How can whales rest when they spend their entire lives in water and they have to breath? Dolphins sleep with one eye open while part of their brain remains awake. Some whales float on the surface, others slow down and refrain from diving deep, and others still let themselves sink to the seabed! But we still don’t know whether or not they dream…
The main challenge for any mammal that sleeps in the water is to constantly come up to the surface to breath and thereby avoid drowning. As breathing is a voluntary behaviour in cetaceans, they must maintain a certain degree of consciousness at all times in order to “think” to breath. Studies on dolphins in captivity have demonstrated that while half of their brain is at rest, the other half ensures that breathing occurs. In other words, dolphins sleep with one eye open! With regard to large cetaceans such as mysticetes, studies aiming to characterize their sleeping behaviour have yet to be conducted. Is their sleep similar to that of dolphins, that of other marine mammals, or do they have a technique all their own?
It’s not unusual to see a whale floating on the surface, a behaviour which brings to mind a floating log. Consequently, this technique is called “logging”. Belugas, humpbacks, and North Atlantic right whales can be observed exhibiting this behaviour while breathing slowly. Other species such as the fin whale swim slowly and quite close to the surface, partially emerging their bodies at regular intervals to breath. In captivity, belugas have also been seen resting at the bottom of the pool.
Most land mammals have a period of sleep characterized by rapid eye movement; this is REM sleep, which is when dreams are most likely to occur. Similar movements typical of REM sleep have been observed by researchers in a young gray whale and a beluga in captivity. Do cetaceans dream, too?
