Meanwhile, the other half of brain sleeps and the opposite eye is closed. After about two hours, the sides switch so the entire brain gets rest. This kind of dolphin sleeping is called cat-napping. During humans' long hours of unconscious sleep, we aren't aware of our surroundings and we breathe automatically. Dolphins have a voluntary respiration system, which is why they have to keep part of their brain alert to breathe.
To avoid drowning, they also have to control their blowhole, a flap of skin that opens and closes to breathe and make sounds. Dolphins slumber by resting in the water, either vertically or horizontally, or while swimming slowly with another dolphin.
They also have periods of deep sleep floating at the surface of the water like a log. This is known as logging. Normal human respiration is about 12 to 20 breaths per minute. Each dolphin breath is bigger than ours and their red blood cells carry more oxygen, so they don't need to breathe as often. Bottlenose dolphins, for example, can stay underwater for up to 10 minutes. A study completed in by Brian Branstetter and colleagues revealed dolphins can stay alert to the point of completing another task for 15 days straight.
Other sea animals, like manatees and baleen whales, as well as some birds, share the alert sleep pattern. The Blue Wave Adventures team is excited to share these dolphin facts and many more with you on your Murrells Inlet dolphin cruise.
When sleeping, whales typically stay in a horizontal or vertical position close to the surface of the water. Living in a water environment means whales and dolphins can lose a great deal of body heat when not active or moving, so some species keep swimming even while they are sleeping. Humpback Whales have been found resting motionless on the surface of the water, but for only 30 minutes so they can start moving again to keep warm.
The ability of different species to hold their breath varies between a few minutes to over an hour, so their sleeping habits vary. Sperm Whales spend just 7 percent of their day napping for a period of 10 to 15 minutes each time. Bottlenose Dolphins and Belugas can spend more than 30 percent of their day sleeping, and Gray Whales spend up to 41 percent of their time resting or sleeping. Dolphins generally sleep at night but only for a couple hours at a time.
They generally sleep along the surface of the water but occasionally sleep along the bottom of a shallow area and rise to the surface for air as needed. From a distance, sleeping whales and dolphins can look like logs in the water; boaters should take care to keep their distance from whales and other marine mammals that are at rest, as well as when these animals are underway.
Lorena and Leonard Landon have been plying Pacific Northwest waters for over 35 years. They have had the opportunity to operate boats of varying sizes, speed, and configurations, providing them with a wide range of boat-handling experience.
And necropsies sometimes show that an animal never gets to the surface to take its first breath of air. The same problem can occur when an animal is caught in a fishing net. If unable to reach the surface, or if in a panic, the animal may dive deeper, where it will be unable to breathe and suffocate.
Obviously sleeping safely at sea can pose problems, but the marine mammal system has addressed them. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue.
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