Britannica Sources used in this answer

Why do most sharks need to keep swimming to avoid sinking?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Shortfin mako shark swimming in clear blue water near the surface off the West Coast of New Zealand, mouth slightly open showing teeth. — shark Shortfin mako shark (*Isurus oxyrinchus*), found throughout tropical and temperate seas worldwide.

It is a common misconception that all sharks must swim constantly to avoid sinking or dying. In reality, the need to swim varies significantly among species due to differences in anatomy and respiratory methods.1

Unlike most bony fish, sharks lack a swim bladder, a gas-filled organ that provides buoyancy and allows fish to maintain their depth without active movement. Because they lack this ballast organ, many sharks must rely on forward motion to generate lift, though this is not the only factor in their survival.23

Regarding respiration, the belief that all sharks die if they stop swimming is false. Many species, such as the nurse shark, use buccal pumping to draw water over their gills while stationary. Only species that rely exclusively on obligate ram ventilation—such as the great white shark—must keep swimming with their mouths open to receive oxygen. Most shark species actually use a combination of these methods, allowing them to rest when necessary.1