Sperm whales blow bubbles in their sleep to stay submerged, study finds

Sperm whales release gas bubbles while napping vertically underwater to keep themselves from floating to the surface, according to research published on Wednesday in the Journal of Experimental Biology. The study, conducted by scientists at the University of St Andrews and Université de Neuchâtel, reveals for the first time the physiological mechanism that allows these marine giants to maintain their unusual sleeping posture.miragenews+2

Bubble Release Regulates Buoyancy

Sperm whales are the only whales known to rest vertically, hanging head-up beneath the ocean surface for 10 to 15 minutes at a time. Their bodies are naturally positively buoyant due to large amounts of low-density spermaceti oil in their heads and the gas they carry in their lungs. As a resting whale drifts upward, decreasing water pressure causes that gas to expand, pushing it further toward the surface.miragenews+1

Releasing bubbles reduces the gas volume and brings the whale closer to neutral buoyancy, allowing it to remain submerged without swimming. Researchers recorded bubbles during 56 of 61 rest periods — nearly 92 percent — with whales releasing gas an average of about eight times per nap. One dive included 36 separate bubble releases. Whales resting closer to the surface blew more bubbles, approximately 11 times per nap, while those drifting up from deeper waters released only three or four.discovermagazine+1

Tagging 42 Whales Across Eight Summers

Working from small boats off Norway's Lofoten Islands, the team used poles to attach recording tags with suction cups to 42 male sperm whales tagged across eight summers between 2005 and 2019. The tags' microphones captured bursts of bubbles as the animals stopped swimming and rotated into their upright resting positions.discovermagazine

A computer model confirmed that bubble releases functioned to slow the whales' ascent. When the researchers kept the gas volume constant in their simulation, the modeled whales rose much faster than the real ones. The estimated gas volume fell by an average of 5.2 percent between sections of a resting dive.discovermagazine

The whales also began resting dives with far less gas — about 8 milliliters per kilogram of body mass — compared with 26.4 milliliters during foraging dives.discovermagazine

A Feat of Unconscious Control

"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," said Patrick Miller, a professor with the Sea Mammal Research Unit at the University of St Andrews.miragenews+1

Researchers still do not know what triggers each bubble release or whether the whales make these adjustments deliberately. The bubbles may also clear excess carbon dioxide or nitrogen, meaning buoyancy control may not be their only function.discovermagazine