Sharks need to keep moving in order to breathe. When you see a shark resting on the sea bed or in a cave it is using muscles to pump water over its gills. If it stops, it will die.

Sharks never enter a true state of sleep. Some species are able to ‘sleep swim’, as their swimming is coordinated by their spinal cord as opposed to their brain.

If your bucket list includes diving with Whale sharks you better hurry. Whale sharks long life spans and late sexual maturation doesn't help their threatened status. Officially they are now listed as vulnerable which is one level under endangered. They are still hunted for their meat, skin, fins and oil. With Humans being their greatest predator.