January 18, 2011

Research Finds Sharks Are Unable To Distinguish Colors

According to a laboratory study published on Tuesday, sharks may be unable to distinguish between colors, which could benefit swimmers, fishermen and sharks themselves.

Australian researchers looked at the retinal cells of 17 shark species caught off Queensland and Western Australia.

They found that the most common kind of light receptors were "rod" cells, which are highly sensitive to light and allow night vision but cannot tell colors apart.

However, the sharks lacked cone cells, which respond individually to light at specific wavelengths.  A variety of cone cells help us to distinguish between colors.

No cone cells were found at all in 10 of the 17 shark species.  The cone cells found in the other seven species were a single type, which helps see green.

The investigators said that this retinal system means sharks are able to distinguish between shades of grey but not between odors.

Monochromatic vision is very rare among land species, because color vision is a tool for survival in terrestrial habitats.

However, color vision is less important in the marine environment, where colors are filtered out at depth and survival depends on distinguishing contrasts to help determine shapes of prey or predator.

The paper said that previous research has found that whales, dolphins and seals also possess green-sensitive cone cells, which suggests that these marine mammals and sharks arrived at the same visual design in parallel.

The study could help prevent shark attacks on humans and develop fishing gear that could reduce accidental catches of sharks by long-line trawlers.

"Our study shows that contrast against the background, rather than color per se, may be more important for object detection by sharks," lead scientist Nathan Scott Hart at the University of Western Australia said in a statement.

"This may help us to design long-line fishing lures that are less attractive to sharks as well as to design swimming attire and surf craft that have a lower visual contrast to sharks and therefore are less 'attractive' to them."

The study was published in English in the German journal Naturwissenschaften.


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