Scientists Discover How Sperm Whales Control Buoyancy During Vertical Sleep

When it comes to marine life, there are facts beyond human imagination. In the most recent findings, scientists discovered a lesser-known fact about sperm whales and their resting mechanism. According to them, sperm whales have a fantastic way of resting far beneath the ocean waves. Researchers from the University of St Andrews and Université de Neuchâtel provided a rare insight into the secretive lives of one of the ocean’s largest and most intelligent marine animals.

What does the research say

The research found that unlike most marine mammals, sperm whales sleep in a strange upright position, bobbing almost motionless just below the sea surface. The experts revealed the interesting mechanism they use to maintain this strange sleeping posture: they release a gas bubble to regulate their buoyancy, allowing them to stay suspended in the water.

What is this unique sleeping position and its benefits?

You will be surprised to know that sperm whales are the only known species of whale that routinely sleeps in a vertical position. They spend these periods of rest hanging vertically in the water column, often with their heads pointing to the surface and their bodies trailing down. According to researchers, this sleeping position has several benefits. Whales stay near the surface so that they can breathe easily when they wake up, and the vertical position may protect them from the motion of ocean waves. It may also help them avoid the energy drain of drifting into deeper waters.

The difficulty of staying suspended

Scientists found that sperm whales have a strange buoyancy problem and their big heads contain a special organ filled with a waxy substance called spermaceti oil that helps them to be naturally buoyant. They are naturally positively buoyant, which means they tend to rise towards the surface. They are also deep-diving animals that hold their breath. So, when they dive and hold their breath, gases in their lungs change as pressure increases and decreases. When they rest near the surface, the gas in their lungs slowly expands, increasing their chances of coming up. Sperm whales deal with this by releasing small amounts of gas, in the form of bubbles, which helps them control their buoyancy and float almost weightlessly.

How did the scientists figure this out

Understanding the sleeping mechanism of sperm whale

For this analysis, researchers put small suction-cup tags on sperm whales off the coast of Norway to collect data. The benign tags recorded the whales’ movements and sounds in detail as the animals rested and traveled through the ocean. The tags also recorded clear bubble-release sounds during the whales' rest periods. And when scientists combined this acoustic information with movement data, it helped them reveal this unique resting style of sperm whales, which left them amazed. The results duly showed that the release of bubbles helped the whales to overcome their natural buoyancy and stay suspended under the surface, close to neutral buoyancy.

How do they manage this control

The most surprising finding of this research was that sperm whales seem to be able to make these fine buoyancy adjustments while they are asleep. Professor Patrick Miller from the Sea Mammal Research Unit at the University of St Andrews said: “Sperm whales have an incredible ability to control their buoyancy by releasing gases when they are resting. "Such delicate adjustments during sleep are very different behaviorally from anything seen in terrestrial mammals, including us," he added. The study also revealed that the sperm whales’ resting dives start with a lower gas volume than the dives they make at greater depths while actively hunting food and this difference allows them to maintain a stable position in sleep.

Possible link with gas exchange

According to scientists, the bubble release act may have another vital role. It is being believed that it might have something to do with the elimination of excess carbon dioxide or nitrogen from body tissues into the lungs. If confirmed, the finding could offer new insights into how sperm whales cope with the physical stresses of deep diving, breath-holding and sleeping underwater.