Sharks Are Color Blind: new study shows they live in a world of contrast

According to a new study by scientists from Australia, sharks are color blind.  This puts them in the same category as whales and dolphins as sea creatures that may have had color vision at one time but evolved to a black and white world, perhaps as a more effective means of hunting.

Previous studies of several species of rays, part of the same general family as sharks, were found to have several types of ospins or light sensitive proteins in the photoreceptors of their retinas which provide them with the ability to see in color.  But studies of wobbegong sharks showed them to not have the necessary levels of ospins for color, only black and white.

Dr. Susan Theiss, University of Queensland (yes, we're related - she is my niece), and her colleagues studied two different species of wobbegong sharks; each of which prefer different levels of depth in the sea as their normal habitat.  Because of those differences in depth, the vision of the two species is more sensitive to different wavelengths of light.  Each species is better attuned to the type of light that predominantly penetrates their environment.  One wobbegong shark species preferred deeper water where it is penetrated by shorter wavelengths - a bluish kind of light.  Sharks in shallower water can be more sensitive to red or green spectrums of light.

Color blind as they are then, sharks live in a world of contrast.  Their other senses of sound and scent can aid them in their search for prey then, at some point, contrasting visual stimuli kicks in, and at close range sensing electrical impulses can come into play.

Sometimes color can be a distraction and can prevent the shark from staying focused on a potential target.  Color exists in nature for a variety of reasons and in some environments it can actually act as a kind of camouflage.  Oddly enough, as a filmmaker, I typically use a black and white viewfinder with my camera as it can often provide a sharper image for focusing purposes.

Playing off that sense of visual contrast, it might be possible to help keep sharks from becoming accidental bycatch by camouflaging or making hooks less visually interesting.  And the same could possibly be said for surfers who provide considerable contrast (as does a seal) in their black wetsuits. 

"If we can use this knowledge to design longline fishing lures that are less visible to sharks then we will be able to reduce the amount of shark bycatch. We may also be able to make wetsuits less attractive, and make the water safer for surfers and divers," says co-author Associate professor Nathan Hart of the University of Western Australia and reported in Australia's ABC Science. 

Source: ABC Science

Wobbegongs: behavior to light can help determine ocean health

One of the more unusual sharks found throughout the temperate and tropical waters of the western Pacific Ocean is the wobbegong. A bottom-feeder, the wobbegong has camouflaging motley coloration and frilly appendages around its mouth that some believe act as a lure for unsuspecting prey.

While the populations of various shark species that cruise the reefs can be used as a barometer as to the overall health of the ecosystem, according to researchers in Australia, the behavior of the wobbegong can also be used as an indicator of a healthy environment. By studying the behavior and understanding what geographical or habitat factors determine that behavior, then any recorded change in behavior may point to changes in the marine environment.

Dr. Susan Theiss of the University of Queensland has studied the light sensitivity of several wobbegong species and how different sensitivity establishes different levels of activity. She reported, "It appears that the wobbegong species we studied have different visual adaptations that could be linked to times of increased activity. For example, the spotted and dwarf spotted wobbegongs are probably more active in low-light conditions such as night time, or in the early morning or late afternoon, whereas the western and ornate wobbegongs are visually suited to a range of light conditions."

Professor Shaun Collin of the University of Western Australia, who also worked with Dr. Theiss in the study, said, "Almost nothing is known about the behaviour of wobbegongs, but what our research on the visual systems can do is predict their behaviour, so we look at the shark's visual system at the level of the photoreceptors, which are the cells that detect light. If you see these common species interacting and behaving normally in a particular environment, this can be a good indicator of the health of that part of the ocean."

Marine biologists study the role that sharks play as predators and scavengers in maintaining a healthy marine ecosystem. Declining shark populations, due to commercial overfishing, can have pronounced effects on the ocean environment - from changes in the health of other fish species to degraded water quality and even reduced oxygen levels. By monitoring the behaviors of animals like the wobbegong shark, researchers gain insight into how animals respond to changes in their environment.

"This research is important in establishing general trends and predictions in biogeography and ecology that we don't yet have data for," Dr Theiss said.

Oh, and yes, we are related. I am her proud uncle. Dr. Theiss is a U.S. national working for the University of Queensland and I someday hope to get across the Pacific and have her show me some of her frilly-mouthed friends first hand.

Read about the wobbegong research in Science Alert.