A 2021 study revealed the largest known bioluminescent vertebrate, the kitefin shark (Dalatias licha), deepening scientific understanding of how light-producing species operate in the world’s twilight oceans. Collected during a deep-sea survey off the coast of New Zealand, the specimens were analyzed to document their unusual glowing features.
According to The Guardian, the findings involved three species of sharks that glow in the dark, observed for the first time under controlled conditions. The results point to a broader occurrence of natural light emission in deep-sea environments, raising new questions about its role in behavior, adaptation, and ecological function.
Observation From Chatham Rise Reveals Surprising Glow
In January 2020, marine researchers aboard a deep-sea trawler surveyed the Chatham Rise, an underwater plateau off the east coast of New Zealand. At depths ranging from 200 to 1,000 meters (650 to 3,300 feet), they recovered three shark species exhibiting bioluminescence. The findings were officially published on 26 February 2021 in Frontiers in Marine Science.
Dalatias Licha . Credit Mallefet Et Al.
The kitefin shark, known to reach up to 1.8 meters (5 ft 11 in) in length, was identified as the largest bioluminescent vertebrate ever recorded. It resides between 200 and 600 meters (650–1,970 feet), close to the seafloor. Its luminous body was found to emit light from multiple regions — the ventral surface, dorsal fins, and more faintly, laterally and dorsally, making it a notable example of natural light production in large vertebrates.
How the Kitefin Shark Glows
Bioluminescence in this species is caused by photocytes, specialized skin cells that emit a blue-green light with wavelengths between 455 and 486 nanometers. Unlike other organisms that rely on bioluminescent bacteria, analysis of the kitefin shark’s skin revealed no luciferin compounds or bacteria, leaving the mechanism internal. The study suggests that melatonin, a hormone more commonly associated with circadian rhythms in animals, triggers the light emission in these cells.
Lead researcher Jérôme Mallefet of the Université Catholique de Louvain remarked on the unexpected glow patterns:
The luminous pattern of the kitefin shark was unknown and we are still very surprised by the glow on the dorsal fin. Why? For which purpose?
What Purpose Does Bioluminescence Serve?
Though the precise function of the glow is unconfirmed, researchers proposed several theories. The light may aid the kitefin — a slow-moving predator with few natural enemies — in illuminating the seafloor to locate prey. Alternatively, it may assist in camouflage by reducing its silhouette when viewed from below, a strategy known as counterillumination.
Mallefet described his reaction to seeing the phenomenon live:
I nearly cried when I saw it. It was so exciting.
The two other species documented — the blackbelly lanternshark (Etmopterus lucifer) and the southern lanternshark (Etmopterus granulosus) — were also found to glow in the dark for the first time. This experimental documentation offered a new look into the diversity and ecological strategies of bioluminescent vertebrates.
Broader Significance for Deep-Sea Ecosystems
The findings suggest that light production at depth may be far more common and ecologically significant than previously believed. As the authors note:
Bioluminescence has often been seen as a spectacular yet uncommon event at sea 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.
They also emphasized the difficulty of studying such animals due to the immense size and remoteness of their habitat.
The two other Etmopterus sharks were also not documented, so it is the first time.
Not All Glowing Sharks Are Bioluminescent
While the kitefin shark is the largest bioluminescent vertebrate, it is not the largest glowing vertebrate overall. That title belongs to the whale shark (Rhincodon typus), which can grow to 18.8 meters (61.7 feet). Its glow is not caused by bioluminescence but by biofluorescence, a distinct process where absorbed light is re-emitted at a visible wavelength, typically under ultraviolet exposure.
Whale Shark Underwater. Credit Canva
This distinction matters when comparing light-producing strategies across marine species and adds complexity to the field of deep-sea optical biology.
Need for Continued Research
As bioluminescence emerges as a key trait in oceanic survival strategies, especially among bioluminescent vertebrates, researchers are calling for further expeditions. Understanding how and why these sharks glow may provide new insight into predator-prey dynamics, communication, and evolution in the planet’s most expansive ecosystem.
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.