Catsharks May Communicate With Biofluorescence

Posted on April 29, 2016

Catsharks may use biofluorescence to communicate with each other deep underwater. Researchers led by scientists from the American Museum of Natural History have found the catsharks can see their own bright green biofluorescence. The scientists also found catsharks increase contrast of their glowing pattern when deep underwater.

The study was conducted using a custom-built "shark-eye" camera that simulates how the shark sees underwater. It shows that fluorescence makes catsharks more visible to neighbors of the same species at the depths that they live.

John Sparks, a curator in the American Museum of Natural History's Department of Ichthyology and a co-author on the paper, says in a statement, "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. 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."

The researchers built a mathematical model using images taken with the shark-eye camera. They found that the contrast of the patterns on the biofluorescent sharks increases with depth. The scientists say this suggests that the animals can not only see the light but are also likely using it to communicate with one another. The researchers were only able to dive to the top depth range of where this shark lives. At this depth there is blue and some green light. The model developed by the scientists shows that at deeper depths - where the water is bluer - the contrast created by the fluorescence is even greater.

David Gruber, an associate professor of biology at Baruch College and a research associate at the American Museum of Natural History, adds, "Some sharks' eyes are 100 times better than ours in low-light conditions. 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."

A research paper on the study was published here in the journal, Scientific Reports. The scientists note that biofluorescence was even recently been observed in sea turtles. They say there are many unanswered questions about the biological and ecological role of biofluorescence in the marine realm as both fishes and turtles possess advanced visual systems.

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