Whales are marine mammals that must surface regularly to breathe air, making their existence a continuous balance between the ocean depths and the atmosphere. The answer is yes, whales can drown, but the mechanism is fundamentally different from that of land mammals, stemming from their unique respiratory control and the external threats they face in the ocean.
The Key Difference: Voluntary Breathing
Unlike humans and most other mammals, whose breathing is a reflex controlled automatically by the brainstem, a whale’s breathing is a conscious, voluntary action. This means cetaceans must actively initiate every single breath they take. This voluntary control is an adaptation that ensures the whale never accidentally inhales water while submerged.
This voluntary control is why the loss of consciousness is so dangerous for a whale. If a whale becomes severely injured, sick, or otherwise incapacitated, it can no longer make the conscious choice to swim to the surface and open its blowhole. In this state, the whale will eventually succumb to hypoxia, or lack of oxygen, and fail to prevent water from entering the lungs.
To manage this requirement for conscious breathing, whales and dolphins utilize a unique sleeping pattern called unihemispheric slow-wave sleep. They rest only one hemisphere of their brain at a time, allowing the other half to remain awake and alert. This partial wakefulness is enough to maintain awareness of their surroundings and ensure they surface to breathe at the appropriate time, preventing accidental drowning during periods of rest.
Physiological Safeguards Against Water Intake
Whales possess several specialized anatomical features that provide a highly effective defense against water entering their respiratory system during normal activities like diving and feeding. The blowhole, which is the whale’s nostril, is equipped with robust muscular flaps and plugs. These structures create a tight, watertight seal that remains closed unless the muscles are deliberately contracted to take a breath at the surface.
Internally, the whale’s respiratory and digestive tracts are largely separated, unlike the shared pharynx in humans that can lead to choking. In baleen whales, a specialized oral plug, a fatty and muscular sac, swings to block the lower airway when the whale opens its mouth to engulf massive volumes of water and krill. This mechanism ensures that water taken in for feeding does not enter the lungs.
Furthermore, whales exhibit a powerful physiological response known as the diving reflex when they submerge. This reflex immediately triggers bradycardia, a dramatic slowing of the heart rate, and peripheral vasoconstriction, which restricts blood flow to the extremities. These actions conserve oxygen by prioritizing its delivery to the brain and other vital organs, effectively extending the time a whale can remain underwater.
Specific Causes of Fatal Water Inhalation
While a healthy, conscious whale rarely drowns, external factors can override both its voluntary control and its anatomical safeguards.
Entanglement and Physical Trauma
The most common human-related cause of drowning is entanglement in fishing gear. When a whale is severely restricted by heavy, unforgiving gear, it can be physically prevented from reaching the surface to initiate a voluntary breath, leading to suffocation and subsequent water inhalation. Severe physical trauma, such as a major vessel strike, can also lead to drowning by causing immediate loss of consciousness. A concussed or injured whale may be unable to coordinate the complex muscle movements needed to surface and open its blowhole.
Illness and Stress
Similarly, severe illness or pathology, such as a respiratory infection or neurological disorder, can cause extreme lethargy, leading to the failure to surface or the inability to keep the blowhole sealed. Extreme stress also impairs the whale’s ability to breathe consciously. Exposure to intense acoustic trauma, such as loud underwater sonar, can induce panic or disorientation that disrupts the precise, voluntary control over breathing. In these scenarios, the whale’s system becomes overwhelmed, and the protective mechanisms fail, making the inhalation of water a tragic possibility.