As divers, we spend a lot of time thinking about depth. But how deep can nature’s deepest diving animals go? The answer will amaze you.

As divers, we spend a lot of time thinking about depth. How deep can we go before we experience nitrogen narcosis or exceed no-decompression limits? How deep before the oxygen in our dive cylinder becomes toxic? As a community, we’re always testing the boundaries imposed on us by depth. But several remarkable marine species have adapted to reach much greater depths with comparatively little effort. Here are the top five deepest diving animals, all air-breathing birds or mammals, for whom extreme diving is a way of life.

Emperor Penguin

The deepest diving of all seabirds, the emperor penguin feeds primarily on fish. However, their diet also includes deep-dwelling squid and other cephalopods. Records show that they’ve dived down to 1,755 feet (535 m) in pursuit of prey. The emperor penguin is perfectly adapted to survive these deep dives. Its wings are flatter and stiffer than those of other birds, enabling extra propulsion. Its bones are solid, rather than air-filled, to reduce the risk of barotrauma. These penguins can also slow their heart rate to just 15 to 20 beats per minute while diving in order to minimize oxygen use. To counter the icy temperatures of the Antarctic waters, emperor penguins have the highest feather density of any bird species, and a layer of sub-dermal fat measures over an inch thick.

Leatherback Turtle

The leatherback turtle is unique among turtles in that its carapace is made of toughened skin — hence the name leatherback — rather than a bony shell. This adaptation gives the turtle added flexibility under pressure, and signals the leatherback’s status as one of the deepest diving animals. Scientists have recorded leatherbacks at depths of 4,200 feet (1,280 m), following the daily daylight migration of the jellyfish they eat. In order to cope with the incredible pressure at such depths, these turtles have developed several other important adaptations. These include collapsible lungs, which reducing the risk of the bends; the ability to slow their heart rate to conserve oxygen; a pulmonary sphincter that circulates blood away from the lungs while they are collapsed; and the ability to regulate body temperature so that it remains constant regardless of the surrounding water temperature.

Elephant Seal

Both species of elephant seal have a breath-hold time of more than 100 minutes. This makes their dives as remarkable for their length as they are for depth. Male elephant seals often dive for more than 60 minutes at a time, and the depth record for this species is an incredible 7,835 feet (2,388 m). Like the leatherback turtle and the emperor penguin, food is the incentive for the seals’ astonishing dives. They prey primarily on deep-dwelling species including skates, rays, squid and octopus. Elephant seals are a deep-diving success because their bodies hold an abnormally large volume of blood. This allows them to store additional oxygen. They also have increased levels of myoglobin, allowing them to store oxygen in their muscles, a larger percentage of oxygen-carrying red blood cells, and exceptionally thick blubber to protect them from the cold at depth.

Sperm Whale

Reaching lengths of up to 66 feet (20 m), sperm whales are the world’s largest toothed predators. They sustain their huge size by diving to incredible depths in search of their preferred prey, squid. Scientists have recorded sperm whales at depths of up 7,380 feet (2,250 meters). They can remain submerged for as long as 90 minutes and have also evolved to survive under extreme pressure. One of their most important physiological features is a flexible ribcage that allows for lung collapse and the reduced absorption of nitrogen. Like elephant seals, their blood carries extra myoglobin and red blood cells, and they are able to direct their bloodstream away from non-essential organs while diving in order to make the most of depleted oxygen levels. In the pitch black of the abyss, sperm whales find their prey through echolocation.

Cuvier’s Beaked Whale

In 2014, scientists named Cuvier’s beaked whales the deepest diving animals of all when they tracked one on a dive to 9,874 feet (2,992 m). The dive lasted for 2 hours and 17 minutes, making this whale the longest-diving mammal on record as well as the deepest. Cuvier’s beaked whales dine a diet of squid and deep-dwelling fish and, like the sperm whale, have fully flexible ribcages.

Before taking the plunge, these whales exhale almost all of the air in their lungs. This helps them become negatively buoyant and descend quickly to depth. The elimination of air spaces makes the whale’s body more resistant to the crushing effects of pressure while also reducing gas absorption. They are also able to divert blood flow from their extremities to essential organs like the brain and the heart. While they’re diving, their digestion, kidney and liver functions shut down completely to conserve oxygen.

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