They can, but only if they stay still for a while. Some species don’t have muscles for breathing, and can only filter water through their gills by swimming forwards.
Only a few shark species rely on constant motion to breathe, but this group includes some you’d recognize, like the great white, mako, and whale sharks.
All sharks use their gills to breathe, but there are two main methods for filtering water over and through them.
- Sharks that can breathe when still mostly rely on a process called buccal pumping, which uses muscles inside the mouth to draw water into the mouth and over the gills. Many of these species also have openings (called spiracles) behind the eyes to bring in water while hiding in the sand.
- The process of filtering water through the gills by swimming forward is formally known as ram ventilation.
Most species of sharks rely on one or the other, but some species (such as tiger sharks), can switch between the two depending on the situation.
Species of sharks that use ram ventilation only are known as obligate ram ventilators.
[About] two dozen species—including the great white, the whale shark, and the mako shark—are known as “obligate ram ventilators,” meaning it is mostly essential for them to keep moving to stay alive. Instead of breathing via buccal pumping, obligate ram ventilators pass water through their opened mouths and over the gills while in constant swimming motion so as not to asphyxiate. It’s actually easier for these particular species of sharks to keep moving than to stay still, but it is possible for them to catch a break every once in awhile to rest up for a moment before swimming off again.
Yes, it is possible for sharks to die if they don’t move. However, most sharks would be completely fine, and even in species where it’s a possibility, it may not be as serious as you may have thought. It’s much more similar to a human holding their breath: While it’s certainly possible to die from it, it’s usually not a major concern.