Sperm whales don’t sleep the way most animals do. Instead of drifting quietly at the surface, these massive mammals can hang suspended roughly 25 meters below, forming “sleeping columns” that look like towering structures from the boat. Researchers have long known that sperm whales can rest underwater in short bursts, typically 10–15 minutes, but the mechanics of how they avoid rising—despite buoyant head anatomy—has been a puzzle.
A sperm whale’s head takes up about a third of its total body mass and is packed with oil, wax, and air. Since these components are buoyant, scientists have wondered how the whales stay underwater without behaving like corks. The new study suggests a surprising solution: during sleep, sperm whales regulate their buoyancy by actively modulating the gas volume they carry—specifically by blowing bubbles from the blowhole.
To test this idea, the team used advanced suction-attached recording devices on 42 sperm whales around the Lofoten Islands in northern Norway. The instruments captured bubble sounds, recorded the timing and frequency of bubble release, and tracked key context variables such as whale depth and head orientation (up versus down). The recorders were later recovered after the animals surfaced.
The results show that resting depth strongly predicts bubble activity. Whales sleeping closer to the surface released bubbles about 11 times per power nap, while whales resting after deep dives of more than 200 meters produced only around three to four bubble events during their ascent-related rest. In other words: the whales blow more bubbles when they are “buoyancy-prone” to rise too quickly.
The technical logic behind this pattern is tied to pressure and oxygen supply. At greater depths, the surrounding pressure compresses air in the whale’s lungs and reduces buoyancy, meaning the animals need fewer bubble releases to prevent upward drift. Closer to the surface, air expands gradually and pushes the whale upward, so blowing bubbles releases some onboard gas and reduces lift, helping the whale stay in the right depth window.
The study also raises a biological question: is bubble blowing a purely physiological response driven by sensing buoyancy, or does it reflect a conscious strategy during sleep? Because researchers don’t yet know whether sperm whales sleep with both hemispheres fully inactive or in a partially awake state, the behavioral control behind bubble release remains uncertain.
Still, the pattern is clear—and it reframes what “sleeping underwater” means for one of the ocean’s most iconic giants. Rather than floating passively, sperm whales appear to fine-tune their internal gas balance in real time, trading small, periodic bubble releases for sustained, stable rest below the surface.
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Subject of Research: Animals
Article Title: Buoyancy regulation through modulation of onboard gas volume by resting sperm whales (Physeter macrocephalus Linnaeus)
News Publication Date: 23-Jul-2026
Web References: https://doi.org/10.1242/jeb.251920
References: Freymond, N., Burslem, A. and Miller, P. J. O. (2026). Buoyancy regulation through modulation of onboard gas volume by resting sperm whales (Physeter macrocephalus Linnaeus). J. Exp. Biol. 229, jeb.251920. doi:10.1242/jeb.251920.
Image Credits: Stéphane Granzotto www.stephanegranzotto.com
Keywords: sperm whale, buoyancy regulation, sleeping behaviour, bubble release, onboard gas volume, underwater resting, marine mammals, Journal of Experimental Biology
