Sharks keep moving primarily because many species rely on a method called ram ventilation to breathe. Unlike bony fish that use swim bladders and muscles to pump water over their gills, many sharks lack this ability and must swim continuously with their mouths open to force water over their gills for oxygen extraction. If they stop swimming, they risk suffocation due to lack of oxygen flow. Additionally, since sharks do not have swim bladders and are negatively buoyant, continuous swimming also helps them maintain buoyancy and avoid sinking. However, not all sharks exhibit this behavior; some species, like nurse sharks, can pump water over their gills while stationary using a method called buccal pumping and can rest without constant movement.
