Our curiosity with sharks, and other aquatic creatures, is a fascination that has enveloped us long before Shark Week was around. A large part of this curiosity comes from the fact that even though we have studied the ocean and all its marvelous creatures for so long, we still know very little about the things that inhabit the deep.
Sharks have especially remained the pinnacle of marine life researchers’ focus for a long time, as they are the apex predators of the ocean. A popular topic of discussion when studying sharks is how exactly they see.
Rather, how exactly do they use their vision in dark, pressurized, waters to hunt. The intricacies of sharks’ eyesight have slowly begun to be unraveled by dedicated scientists around the world who have set out to uncover the use and utility of sharks’ eyes. Here are some of the things science has shown us about them:
Similar Anatomy to Us
Retina, pupil, cornea, lens, and iris. These are all important parts of the human eye, each with its own function and purpose to help us see on a daily basis.
Careful examination of the structure of a shark’s eye has shown us that they have all of these parts too.
What does that mean?
In short, that means that a shark’s eyes work in a similar manner to ours, with each of these parts performing the same or similar functions in order for the shark to see.
Additionally, shark eyes have been proven to have duplex retinas. That is, retinas that contain both rods to detect light and darkness, and cones to detect color. Sound familiar?
These rods and cones are exactly how humans perceive both light and darkness, and color.
One Noticeable Difference
There are differences in anatomy from humans to sharks, though. These differences allow the shark to be more suited to the environment in which it lives: Murky, often dark, water.
A sharks eyes are lined with a layer of mirrored crystals that sit just behind their retinas, called a tapetum lucidum. These mirrored crystals allow light that was previously undetected by the rods to be detected once it passes through the eyes a second time. This lets a shark see more even in extremely low light situations; as the less light that is detected by the shark’s eyes, the more sensitive to it they are.
If these mirrored crystals sound familiar, it’s because your pet cat has the same thing behind its retina. Cat eyes have tapetum lucidum as well, which is why both cat eyes and shark eyes glow in the dark.
This heightened vision comes at a cost, though. These tapetum lucidum provide a boost in light sensitivity at the cost of visual acuity; meaning the shark can see, but not very clearly. They will not be able to get as clear an image in low light as they would in normal light situations.
Their boost in light sensitivity isn’t only affected in low light situations, though. Studies have shown that sharks can see about 10x greater than humans, even in clear water.
While sharks rely on many other highly tuned senses to maneuver the vast oceans they call home, they still rely on their impressive eyesight to find and catch their food. Discoveries like these have reshaped the way we view sharks, and subsequently, the way we approach them.
What were once thought to be blind creatures that rely on scent, have now been proven to be incredible creatures with an immense ability to see in many different light conditions. These findings, among many others, have provided an incredible insight on how sharks, and so many other aquatic animals survive, and thrive.