Aquatic mammals need to come to the surface to breathe because they have lungs and need to exchange oxygen with the atmospheric air.
Aquatic mammals like whales, dolphins, or seals breathe with lungs, not with gills like fish. Their lungs surprisingly resemble ours, except they are more efficient at exchanging oxygen more quickly. They also have special nostrils, called blowholes, located on top of their heads to breathe easily without exposing themselves too much. These animals quickly inhale large amounts of air at the surface, then dive underwater to hunt, play, or rest. Their ribcage is flexible, allowing their lungs to withstand enormous pressures when they dive deep. And when they approach the surface, everything relaxes again. A practical function, it was worth thinking of.
Aquatic mammals like dolphins or whales have lungs, not gills. Yes, that means they must breathe air at the surface; it's impossible to extract oxygen directly from the water. Their lungs are efficient, but they also have a very limited air capacity compared to their size. Additionally, they produce carbon dioxide that must be regularly expelled by surfacing to avoid toxic buildup. Essentially, despite their aquatic life, these animals are constrained by a terrestrial physiology inherited from their ancestors, which compels them to manage their air supply carefully.
To stay underwater for long periods, aquatic mammals have several practical evolutionary tricks. For example, they have developed the ability to store much more oxygen in their muscles thanks to the high presence of a protein called myoglobin: it's like filling up on oxygen before a long dive. Their heart rate slows down when they dive (bradycardia), thus conserving their oxygen by reducing the needs of their bodies. Additionally, their blood circulation focuses primarily on vital organs—this is called peripheral vasoconstriction. These animals also have a flexible rib cage capable of collapsing under pressure to protect their lungs at depth. Most importantly, some aquatic mammals, such as sperm whales or beaked whales, have specialized in very efficient management of their air reserves, enabling them to make impressive dives lasting sometimes over an hour.
Aquatic mammals have lungs and must breathe air at the surface, unlike fish, which use gills capable of directly extracting dissolved oxygen from water. These gills, which function as highly efficient filters, allow fish to breathe continuously without having to surface. In contrast, marine mammals hold their breath during dives, hence the regular necessity to resurface to renew the air in their lungs. Fish can therefore remain constantly submerged thanks to their respiratory system fully adapted to the aquatic environment, an advantage that aquatic mammals do not have.
When it's time to breathe, aquatic mammals adopt specific strategies to quickly and efficiently reach the surface. Many, like dolphins and whales, carefully control their buoyancy by finely adjusting their lung volume or using their body fat. In general, they conserve energy by swimming gently underwater, then accelerating to the surface just before breathing. Some adopt a gradual spiral ascent to save energy, while others, like seals, dive diagonally to facilitate a quick ascent without significant muscular effort. As they approach the surface, they exhale powerfully, often projecting a visible cloud of air and water from a distance: the famous blow of large cetaceans. These instinctive behaviors are fundamental to their survival; everything is optimized for breathing efficiently and discreetly, without wasting their precious oxygen reserves.
Manatees, although they spend the majority of their time underwater, must come to the surface to breathe very regularly, every 3 to 5 minutes on average, due to their high metabolism and their pulmonary anatomy being less suited for prolonged apnea.
The sperm whale uses a special organ called spermaceti, located in its head, which allows it to adjust its buoyancy and facilitates its dives to great depths.
Some aquatic mammals, like dolphins, sleep by resting only one half of their brain at a time, allowing them to continue breathing at the surface even while they are asleep.
Seals and sea lions have remarkable physiological mechanisms: their heart rate can significantly decrease during a deep dive, allowing their bodies to conserve oxygen and extend their breath-holding capacity.
Aquatic mammal babies breathe atmospheric air immediately upon birth. Typically assisted by their mother, they are quickly brought to the surface to take their first breaths. They learn very quickly to control their breathing and to surface regularly.
Yes, many aquatic mammals sleep underwater. For example, dolphins practice unihemispheric sleep: only one hemisphere of the brain rests at a time, allowing the individual to remain alert and regularly come to the surface to breathe.
Evolution does not follow a linear logic. Aquatic mammals descend from terrestrial animals that already breathed air through lungs. Returning to a gill system would have required significant anatomical and physiological restructuring that is incompatible with the evolutionary history of marine mammals.
No, unlike humans, breathing in most aquatic mammals is a conscious act. They must consciously come to the surface to breathe, which explains why they sleep with part of their brain awake.
Sure! Here’s the translation: "It depends on the species. Whales can hold their breath for up to 90 minutes, while dolphins typically do so for 10 to 20 minutes. The duration depends on physiological adaptations such as lung size, the ability to store oxygen in the blood and muscles, and the level of underwater physical activity."
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