Catsharks produce bright green biofluorescence which is only visible to other members of the same species. The contrast of the glowing patterns on sharks increases with depth, indicating they may likely use it to communicate with one another
Scientists have found a way to learn how sharks see each other deep down in the ocean.
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A new research reveals that catsharks produce bright green light only visible to the members of their own species and their glowing patterns continue to get clearer with depth.
Catsharks have a special pigment in their skin that absorbs blue light usually found in the depths of the ocean, transforms it and then discharges it as green color, in a process called biofluorescence.
To understand how biofluorescence works, researchers have developed a camera named ‘shark-eye’ that stimulates how catsharks see underwater, revealing that fluorescence makes them visible only to sharks related to their own species and also they may use it to communicate with each other.
“We’ve already shown that catsharks arerightly fluorescent, and this work takes that research a step further, making the case that biofluorescence makes them easier to see by members of the same species,” said co-author John Sparks, a curator in American Museum of Natural History.
“This is one of the first papers on biofluorescence to show a connection between visual capability and fluorescence emission and a big step toward a functional explanation for florescence in fishes.
Many researchers have discovered a number of species in the oceans such as fishes and marine turtles that can glow in a wide range of colors and patterns. Fishes live in the depths of the ocean and in a place where light is predominantly blue. They absorb blue light and re-emit in neon green, red or orange. But it is hard to observe these lights through human eyes. Humans develop color vision using three types of pigments red, green and blue. Sharks, in contrast, have just one pigment.
To explore how a shark sees, researchers focused on the visual ability of two different catsharks, chain catsharks and shellsharks. Researchers examined the eyes of the sharks by using a technique called microspectrophotometry and found that sharks have really long rod pigments that help them see in low-light environments.
Researchers created a camera by adding filters in front of its lens to capture the shark’s fluorescent light. During night dives, they shone high intensity blue light onto the animal. Then, they used custom built underwater camera with green filters to block out blue light and stimulated how light what shark eyes sees in the depths of the ocean. The resulting underwater light show was not visible to the human eye. But through the shark-eye camera, they found that animal appeared to glow a bright green, thanks to their biofluorescence.
Researchers also found that contrast of the patterns increased with depth, indicating that sharks not only use this light to see but also to communicate each other.
“Imagine being at a disco party with only blue lighting, so everything looks blue. Some things will look lighter blue and others will look darker blue. "Suddenly, someone jumps onto the dance floor with an outfit covered in patterned fluorescent paint that converts blue light into green. They would stand out like a sore thumb. That's what these sharks are doing.” Lead author David Gruber a researcher at Baruch College, City University of New York and the American Museum of Natural History told National Geographic.
“They might also be using biofluorescence to communicate in a way we haven’t thought of.”
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