At Jervis Bay Wild, we run eco cruises 365 days per year. As our local bottlenose dolphins and our passing humpback whales are two of our most popular options, it might seem that these animals are constantly on the go. Do dolphins and whales ever sleep? And if so, how does it work?
Today, we take a more detailed look at the sleeping and resting habits of some of our favourite creatures. If you are curious about these fascinating and beautiful marine animals, we hope you’ll read on to learn something new. and for even more facts and up-close experiences with whales, dolphins, fur seals, and more, be sure to book your space on one of our upcoming eco cruises here in Jervis Bay.
Getting Your Zzz’s
When we humans go to sleep for the night, we get a deep rest, falling into a state of near-unconsciousness that restores our energy and keeps us in good health. Scientists are not entirely sure if all living creatures require sleep, but evidence shows the vast majority of species do, even if the patterns and behaviours surrounding sleep differ widely.
The Mysterious Sleep of Dolphins and Whales
It might seem hard to picture the large humpback whale or the active bottlenose dolphin in a period of sleep that resembles our human approach. As underwater creatures, it is indeed a bit baffling to understand how these animals can get any rest at all. But here is what science tells us.
Dolphins and whales belong to an infraorder of marine mammals called cetaceans. These animals do, in fact, sleep, but unlike human beings, their minds do not reach the same state of sensory shutdown and low consciousness. Rather, cetaceans participate in what is known as unihemispheric slow-wave sleep. This ensures they can keep breathing, which, unlike humans, is not an involuntary process.
A Half-Brained Rest
The slow-wave sleep of dolphins and humpback whales involves the shutdown of one hemisphere of their brain at a time. Generally, the opposite eye will close in tandem. During this time, the other half of the brain stays engaged at a low level of alertness, monitoring the surrounding environment, keeping a lookout for predators, and reminding the dolphin or whale to rise to the water’s surface every few hours to take an important breath of air. The alert side of the brain keeps the blowhole under voluntary control of the mammal so that it can expel at the surface and obtain that crucial intake of oxygen. Without this, the creatures would drown. Scientists are still debating about whether or not the dolphin or whale is conscious when utilising its blowhole at the surface.
It is believed that approximately every 2 hours, cetaceans switch which hemisphere of the brain is alert. This gives each side an opportunity to get some sleep. Over a 24-hour period, it is thought that each hemisphere receives 4 hours of slow-wave sleep.
Other Kinds of Cetacean Sleep
There are other methods of sleeping that have been observed in dolphins and whales. Aside from the deep, slow-wave sleep, these mammals are sometimes seen swimming slowly alongside other dolphins and whales as they sleep. This state is similar to napping and is frequently seen in young dolphins and whales. As they rest, they are carried in their mother’s slipstream. Sometimes the mother sleeps in this way as well, as the needs to move when the calf is still young.
To see dolphins and whales in action in Jervis Bay, come visit us and hop aboard our whale watching tour or dolphin eco cruise.
Sources: http://www.whalefacts.org/do-whales-sleep/, http://www.scientificamerican.com/article/how-do-whales-and-dolphin/
