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| Discovered in the deep: the sharks that glow in the dark | Discovered in the deep: the sharks that glow in the dark |
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| Measuring up to 1.8 metres, kitefin sharks are by far the biggest bioluminescent sharks to have been found | Measuring up to 1.8 metres, kitefin sharks are by far the biggest bioluminescent sharks to have been found |
| Discovered in the deep: the ‘mermaid’s wineglass’ single-cell organism | Discovered in the deep: the ‘mermaid’s wineglass’ single-cell organism |
| Kitefin sharks (Dalatias licha) have been known about since the 18th century, but it was only in January 2020 that scientists saw them glowing in the dark for the first time. They are not the only bioluminescent sharks – roughly one in 10 species has that ability – but at up to 1.8 metres, kitefins are by far the biggest that have been found.Jérôme Mallefet, a biologist at the Université catholique de Louvain, Belgium, had been hoping for years to see a glowing kitefin shark. “That was one of my holy grails, to see that big shark glowing,” he says. Studies in the 1980s suggested they have light-emitting organs in their brown skin, but nobody had seen one alive and illuminated. | Kitefin sharks (Dalatias licha) have been known about since the 18th century, but it was only in January 2020 that scientists saw them glowing in the dark for the first time. They are not the only bioluminescent sharks – roughly one in 10 species has that ability – but at up to 1.8 metres, kitefins are by far the biggest that have been found.Jérôme Mallefet, a biologist at the Université catholique de Louvain, Belgium, had been hoping for years to see a glowing kitefin shark. “That was one of my holy grails, to see that big shark glowing,” he says. Studies in the 1980s suggested they have light-emitting organs in their brown skin, but nobody had seen one alive and illuminated. |
| His dream came true 1,000 miles east of New Zealand, onboard a fisheries research vessel that was using a huge, commercial-scale trawl net to survey species inhabiting the twilight zone, about 800 metres down. Previous surveys of the area regularly caught kitefin sharks, but Mallefet was the first person to carefully transfer them into a darkened room. With the lights turned down low, he saw the live kitefin sharks had a blue-green glow across their bodies. | His dream came true 1,000 miles east of New Zealand, onboard a fisheries research vessel that was using a huge, commercial-scale trawl net to survey species inhabiting the twilight zone, about 800 metres down. Previous surveys of the area regularly caught kitefin sharks, but Mallefet was the first person to carefully transfer them into a darkened room. With the lights turned down low, he saw the live kitefin sharks had a blue-green glow across their bodies. |
| Smaller species of deep-sea sharks use their lights for survival and to communicate with one another. Some have spines on their backs that are illuminated like lightsabers, warning intruders to leave them alone. Some males illuminate their claspers, the shark equivalent of a penis, a trick that presumably helps attract mates. And many of the sharks have glowing bellies, which help them hide their silhouettes from predators lurking beneath them in the deep, by blending into the blue light from the surface. | Smaller species of deep-sea sharks use their lights for survival and to communicate with one another. Some have spines on their backs that are illuminated like lightsabers, warning intruders to leave them alone. Some males illuminate their claspers, the shark equivalent of a penis, a trick that presumably helps attract mates. And many of the sharks have glowing bellies, which help them hide their silhouettes from predators lurking beneath them in the deep, by blending into the blue light from the surface. |
| But kitefin sharks are so big they don’t need to worry much about hiding from other predators. | But kitefin sharks are so big they don’t need to worry much about hiding from other predators. |
| Mallefet believes their glowing underside may illuminate the seabed to help them hunt, while at the same time letting them sneak up on prey without being seen. | Mallefet believes their glowing underside may illuminate the seabed to help them hunt, while at the same time letting them sneak up on prey without being seen. |
| This would also explain how kitefins have been found with much faster-swimming sharks in their stomachs. Kitefins are among the slowest of all sharks; at their normal cruising speed, it would take them more than 10 minutes to amble 100 metres. These big, slow sharks are probably gliding around the twilight zone and launching surprise attacks on prey that rest on the bottom. “Just like a cat jumping on the mouse,” says Mallefet. | This would also explain how kitefins have been found with much faster-swimming sharks in their stomachs. Kitefins are among the slowest of all sharks; at their normal cruising speed, it would take them more than 10 minutes to amble 100 metres. These big, slow sharks are probably gliding around the twilight zone and launching surprise attacks on prey that rest on the bottom. “Just like a cat jumping on the mouse,” says Mallefet. |
| To produce light, sharks have tiny cup-shaped structures, called photophores, dotted across their skin. In the centre of each cup are light-emitting cells, and a lens on top directs the light outwards. Bioluminescence in sharks is controlled by hormones. | To produce light, sharks have tiny cup-shaped structures, called photophores, dotted across their skin. In the centre of each cup are light-emitting cells, and a lens on top directs the light outwards. Bioluminescence in sharks is controlled by hormones. |
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| The ocean is one of the world’s last truly wild spaces. It teems with fascinating species that sometimes seems to border on the absurd, from fish that look up through transparent heads to golden snails with iron armour. We know more about deep space than deep oceans, and science is only beginning to scratch the surface of the rich variety of life in the depths. | The ocean is one of the world’s last truly wild spaces. It teems with fascinating species that sometimes seems to border on the absurd, from fish that look up through transparent heads to golden snails with iron armour. We know more about deep space than deep oceans, and science is only beginning to scratch the surface of the rich variety of life in the depths. |
| As mining companies push to industrialise the sea floor and global leaders continue to squabble over how to protect the high seas, the Guardian's Seascape series, Discovered in the deep, will profile some of the most recently discovered weird, wonderful, majestic, ridiculous, hardcore and mind-blowing creatures. They reveal how much there is still to learn about the least known environment on Earth – and how much there is to protect. | |
| “They use two or three hormones, at least, to trigger or slow down the light emission,” says Mallefet. It is a slow process, and sharks can glow for an hour or two. “Once they light up, they cannot change rapidly,” he says.One aspect of shark bioluminescence that remains enigmatic, including for kitefin sharks, is how exactly they produce light. Many glowing animals house symbiotic bacteria in their bodies that act as luminous partners, but none have been found in sharks. Other glowing creatures produce chemicals that carry out light-emitting reactions. | “They use two or three hormones, at least, to trigger or slow down the light emission,” says Mallefet. It is a slow process, and sharks can glow for an hour or two. “Once they light up, they cannot change rapidly,” he says.One aspect of shark bioluminescence that remains enigmatic, including for kitefin sharks, is how exactly they produce light. Many glowing animals house symbiotic bacteria in their bodies that act as luminous partners, but none have been found in sharks. Other glowing creatures produce chemicals that carry out light-emitting reactions. |
| In sharks, these are also proving difficult to track down. “It’s still a mystery,” says Mallefet. | In sharks, these are also proving difficult to track down. “It’s still a mystery,” says Mallefet. |