Unlike most deep diving mammals, dolphins are far more similar to humans with respect to the amount of time they can hold their breath underwater. Despite this fact, their unique anatomy allow dolphins more freedom of movement at greater depths, and going back to the surface for a breath of air can be done with little or no hassle, due to the dolphins’ ability to breathe through their blowholes.
Dolphins are aquatic mammals that don’t seem to be much more different than other cetaceans. However, despite their relatively normal size bodies and normal proportion between lung and body size, dolphins can hold their breath for an impressive amount of time due to their unique lung structure. A dolphin’s lungs contain a greater number of alveoli than most other sea mammals. These small air sacs are able to hold more air in each lung, which allows dolphins to hold their breath longer and withstand the crushing pressures of the deep ocean. After drawing a single breath at the surface, dolphins are therefore able to benefit from a highly efficient exchange of gases, squeezing every little amount of oxygen out of their air supply.
In terms of numbers, dolphins can typically stay underwater between 8 and 10 minutes on a single breath of air. Some dolphins are capable of holding their breath even longer, staying submerged for more than 15 minutes at a time. Considering dolphins’ efficient and agile swimming ability, these values typically translate into depths of more than 500 feet. Adult dolphins in their prime are even able to get close to depths of more than 1,700 feet.
Dolphins can take deep enough dives to reach the depths that would normally cause human divers to experience a type of decompression sickness known as “the bends,” primarily due to increased exposure to high-pressure oxygen. Since dolphins are just holding their breath throughout the dive, they do not experience this problem. Also, the internal body functions of dolphins change as they submerge to greater depths. These magnificent creatures are able to slow down or even halt their blood flow to the skin, some outer extremities and their digestive system, so that the heart can pump blood under enough pressure to reach their brain and tail muscles. Due to the unique structure of the dolphins’ lungs, and their special bone physique, they are also able to sleep underwater, floating just below the surface, and able to propel themselves above it, should they need a breath of fresh air.