If you could go 15 days at a time without sleeping, what would you do? Researchers have found that dolphins can go for at least 15 days without sleeping, and have no signs of fatigue.

In a study published yesterday in PLoS One journal, researchers looked at a pair of dolphins and their use of echolocation. Dolphins use clicks and listen to the echoes in order to accurately determine the distance of an object, because there is not great visibility in the ocean. Researchers studied dolphins' ability to echolocate for five days at a time, three times, apiece.

The researchers found that dolphins were able to successfully echolocate over the course of 15 days, with no interruption or significant cognitive impairment. One dolphin was successful, overall, at echolocation for 75 to 36 percent of the time. The other dolphin was successful an astonishing 97 to 99 percent of the time at this task.

Researchers found that the reason that dolphins are able to do this is that they sleep with one hemisphere at a time. It is believed that dolphins evolved this mechanism because, by shutting off only one hemisphere at once, the animals are able to breathe at the surface of the ocean. Such ability also allowed dolphins to be able to stay vigilant, an important tool for an environment in which predators lurk everywhere and in which dolphins are probably too large to hide in most places in the ocean.

"These majestic beasts are true unwavering sentinels of the sea. The demands of ocean life on air breathing dolphins have led to incredible capabilities, one of which is the ability to continuously, perhaps indefinitely, maintain vigilant behavior through echolocation," Brian K. Branstetter, a researcher involved in the study, said in a statement.

The study was conducted by researchers from the National Marine Mammal Foundation, the U.S. Navy Marine Mammal Program, and the Science Applications International Cooperation.