Wednesday, 18 April 2012

Cetacean Sleep


How do Cetaceans Sleep and Rest?


Whales, dolphins and porpoises are remarkable creatures and can stay underwater for very long periods of time. But that is not to say that they do not need to come up for air very regularly as they do not have gills, like fish or sharks. Cetaceans are ‘conscious breathers’, meaning they must always be thinking about when to breathe, whilst we humans are ‘involuntary breathers’ and have a reflex to make ourselves breathe when we are not thinking about it. So this already brings up some obstacles for a tired whale or dolphin. Though there is a way for them to get all the rest they need. Some cetaceans will lie at the surface of the ocean usually with their blowholes somewhat exposed to air, this is called “logging” as they look like a large logs floating at the surface of the ocean. They then shut down half of their brain and may close one eye. This puts them in the similar state humans are in when having a light nap. This way the whale can still be alert for predators and other dangers. Some whales and dolphins may not lie directly at the surface, but can still float to the top when they need to breathe. Some may even continuously swim forward. A sleeping whale’s breathing is much less frequent than that of a moving whale’s. As you can see, cetacean sleep differs throughout species. Captive dolphins have been known to rest at the bottom of their tanks for minutes at a time.
          One thing that researchers have noticed about sleep in whales and dolphins is that they do not seem to experience rapid eye movement. This is the stage of which most of our dreaming occurs. This could be because they only shut down half of their brain and do not drift into a deep sleep.
Sleep is important for juvenile whales too. A young cetacean will usually sleep and rest behind their mother while she tows them along in her slipstream. The mother may sleep at this time, but will still be constantly moving forward. Sleeping is risky for young whales as they are not able to swim strongly and may still rely on their mother for protection.

             Sleep in cetaceans is being constantly studied. There are still many undiscovered things about whales and dolphins. For instance there is still speculation over the fact that sperm whales may actually sleep with both sides of their brain shut down. This is because a research boat once approached a resting sperm whale, and it did not react in the slightest. Scientists believe that some whales sleep about 71% of the time, between the hours of 6pm and midnight. As a general comparison, humans sleep about 28-30% of the time.

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