Unlike most marine creatures, bottlenose dolphins cannot breathe underwater because they lack a vital part of their anatomy, the gills.
Dolphins do not have gills. Dolphins have lungs, and they breathe using their blowholes, which are located on the tops of their heads. When swimming underwater, dolphins need to hold their breath because they are unable to draw in oxygen through their non-existent gills. Whales, which are cetaceans as well, lack gills too.
They are aquatic animals, so they live underwater, but in order to breathe, they need to float up. Well, bottlenose dolphins come out of the water briefly to socialize with others and look at their surroundings, but mostly to breathe.
Just as humans breathe air through their nostrils, dolphins have a breathing apparatus on the top of their heads that serves the same purpose. Unlike bottlenose dolphins, most people can only hold their breath for 30 seconds or a minute.
How Dolphins Proceed without Gills
Unlike fish, which breathe underwater with gills, dolphins hold the breath of dolphins until they float to the surface. They need to hold their breath long enough to catch fish, and their babies are born underwater. Dolphins stay underwater to catch prey but must return to the surface to breathe. Like other mammals, dolphins need to breathe in order for their bodies to function.
Dolphins are mammals, which means they suck air into their lungs just like we do. Dolphins and other mammals are warm-blooded animals that give birth, nurse their young, are born with fur, and breathe air. Whales and dolphins have bodies that look like fish, but function like mammals, giving birth like mammals and feeding their young with their milk, more like mammals. The first difference between sharks and dolphins is that they are types of animals: sharks are fish, while dolphins are mammals (just like us).
Dolphins can swim as gracefully in the water as any fish, but they are not fish. Dolphins cannot breathe underwater like fish because they don’t have gills. Otherwise, they can breathe through the stomata and stay that way for hours, even while they sleep. Even when the dolphin sleeps, it swims near the surface and breathes air when necessary.
Dolphin Sleep and Breathing Behavior
Dolphins usually sleep at night, but only for a few hours at a time; they are often active late at night, perhaps combining this alert period with feeding on fish or squid before rising from the depths. Individual dolphins also go into deeper sleep, mostly at night. A deeper form of sleep is called a log, because in this state the dolphin is like a log floating on the water.
When dolphins sleep, dolphins stay below the surface because they must breathe oxygen from the air to stay alive. When people try to swim with dolphins, they get stressed when they breathe compressed air underwater, and the dolphins just hold their breath. For example, dolphin breathing is a more selective process than humans because dolphins can choose when to get up to breathe.
For example, dolphins exchange 80% of the air in their lungs with each breath, while humans are only able to exchange 17%. The lungs of dolphins are proportional to their body, like those of other mammals. When a dolphin breathes, air enters directly into its lungs, expiration and inhalation rarely take more than a fraction of a second and take on average about 2-3 breaths per minute (Ponganis et al, 2003). Cetaceans reduce the number of inhalations and exhalations during periods of rest; a dolphin can average 8-12 breaths per minute when it is active enough to reduce its respiratory rate from 3 to 7 per minute while resting.
Dolphin Brain Activity, Sleep, and Breathing
Equipped with an arbitrary respiratory system, whales and dolphins must keep a part of the brain in a state of readiness to activate each breath. While this is still a matter of debate, most researchers believe that in order to breathe, a dolphin or whale must be conscious and ready to recognize that they are on the surface.
Dolphins, like whales, need to surface regularly to replenish their air supply. Dolphins must live where they can float to breathe air, as sharks spend their entire lives underwater, making their homes in the open ocean, shallow coastal waters, coral reefs, and in some cases even rivers.
When dolphins need to catch fish, they can manipulate their circulatory system and reduce their oxygen intake. Thus, dolphins’ breathing and eating are completely separated, so they can catch prey with their mouths and swallow them without the risk of water entering their mouths. Dolphins don’t actually go into deep sleep, otherwise dolphins can drown just like us humans. Dolphins can probably swim for very long periods of time (definitely hours and maybe even days) if they move slowly.
Young whales and dolphins rest, eat and sleep while their mother swims, dragging them along, a position called floating in trains. Striped dolphins can live in very large groups, and when they jump into the air, they perform complex tricks.
