They shine in the darkness, they do not produce flashes
In the deep waters off New Zealand's eastern coast, science has confirmed what darkness long concealed: a 1.8-meter shark that glows. The discovery of Dalatias licha as the largest known bioluminescent vertebrate reminds us that the ocean's twilight zones — vast, pressurized, and lightless — are not empty voids but intricate worlds where life has learned to illuminate itself. What appears as a single remarkable specimen is, in truth, a doorway into understanding how light itself structures the architecture of the deep.
- A shark pulled from New Zealand's Chatham Rise was found producing a steady blue-green glow, shattering the previous record for the largest bioluminescent vertebrate ever documented.
- Three shark species captured during a 2020 NIWA expedition were confirmed to produce visible light — not in flashes, but as a constant, living luminescence in the pitch black of the deep.
- Scientists are grappling with why sharks glow at all: the answers span hunting, mating, communication, and a camouflage strategy called counterillumination that renders them invisible to predators below.
- With roughly 57 of 540 known shark species potentially bioluminescent, researchers now suspect light production is not a biological curiosity but a foundational force shaping deep-sea ecosystems.
In January 2020, a research team from New Zealand's National Institute of Water and Atmospheric Research set out across the Chatham Rise — a vast underwater plateau stretching a thousand kilometers east of the country's coast — and returned with something extraordinary: sharks that glowed. Among the three bioluminescent species they captured, one stood apart. A 1.8-meter Dalatias licha, the kitefin shark, was producing a steady blue-green light from its body, making it the largest bioluminescent vertebrate ever confirmed by science.
Belgian scientist Jérôme Mallefet, lead author of the study published in Frontiers in Marine Science, was able to observe the light production firsthand on freshly caught specimens. What struck him was its constancy — these sharks did not flash like fireflies, but maintained an unbroken glow in the darkness. "They shine," he noted, "they do not produce flashes." That distinction carries weight: the light is not a signal sent and received, but a permanent feature of how these animals inhabit their world.
The reasons for that glow are layered. Bioluminescence helps some sharks lure prey, find mates, or communicate within groups. In waters where faint sunlight still filters down from above, it can also serve as counterillumination — matching the ambient light from the surface to make the shark invisible to anything watching from below.
Mallefet's broader research suggests that as many as 57 of the 540 known shark species may be capable of producing light, most of them small creatures living in the ocean's twilight zone below 200 meters. The confirmation of the kitefin shark as the record-holder points toward something larger: in the deep ocean, light is not an accident of biology but a structural element of the ecosystem itself. In a habitat defined by crushing pressure and absolute darkness, life has not merely survived — it has learned to paint its own world with light.
In the deep waters off New Zealand's eastern coast, researchers pulled from the ocean something that glowed. A shark, 1.8 meters long, belonging to the species Dalatias licha, was producing light—a steady blue-green luminescence that brightened and dimmed in the darkness. When scientists examined it closely, they confirmed what had never been proven before: this was the largest bioluminescent vertebrate ever documented.
The discovery came during an expedition in January 2020 across the Chatham Rise, a vast underwater plateau stretching a thousand kilometers east of New Zealand. The team from the country's National Institute of Water and Atmospheric Research, known as NIWA, was surveying the seafloor when they captured specimens of three shark species capable of producing visible light through biochemical reactions. Two of these species—Etmopterus lucifer and Etmopterus granulosus—were already known to science. The third, the sixgill shark, was the revelation.
Jérôme Mallefet, a Belgian scientist and lead author of the study published in Frontiers in Marine Science, had the rare opportunity to examine freshly caught specimens and observe their light production directly. Unlike fireflies or other creatures that flash, these sharks maintained a steady glow, their bodies emanating that distinctive blue-green hue in the pitch black of the deep. Mallefet noted in NIWA's statement that the sharks "shine in the darkness, they do not produce flashes." The distinction matters—it speaks to how these animals use light, not as a signal sent in bursts, but as a constant presence in their world.
The question of why sharks glow at such depths has several answers. Some use bioluminescence to hunt, attracting prey toward their mouths. Others use it to find mates in the reproductive season. When gathered in groups, the light may serve as a form of communication. And in waters where some ambient light filters down from above, bioluminescence can help a shark match the faint illumination from above, rendering itself invisible to predators lurking below—a survival strategy called counterillumination.
Mallefet's research suggests that roughly 57 of the 540 known shark species worldwide may possess bioluminescent capabilities. Most are small creatures living in what scientists call the twilight zone, depths beyond 200 meters where sunlight no longer penetrates. The discovery of three bioluminescent species in New Zealand waters, and the confirmation of the sixgill shark as the largest such vertebrate on record, points to something larger: light production in the deep ocean is not a curiosity but a fundamental feature of how the ecosystem is organized. In the crushing darkness miles below the surface, where pressure and cold would seem to permit only the simplest life, creatures have evolved to paint their world with their own light. The research by Mallefet, working alongside Laurent Duchatelet of the Catholic University of Louvain and Darren Stevens of NIWA, opens a window into how little we still understand about the animals that inhabit Earth's largest habitat.
Notable Quotes
They shine in the darkness, they do not produce flashes— Jérôme Mallefet, lead researcher
The existence of luminous organisms in this zone makes increasingly clear that producing light in the deep has an important role in structuring the planet's vast ecosystem— NIWA research statement
The Hearth Conversation Another angle on the story
Why does a shark need to glow? What's the advantage in water that deep?
It depends on the shark's needs. Some use it to lure prey close enough to eat. Others use it to find a mate in the darkness. But there's also camouflage—if you match the faint light coming from above, predators below can't see your silhouette.
So it's not just one function. It's a toolkit.
Exactly. And we're only now confirming it happens at all in these larger species. For decades, scientists knew small sharks could glow. Finding a 1.8-meter animal doing it changes the scale of the question.
How many sharks are we talking about? Is this common?
Not common at all. Out of 540 shark species, maybe 57 can produce light. Most are small. This sixgill shark is the largest we've ever confirmed. That's why the discovery matters—it suggests bioluminescence isn't just a trick for tiny deep-sea creatures.
What does that tell us about the deep ocean itself?
That light is important down there in ways we're still learning. If so many animals evolved to produce it, it must be doing real work in the ecosystem. It's not random. It's structural.
Did they study the light itself? What does it actually look like?
Blue-green, steady and slow. Not flashing like a firefly. It glows and dims gradually. That steadiness is part of the story—it suggests a different purpose than a quick signal.