By Blaise Jones
The short answer is no, probably not. But as with all things in nature, the full answer is never that simple. Sharks are diverse animals. They range in size from the length of a finger to the size of a bus. Several species have unique adaptations found nowhere else among the sharks. So what is true for one species could be false for another.
Retinal Rods and Colorful Cones
To understand why it is so difficult to answer this question across the broad spectrum of shark species, one first must know how seeing colors works. The eyes of vertebrate animals contain two main types of light-sensing cells, or photoreceptors. These cells are called rods and cones. Rods allow animals to see in low levels of light, but cannot detect color. Cones, on the other hand, cannot detect low light levels, but can see color. What colors an organism can see depends upon what kinds of cones they have in their eyes. In fact, in order to have true color vision as scientists understand it there needs to be at least three different types of cone present in the eyes.
One Cone to Rule Them All
An experiment performed by scientists from the University of Western Australia tested for the presence of cones in the eyes of 17 different species of shark. They found that seven of the tested species had only one type of cone. The type of cone found in the shark varied across the species, with the shallower sharks having red light-detecting cones, and the deeper species having blue light-detecting cones. The remaining ten species had no cones at all.
Since these sharks possess only the one cone, they are unable to actually distinguish different colors. However, they are able to see the differences between shades and contrasts of the one color they can see, either blue or red, depending upon the species. This is common across most marine organisms; fish, whales, seals, and dolphins all lack more than one cone and are believed to be colorblind.
Catch a Wave
But why do sharks have just one cone, if it only allows them to see contrasts in the shades of one color? It is because while light and color are easy to see on land, water works as a filter that dilutes them both. Light travels in waves and different colored light has different wavelengths.
Each wavelength of light is affected differently when it hits water,; some are able to pass through it more easily, while others have a more difficult time. Blue and green wavelengths can be seen as deep as 300 feet, while red light disappears at around 33 feet. That is why the shallow water sharks have the red cone, and the deeper water sharks have the blue cone. That is also why so many deep sea animals are red; red light does not penetrate that deep into the ocean, which makes them effectively invisible.
So while it cannot be definitively said that every species of shark is completely color blind, there is strong evidence to suggest that many, if not the majority, cannot see color.
“Marine Biology” by Jeffery S. Levinton
“Sharks: The Animal Answer Guide” by Gene Helfman and George H. Burgess
Alan Moore, Director of the Coastal Marine Education and Research Academy