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| Earth on Jan 26, 2011

Sharks don’t see red

A new study by scientists in Australia shows that sharks don’t see their world as we do.

What’s the view like through the eyes of a shark? That’s what some shark researchers in Australia wanted to know. They used an instrument called a microspectrophotometer to measure light-sensitive cells in the eyes of several shark species. Professor Nathan Hart, who led the study, explained their results in a press release from University of Western Australia:

Humans have three cone types that are sensitive to blue, green, and red light, respectively, and by comparing signals from the different cone types we get the sensation of color vision.

However, we found that sharks have only a single cone type and by conventional reckoning this means that they don’t have color vision.

Mark Changizi: Why human eyes see in color

Caribbean Reef Sharks at The Bahamas. Image Credit: Albert Kok

But does this mean that sharks see in black and white? Probably not, but they’re certainly color-blind. Studies by the U.S. Navy have found that some shark species are more attracted to yellow – or as they call it, “yum, yum, yellow!” – than any other color. This raised concerns because they wanted to equip their sailors with yellow life vests to make them more visible during rescue operations.

It’s hard to know exactly what a shark sees but it appears that they’re able to discern an object by gauging its contrast against a background. This could help scientists figure out how to make long-line fishing lures that are less attractive to sharks, which could reduce the numbers of sharks killed as by-catch in the fishing industry.

Colin Simpfendorfer on overfishing deep sea sharks

Understanding shark vision could also help cut down on the number of shark attacks on people. One of the species in the study was the bull shark – they’re found in shallow murky waters, and are often implicated in attacks on people. Said Dr. Hart,

Now we know a bit more about how such sharks see the world, it may be possible to design swimming attire and surf craft that have a lower visual contrast to sharks and, therefore, are less “attractive” to them. After all, most shark attacks are thought to be the result of curiosity on the part of a shark that has been attracted to an unusual stimulus, rather than some premeditated ambush.

Sharks are in trouble. Across the world, their populations have plummeted to dangerously-low numbers, much of it due to over-fishing. As apex predators, sharks play a critical role in marine environments, and as their numbers continue to decline at an alarming rate, the ripple effect is felt down the food chain, upsetting a well-honed natural balance that has been millions of years in the making.

Shark Conservation Act passed by U.S. lawmakers to protect sharks from fin trade

For more information about shark conservation, please visit The Shark Trust and The Pew Charitable Trust Shark Conservation Campaign

And just for fun … here’s a video from The Mythbusters: Do sharks prefer red?

Port Jackson shark (Heterodontus portusjacksoni). Shelly Beach, New South Wales, Australia. Image Credit: Richard Ling