Do Whales Sleep? (Adaptations of Marine Mammals)
Whales need to breathe to stay alive and don’t have gills like fish. This means that whales will regularly need to come to the surface. But how do whales do this when they sleep? Do whales sleep or have they developed a way to live a life without sleep?
Whales need sleep just like other mammals. However, contrary to land mammals, whales have developed unique sleeping methods to sleep and still be able to be aware of their surroundings. Whales also are aware that they need to come to the surface to breathe, while sleeping.
There’s more to whale’s sleep than meets the eye. Their sleeping behavior may seem a bit odd to us, but whales have evolved this behavior to sleep while staying in the water. Because whales are in the water while sleeping, we still need to do more research to understand all different aspects of their sleep.
Do Whales Sleep? (Sleeping Behavior)
How Do Whales Sleep?
Whales can sleep in two different ways, and all whales do this. The first way is to sleep resting in the water either horizontally or vertically. Another way that whales use to sleep is to sleep while slowly swimming next to another animal.
Males, who often travel in pairs, will usually sleep next to one another while slowly swimming. Females with calves, on the other hand, usually sleep while swimming. They must do so because, when the calves are born, they do not have enough blubber or fat in order to float. The calves will need to ride on the pressure created by the swimming mother otherwise they would sink. This type of swimming is also known as echelon swimming.
Another benefit of this type of sleep is that it will reduce the stress placed on the calves as they will not require much energy to swim on their own, thus reducing their risk of infection or disease. This combination of swimming and sleeping will go on for several weeks until the calves are either able to swim or float on their own.
As whales spend their entire lives underwater, they have naturally evolved mechanisms that enable them to remain underwater for long periods of time (such as when they sleep). Technically, like us, whales stay underwater by holding their breath. However, what mainly differentiates them from us is that they can both inhale more air and that they are much less susceptible to CO2 than us.
Because whales have larger respiratory systems than us, they can inhale much more air in one breath. Their red blood cells also carry more oxygen and, in order to reduce excess loss, their oxygen is directed to only the life-sustaining organs (i.e. heart, brain, and swimming muscles) when they dive.
Not only do whales have a greater supply of oxygen, but they are also much more tolerant to CO2. This means that they require a much greater amount of CO2 to build up in their blood before they’re required to resurface and breathe again.
Both of these mechanisms thus enable a much more efficient respiratory system than ours, having evolved in order to help whales sleep in their aquatic environment.[1]Hecker, B. 1998. How do Whales and Dolphins Sleep Without Drowning, Scientific American, accessed 11 September 2021, < https://www.scientificamerican.com/article/how-do-whales-and-dolphin/#>
How Do Whales Sleep Without Drowning?
Whales use their blowhole to breathe and have voluntary control over the blowhole to prevent water from coming into this blowhole. But voluntary control also means that breathing would be difficult while sleeping entirely. Luckily, whales have developed a special sleeping method.
Whales use a unique method of sleep called unihemispheric slow-wave sleep to prevent drowning while sleeping. This method of sleeping allows whales to keep one hemisphere of their brain active so they are always aware of their surroundings and know when to come up to breathe.
This type of sleep is necessary for whales because they need to retain some type of voluntary control over their bodies in order to use their blowhole (and breathe), even while asleep. This is an important difference between whales and most mammals who breathe while sleeping due to involuntary control by the nervous system.[2]Liamin, O.I. & Mukhametov, L.M. 2013. Sleep in cetaceans. И. В. Павлова, 63, 61
Where Do Whales Sleep?
Whales usually come up to the water surface to breathe every few seconds. For this reason whales usually don’t sleep far from the surface.
The actual locations where they sleep will vary depending on the species, but they usually don’t venture off far from the surface. For example, the sperm whale has been seen either sleeping while drifting at the surface or at a 10-meter depth. This distance would be enough to give them ample time to return to the surface a few times a minute to breathe.[3]Amano, M., Aoki, K., Miller, P.J.O, & Rendell, L.E. 2008. Stereotypical resting behavior of the sperm whale. Current Biology, 18, 21-23
When Do Whales Sleep?
Whales will often sleep for short periods of time throughout the day and will become more active at night. Some species of whales can dive to over 1,000 meters for food and prefer hunting at night. At that time their prey is more likely to emerge.
How Long Do Whales Sleep?
Whales have been seen sleeping for varying lengths of time, depending on their species. For example, the sperm whale has been known to sleep for only ten to fifteen minutes.
Assuming sperm whales are fully asleep during this time, this means that they only sleep for roughly 7% of the time. This contrasts sharply with smaller whale species such as the beluga and grey whales, who sleep 32% and 41% of the time respectively.[4]Kaplan, M. 2008. Researchers sneak up on sleeping whales, Nature, accessed 11 September 2021, <https://www.nature.com/articles/news.2008.613>
It’s possible that sperm whales, or perhaps all whales in general, have an ability to sleep both fully and semiconsciously. Because the sperm whales that were observed were not disturbed at all by the nearby motorboats, it can possibly be assumed that they were fully asleep. [5]Kaplan, M. 2008. Researchers sneak up on sleeping whales, Nature, accessed 11 September 2021, <https://www.nature.com/articles/news.2008.613> Of course, without actually diving down to see the whales’ eyes up close, it will be hard to determine if they can or cannot sleep in different types.
Want To Learn More About Whales?
If you’re interested in learning more about whales you should definitely read the following articles:
- Do Whales Have Teeth?
- Are Whales Mammals or Fish?
- Are Whales Omnivores?
References
↑1 | Hecker, B. 1998. How do Whales and Dolphins Sleep Without Drowning, Scientific American, accessed 11 September 2021, < https://www.scientificamerican.com/article/how-do-whales-and-dolphin/#> |
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↑2 | Liamin, O.I. & Mukhametov, L.M. 2013. Sleep in cetaceans. И. В. Павлова, 63, 61 |
↑3 | Amano, M., Aoki, K., Miller, P.J.O, & Rendell, L.E. 2008. Stereotypical resting behavior of the sperm whale. Current Biology, 18, 21-23 |
↑4, ↑5 | Kaplan, M. 2008. Researchers sneak up on sleeping whales, Nature, accessed 11 September 2021, <https://www.nature.com/articles/news.2008.613> |