Sharks may be able to smell blood from miles away, but they probably don't know how red it is. It is likely that they only see the world in black and white according to a study that is the first to look into sharks' visual systems.
A team at the University of Western Australia studied the visual systems of many different species of sharks and what they have found is diversity in eye design that mirrors the ecological and behavioral diversity of the shark species. The team looked at the retinal cells of 17 species of sharks caught from Queensland and Western Australia and found out that the cells are responsible for sharks' color blindness.
According to the study, these animals are color-blind due to the light receptors they have got in their eyes. There are two main types of light-sensitive ceils to allow animals to see: rod cells help measure brightness because they are highly sensitive to light and allow night vision but cannot tell colors apart, while various types of cone cells help distinguish colors. They looked at the structure of sharks' rod and cone cells in the retina. Human eyes come with red, green and blue cone variations, while sharks appear to have just one kind of cone cell.
The study suggests that contrast against the background, rather than color itself, might be more important for object detection by sharks. Costumes that camouflage swimmers' bodies in sea water are less likely to draw a shark's attention than ones with bright, solid colors that emphasize their outline. "It's the high contrast against the water rather than the color itself which is probably attractive to sharks," said Professor Nathan Hart who led the study.
