Scientists have discovered three species of glowing sharks in the deep ocean near New Zealand, reports Elle Hunt for the Guardian. One of the species, the kitefin shark, can reach lengths of nearly six feet and researchers say its cool blue glow makes it the largest known species of luminous vertebrate on Earth.
The three bioluminescent sharks—the kitefin shark, the blackbelly lanternshark and the southern lanternshark—were hauled up from the deep during fish surveys of an ocean bottom feature called the Chatham Rise off the east coast of New Zealand in January 2020. All three sharks inhabit the ocean’s mesopelagic or “twilight” zone, which spans depths of 660 to 3,300 feet below the surface.
Bioluminescence had previously been documented in only around a dozen shark species, so this discovery significantly adds to our knowledge of how prevalent the phenomenon is in these and other marine animals, says Jérôme Mallefet, a research associate at the Université Catholique de Louvain in Belgium and lead author of the new study.
The expedition involved hauling up a small number of blackbelly lanternsharks, southern lanternsharks, and kitefin sharks from the ocean’s twilight zone, a scantly illuminated region that extends from a depth of 660 to 3,300 feet.
Most bioluminescence in the deep sea involves a chemical compound called luciferin that glows when it interacts with oxygen. In the deep sea, where scientists estimate three-quarters of all creatures are bioluminescent, having the ability to create light can be extremely advantageous. Deep-sea animals use bioluminescence to do everything from attracting prey to deterring predators. Being bioluminescent can even help deep-sea animals camouflage themselves.
In the ocean’s twilight zone, which receives minimal amounts of sunlight, bioluminescent animals can hide their silhouette from predators lurking below by producing enough light to match their surroundings—a trick known as counter-illumination. All three species examined in this study had large concentrations of photocytes on their undersides, which suggests that these sharks may hide from predators—thought to include primarily larger sharks—in just this way.
Researchers tell Mongabay that this trio of sharks appears to produce light some other way.
Researchers aren’t exactly sure what purpose the ability to glow serves for the sharks but speculate that their glowing bellies could make them harder to see from below. In the darkness of the deep sea, the ocean surface is a faintly luminous backdrop against which a glowing shark would disappear when viewed from below, concealing it from predators or prey. Per the Guardian, the kitefin may also be using its glow to illuminate prey on the seafloor.
“I tend to say they are the MacGyver users of light, because they use bioluminescence in many different ways,” Jérôme Mallefet says.
Curiously, the kitefin’s dorsal fin also emits light. Speaking with the Guardian, Mallefet says “we are still very surprised by the glow on the dorsal fin. Why? For which purpose?”
Mallefet says he hopes he will soon be able to safely travel for his research and continue investigating the glowing denizens of the deep. “We hope by highlighting something new in the deep sea of New Zealand—glowing sharks—that maybe people will start thinking we should protect this environment before ᴅᴇsᴛʀᴏʏing it,” he tells Mongabay.
The discovery that these three species produce light “is not surprising,” says David Ebert, director of the Pacific Shark Research Center at Moss Landing Marine Laboratories in California, but it is still exciting.
That’s because researchers think many more species of sharks are likely capable of producing light—Mallefet estimates that perhaps 10 percent of the 540 known species of shark are bioluminescent. But Ebert thinks even this is a conservative guess. As the field of deep-sea shark research advances, “I think that number will go even higher,” he says.
Both Ebert and Mallefet hope that more attention will be paid to deep-sea sharks in the future, as the creatures and their habitat are understudied and under ᴛʜʀᴇᴀᴛ.
“A lot of people know that sharks can bite, thanks to Jaws,” says Mallefet, “but few people know that they can glow in the dark.”