Scientists from the American Museum of Natural History have created a custom-built "shark vision" camera that simulates how sharks see underwater. The novel device helped them lead a team of researchers to the discovery that catsharks can see the bright green biofluorescence that they produce as well as increase the contrast of the glowing pattern when they are deep underwater. The findings reveal the role of this biofluorescence in the communication process between members of the same shark species.
"We've already shown that catsharks are brightly 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 John Sparks, a curator at the American Museum of Natural History and a co-author of the paper. "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 fluorescence in fishes."
Sparks recently worked with a team of researchers examining biofluorescence, which is the process by which some organisms absorb light, transform it and emit it as a different color.
"Our next question was 'What does all this newfound biofluorescence we are finding in the ocean mean?'" said David Gruber, a research associate at the American Museum of Natural History and first author on the study. "Can these animals see other animals that are biofluorescing in the deep blue sea? And are they using it in some way?"
The team focused on the visual ability of two different kinds of catsharks: chain catsharks (Scyliorhinus retifer) and swellsharks (Cephaloscyllium ventriosum). Using a technique called microspectrophotometry, they revealed that the sharks possess long rod pigments that help them see in environments with insufficient light, a finding that they used to create their unique camera that simulates the world from a shark's eyes.
After creating the shark vision camera, the team conducted numerous night dives in Scripps Canyon in San Diego County, taking note of swellsharks in their native habitat 100 feet underwater and examining their use of biofluorescence.
"Some sharks' eyes are 100 times better than ours in low-light conditions," Gruber said. "They swim many meters below the surface, in areas that are incredibly difficult for a human to see anything. But that's where they've been living for 400 million years, so their eyes have adapted well to that dim, pure-blue environment. Our work enhances the light to bring it to a human perspective."
Mathematical modeling of the images captured by the shark vision camera revealed a unique contrast of the patterns on biofluorescent sharks at low depths, suggesting that they use the light to communicate with one another.
The findings were published in the April 25 issue of Scientific Reports.
