Shark Myth—Sharks Have Poor Vision

Whitetip, Blacktip, Porbeagle

Whitetip, Blacktip, Porbeagle

Sharks actually have sharp eyesight. Here’s three reasons why sharks have good, if not impressive, vision:

Sharks have great night vision.
A shark’s eyes are about 10 times more sensitive to light than our own. Like cats and other nocturnal animals, they owe this sensitivity to a mirror-like membrane behind their retinas called the tapetum lucidum. Light is reflected off the tapetum lucidum, back to the photoreceptors in the retina, effectively reusing and thus doubling the amount of light that reaches the eye’s photoreceptors. This is why sharks are so adept at hunting after dark, even with only starlight to illuminate the ocean. Because of their high sensitivity to light, sharks have also evolved a way to avoid being blinded in bright light conditions. They have mobile pigment cells in their eyes called melanoblasts. Melanoblasts cover the tapetum lucidum when light levels get too intense. It’s kinda like wearing those Transitions brand eyeglasses that darken or lighten in response to light levels.

Sharks have a high flicker fusion rate.
When light strikes the retina of an eye, it initiates a series of chemical and electrical reactions that ultimately trigger a nerve impulse. The brain translates this nerve impulse into a visual image. The frequency at which an intermittent light stimulus is perceived as a steady image is called the flicker fusion rate. Humans have a flicker fusion rate of about 24 images per second, while sharks have a flicker fusion rate of about 45 images per second. It’s our comparatively low flicker fusion rate that allows the swiftly moving frames of a film to appear as a moving image. If a shark were to watch a movie, it’d see a rapid-fire slide show of distinct still images. A shark’s higher flicker fusion rate keeps objects in its surroundings from blurring together while it swims at high speeds and also enables it to detect the movements of quick prey.

Sharks can see color and details.
In the past few decades, biologists have discovered that almost all sharks have the two typical types of photoreceptors: rods and cones. Rods are adept at detecting contrast and movement and can operate under low light levels. Cones excel at discerning fine details and color in brighter light conditions.


There are no comments on this post.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: