The question of whether whales sleep or not is actually a very common one. Whales and dolphins are mammals and need sleep to survive, but they sleep very differently than humans and other land mammals.
Humans are unconscious breathers, meaning that our bodies will automatically breathe to take in air even when we are sleeping. Whales and dolphins are conscious breathers – they have to actively decide when to breathe, which can seem tricky for an animal that spends all of its time underwater!
Luckily whales and dolphins are well adapted to their lives underwater. While all whales sleep, it seems that different species have different sleeping requirements and methods. The amount of sleep and the way that they sleep can vary greatly between species – and since it is quite difficult to study their sleep in the wild, varying information has been reported.
There are a few more common sleeping positions: resting quietly in the water (horizontally or vertically), sleeping while swimming slowly next to another animal or in a group, or floating on the surface (often called logging). Dolphins in captivity have also been recorded sleeping for short periods of time at the bottom of their tanks. Humpback whales seem to be most often found resting motionless on the surface for increments of up to 30 minutes. They cannot sleep much longer than this without losing too much of their body temperature when inactive.
One of the more common assumptions across species is that whales sleep with half of their brain ‚shut down‘ and one eye closed. They are thought to do this in order to maintain an awareness of potential predators or problems around them, and to remember to breathe. This has been reported for several different types of dolphins, including bottle-nose dolphins. Dolphins can sleep for a couple of hours at a time, usually at night. One species was reported to sleep for approximately 33% of the day, where sperm whales are estimated to sleep for just 7% of the day!
Encounters with sperm whales also suggest that they enter a deeper sleep. A group of scientists accidentally came across a pod of sleeping sperm whales off the coast of Chile in 2008. Their boat engine was off and the team was below deck working on recording sperm whale calls, when they suddenly realized they had drifted directly into a pod of sleeping sperm whales. The whales did not notice until the boat accidentally nudged one of the whales, waking it up. Luckily the whales moved away and began sleeping again shortly after.
As you can see, we still have a lot to learn about the sleeping patterns, requirements, and behavior of whales and dolphins! Among the many questions remaining is: do whales dream? This we still don‘t know, but we‘re excited to see what future encounters and research reveals! Until then, we will keep dreaming about whales.