A biofluorescent chain catshark as seen through special goggles. A biofluorescent chain catshark as seen through special goggles. A biofluorescent chain catshark as seen through special goggles. (Photo: J. Sparks, D. Gruber, and V. Pieribone)

Why do some sharks glow in the dark?

Scientists created a special underwater camera to find the answer.

Dating is a diverse ritual that happens all the time. In some cases, people use apps and simply swipe to find that perfect companion. Other times, singles are mingling at bars and social soirees looking to find the ideal companion.

But news out of the science world today offers up something completely different: A group of international scientists from the United States and Israel discovered that certain types of sharks actually glow in the dark underwater to attract a mate.

A study was conducted using a custom-built "shark-eye" camera that simulates how the shark sees underwater, giving the scientists unprecedented access into the inner worlds of catsharks. This particular species produces fluorescence that makes them more visible to neighbors of the same species and may aid in communication between one another. The work was published in the journal Scientific Reports and included scientists from Yale University, Cornell University, Baruch College, the American Museum of Natural History and the University of Haifa in Israel.

Unlike the full-color environment that we experience above water, fish inhabit a world that is mostly blue, because with depth, water quickly absorbs the majority of the visible light spectrum. The research team discovered that many fish absorb the remaining blue light and re-emit it in neon greens, reds and oranges.

This results in an underwater light show that is practically invisible to the human eye, but can be seen with the specially developed "shark-eye" camera.

"Imagine being at a disco party with only blue lighting, so everything looks blue," David Gruber, the study's lead author, 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."

Predators from a different species, who can't see these color changes, are oblivious to the bright neon light. This leads the scientists to believe that the sharks are communicating with each other. In particular, they noticed distinct glowing patterns among the sexes. In male catsharks, for example, the pelvic area is what glows the most.

"This work forces us to take a step out of the human perspective and start imagining the world through a shark's perspective," said Gruber. "Hopefully it will also inspire us to protect them better."

And are these scientists scared to be so close to sharks? "Sharks hardly ever target humans to attack," Derya Akkaynak, the oceanographer from the University of Haifa in Israel who worked on the study, told From The Grapevine. "So in most cases if they have attacked a human, it is because they have horrible vision and they mistook the person for a fatty seal!"

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Why do some sharks glow in the dark?
Why do sharks glow in the dark? Scientists created special underwater camera to find an answer.