Screenshot from footage of swell sharks taken by David Gruber and Vincent Pieribone

A shark that glows in the dark... I don't know if that makes them more or less terrifying.

The glowing breed of shark is known as the swell shark, or Cephaloscyllium ventriosum, and is fluorescent thanks to a protein within its skin that glows bright green when activated by blue light. Humans can't see this spectacular light display, but swell sharks can. Their eyes have yellow filters that block out natural blue light in order to see a new world of colors.

"“What the swell sharks are doing is using the blue light to create other colours of light to make their world richer in color,”" said Dr. David Gruber, an associate professor of biology at City University of New York. Gruber thinks that the sharks use their biofluorescence to communicate with each other.

The sharks have been filmed in a BBC/Discovery collaboration. It was the first time Gruber had ever seen the sharks' biofluorescent properties in the wild. 

 

 

Filming biofluorescent sea life snippet

It was not a risk-free dive to get this footage. The sharks live 500 meters (1,640 feet) beneath the surface of the ocean, and all this had to be done in the dark to see the biofluorescence. They aren't in the habit of taking selfies either; swell sharks are shy and wriggle in between rocks to hide from predators.

The fluorescence also can't be seen by any ordinary lens. The camera that Gruber used is inspired by the swell shark's eye, blocking out yellow light. Gruber then shines a light the same wavelength as moonlight on the sharks, which makes them fluoresce. You can only see this through the shark-vision lens though. "This camera allows us to get a little portal into the world of a very shy species of shark," says Gruber in the video. 

“It is almost like a hidden mode of communication, like a covert form of communication just among themselves or just among animals with similar kinds of vision,” he says.

The swell sharks are by no means the first underwater animals to glow in the dark; Gruber was part of a team who discovered biofluorescence in over 180 species of fish. The biofluorescence, instead of making the animals more visible, may actually be used as camouflage since a lot of underwater fauna have a ghostly glow. Whatever the reason, Gruber and his team are excited to keep researching to find out the answer.

A well-disguised biofluorescent fish hiding amongst coral by Gruber and his team via PLOS

[Via BBCPLOS]

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