Dolphins are marine mammals that, unlike fish, possess lungs and must periodically return to the surface to breathe air. This biological requirement shapes their behavior and physiology, and understanding their surfacing frequency provides insight into their underwater lives.
How Dolphins Breathe
Dolphins breathe air using lungs, similar to humans. They do not breathe through their mouths; instead, they utilize a specialized nostril called a blowhole, located on top of their head. This placement allows them to easily take a breath by exposing only a small part of their head at the water’s surface.
Breathing for a dolphin is a conscious act, unlike the automatic respiratory reflex in humans. They actively decide when to open their muscular blowhole, rapidly exhaling and then inhaling in approximately 0.3 seconds. This efficient process allows them to exchange 80% to 90% of lung air with each breath, significantly more than the 17% exchanged by humans. After inhaling, the blowhole seals tightly, preventing water from entering their lungs as they submerge.
How Often They Surface for Air
The frequency at which dolphins surface for air varies based on their activity level and age. Adult dolphins generally surface every 30 seconds to 2 minutes, or 2 to 5 times per minute.
When resting or sleeping, dolphins can extend the time between breaths, often surfacing as few as 1.5 to 4 times per minute. During periods of increased activity, such as active swimming, hunting, or playing, their breathing frequency increases to meet higher oxygen demands, sometimes reaching 8 to 12 breaths per minute. Dolphins can hold their breath for 8 to 10 minutes, with some species capable of remaining submerged for up to 15 minutes. Coastal bottlenose dolphins often dive for 20 to 40 seconds but have a maximum breath-hold capability of 10 to 15 minutes.
Dolphin calves, with developing respiratory systems, need to surface more frequently than adults. In their first month, calves may breathe as often as 15.2 times per minute, decreasing to 10.97 times per minute by their third month. Mothers often assist their newborns by nudging them to the surface for their initial breaths and maintaining close proximity.
What Affects Breathing Frequency
A dolphin’s breathing frequency is directly influenced by its metabolic needs, which fluctuate with its activity level. When dolphins are engaged in high-energy behaviors like hunting, chasing prey, or performing acrobatic leaps, their bodies require more oxygen, leading to more frequent trips to the surface. Conversely, during periods of rest or slow travel, their metabolic rate decreases, allowing them to remain submerged for longer durations between breaths.
Age also plays a significant role in determining how often a dolphin breathes. Young calves have immature lungs and higher metabolic rates relative to their body size, necessitating more frequent breaths than adult dolphins. Their developing physiology means they cannot hold their breath for as long as mature individuals.
Dolphins exhibit a unique sleep pattern known as unihemispheric slow-wave sleep, where only one half of their brain rests at a time. This allows the other hemisphere to remain active, ensuring conscious control over breathing and maintaining awareness of their surroundings. During this state of partial sleep, their breathing rate slows, typically to 3 to 7 breaths per minute, enabling them to continue surfacing for air without entering a state of unconsciousness where they might drown.
Dolphin Diving Adaptations
Dolphins possess several physiological adaptations that enable them to perform prolonged dives and efficiently manage oxygen underwater. They have an effective system for oxygen utilization and storage, surpassing that of many terrestrial mammals. Their blood contains a higher volume, and their muscles are rich in myoglobin, a protein that stores oxygen, allowing them to store approximately 41% of their oxygen intake in muscle tissue compared to 19% in humans.
During a dive, dolphins exhibit bradycardia, a slowing of their heart rate, which conserves oxygen. Blood flow is redirected, shunting oxygen-rich blood primarily to vital organs like the brain and heart, while reducing circulation to tissues that are more tolerant of temporary oxygen deprivation.
Their respiratory system also features collapsible lungs and a flexible ribcage, which are crucial for deep diving. As a dolphin descends, the increasing water pressure causes its lungs to compress, and the alveoli, the tiny air sacs where gas exchange occurs, collapse.
This mechanism helps minimize the absorption of nitrogen into the bloodstream at depth, thereby reducing the risk of decompression sickness, commonly known as “the bends,” which can affect human divers. Specialized networks of blood vessels, such as the retia mirabilia, further assist in managing pressure changes and maintaining stable blood flow to the brain during dives and ascents.