Some sharks do need to keep swimming to stay alive, but not all. Like other fish, sharks extract oxygen by passing water over their gills, says Ellen Husain.
Many of the larger, faster species use ram ventilation: as they swim, water passes in through the mouth and is forced, or rammed, out over the gills.
Faster swimming delivers an enhanced supply of life-giving oxygen when it's most needed.
More sedentary species, such as the wobbegong, an ambush predator that lies on the seabed, use buccal (mouth) pumping. Water is drawn into the mouth and forced out through the gills by the cheek muscles.
Some species, such as sand tigers, can switch between techniques depending on speed, but makos and great whites rely on ram ventilation so would indeed suffocate if they stopped swimming.
