Whether sharks die if they stop swimming depends on the species. Different shark species have evolved varied physiological mechanisms for breathing, which determine if a shark must remain in constant motion or can rest while still taking in oxygen.
How Sharks Breathe
Sharks extract oxygen from water as it passes over their gills. They rely on specialized gill structures located on either side of their heads. Water flows into the shark’s mouth or through specialized openings, then moves across the gill filaments where oxygen is absorbed into the bloodstream, and carbon dioxide is released.
There are two primary methods sharks employ to achieve this water flow: ram ventilation and buccal pumping. Ram ventilation is a passive process where the shark swims forward with its mouth open, forcing water over its gills. Buccal pumping is an active process where the shark uses muscles in its mouth to draw water in and pump it over the gills. This muscular action allows the shark to breathe even when stationary. Some sharks also possess spiracles, small respiratory openings behind their eyes, which assist in drawing water over the gills, particularly when the mouth is closed or buried in sand.
Sharks That Need to Swim
Some shark species are obligate ram ventilators, meaning they must swim continuously to force oxygen-rich water over their gills. If these sharks stop swimming, insufficient water flows over their gills, leading to oxygen deprivation and potential suffocation. Their active, open-water lifestyles align with this breathing method.
Examples of sharks that depend on ram ventilation include the great white shark, mako sharks, and whale sharks. The mako shark, known for its speed, is an obligate ram ventilator and must maintain continuous movement to meet its high oxygen demands. For these species, periods of rest involve continued, albeit sometimes slower, movement.
Sharks That Can Rest
Many shark species can breathe without continuous swimming, primarily through buccal pumping. This allows them to remain stationary on the seafloor, in crevices, or inside caves while maintaining adequate oxygen intake. Their ability to stay still is often advantageous for hunting or conserving energy.
Examples of sharks that can rest include nurse sharks, carpet sharks, and angel sharks. Nurse sharks commonly rest on the ocean bottom, utilizing buccal pumping. Angel sharks, which are flattened bottom-dwellers, can remain buried in sand while pumping water. Some species, like the reef shark, can even switch between buccal pumping and ram ventilation depending on their activity level.