Seals can dive so deeply underwater thanks to their ability to hold their breath for long periods and their physiological adaptation that allows them to regulate their blood circulation and store oxygen in their muscles and organs.
Seals have a streamlined body that is highly hydrodynamic, ideal for minimizing resistance in water and conserving their energy. Their limbs are transformed into powerful flippers, perfect for quickly propelling their body underwater. They also have a flexible rib cage, capable of compressing under pressure without causing internal injuries. Their skull features reinforced sinuses, allowing them to withstand high underwater pressures without pain or discomfort. Finally, their thick skin and insulating layer of fat, known as blubber, protect them from the cold during prolonged dives in icy waters.
Seals can hold their breath for an impressive duration, sometimes up to two hours depending on the species. They owe this exceptional ability to their muscles and blood, which store significantly more oxygen than ours. The secret lies in special proteins like myoglobin, which are very abundant in their muscles, that capture and retain a large amount of oxygen for use when they really need it. In other words, each dive comes with a built-in air reservoir, very handy when one wants to explore deeply and for a long time without breathing.
Seals have a real array of practical adaptations to withstand the enormous pressure of the depths. Their ribs are particularly flexible, allowing the ribcage to compress without damage under the high pressures of water. Their lungs, highly flexible, can flatten completely, thus avoiding the risks associated with gas accumulation, such as the dreaded bubbles responsible for diving accidents in humans (decompression sickness). Moreover, their circulatory system has reinforced blood vessels and an efficient blood flow to essential organs, thereby protecting tissues sensitive to high pressure. In short, a well-honed internal armor against underwater discomforts!
Seals can store a lot of oxygen directly in their muscles thanks to a very high amount of myoglobin. This protein acts as a highly efficient personal reserve during long dives. Their bodies also automatically limit oxygen consumption by significantly slowing down their heart rate while reducing blood circulation to non-essential parts of the body — basically, only vital organs remain prioritized. As a result, they use their oxygen supply sparingly, in an extreme energy-saving mode.
Seals have an incredible control over their buoyancy. They can easily reduce their lung volume to become less buoyant and effortlessly descend to the depths. Conversely, by holding more air in their lungs or adjusting their position, they rise slowly without expending much energy. They also perfectly manage their heart rate, thanks to a phenomenon called bradycardia: when they dive, their heart significantly slows down, allowing them to use the oxygen stored in their bodies with extreme efficiency, thus extending their time underwater.
Elephant seals hold the record for diving among non-cetacean marine mammals, sometimes reaching depths of over 1500 meters for nearly 2 hours.
When they dive, seals primarily use the oxygen stored directly in their muscles and blood rather than in their lungs, thus reducing the risks associated with decompression.
Seals have extremely sensitive whiskers that allow them to detect subtle movements of fish in the darkness of the deep sea.
Seals can expel the air contained in their lungs before diving to reduce their buoyancy and facilitate their rapid immersion into deep marine areas.
In depth, the main predators of seals are large marine predators, particularly big sharks like the great white shark, or certain cetaceans, such as the orca, which is capable of pursuing seals even at significant depths.
Seals avoid decompression accidents thanks to special physiological adaptations. Their lungs collapse under pressure, thereby limiting gas exchange and the amount of nitrogen absorbed into the blood, thus preventing the formation of dangerous bubbles during ascent.
Seals have an incredible ability to hold their breath, typically managing to do so for 20 to 30 minutes. Some species, such as the elephant seal, can even stay underwater for over an hour by increasing the efficiency of oxygen management stored in their muscles and blood.
Seals use a mechanism called dive bradycardia, a voluntary slowing of the heart rate. This strategy allows them to reduce their oxygen consumption, thereby extending the duration for which they can remain submerged without breathing.
Some seals, like the Weddell seal, can dive to depths of around 600 meters, but this varies greatly among species. The southern elephant seal holds the record, being capable of diving to nearly 2000 meters in depth to search for food.
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