Scientists Create New Camera to Study Glowing Sharks

A swell shark (Cephaloscyllium ventriosum) is seen in normal light and fluorescent lighting conditions. Scientists have built a "shark eye" camera than can see as these fish do. J. Sparks, D. Gruber and V. Pieribone

Scientists now know what it's like to see through the eyes of a shark.

In the past five years or so, research has shown that many different types of fish, rays and sharks can fluoresce, producing brightly colored light when illuminated by even dim sunlight. It isn't yet clear, however, whether they can actually see this fishy glow or what purpose this trait serves.

To find out, John Sparks, a curator of ichthyology at the American Museum of Natural History, his colleague David Gruber and others examined the eyes of two different kinds of sharks that live at depths of around 100 to 150 feet, and whose skin produces a bright-green glow. In the laboratory, they took shark eyes, shined light on them and then measured the wavelengths of light absorbed. They found that these two species—the swell shark (Cephaloscyllium ventriosum) and the chain catshark (Scyliorhinus retifer)—can see bright green, the color of fluorescent light their skin produces.

"This is the first paper to show that a fish eye is capable of absorbing" this biofluorescence, says Sparks, the senior author of the study, published April 25 in the journal Scientific Reports.

At the depths these fish live, where all but blue is filtered out by the water column, bright-green light makes them stand out against the background, and the sharks' eyes allow them to see and recognize one another, Sparks says.

David Gruber with the special shark-eyed camera developed for the study. K. McBurnie

To further understand how these fish appear to one another, the researchers created a camera that mimics the workings of a shark's eye and took photos of the underwater beasts using this new device. They found that the two species they'd examined popped bright green against the blue background.

"It really makes them stick out," Sparks says.

Chain catshark composite
Items (a) through (f) show the fluorescent and white light pigmentation of a female chain catshark (Scyliorhinus retifer), and (e) through (h) show a male of the same species. David Gruber et al.

In many areas of the ocean one can find glowing fish and sharks schooling together underwater at dusk, fluorescing in a variety of colors. "It's a rainbow of colors out there at night…and you can't believe how bright it is," Sparks says.

The finding supports the idea that these fish use fluorescence to communicate with one another. But exactly how they employ it, and what function it serves, are still open questions that Sparks and colleagues plan to address in the future.