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: RTSea
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: RTSea
Shark's Sense of Smell: scientist sniffs out the subtleties of acute sense
We have long heard about a shark's acute sense of smell. It's ability to detect the odors or scents given off by an injured fish was long considered one of a shark's primary tools in its predator tool kit. But just how sensitive is it? With currents or water motion moving odors around, just how does a shark sense a smell and then begin tracking it to its source? Dr. Jelle Atema has been studying sharks for some 20 years, working with the Boston University and the Woods Hole Oceanographic Institution. He has spent considerable time investigating just how sharks utilize their sense of smell to their best advantage. Reporting in BU Today, Susan Seligson writes of Dr. Atema's work with smooth dogfish, a small shark that is often found in the U.S. northeast (BTW: And one that has been severely hit by commercial shark fishing operations). Using controlled plumes of odors like squid scent in a long observation tank, he is unlocking many of the secret subtleties as to how a shark senses odor and tracks it to its source. Often we think of sharks as sensing the smell given off by an injured animal. That may be true but, when hunting, sharks are attracted to the odors of familiar prey, injured or otherwise. “All animals give off some kind of body odor,” says Atema.“The science here is to understand how odor is dispersed into the water, and how many molecules does a shark need in his nose to track that odor.” Dr. Atema's experiments have also provided new insight as to how a shark responds to odors and how they just where to go to get to the source. As reported in BU Today, "Working along with Jayne Gardiner at the University of South Florida, in Tampa, Atema’s most recent discovery is that sharks are guided by the nostril that first detects the prey’s odor, rather than orienting themselves based on which nostril senses the greater odor concentration. The finding—that smell reaches one nostril before the other, signaling whether to veer left or right—means that sharks can decipher very quickly, a matter of seconds as opposed to minutes, where their next meal is, no matter how chaotic the dispersed odor plume. Before this discovery, published in Current Biology, scientists had long believed that sharks’ sense of smell was a function of the plume’s surface area—the bigger the plume, the easier it would be for sharks to smell it." In some respects, the ocean is a very smelly place, full of scents or odors of hundreds of different organisms and at varying strengths or intensities. Bombarded with all these stimuli, sharks can amazingly sort it all out and, along with its other senses, be the efficient predator that it is. Source: RTSea
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