By Blaise Jones
Finding prey in the ocean is no easy task. The ocean is, in a word, big. Some would say massive even. The likelihood of stumbling upon a prey item by chance is astronomical for sharks. Therefore, it’s a good thing sharks do not rely on chance.
Sharks have a whole array of powerful sensory organs that allow them to find their prey in all sorts of conditions, be it murky water, darkness, or simply over very long distances. While sharks do have some utterly alien senses to humans, the one they share with us are far more advanced.
Mirror, Mirror, in the Eye…
Sharks have very good eyesight, and in some cases it’s even better than ours. Sharks have eyes very similar in structure to human eyes, with a few key differences. For one, sharks have either only one or no cones in their eyes at all, making them effectively colorblind. However, they make up for it with a special ability their eyes have.
Sharks have something known as the “tapetum lucidum.” The tapetum lucidum is a layer of mirrored crystals located behind the retina. Like a mirror, these crystals are reflective and refocus the light through the retina a second time to pick up more light in low light conditions, effectively allowing sharks to see in the dark. Not only does the tapetum lucidum allow sharks to see at night, it enhances their day time vision as well. Sharks underwater vision is ten times better than that of a human.
The Nose Knows
However, sight is not the shark’s only sense it relies on. Its sense of smell is nothing to sneeze at. Sharks have a fantastic sense of smell, though many people hold misconceptions over it. A shark cannot smell a single drop of blood from miles away. A shark’s sense of smell is limited to about 1,300 feet. However, it’s not how far away a shark can smell things that make a shark’s sense of smell extraordinary. It’s how little of a thing a shark needs in order to be able to smell it that makes it truly amazing.
A shark can detect something via its sense of smell even if that thing is made up of only a few molecules. Not only that, shark’s noses are so sensitive that they can even determine which nostril is getting the stronger whiff of the scent and will in turn follow that direction back to the source. Some sharks, such as the Oceanic Whitetip, can even detect scents over the air by sticking their noses out of the water. This is hugely important because chemicals dilute extremely quickly in water, and thus smells are quickly dispersed into nothingness.
However, it is a shark’s hearing that might be its single greatest asset. This is because, unlike the other senses we share with a shark, sound is actually enhanced by water. Sound travels through water at speeds of 5000 feet per second, 5 times as fast as it does through air.
A shark’s ears are two tiny holes, located behind the eyes, and often times get confused with the spiracles. The ears are connected to a vast maze of fluid-filled tubes, appropriately called the labyrinth. The lining of the labyrinth is filled with tiny “microhairs,” which are in turn, stimulated by stone-like lumps known as otoliths.
Since the flesh of sharks is roughly the same density as the water surrounding it, it conducts sounds waves just as efficiently as water does. This makes the head of a shark acoustically transparent, meaning that sound waves meet almost no resistance as the pass through the shark.
As the sound waves pass through the shark, they cause the denser otoliths to move, which in turn stimulates the microhairs, which in turn send nerve signals to the shark’s brain. In a sense, the entirety of a shark’s head is one giant ear.
“Sharks. The Mysterious Killers” by Downs Matthews
Alan Moore, Director of the Coastal Marine Education and Research Academy
“The Encyclopedia of Sharks” by Steve Parker