Like many other wild mammals, seals sleep in short bursts of time rather than spending a single daily period of hours sleeping like humans do. How long seals sleep depends on many factors, such as whether they're looking after pups and how many predators inhabit the area.
Seals can sleep both in the water and on land, making it easier for them to choose whatever's best for their situation to avoid dangers. Seals tend to sleep on land when they're searching for warmth or when they have pups. This allows them to leave the pups with a group of other seals when they return to the water for hunting. Sleeping primary on land is common among harbor seals.
When seals sleep in water, they sleep in a position known as bottling. This is a position in which their bodies float but remain completely underwater except for their snouts, which remain above water at all times. Some species of seals sleep completely submerged but remain close to the surface of the water. To avoid drowning, they can open or close their nostrils to prevent water from entering. This way, they nap for short periods of time, then wake up and emerge to breathe before closing up their nostrils and going back into the water.
Researchers from the University of Toronto have discovered that seals sleep with only half their brains. The other half of the brain remains awake and alert. The researchers believe this serves to help the seals remain alert to potential dangers. In fact, the part of the brain that remains awake contains high levels of acetylcholine, which helps with alertness -- while the half that's asleep has low levels of the same chemical.
Seals tend to sleep on the beach if the water they inhabit has predators such as great white sharks or orcas. Seals live in such large groups that they can often be found sleeping one on top of another. Harbor seals have adapted to life on the shore and spend most of their time there, sometimes going into the water only to hunt or for a quick splash, according to the ReefNews website.
Tammy Dray has been writing since 1996. She specializes in health, wellness and travel topics and has credits in various publications including Woman's Day, Marie Claire, Adirondack Life and Self. She is also a seasoned independent traveler and a certified personal trainer and nutrition consultant. Dray is pursuing a criminal justice degree at Penn Foster College.