Whales are mammals that possess lungs, not the gills found in fish. Like all mammals, they rely on breathing atmospheric air to oxygenate their blood and sustain life. This dependency means that even the largest whales, which spend their lives in the deep ocean, must regularly break the water’s surface to perform a mandatory air exchange.
How Whales Take a Breath
Whales possess a specialized respiratory opening called the blowhole, which is essentially a modified nostril located on the top of the head. This dorsal positioning allows the animal to expose only a minimal portion of its body to the air, making the process of breathing at the surface highly efficient. Toothed whales, such as sperm whales, have a single blowhole, while baleen whales, like humpbacks, have two blowholes positioned side-by-side.
A powerful muscular plug and surrounding tissues seal the blowhole tightly when the whale is underwater, preventing any water from entering the respiratory system. Unlike terrestrial mammals, a whale’s respiratory tract is completely separate from its digestive tract, which prevents them from breathing through their mouth and eliminates the risk of water entering the lungs while feeding.
Breathing for a whale is not an automatic, reflexive action like it is for a human, but rather a conscious, voluntary decision. Upon reaching the surface, the whale first performs an explosive exhalation, often visible as the characteristic “blow” or spout, which is a mix of warm air, water vapor, and mucus. This forceful expulsion can travel at speeds up to 300 miles per hour.
Following the rapid exhalation, the whale takes a quick, deep inhalation, completing the entire air exchange in just one or two seconds for larger species. This breath is remarkably efficient, allowing the whale to exchange approximately 80 to 90% of the air in its lungs with each breath, a significant contrast to the 10 to 15% exchanged by humans. This efficiency maximizes oxygen uptake during their brief time at the surface before descending again.
The Diving Adaptations That Maximize Time Underwater
The ability of whales to remain submerged for extended periods relies on a suite of complex physiological adaptations known as the “diving reflex.” These mechanisms allow the animal to conserve and efficiently utilize the oxygen stored within its body.
One of the most important adaptations is the dramatic increase in oxygen-carrying proteins within the blood and muscle tissue. Whales have a significantly higher concentration of hemoglobin in their blood compared to land mammals. Furthermore, their muscle tissue contains very high amounts of myoglobin, a protein that stores oxygen directly in the muscles, which can be up to 30% higher than in their terrestrial relatives.
When a whale begins a deep dive, a reflex known as bradycardia immediately slows the heart rate, often by more than half. Simultaneously, peripheral vasoconstriction, or blood shunting, occurs, which redirects oxygenated blood flow primarily to the most oxygen-sensitive organs, such as the brain and the heart. Blood is temporarily restricted from less essential areas like the digestive tract and certain muscle groups, reserving the oxygen stores for the functions that sustain life.
To avoid decompression sickness, or “the bends,” which results from nitrogen gas dissolving into the bloodstream under high pressure, whales have evolved a specialized lung structure. Their lungs are relatively small for their body size and are designed to collapse completely under the immense pressure of deep water. This mechanical collapse forces the residual air, and the nitrogen it contains, out of the gas-exchanging alveoli and into the non-diffusible, cartilaginous airways like the trachea and bronchi. By preventing nitrogen from entering the bloodstream in large quantities, the collapse of the lungs effectively eliminates the risk of nitrogen bubbles forming in the blood upon ascent.
How Whales Rest Without Drowning
Since breathing is a voluntary act, a whale cannot fall into a deep, unconscious sleep like a human without risking suffocation. To overcome this challenge, whales rely on a unique neurological state called unihemispheric slow-wave sleep (USWS). This adaptation allows one half of the brain to enter a state of rest while the other half remains active and alert.
The awake half of the brain maintains the muscle control necessary for swimming and retains the consciousness required to initiate a breath and surface. During USWS, the eye opposite the sleeping hemisphere is often closed, while the eye connected to the active half remains open to monitor the environment. This partial awareness ensures the whale never loses control over its mandatory breathing cycle.
This need to maintain partial consciousness informs the whale’s resting behaviors, which typically involve two main forms. One common behavior is called “logging,” where whales float motionless near or at the surface of the water, sometimes vertically, resembling a floating log. The blowhole is positioned just above the waterline, allowing for minimal effort to take a breath.
The second resting behavior involves slow, rhythmic swimming, sometimes referred to as drafting or echelon swimming. This gentle movement maintains forward momentum and allows the whale to continually surface for air with minimal energy expenditure. The constant requirement to surface and breathe means that the amount of sleep varies by species, often involving short, intermittent naps.