But recent scientific work is producing a more complex picture, showing that sharks do rest, and great whites may even enter sleep-like states while still moving through the water.
The shift in understanding began after a study published in 2021 by researchers at La Trobe University in Australia provided the first physiological evidence of sleep in sharks.
Working with draughtsboard sharks, a bottom-dwelling species, the scientists monitored oxygen consumption and found that when the sharks remained motionless for five minutes or more, their metabolic rate dropped significantly.
The team described the lowered activity as a sleep-like state, noting that the animals kept their eyes open but showed classic indicators of rest.
These findings challenged the traditional assumption that sharks only reduce activity rather than sleep. Previous observations had already shown that some sharks, particularly those that breathe by pumping water over their gills, can rest on the seabed for extended periods.
The new research added proof that at least some species undergo a physiological slowdown associated with sleep.
Great white sharks, however, breathe through a different mechanism. They rely on ram ventilation, meaning they must move forward to push water through their gills.
Stopping completely would cut off the supply of oxygen. That requirement has long made scientists cautious about claiming that great whites sleep at all.
Nevertheless, a growing number of field observations suggest that even these large pelagic sharks may have ways of resting without shutting down the flow of water to their gills.
One widely cited example involved a female great white off Guadalupe Island that was filmed drifting slowly in a steady current, her mouth slightly open.
Researchers noted that she was moving far more slowly than during normal activity and described the behaviour as a rest-like drift, with the current doing much of the work needed to keep water moving across her gills.
Marine biologists say this kind of behaviour may represent a form of sleep swimming. The concept proposes that the shark continues to move at a very slow, energy-saving pace while parts of its brain enter a reduced-activity state.
Similar patterns are seen in animals like dolphins and certain bird species, which rest one side of the brain at a time.
Although such brain activity has not yet been measured directly in great whites, the behaviour is consistent enough to draw scientific interest.
Experts caution that definitive evidence of sleep in great whites will require more sophisticated tracking and physiological monitoring. They also note that the species spends much of its life in deep or remote waters that are difficult to study.
Still, the changing scientific view is clear: while great whites cannot lie motionless on the ocean floor, they do appear capable of resting while still in motion.
Researchers say these discoveries may help explain how sleep itself evolved across different animal groups.
Sharks represent some of the oldest known vertebrates, and understanding how they rest could offer insight into ancient biological processes shared across species.
For now, scientists agree on one point. Great white sharks keep moving because they must maintain the flow of water across their gills, but that does not mean they never rest.
Instead, they have adapted to sleep on the move, in a quiet, energy-saving rhythm that allows them to survive in the open ocean.