New study suggests sharks are colour blind

Washington, Jan 19 (ANI): A new study from the University of Western Australia and the University of Queensland in Australia has suggested that sharks are colour blind.

Dr. Nathan Scott Hart and colleagues said that sharks have only one type of cone cell in their eyes so they can't distinguish between colours.

Our study shows that contrast against the background, rather than colour per se, may be more important for object detection by sharks. 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," said Hart.

For their study, Hart and his team used a different technique - microspectrophotometry - to identify cone visual pigments in shark retinas and measure their spectral absorbance.

They looked at the retinas of 17 shark species caught in a variety of waters in both Queensland and Western Australia.

In ten of the 17 species, no cone cells were observed. However, cones were found in the retinae of 7 species of shark from three different families and in each case only a single type of long-wavelength-sensitive cone photoreceptor was present.

The results suggest that sharks have only a single cone type, suggesting that they are colour blind.

"While cone monochromacy on land is rare, it may be a common strategy in the marine environment. Many aquatic mammals - whales, dolphins and seals - also possess only a single, green-sensitive cone type. It appears that both sharks and marine mammals may have arrived at the same visual design by convergent evolution, in other words, they acquired the same biological trait in unrelated lineages," said Hart.

"*There are two main types of photoreceptor cells in the retina of the eye. Rod cells are very sensitive to light and allow night vision. Cone cells also react to light but are less sensitive to it. Eyes with different spectral types of cone cells can distinguish different colors. Rod cells cannot tell colors apart," he concluded.

The study appears in Naturwissenschaften - The Science of Nature. (ANI)