Color vision in sharks

Sharks can smell blood at a great distance; however, it is not known whether they can also see that it is red. Research seems to indicate that sharks are color blind. This is not very surprising: as there is ...
little light in deep water, colors are almost impossible to see, making contrast much more important.
Two different types of cells in the retina are important for vision in animals (and humans). Rods help to perceive brightness; various kinds of cones allow color vision. Microspectrophotometry had already been used to show that rays and chimaeras (distant relatives of the shark) do see colors. Scientists at the University of Western Australia used this technique to study seventeen shark species, including both tiger sharks and bull sharks.

Because rods were found in all seventeen shark species, it can be concluded that they can clearly see differences in dark and light (contrast). In ten shark species, no cones at all were found; in the other seven species only one type of cone was found. This suggests that sharks cannot discriminate any colors at all. The researchers, by the way, do not claim that all sharks are color blind: after all, there are 400 different species.

Interestingly, there are other ocean predators suspected of colorblindness, including whales, dolphins and seals. In their blue-green environment, discernment of colors is relatively unimportant.

The researchers maintain that knowledge about color vision in sharks is of interest: contrast can be employed to prevent sharks from being caught as bycatch, and surfing and diving equipment can be made less attractive for sharks in order to reduce the number of accidents.

The shark study is published in the journal Naturwissenschaften.