Dolphin Tales: Manatees, dolphins rest through slow-wave sleep
When I tell my onboard guests that dolphins and manatees never completely sleep, they are astounded. But in truth, if dolphins and manatees fell completely asleep as humans do, they would drown. They are mammals and breathe air just as we do, but their breathing is not automatic. They have to consciously decide to surface to breathe. Humans have prolonged periods of unconscious sleep when we are not completely aware of our surroundings. Dolphins and manatees have to be aware and alert to make the decision to surface to breathe.
This slow-wave type of sleep is known as unihemispheric sleep. Dolphins and manatees have two hemispheres of the brain that are able to sleep at different times. The animals alternate which half of the brain is sleeping so that they can be alert and also get the rest they need. The process switches from left brain to right brain about every two hours. The left eye will be closed when the right half of the brain sleeps. The right eye will be closed when the left half of the brain sleeps. The attentive side of the brain is used to watch for predators, obstacles and other animals.
While resting, dolphins either float near the surface of the water — called logging — or swim very closely next to other pod members. They rest about eight hours a day, typically coming up to breathe two to five times a minute when active at the surface. However, they can hold their breath for 10-15 minutes during deeper dives or when resting underwater.
In contrast, most manatees sink to the floor of canals, rivers or seagrass beds while resting. They sink like a bag of rocks, resting belly-down or in the mud. They sometimes float near the surface with their backs exposed to be warmed by the sun. They come up for air every 20 minutes or so expending as little energy as possible. They rest about 12 hours a day.
Capt. Cathy Eagle has spent over 45 years boating our local waters. As a professional charter captain, she specializes in dolphin and nature tours. For more information, visit CaptainCathy.com or text/call at 239-994-2572.