Say What?! Sharks are colour blind?

This may be old news to some, but it has always been a bit of a "grey" area for me. Since i've been in the diving world (albiet, not very long) it has always been the contention that if you wore bright/fluro coloured dive gear you would stand out amongst the crowd in a Sharks eyes. I must admit, I never thought much into it until recently...

While doing a bit of research on varying marine creatures eyes I came across an interesting article that came out in January of this year that Sharks are most likely unable to distinguish between colours and that this research could benefit both humans and sharks alike.

The researchers used a technique called micro-spectrophotometry that enabled them to look at retinal cells of 17 Shark species commonly found off Western Australia and Queenlands coasts. In human eyes, we both rod and cone cells. We especially have a number of cone cells which enable us to distinguish between a variety of colours.

In Sharks, the cells were mostly made up of 'rod' components, which are highly sensitive to light and allow night vision but cannot tell colours apart. In 10 of the 17 shark species, no cone cells were found at all. As for the other 7 species only 1 single type of cone cell was found, this cone cell corresponded to the colour green.

So, what on earth does all this mean?
Basically, the study shows that contrast against the background, rather than colour, may be more important for object detection by sharks. Which for me, makes sense as unlike terrestrial environments, colours are filtered out at certain depths and being able to distinguish shapes in the gloom could be the answer to survivial.

Furthermore, the paper showed that whales, dolphins and seals all possess the same type of green-sensitive cone cells which suggests that these marine mammals and sharks arrived at the same visual design by convergent evolution.

The lead scientist on the research, Nathan Scott Hart (University of Western Australia) said that "this research can help us design long-line fishing lures that are less attractive to sharks and design swimming attire and surf craft that have lower visual constrast to sharks and therefore less 'attractive' to them."

Check out the full article here http://www.springerlink.com/content/05427357r3uw8q35/

Sarah Shark
www.sarahshark.com