Researchers in Australia have discovered a secret weakness of one of the ocean's most impressive predators.

The scientists, who examined the 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.

Their study led Dr. Nathan Scott Hart and colleagues from the University of Western Australia and the University of Queensland in Australia, shows that although the eyes of sharks function over a wide range of light levels, they only have a single long-wavelength-sensitive cone* type in the retina and therefore are potentially totally colour blind.

Contrasts, not colour

The study shows that contrast against the background, rather than colour per se, maybe more important for object detection by sharks. These new insights may help to prevent attacks on humans and assist in the development of fishing gear that may reduce shark bycatch in long-line fisheries. Long-line fishing lures could possibly be designed so they are less attractive to sharks and swimming attire and surf craft could have a lower visual contrast to sharks and, therefore, be less 'attractive' to them, Prof. Hart explains.