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Seals have a remarkable ability to sleep underwater without drowning. This seems impossible since most mammals need to breathe air regularly to get oxygen. So how can seals sleep so soundly at the bottom of the ocean without needing to come up for air? The secret lies in their ability to conserve oxygen.
Reduced Heart Rate Conserves Oxygen
When seals sleep underwater, their bodies make physiological changes to drastically slow down their metabolism. Their heart rate drops from 100-150 beats per minute down to just 4-8 bpm. This allows them to conserve oxygen and extend the time between breaths from 5-10 minutes to up to 2 hours! Their slowed heartbeat means their organs require less oxygen to function.
High Myoglobin Stores Oxygen in Muscles
In addition to a slowed heart rate, seals have high amounts of oxygen-storing proteins called myoglobin in their muscles. Myoglobin allows their muscles to function with less oxygen. With a reduced need for oxygen throughout their body, seals can sleep underwater for long periods before needing to come up for more air.
Elephant Seals – Extreme Underwater Sleepers
Some seal species, like elephant seals, take specialized sleeping underwater to the extreme. They have adapted to sleep while diving for up to two hours at a time at depths of up to 1,000 feet! At these crushing depths, oxygen is even more limited. But their physiology and adaptations allow them to make use of what little oxygen exists.
Risks of Sleeping Underwater
While underwater sleeping is crucial for a seal’s survival in the ocean, it does come with risks. If a sleeping seal is startled, its oxygen reserves could become depleted too quickly for it to make it back to the surface. However, mother seals have been observed taking birthing dens underwater so they can sleep next to their pups while nursing them.
Remember Their Amazing Adaptations
The next time you see seals diving and sleeping at aquariums or in the wild, remember their special ability to conserve oxygen. It allows them to survive and rest in an environment that requires most mammals to breathe regularly. Scientists continue to study seals to understand how humans might apply their underwater sleeping adaptations in extreme environments.
Seals – Remarkable Underwater Sleepers
Seals never cease to amaze with their diving capabilities and their ability to sleep underwater without drowning. Their specialized adaptations in physiology and oxygen-conserving proteins allow them to withstand low oxygen environments. Understanding how seals’ bodies accomplish this remarkable feat gives us insight into marine mammal biology.
