The sperm whale is the largest of the toothed whales and is actually the largest toothed predator on the planet.
But one of the most interesting facts about sperm whales is that they actually sleep vertically. Yep, that’s right. Vertically.
But why do sperm whales sleep vertically?
In a nutshell, it’s so that they can float near the surface and stay alert to potential predators. Sleeping vertically means they can breathe when needed and quite literally keep one eye open whilst they sleep!
Let’s take a closer look…
Do Sperm Whales Actually Sleep Vertically?
Yes, sperm whales do sleep vertically, which looks a little strange and seems rather bizarre at first glance. But it’s actually for a very practical cause.
Whales need oxygen to survive in the ocean, they are unlike sharks in the fact that they don’t have gills that allow them to stay submerged.
This means whales need to surface every so often to replenish their oxygen supply.
But Why Do Sperm Whales Sleep Vertically?
Sperm whales sleep vertically to replenish their oxygen supply when needed and to stay alert to potential threats.
As mentioned above, whales need to surface for their oxygen, so it makes sense that whilst they are sleeping it’s best to be as close to the surface as possible so that they can pop up for a fresh breath when they need to.
But that’s not the only reason why sperm whales sleep vertically.
This sleeping position also allows them to stay alert to potential predators. Orcas are the largest natural threat to sperm whales, but false killer whales and pilot whales are also known to hunt sperm whales.
This means that they need to keep one eye open whilst they sleep, and that’s exactly what they do! Literally.
They also keep 50% of their brain active whilst they sleep, ensuring that they are alert, aware, and ready to move if a predator moves in too close.
Sperm whales can sleep in a couple of interesting ways. They can sleep upright vertically, as we have discussed.
But they can also keep swimming whilst asleep, or sleep whilst floating at the surface (also known as logging).
These whales are masters of sneaking in a quick nap whilst also staying alert and on the move if needed, pretty impressive, right?
Do Sperm Whales Breathe When They Sleep?
Sperm whales have one of the most remarkable sets of lungs in the marine kingdom.
Their huge lungs allow them to dive down to depths of 2250m, and the air in the lungs are squished to 1/4 of the volume that it was on the surface.
This means that sperm whales are able to hold their breath for a very long time, around 90 minutes to be exact.
This not only allows them to dive to the depths to hunt for prey but also means they can hold their breath whilst sleeping too.
Sperm whales will hold their breath whilst they sleep, as they simply don’t have the requirement to keep breathing whilst they are asleep as they can store a lot of oxygen in those big lungs.
How Long Do Sperm Whales Sleep For?
Sperm whales do not require the length of sleep that we humans do. This would have them in a bit of a pickle being as though their 90 minutes of oxygen wouldn’t suffice for the 8 hours we humans require.
Thankfully sperm whales only take naps, usually for between 10 – 15 minutes at a time.
This cat-napping behavior allows them to benefit from a quick nap whilst still being able to stay submerged in the water and keep a lookout for predators.
Research from the University of St. Andrews and the University of Tokyo suggests that sperm whales spend around 7% of their day asleep and that they are one of the least sleep-dependent animals on the planet.
They don’t require a large amount of sleep at all, and the short naps they take are more than enough to satisfy their sleepiness and keep them ready to tackle the day ahead.
Sperm Whales Sleeping
Sleeping for whales is dangerous. There are many hungry predators in the ocean that would love the opportunity to feast on a sperm whale.
Whales, including sperm whales, need to sleep near the surface so that they can breathe when they need to.
They’re conscious breathers, which means they don’t do it on autopilot as we humans do. Instead, they need to make the choice to breathe which is why they have a unique sleeping ability.
Sperm whales and other whales shut one-half of their brain off whilst they sleep. This allows them to get some shut-eye whilst the other half of the brain remains active and alert.
These deep-diving whales also sleep close to one another so that they can quickly alert one another should a predator come into the area.
Sperm whales sleeping behavior is amazing. They’re the only whale species that sleep like this and doing so provides a whole host of benefits that keep the whales safe.
There are a number of reasons why sperm whales choose to sleep vertically. Mainly to stay close to the surface to come up for air when required, but also to keep a watchful eye on predators.
They are also able to sleep whilst still moving or floating on the surface. Sperm whales are fascinating sleepers and only nap for a short period of time.
This allows them to reap the cognitive benefits of sleep whilst also not endangering themselves too much by sinking to the bottom of the ocean where they could be ambushed.
Hopefully, this post has been useful to you and you now know why sperm whales sleep vertically.
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Hi, I’m George – the founder of MarinePatch. I created this blog as marine wildlife has been my passion for many years. I’ve spent over a decade in the marine wildlife industry and spent years out in the field conducting research. In today’s modern world, an online blog is the best place for me to share my findings and reach as many people as possible to help educate and inspire others. Enjoy your time here and you’re welcome back anytime!