“Sharks must keep swimming or they die”

The idea that sharks must constantly swim to survive is a pervasive misconception, largely fueled by observations of iconic species like the great white shark and a historical understanding of shark biology. For a long time, scientists believed that all sharks relied solely on a method called "ram ventilation," where forward movement forces water over their gills, allowing them to extract oxygen. This led to the assumption that stopping would mean suffocation.

However, scientific evidence reveals a more nuanced truth about shark respiration. While some species, known as obligate ram ventilators, indeed must keep swimming to breathe—including great whites, mako sharks, and whale sharks—many others possess a different mechanism. These sharks, such as nurse sharks and bullhead sharks, utilize "buccal pumping." They actively pump water over their gills by opening and closing their mouths, allowing them to remain stationary, rest on the seafloor, or even hide in the sand while still breathing effectively. Some bottom-dwelling species also have spiracles, small openings behind their eyes, to assist in drawing water over their gills when their mouths are obstructed.

The common belief persists because the most active and often sensationalized sharks, like the powerful oceanic predators that are obligate ram ventilators, are highly visible and frequently featured in media. This exposure, combined with a general tendency to simplify complex biological processes, contributes to the widespread but incomplete understanding of how these diverse creatures respire. In reality, the breathing strategies of the over 500 shark species are as varied as their habitats and lifestyles.