Sharks & Rays
Myth 1: Sharks Must Swim Constantly or They Die!
Myth 2: Sharks are the Number One Cause of Animal-Related Deaths!
Myth 3: All Rays Have Poisonous Stingers!
Myth 4: All Sharks are Like the Great White!
Myth 5: Sharks Can Detect a Single Drop of Blood in the Ocean!
Myth 6: Sharks Do Not Get Cancer!

nurse shark
Nurse shark in warm...

Myth 1:

Sharks Must Swim Constantly or They Die!

Some sharks must swim constantly in order to keep oxygen-rich water flowing over their gills, but others are able to pass water through their respiratory system by a pumping motion of their pharynx. This allows them to rest on the sea floor and still breathe. However, sharks do have to swim to avoid sinking to the bottom of the water column. The ability to move up and down freely in the water column is, in fact, one of the extraordinary adaptations of sharks.

Unlike bony fishes, which tend to be restricted to certain depth ranges, sharks are able to move easily between varying depths in the water. Bony fishes utilize swim bladders to move up or down vertically in the water or remain at a uniform depth. The swim bladder works by varying the amount of gas it contains, giving the fish buoyancy. Sharks, on the other hand, do not have a swim bladder. Instead, they rely on lift generated by their large pectoral fins, much like the way an airplane's wings provide lift in the air. In addition to the lift by the fins, sharks also have very large livers that contain a high proportion of oil. This oil is lighter than water, providing the shark with additional buoyancy.

The lack of a swim bladder gives sharks some unique advantages. One benefit of not having this organ is that the shark's body is incompressible, allowing it to move between different depths without the risk of exploding or imploding. Bony fishes with swim bladders, on the other hand, risk their lives if they go too shallow or too deep in the water, because the air contained in a swim bladder compresses or decompresses depending on pressure changes. A bony fish living at great depths and pressures would die if it came too far up in the water column, because of the pressure differential. Since sharks don't have the air bladder, they can come from great depths up to the surface and survive.