There are a few things you should know about whales sleeping.
The first is how they breathe. Whales are voluntary breathers, which means they consciously and actively control their breathing. Unlike humans and most land mammals that breathe involuntarily, whales have to consciously come to the water's surface to breathe … through blowholes located on the top of their heads.
Whales vary in the frequency of their breathing, depending on factors such as species, activity level, and environmental conditions. Some whales may need to surface to breathe every few minutes, while others can stay submerged for more extended periods.
Regardless, they need to keep surfacing to breathe. Which begs the question … how do they get a chance to sleep?
It turns out that whales, like other cetaceans (dolphins and porpoises) have a unique way of resting while still maintaining some level of awareness to surface for breathing. When they sleep (called "logging" because they resemble floating logs) they have the capacity to rest one hemisphere of their brain at a time, with just one eye closed. While one hemisphere rests, the other remains active and aware, allowing the whale to continue surfacing for air and maintaining basic bodily functions. This is known as unihemispheric slow-wave sleep (USWS). Handy, right?
Exceptions maketh the rule, and the exceptions in this case are sperm whales in the wild. When they need a nap, they take a deep breath, dive down about 10 to 15m and arrange themselves into a group. They sleep unconsciously and still for up to 15 minutes at a time between breaths, in pods of 5 or 6 whales, presumably for protection; and they don’t sleep much. Researchers have monitored their naps, and they add up to only 7% of the day, making sperm whales the least sleep-dependant animals on earth, beating out the previous sleepless record holders … giraffes at 8%.
And that’s not all. The other thing you need to know about sleeping sperm whales, is that they do it vertically. No one knew this until a 2008 study undertaken by a team of scientists from Scotland and Japan documented the behaviour. And no one captured really good photography of it in the wild until 2017. French photographer Stéphane Granzotto was documenting sperm whales in the Mediterranean for a book when he came across these sleeping sperm whales. Other worldly, don’t you reckon?
Story Idea: Remo Giuffré
1 to 3. Sleeping sperm whales in the Mediterranean, 2017. Photo: Stéphane Granzotto.
4. Unihemispheric slow-wave sleep in dolphins, seals and ducks
5. Preserved brain of a sperm whale, on display in Miraikan, Japan. Photo:
6. Video: The Fascinating Way Sperm Whales Sleep | Concerning Reality