New research shows that blowing bubbles helps sperm whales to sleep soundly, hidden beneath the waves.
It actually stops them from floating to the surface during nap time.
While little is known about how sperm whales sleep, researchers believe that the ocean giants doze underwater for 10 to 15 minutes at a time with their heads facing upwards.
They keep away from the choppy waters of the surface while still remaining close enough to get a breath of fresh air if the need arises.
However, one issue has puzzled scientists. A sperm whale’s head is massive—taking up nearly a third of its body—and filled with oil, wax and air.
Those materials float, so how does the species stay underwater without popping to the surface like a cork while they sleep?
Now we know, after researchers from the University of St. Andrews, Scotland, and the University of Neuchâtel, Switzerland, dug into the question with high tech underwater equipment.
They used devices that would allow them to tell whether the whales were asleep and also record the bubbles.
Suctioned to each whale, the equipment recorded the sound of the bubbles as they were released from the blowhole while also telling researchers how deep the whales were and whether their heads were facing up or down.
After affixing the recorders on 42 sperm whales in the Loften Islands off the coast of Norway, the research team recovered the devices.
Sperm whales can rest in three different ways. One is to put their head down and dive a bit, before their buoyant heads turn up towards the surface. They can also sink gently, tail-first about eight meters down, or they can rest as they ascend from deep dives over 200 meters.
The findings, published in the Journal of Experimental Biology, showed that those whales dozing closer to the surface blew more bubbles in their sleep, releasing bubbles around 11 times per power nap.
However, those drifting up from the depths only blew bubbles three or four times during their restful ascent.
Different resting depths require the whales to carry different amounts of oxygen—and last different lengths of time.
Deep diving means the whales need a lot of oxygen, explained study co-author Professor Patrick Miller, of the University of St. Andrews. But the pressure of the water compresses the air in their lungs causing the whales to be less buoyant.
“This means they need to blow fewer bubbles to stop themselves from floating upwards.
“However, when the whales rest closer to the surface, the air in their lungs will slowly cause them to rise to the surface. Blowing bubbles releases some of the air, making them less buoyant in the process.”
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But it was still not clear if blowing bubbles is a conscious decision by the whales to release some air as they sleep.
Study lead author Noémie Freymond, from the University of Neuchâtel, admits no one knows whether sperm whales sleep as we do—or if they sleep like dolphins and keep one half of their brain awake while the other snoozes.
“Blowing bubbles to make sure they don’t come too near the surface requires the whales to sense their environment and realize that they are coming too close to the surface.”
“Whether they turn out to be partially awake or fully asleep, sperm whales have definitely come up with a creative solution to ensure a restful slumber beneath the waves.”
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