Biologist Goes on a Trawling Trip and Stumbles Upon a Rare Shark That Glows in the Dark

Biologist Jérôme Mallefet always dreamed about witnessing a glowing shark. He knew that it existed somewhere, patrolling some deep, dark waters. But where, he didn’t know yet. In January 2020, when he ventured on a trawling trip 1,000 miles east of New Zealand to monitor fish swimming in the twilight zone, his dream erupted into reality. For the first time in his life, he witnessed a striking shark glowing blue-green in the dark, gliding in the waters. Documenting the discovery in a study published in Frontiers in Marine Science, he noted that the glowing creature was a kitefin shark, Dalatias licha, about 5 feet 11 inches long.

This is not the first account of a creature emitting an unusual glow in the dark. Called “bioluminescence,” this glow is an adaptive strategy zillions of living organisms use for a variety of purposes, to attract a mate, to defend themselves against predators, for camouflaging, and so on. From fireflies fluttering in tropical forests to plankton algae in the Southern Ocean, life hums and chimes with these luminaries. But this is the first time bioluminescence has been observed in a shark.

"Bioluminescence has often been seen as a spectacular yet uncommon event at sea," the researchers wrote in the study, "but considering the vastness of the deep sea and the occurrence of luminous organisms in this zone, it is now more and more obvious that producing light at depth must play an important role in structuring the biggest ecosystem on our planet."

Deconstructing the mechanism behind the shark’s glow, scientists described that they have tiny light-emitting organs embedded in their brown skin that help them convert chemical energy into light energy. These sharks, they explained, feature little cup-shaped structures called “photopores,” dotted across their skin. In the center of each cup are light-emitting cells. There’s also a lens on top that directs the light outwards, pouring out the radiant orbs of light. The entire bioluminescence mechanism is controlled by their hormones.

“They use two or three hormones, at least, to trigger or slow down the light emission,” Mallefet explained to The Guardian. He added that the shark can glow for an hour or two, but once they lights up, they cannot change rapidly. When Mallefet stumbled upon the shark, softly glowing, he gently transferred them into a darkened room. His eyes popped wide open as he noticed the unusual radiance emanating from its flesh. The spine on its back was illuminated like lightsabers. “I was just like a kid at the bottom of a Christmas tree,” he described to CNN.

The sharks' vivid glow serves not just for survival, but also to communicate with each other. Some males illuminate their claspers, the shark’s equivalent of a penis, a trick that helps attract mates. Many sharks also have glowing bellies, which help them hide their silhouettes from predators lurking in the deep. Of the hundreds of sharks caught by Mallefet and his team, 13 were kitefin sharks, seven blackbelly sharks, and four southern lantern sharks, all of which were found to be glowing. "This first experimental study of three luminous shark species from New Zealand provides an insight into the diversity of shark bioluminescence and highlights the need for more research to help understand these unusual deep-sea inhabitants: the glowing sharks," researchers concluded.