There's a common notion that sharks need to swim continuously or they will drown. This myth has certainly become an overused trope when it comes to motivational quotes, but is there any truth to it? Can a shark actually drown if it stops swimming? Let’s investigate!

Sharks have two methods of breathing, i.e. getting oxygen-rich water to flow across their gills. The first method is “ram ventilation” – the shark swims with its mouth open and its speed pushes water through its gills, if it stops swimming, it stops breathing.

The second method is called “buccal pumping”, which is basically a process where they use their cheek muscles to suck water through their gills.

Many of these sharks make obvious use of this technique by lying completely still on the seabed, sucking water in through spiracles (modified tubes just behind their eyes) so that they can keep their mouths closed while breathing.

You might be forgiven for thinking that most sharks do not fit the cheek-sucker description, but the reality is that of the over 400 species of shark that currently inhabit our ocean, only about 20 of them are “obligate ram ventilators”. In other words, most sharks suck.

Most sharks use a combination of these two techniques, switching back and forth depending on how fast they are swimming. Even stereotypical-looking sharks, like the ragged-tooth sharks in the Save Our Seas Foundation Shark Exhibit at the Aquarium, are capable of this, using buccal pumping to supplement their ram ventilation when they are swimming at slow speeds.

Spotted ragged-tooth sharks, a species that many of you might consider a "typical" shark, is a prime example of a shark that uses both ram ventilation and buccal pumping. The ragged-tooth sharks at the Two Oceans Aquarium's Save Our Seas Foundation Shark Exhibit regularly choose to remain motionless in the water proving to Brad Pitt that they can, in fact, stop.

So, while most sharks will be 100% fine if they stop swimming, a few iconic species such as great white sharks, whale sharks, hammerheads and mako sharks would suffocate without forward motion or a strong current flowing towards their mouths.

In answer to our titular question – NO, most sharks will not drown if they stop swimming. Which brings us to another question: Can sharks swim backwards? (You'll need to wait and see!)

Great white sharks, and other obligate ram ventilators, are typically sharks that cover huge distances and rarely need to navigate shallow-water environments. In the case of these few sharks, stopping is not a good thing! Credit: Elias Levy [CC BY 2.0]
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