Published October 2004
Dear Sea Scoop,
Do dolphins sleep?
– Clayt Lauter, Erie, Pa.
Dolphins are part of the group of animals called Cetaceans (se-TAY-shuns), and yes, they do sleep, but they do it in a remarkable way. Dolphins are capable of "unihemispheric slow-wave sleep," which means they can sleep with one eye open and one hemisphere of the brain awake. Several times throughout the day and night, a pod of dolphins (dolphins that live and travel together) will sleep with half of their brains and swim in a circle together. The entire group rests the same half of their brains and swims in the same direction. They swim with one eye open and one eye closed.
Why should dolphins sleep in such an odd way? There are two reasons. First, they always need to be on the alert for predators or even prey. The second reason is because dolphins are considered "voluntary breathers." This means that, unlike us, dolphins need to make a conscious (or voluntary) decision to take a breath. If they were to fall asleep completely, they wouldn't be awake to breathe and they could suffocate. Imagine if we had to wake up every time we needed to breathe!
Research has shown that some species of birds are also capable of unihemispheric slow-wave sleep.
Dolphins are intelligent and curious animals. Sometimes in the wild, they may come into the area where you are swimming. While the temptation to play with them is great, remember that these are wild animals weighing up to 1,000 pounds with lots of teeth and very strong jaws. They can be very unpredictable and could easily hurt you. Never try to feed them or ride on them. Not only is it dangerous, it's also against the law. Watch these amazing creatures from a safe distance, and be grateful that you had the opportunity to witness one of the smartest animals in the sea.
Have a question for about the world beneath the waves? Write it down and send it to Sea Scoop! Please remember to include your name and where you're from.
For more information on dolphins visit:
Seaworld's Education Site.
The National Oceanic and Atmospheric Administration's
Office of Protected Resources.
The American Cetacean Society.
For more information on marine science in the Virgin Islands, visit the University of the Virgin Islands' Center for Marine & Environmental Studies.
Elizabeth Ban is the University of the Virgin Islands Marine Adviser for St. Thomas and St. John. She works to inform and educate citizens about ocean resources and promote coastal ecosystem health. She is based at UVI's Center for Marine and Environmental studies on the St. Thomas Campus. For more information about UVI's Marine Advisory programs, please call 340-693-1392.
Published October 2004