Orcas, often recognized as killer whales, are apex predators of the ocean. They are marine mammals that possess lungs and breathe air, much like humans. Unlike fish, which use gills, orcas cannot breathe underwater and must surface regularly to inhale and exhale. This mammalian trait means they constantly interact with the atmosphere despite living in water.
Breathing Mechanics
Orcas breathe through a single blowhole, their nostril, situated on top of their heads. This strategic placement allows them to take a breath by exposing only a small portion of their head, minimizing the effort to surface. A muscular flap covers the blowhole, sealing it tightly when submerged to prevent water from entering the lungs.
Breathing in orcas is a conscious act, unlike the automatic respiration seen in many land mammals. They must actively decide to breathe, even during sleep, a process managed through unihemispheric sleep where only half of their brain rests. When surfacing, an orca rapidly exhales a powerful burst of air, often creating a visible “blow” of water vapor, followed by a swift inhalation. This entire respiratory exchange can occur in just a fraction of a second.
Orca lungs are highly efficient, exchanging 80% to 90% of their total lung volume per breath, far more than the 15% exchanged by humans. This efficiency allows them to take fewer breaths; resting orcas may breathe only 1.2 to 1.3 times per minute, increasing to 1.5 to 1.8 when active. This contrasts sharply with human rates, which range from 15 to 60 breaths per minute.
Diving Adaptations
Despite needing to breathe air, orcas have physiological adaptations for extended underwater periods. They can hold their breath for 5 to 15 minutes, storing significant oxygen in their blood and muscles. Orcas possess higher blood volume and more hemoglobin, the oxygen-carrying protein, than similarly sized land mammals.
Their muscles also contain a high concentration of myoglobin, a protein that stores oxygen directly within muscle tissue. When an orca dives, it initiates a “diving response,” which includes bradycardia, a slowing of the heart rate. An orca’s heart rate can decrease from around 60 beats per minute at the surface to as low as 30, or even 4 to 8, during a dive.
Peripheral vasoconstriction is another adaptation, redirecting blood flow from non-essential organs to prioritize the heart, lungs, and brain. This conserves the limited oxygen supply for critical functions.
As orcas descend, their lungs are adapted to collapse. This collapse, occurring at about three atmospheres of pressure, forces air into rigid airways where gas exchange does not happen. This helps prevent nitrogen absorption into the bloodstream, avoiding decompression sickness, or “the bends.” These adaptations allow orcas to effectively hunt and navigate their underwater environment.