A STUDY OF 17 SHARK SPECIES has determined that the animals have only one type of photoreceptor cells in their eyes, leading researchers to conclude that they are potentially completely color blind. The work by Dr. Nathan Scott Hart and colleagues at the University of Western Australia and the University of Queensland found that sharks have only a single long-wavelength-sensitive type of cone in their retinas. The findings were published in Springer’s online journal Naturwissenschaften –The Science of Nature.
IT’S A CELL THING Retinas contain two main types of photoreceptor cells – cone cells and rod cells. Rods are highly sensitive to light, facilitating night vision. Cones react to light but are less sensitive. The ability to distinguish colors requires multiple kinds of spectral cells – rod cells alone cannot distinguish colors. Rod cells were the most common type of photoreceptors the scientists identified in all 17 species. Ten had no cone cells and those that did had only a single kind of long-wavelength-sensitive cone photoreceptor. The findings suggest that sharks may be cone monochromats – and color blind.
CONTRAST MAY BE MORE IMPORTANT THAN COLOR The study, Dr. Hart says, suggests that an object’s contrast against background may be more important to sharks than color itself, noting that the trait is also carried by many marine mammals (such as whales, dolphins and seals). He adds that the finding may help in the design of swimming attire, surf craft and long-line fishing lures that may be less attractive to sharks — and thus reduce shark by-catch.
Publication: Hart NS et al (2011). Microspectrophotometric evidence for cone monochromacy in sharks. Naturwissenschaften – The Science of Nature; DOI 10.1007/s00114-010-0758-8