Though they inhale air into their lungs like humans, the mechanism of breathing is modified to suit their purpose.
Underwater marine animals being mammals don’t have gills like fish do to help them breathe underwater. Marine species like dolphins and whales breathe like humans. Though they inhale air into their lungs through the nose, called blowholes, the mechanism of breathing, is modified to suit their purpose.
Nose On Top Of Head
Since their blowhole is located right at the top of their heads, these mammals raise their heads just above the water surface to get the air in. Soon after breathing, as they are about to go under, a set of strong muscles present around the blowhole close up very tightly, preventing any water from getting into their lungs.
Air Out Before Air In
When it is time for a repeat inhalation of air, they first expel the air out, as they rise to the surface and then inhale. The air that they are blowing out does not come from their lungs, but it’s the water that gets accumulated on top of the blowhole while they were swimming about or resting. The time taken to exhale and inhale is only a fraction of a second, but the amount of air they displaced during exhalation causes a bellowing spray and produces a massive sound. For this very reasons its often said that you hear a dolphin before you see it.
Breathing Only Through Nose
Another notable difference in the breathing activity between dolphins and humans is that these marine mammals don’t breathe through their mouth. Or so it was thought. This way, the breathing and the eating processes are kept separate from each other to prevent accidental swallowing of water while capturing the prey, which otherwise could have risked getting into the lungs.
Breathing Through Mouth
It is maybe interesting to note that it has been eventually found that dolphins also breathe through their mouths the same way the humans do. The research revealed that owing to very high amounts of haemoglobin and myoglobin in their blood; they can absorb and store a good amount of oxygen in it. This helps them to spend comfortable time underwater. Additionally, during very deep dives or lengthy submersion, they tend to reduce their heart rate and switch off the functioning of some organs to enable them in their quest.
Holding Breath Over Two Hours
As such, a dolphin can hold its breath for several minutes, but on an average, they typically breathe four to five times every minute.
Deep dives by sperm whales or Cuvier’s beaked whales have recorded to last well over an hour, the highest being about 137 minutes by the later.