Sperm Whales Release Gas Bubbles to Maintain Buoyancy While Sleeping

Sperm whales, the ocean’s largest predators, face a unique physical challenge when they sleep: they are naturally positively buoyant, meaning their bodies tend to drift toward the surface. In addition to the air in their lungs, their large heads contain the spermaceti organ, which is filled with a waxy substance that influences their general density. Unlike land mammals, which rest in a horizontal position, sperm whales have been observed remaining almost motionless in a vertical posture, with their heads pointing toward the surface and their bodies trailing down below it. Scientists note that this behavior may represent sleep, although observations alone cannot establish exactly how deeply asleep the animals are.

Buoyancy Control via Bubble Release

A study published in the Journal of Experimental Biology reveals how these giants manage their position. Researchers found that every sperm whale observed during resting periods released bubbles. The study hypothesizes that this behavior helps them regulate their buoyancy, or their ability to float and stay at a particular depth. As a resting whale slowly drifts upward, the gas inside its lungs expands because the pressure of the water decreases. Releasing bubbles would enable them to counteract the expanding diving gas and achieve neutral buoyancy, the study read.

Because they are breath-hold divers, they must remain near the surface to breathe easily when they wake up. The vertical posture and bubble release help them conserve energy by avoiding the need to swim to maintain their depth, while also potentially shielding them from the motion of ocean waves.

Research Methodology off the Coast of Norway

To uncover this behavior, researchers from the University of St Andrews and the Université de Neuchâtel deployed benign suction-cup tags on sperm whales to collect detailed data. These tags recorded the whales’ movements and sounds, including clear bubble-release signals as the animals rested. Scientists then combined this data with hydrodynamic simulations that accounted for factors such as tissue density, drag through the water, and the volume of gas in the whales’ bodies. The simulations confirmed that the bubble release helped them regulate their buoyancy and remain underwater. Researchers also discovered that before starting a resting dive, sperm whales carry less air in their lungs compared with when they dive deep to hunt for food.

Metabolic Implications and Future Questions

While the primary hypothesis focuses on buoyancy regulation, scientists are also exploring other potential functions for the bubble release. It is possible that the bubbles serve a secondary metabolic purpose, assisting in the removal of excess gases like carbon dioxide or nitrogen that build up in body tissues during long, deep dives. We cannot rule out the possibility that releasing bubbles is related to the offgassing of excess CO2 or N2 from tissues into the lungs, so this behaviour could also have implications for metabolic gas exchange, the study read. While observations establish that the whales exercise precise control over their buoyancy even while resting, the study also appeared in Current Biology, highlighting the scientific interest in how these deep-diving giants maintain their position.