Sharks are probably colour-blind
By Victoria Gill
Science and nature reporter, BBC News
Researchers in Australia have discovered a secret weakness of one of the ocean's most impressive predators.
Sharks, it seems, are completely colour blind.
The scientists, who examined retinas of 17 different species of shark, discovered that the creatures had only one type of colour-sensitive cell, known as a cone cell, in their eyes.
Human eyes have three cone cell types, with each type dedicated to receiving either blue, green or red light.
This allows most people to tell the difference between different coloured objects.
The study, carried out by Nathan Scott Hart and colleagues from the University of Western Australia and the University of Queensland, Australia is published in the journal Naturwissenschaften.
Dr Hart said the research could help to prevent shark attacks on humans and assist in the development of fishing gear that may reduce the number of sharks that are caught accidentally in long-line fisheries.
"Our study shows that contrast against the background, rather than colour per se, may be more important for object detection by sharks," he explained.
"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."
To reveal the secrets of shark vision, the team examined the retinas of 17 shark species caught in a variety of waters in both Queensland and Western Australia.
In humans, the retina is densely packed with light-sensitive rod and cone cells. Rods are able to function in much lower light than cones - and these were the most common cell types found in all of the sharks.
In ten of the species they examined, the researchers found no cone cells at all.
In the seven species that did have cones - only a single type, highly sensitive to just one wavelength, and therefore one colour, was present.
If sharks' retinas cannot distinguish between different colours of light, as this research suggests, they may be totally colour-blind.
