Catsharks and swell sharks may not look attractive by the human eye, but other members of their species may see them differently. To each other, these sharks emit a brilliant green glow. Now researchers have created a camera to simulate the way these sharks see each other deep under in the ocean. Scientists say the lenses show that their glow grows stronger and clearer as they swim deeper, according to a research published in the Scientific Reports.
These two species of shark, which dwell in the dark blue depths of the ocean, uses biofluorescence to stand out to each other.
“Imagine being at a disco party with only blue lighting, so everything looks blue,” study lead author David Gruber, a researcher at Baruch College, City University of New York, and the American Museum of Natural History, told National Geographic.
“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.”
Biofluorescence is the mechanism when an organism absorbs light at one wavelength and then re-emits it at another. In this case, the sharks’ skin transforms blue light into green.
The scientists took a shark’s-eye-view to examine biofluorescence.
First, the team looked into the structure of the eyes of these two species. While humans have three color pigments (red, green, and blue) in their eyes, these sharks have just one (monochromatic). However, the remarkably long rod pigments in their eyes enable them to see better in low light.
These creatures live so deep underwater that most wavelengths of light are blocked out by the water over them, but blue light can make it through.
Scientists built a “shark eye” camera to learn about the pigments in a shark’s eye. Then they dove off Scripps Canyon, off San Diego to look for glowing sharks.
After returning to the lab they used the images to create a mathematical model, which suggested that as the sharks swam deeper, the contrast of their glow increased.
Dr. Gruber says sharks aren’t the only marine animals to use biofluorescence. Over 200 species of shark and bony fish have been found to glow in this way.
“It makes perfect sense if you think about life in the blue ocean,” Gruber told The Atlantic.
“Why wouldn’t they come up with a way to make their world richer in texture?”