Editing Shark (section)

===Sleep===
All sharks need to keep water flowing over their gills in order for them to breathe; however, not all species need to be moving to do this. Those that are able to breathe while not swimming do so by using their spiracles to force water over their gills, thereby allowing them to extract oxygen from the water. It has been recorded that their eyes remain open while in this state and actively follow the movements of divers swimming around them<ref name="Sleep"/> and as such they are not truly asleep.

Species that do need to swim continuously to breathe go through a process known as sleep swimming, in which the shark is essentially unconscious. It is known from experiments conducted on the [[spiny dogfish]] that its [[spinal cord]], rather than its brain, coordinates swimming, so [[spiny dogfish]] can continue to swim while sleeping, and this also may be the case in larger shark species.<ref name="Sleep">{{cite web
|url=http://www.elasmo-research.org/education/topics/b_sleep.htm
|title=How Do Sharks Swim When Asleep?
|publisher=ReefQuest Centre for Shark Research
|access-date=2006-08-07
|archive-url=https://archive.today/20120729110757/http://www.elasmo-research.org/education/topics/b_sleep.htm
|archive-date=2012-07-29
|url-status=live
}}</ref> In 2016 a [[great white shark]] was captured on video for the first time in a state researchers believed was sleep swimming.<ref name="npr">{{cite news |title=Great White Shark Caught On Camera Napping For The First Time |url=https://www.npr.org/2016/07/03/484562955/great-white-shark-caught-on-camera-napping-for-the-first-time |access-date=16 December 2019 |publisher=NPR |date=6 July 2016}}</ref>