“Sharks must keep swimming or they die”

The notion that all sharks must perpetually swim to survive is a widespread misconception, often fueled by dramatic portrayals of active, open-ocean predators. This idea likely stems from observing species like the great white or mako shark, which are indeed constantly in motion. For a long time, scientists even assumed that all sharks breathed this way because they lack the operculum, a bony flap that most fish use to pump water over their gills while stationary.

Scientifically, shark respiration is more diverse. Some sharks, known as "obligate ram ventilators," must swim continuously with their mouths open to force oxygen-rich water over their gills. Great whites, whale sharks, and mako sharks fall into this category, and if they stop moving, they will suffocate. However, a significant number of shark species employ a different method called "buccal pumping." These sharks, like nurse sharks, can actively pump water over their gills by using muscles in their cheeks and mouth, allowing them to remain stationary on the seabed without suffocating. Some even have specialized openings behind their eyes called spiracles that aid in this process, particularly useful when buried in sand.

The myth persists largely because the most recognizable and often featured sharks in media are the large, fast-swimming species that rely on ram ventilation. This creates a generalized image of all sharks needing constant motion for survival. In reality, out of over 400 known shark species, only about 20 are obligate ram ventilators. This diversity in respiratory strategies highlights the incredible adaptability of sharks, demonstrating that while some are truly "swimming machines" that must keep moving, many others are perfectly capable of resting peacefully.