Do sharks sleep or do they not?
Some say a shark never sleeps. It is unclear how sharks sleep. Some sharks can lie on the bottom while pumping water over their gills, but their eyes remain open. When a shark is resting, they don’t use their nares, but rather their spiracles. The spiny dogfish's spinal- cord, rather than its brain, coordinates swimming, so it is possible for a spiny dogfish to continue to swim while sleeping. It is also possible that a shark can sleep with only parts of its brain in a manner similar to dolphins.
