Swiss wildlife photographer Franco Banfi and a team of scuba divers were following a pod of sperm whales off the coast of Dominica Island in the Caribbean Sea, when suddenly the large creatures became motionless and fell into vertical slumber. This phenomenon was first discovered only in 2008, when a team of biologists from the UK and Japan inadvertently drifted into a group of sperm whales floating just below the surface, completely oblivious to their surrounding. It was only when one of boats accidentally bumped into one of the whales, did the animal woke up and the entire pod scurried off.
Until then it was thought that sperm whales, like other toothed cetaceans, slept with one side of their brain turned on to do important things that require physical activity, such as swimming or coming to the surface to breathe or avoid predators. It’s like keeping one eye open at all times, never fully letting their guard down.
The 2008 incident suggested that whales might sleep with both sides of the brain turned off. The researchers also discovered that whales take short, but periodic, bouts of sleep throughout the day with periods ranging between 6 and 24 minutes, but drift into deep sleep for only about 7 percent of the time. These these brief naps might be the only time the whales sleep, which would make sperm whales possibly the least sleep-dependent mammals known to man.