Sleeping giant: How sperm whales stay afloat while resting
Researchers found blowing bubbles helps the whales regulate buoyancy while they rest underwater.
A drone captured a humpback whale off the coast of California engaging in “kelping,” a recently documented behavior in which whales roll through and drape themselves in kelp.
A new study revealed a fascinating discovery about the sleep habits of sperm whales.
Sperm whales are known to rest vertically, a behavior believed to help protect them from waves and prevent them from drifting deeper into the water according to the study published in the Journal of Experimental Biology.
Scientists investigated their resting behavior, including how they maintain their position. The findings, published July 23, show that these whales have a unique way of staying buoyant while sleeping: blowing bubbles.
Sperm whale. Physeter macrocephalus. Near the Azores Islands (Portugal). North Atlantic Ocean. (Photo by: Francois Gohier/VW Pics/Universal Images Group via Getty Images)
During the experiment, researchers tagged 42 free-ranging sperm whales in Northern Norway that typically began resting by diving head-down. This means they first descended headfirst before floating into a head-up, vertical position. Scientists recorded biologging data using the tags, which collected audio of the bubbles and movement input.
Data collection took place over eight boreal summers between 2005 and 2019 in the Lofoten Islands region. Out of the 42 tagged whales, 17 were recorded resting for periods ranging from seven minutes to over three hours.
All the tagged whales who rested in head-down/head-up dives released bubbles, which confirmed that bubble release is used to regulate their buoyancy.
“As sperm whales are breath-hold divers, if they slowly drift up while resting, the gas in their lung will slowly expand,” the study authors explained. “Hence, releasing bubbles would enable them to counteract the expanding diving gas and achieve neutral buoyancy.”
(A) Illustration of the forces acting on a drifting whale. (B) Illustration of Boyle–Mariotte’s gas law, showing the compression of the air carried by the whale at depth due to hydrostatic pressure. (Image credit: Journal of Experimental Biology)
Results also showed that these mammals lessen their initial gas volume before they rest to help maintain neutral buoyancy, suggesting they adjust their diving gas volume based on the type of dive.
Study authors Noémie Freymond, Alec Burslem and Patrick Miller said these findings illustrate the unique strategies sperm whales use to rest for extended durations.
“If the whales are indeed sleeping during these resting periods, our findings indicate that they are capable of fine positioning control even during sleep,” the authors explained.
The next step in this investigation would be to confirm the whales are in fact sleeping during their rest time using EEG tags and to identify the cues that trigger bubble release.
Sperm whale. Physeter macrocephalus. Azore Islands (Portugal), North Atlantic Ocean. (Photo by: Francois Gohier/VW Pics/Universal Images Group via Getty Images)
Sperm whales are the largest species of the toothed whales, and they are listed as endangered under the Endangered Species Act, according to NOAA Fisheries. They have one of the widest global distributions of any marine mammal species, inhabiting all the world’s oceans.
Sperm whales received their name from the waxy substance on their heads known as spermaceti, an oil sac that helps them focus sound. Current threats to sperm whales include vessel strikes, entanglement in fishing gear, ocean noise and marine debris.
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