Discover How Long Seals Can Stay Underwater

Also known as pinnipeds, seals are remarkable creatures who have skillfully adapted to life in the water. There are over 30 different seal species in all different shapes and sizes, each with incredible physiological adaptations that allow them to efficiently conserve oxygen and even slow down their heart rate. Let’s dive into the aquatic world of these incredible marine mammals and discover just how long seals can stay underwater!

Discover How Long Seals Can Stay Underwater

So, just how long can seals stay underwater? Well, it depends… Overall, seals can stay underwater from 15 minutes at a time up to two whole hours, depending on the species. 

From small harbor seals to enormous elephant seals, each species can stay underwater for varying amounts of time. For example, the southern elephant seal is the best diver, and can hold its breath for up to two whole hours! Habor seals, on the other hand, are much smaller and usually only hold their breath for around 15 to 30 minutes at a time.

How Do Seals Stay Underwater So Long?

Increased Oxygen, Decreased Heart Rate

Seals are mammals, but their unique physiology is much different than any mammal on land, allowing them to stay underwater for longer periods of time. If we consider their size, seals have about twice as much blood flowing through their bodies as we do. Blood carries oxygen, so this increased blood volume means that seals can carry about three times as much oxygen in their blood as a human can! 

Another unique adaptation for these underwater pinnipeds is that they also have a special protein in their muscle tissue called myoglobin, which carries oxygen. Seals have about 10 times more myoglobin in their muscles than humans do, allowing them to carry much more oxygen.

Seals have another nifty trick up their flippers: they can slow their heart rates down to extremely low levels. Their normal heart rate is usually around 75 to 120 beats per minute, but when they dive deep down into the ocean, they can slow their hearts down to just four to six beats a minute!

In addition, when a seal returns to the surface for air, they can resupply their oxygen levels to incredible amounts. Humans usually capture about 20% of the oxygen we breathe in, whereas seals can capture around 90%! This gives them a much shorter recovery time when they return to the surface, allowing them to go back underwater quicker and for longer periods of time than many other mammals.

Underwater Pressures

Oxygen isn’t the only challenge with spending time underwater. When diving deep down into the ocean, the temperatures drop and the water can be murky and hard to see through. However, seals are protected with a thick layer of blubber to keep them warm. They also have long, very sensitive whiskers, which help them to detect prey and dangers in the water. In addition, there are clear membranes over their eyes for protection, and their nostrils close up to prevent water from getting in. 

When seals dive, the pressure in the water around them increases. This could not only damage their lungs but also allow nitrogen gas to enter the blood. The pressure can make nitrogen gas get into their blood, which is a problem when they come back up. Too much nitrogen in their blood can cause tiny gas bubbles. This is why human divers can’t return to the surface too quickly, otherwise, they’ll suffer from “the bends”. 

However, seals and sea lions have unique ways to avoid this. Their peripheral airways — the smaller tubes in their lungs — are reinforced. This allows them to collapse their lungs when they dive, keeping nitrogen from mixing with oxygen and making them sick. In addition, their flexible rib bones can bend under pressure without breaking. 

As you can see, seals are well-adapted to spend at least half their lives in the water. In fact, seals can even sleep underwater!

Sleeping Underwater

Seals use a unique technique called “unihemispheric sleep” in order to enjoy a bit of shut-eye underwater. “Uni” refers to one, while “hemispheric” refers to the two hemispheres of the brain. So essentially, a seal can turn off half of its brain (one hemisphere) at a time, allowing it to sleep while the other half stays awake! Unihemispheric sleep helps seals catch up on their beauty rest without having to return to land, while at the same time allowing half of their brain to stay alert to predators and other dangers in the water. 

Seals typically only take short naps while underwater, sleeping for just 10 to 15 minutes at a time. However, even in these short periods of sleep, seals can actually enter into REM sleep — the deepest stage of sleep — and they can wake up and react quickly to threats. Sometimes they’ll float carefree on their backs with their heads popping out just above the surface, allowing them to breathe quickly before going back to sleep. Other times, seals sink to the bottom of the ocean, sleeping peacefully with their heads resting gently on their flippers.

How Long Can the Different Seal Species Stay Underwater?

True Seals (Phocidae)

True seals are the most common type of seals. They are also called earless seals, but true seals actually do have ears — they’re just harder to see! Their ears are internal, with just a small opening on each side of their heads. When they dive, their ear canals close in order to keep water from getting inside. There is also a special layer of fat inside the seal’s ear that acts like a supercharged amplifier, helping them to hear while underwater. Internal ears also provide better hydrodynamic performance for true seals, reducing drag in the water so that they can slice through the waves with speed and efficiency. 

The most common true seal is the harbor seal (Phoca vitulina). Harbor seals usually stick to shallow coastal waters, where they hunt for food in three to seven-minute dives underwater. However, harbor seals can dive up to 1,500 feet below the surface and stay underwater for more than 30 minutes at a time!

Harp seals (Pagophilus groenlandicus), on the other hand, are small, agile swimmers who capitalize on shorter diving times. They typically dive from 66 feet down to over 1,640 feet below the surface and stay underwater for between two to 20 minutes. Then there are the massive southern elephant seals (Mirounga leonina). These incredible creatures can dive down more than 6,500 feet below the surface and hold their breath for up to two hours at a time!

Eared Seals (Otariidae)

There are around 15 species of eared seals, which include both fur seals and sea lions. These seals have bigger foreflippers and pectoral muscles than true seals and can move more easily on land. Although they spend more time on land than true seals do, eared seals can still stay underwater for quite a long time. 

The California sea lion (Zalophus californianus), for example, doesn’t dive very deep, sticking to depths of 50 to 100 feet. However, it can stay underwater for up to 20 minutes at a time. On the other hand, the Guadalupe fur seal (Arctocephalus townsendi) — the smallest of the eared seals — only stays underwater for around 12 minutes.  

Walruses (Odobenidae)

The only member of the Odobenidae family is the walrus (Odobenus rosmarus). Only elephant seals can beat these mighty animals when it comes to size — an adult male walrus can weigh more than 4,400 pounds! 

Despite their enormous size and imposing nature, however, walruses can only hold their breath for about two and a half to five minutes. During these brief intervals, walruses may hunt, travel, or even take very brief naps. These quick naps are more rejuvenating than you might imagine. They help walruses to be able to swim continuously in the water for up to 84 hours at a time! Of course, once they return to land, they also enjoy a nice deep sleep for up to 19 hours to recover from their marathon swim. 

The photo featured at the top of this post is © F-Focus by Mati Kose/Shutterstock.com