How Marine Animals Sleep

Whales and dolphins sleep in unique ways.  As mammals, these animals have to be able to go to the surface and breathe quite frequently.  They even need to breathe while they sleep.  In order to do so, whales and dolphins have developed unique sleeping techniques.  One method is to rest vertically or horizontally in the water.  They either sleep in groups, where it is safer from predators, or they sleep alone.  According to Scientific American (1998), "Individual dolphins...enter a deeper form of sleep, mostly at night. It is called logging because in this state, a dolphin resembles a log floating at the water's surface" (para. 1).  Thus, the dolphins sleep at the surface of the water so that their blowholes have access to air to breathe. 

Bottlenose dolphins have a unique sleeping technique, too.  The Scientific American says, "While sleeping, the bottlenose dolphin shuts down only half of its brain, along with the opposite eye. The other half of the brain stays awake at a low level of alertness" (para. 4).  The dolphins do this so that they can protect themselves against potential predators.  They have adapted this sleeping technique for survival. 

Sharks are different from whales and dolphins.  They are fish, not mammals, and they get their oxygen through water passing through their gills.  Some sharks need to swim all of the time in order to get this oxygen flow in their gills, but nurse sharks do not.  Nurse sharks have special muscles that move the water over their gills without the shark having to swim.  According to the Florida Museum of Natural History (2014), "Some sharks such as the nurse shark have spiracles that force water across their gills allowing for stationary rest. Sharks do not sleep like humans do, but instead have active and restful periods" (para. 8).  Sharks sleep in different patterns than humans because of their gill requirements. 

Overall, marine animals have unique sleeping techniques and patterns.

 

Photograph courtesy of Wikipedia (2014) 

References

Florida Museum of Natural History. (2014). FLMNH Ichthyology Department: Most Commonly Asked Shark Questions. Retrieved from https://www.flmnh.ufl.edu/fish/education/questions/Basics.html

Scientific American. (1998, February 2). How do whales and dolphins sleep without drowning? Retrieved from http://www.scientificamerican.com/article/how-do-whales-and-dolphin/

Wikipedia. (2014, August 19). The sickle-shaped pectoral fins of the tawny nurse shark are one of its characteristic traits [Photograph]. Retrieved from http://en.wikipedia.org/wiki/Tawny_nurse_shark