Here's why:
* Gill function: Sharks, like fish, breathe through gills. They use their mouths and gill slits to draw in water and extract oxygen. This process happens even when they are stationary.
* Spiracles: Many sharks have spiracles, which are small openings on the top of their heads. These allow them to draw water directly into their gills, even when their mouths are closed.
So, sharks are perfectly capable of staying underwater without swimming continuously.