, potentially linking buoyancy control with gas exchange processes.
