Archive for the ‘Shark Myths’ Category

Shark Myths—Sharks Eat Anything, Eat Continuously and Must Swim to Breath
August 27, 2009

Blue Shark

Blue Shark

Sharks will eat anything.
Wrong. Sharks are pretty discriminate eaters. Even if we didn’t know this from examining the stomach contents of dissected sharks, it’s obvious from the wide array of adaptations found in different shark species. As I said in my shark diversity posts, each shark has evolved to fit a specific diet. Unless they’re injured or starving, there’s little motivation for a shark to waste energy pursuing something that isn’t their normal prey. Although tiger sharks have been nicknamed the “garbage cans of the sea” because a few odd things (license plates, shoes, glass bottles, ect…) have been found in their stomachs, these finds are actually quite rare.

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Shark Myth—Sharks Have Poor Vision
August 4, 2009

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.

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