Sharks in the Dark: Revisiting the Deep Sea
SHOW NOTES
The deep sea is a place that feels closer to outer space than to the world we know — a silent realm of cold, crushing pressure, where no light reaches but life glows of its own accord. It’s also the place where Dr Brit Finucci feels most at home. A fisheries scientist based in New Zealand, Brit has dedicated her career to understanding the sharks and chimaeras that live beyond the edge of the continental shelf — creatures that few people ever see, but that hold vital clues to the health of our oceans.
Her fascination with the deep began by accident [10.00]. When she first moved from Canada to New Zealand in 2011, she had no intention of studying these strange creatures of the dark. But, while volunteering with local NGOs, she met veteran shark scientist Malcolm Francis, who handed her a report filled with murky photographs of “black blobs” — deep-sea sharks that, at the time, almost no one had studied. He told her to read it. She politely declined. He handed it back. “Go work on deep-sea sharks,” he insisted.
That push sent Brit into a world she never expected. A few months later, she was aboard a research trawler, seasick and exhausted but unable to look away from the creatures rising from the nets — glowing eyes, pale bodies, forms so alien they looked sculpted from another planet. “It was surreal,” she says. “Miserable and mesmerising at the same time.” That moment cemented a lifelong love for the deep.
Today, Brit is one of the world’s leading experts on deep-sea chondrichthyans — sharks, rays, and chimaeras that spend most of their lives below 200 metres [12.30]. “That’s where we start to lose the light,” she explains. “It gets darker, colder, and the pressure builds with every metre you descend.” In New Zealand’s waters, where the seafloor plunges quickly into oceanic trenches, “deep” can mean thousands of metres. The temperature may fall close to freezing, and sunlight disappears entirely, yet this realm is far from empty. It is, as Brit describes it, “the largest ecosystem on the planet — bursting with species we barely know exist.”
Contrary to popular imagination, the deep sea is textured and alive — from smoking hydrothermal vents and ancient corals to undersea ridges and towering seamounts [14.51]. In one case, scientists even observed skates using volcanic vents to warm their eggs, tucking them near the heat to speed their development. New Zealand’s deep waters, among the world’s deepest, host an astonishing range of these environments — a fact that continually surprises even those who study them.
Within this landscape live more than 500 known species of deep-water sharks and rays, and likely hundreds more await discovery [18.30]. Some inhabit the twilight zone around 200–1,000 metres, while others are found much deeper. The record holder, the Portuguese dogfish, has been observed at nearly 3,700 metres — almost four kilometres below the surface — followed closely by a ghost shark recorded at 3,100 metres. Most species, Brit notes, rarely venture below 2,000 metres, but a few push the boundaries of what life can endure.
Studying such creatures requires patience, creativity, and a certain appetite for mystery [20.10]. Much of what we know about the deep sea has come from chance encounters — trawlers hauling up specimens from hundreds of metres down. “I sometimes feel like a vulture,” Brit admits, “picking over what people don’t want.” These incidental catches, called bycatch, form the basis of decades of discovery. Even now, when improved cameras and submersibles can descend to the abyss, many species are still known only from a handful of specimens.
Months at sea are part of the job. Research voyages can last four weeks or more, with the nearest land a twelve-hour steam away. Nets are deployed into the darkness, and each haul brings an element of surprise. “It’s like Christmas every time,” Brit laughs. “You never know what you’ll find — sometimes species you’ve never seen before.” Once, she recalls, a colleague even received a shark in the post — a preserved goblin shark, mailed in a box from someone who didn’t know what to do with it.
These oddities are part of the allure [25.45]. Deep-sea sharks are full of contradictions: primitive and highly evolved, fragile yet perfectly adapted to survive in an environment that would crush almost anything else. Unlike bony fish, they have no swim bladder — an air-filled organ that would implode under deep pressure. Instead, they rely on enormous, oily livers to stay buoyant. “They’re an absolute mess to handle,” Brit laughs, “and the smell never comes out of your clothes.”
And then there’s another, somewhat more glamorous, adaptation [30.30]. Many deep-sea sharks can glow in the dark, thanks to a process called bioluminescence. Lanternsharks, for instance, carry intricate constellations of light-producing cells across their bodies, each species glowing in its own pattern. Some may use this to attract prey, communicate, or camouflage themselves in the faint shimmer from above. The kitefin shark — sometimes called the “seal shark” — is thought to be the largest glowing vertebrate on Earth, its belly emitting a soft blue-green light as it drifts through the dark.
Among Brit’s favourite creatures is the prickly dogfish, a small but ferocious little shark that rarely exceeds 75 centimetres in length [35.00]. Covered in sharp, raised denticles that make it rough to the touch, it looks almost cartoonish — all chunky body and tiny fins — but appearances are deceiving. Prickly dogfish are predators with a peculiar taste: they feed almost exclusively on the eggs of other sharks, rays, and chimaeras. In captivity, they’ve been seen hovering over an egg case before planting themselves on it and sucking out the contents in one swift movement. “They look ridiculous,” Brit says fondly, “but they’re also these higher order predators”.
Another deep-sea icon is the frilled shark — a long, eel-like species often dubbed a “living fossil” [40.12]. Brit has only ever held one, caught during a 2020 research survey. Its mouth is lined with rows of trident-shaped teeth, hundreds of them, perfectly arranged like white lace. Frilled sharks likely cruise with their mouths open, snagging squid and other soft-bodied prey that stumble into their toothy snare. Rarely seen and even more rarely studied, they seem to appear in cycles — every few years, one will turn up as if to remind scientists just how little they know.
And then there are the ghost sharks, or chimaeras — ethereal relatives of sharks and rays, named for their silvery sheen and ancient lineage [50.53]. Brit has spent years studying them and is the lead author of Ghost Sharks of the World, a forthcoming global guidebook to the group. “They’re found in every ocean except the polar seas,” she explains, “but for most species, we know virtually nothing.” Some are known from a single specimen. Others, like the elephant fish (or ‘Australian ghost shark) of New Zealand and Australia, are better studied, revealing a diet of crustaceans and worms and a lifespan that may stretch decades.
Chimaeras come in all sizes, from half-metre miniatures to giants longer than a human. Their skin shimmers with iridescence, and each sports a fearsome dorsal spine. Brit describes one extraordinary specimen she’s working on now — a large black ghost shark nearly as tall as she is, likely a species new to science. Among the 59 recognised species so far, new ones continue to emerge every year.
One of her proudest discoveries is the Australian narrow-nosed spookfish, described in 2024 after years of work [56.00]. The species had long been mistaken for a similar North Atlantic chimaera, hiding in plain sight until careful genetic and anatomical studies revealed it was unique to New Zealand and Australian waters. The specimen she named “Colin” — a long-snouted, wide-eyed ghost of the deep — became the type for the species. Its elongated nose, lined with sensory pores, may help it detect prey on the seafloor, though the exact purpose remains a mystery. “There are still so many mysteries down there,” Brit says. “Every time we think we understand something, the deep reminds us we don’t.”
But fascination is shadowed by concern [1.00.03]. Despite living in remote, inhospitable places, deep-sea sharks are far from safe. Their greatest threat comes not from predators but from us. Many are caught incidentally in deep-water trawl and longline fisheries, unable to survive the sudden change in pressure when brought to the surface. Some are kept for their oil — particularly gulper sharks, whose livers produce squalene used in cosmetics and pharmaceuticals. “Most species have little or no commercial value,” Brit explains, “so there’s been little incentive to monitor what’s caught. We often have no idea how much bycatch occurs, or how it’s affecting populations.”
Her current project, supported by the Save Our Seas Foundation, focuses on exactly that problem. By tagging gulper sharks caught in longline fisheries and monitoring whether they survive when released, Brit hopes to understand their resilience — or vulnerability — to capture. So far, her results are both sobering and inspiring. Some tagged sharks have survived and sent back data, revealing how they move through their shadowy world hundreds of metres below. “One tag even washed up on a remote beach months later,” she says, “after travelling through currents and storms. To hold that tag again, knowing where it had been — that was incredible.”
Each recovered tag is a message from the deep — a tiny pocket of information from an unseen realm. For Brit, they symbolise hope: that with better understanding, we might learn to coexist with the ocean’s most mysterious inhabitants. “The deep sea is full of life we’re only just beginning to know,” she says. “It’s not empty. It’s not silent. It’s alive, and it matters.”
ABOUT OUR GUEST
Brit grew up in Canada but completed her PhD at the Victoria University of Wellington in New Zealand, studying the ecology of deep-sea chondrichthyans in the region. Her research described the life histories of poorly studied species caught as by-catch in deep-sea fisheries, including the prickly dogfish, longnose spookfish and black ghost shark. She is now a fisheries scientist with the National Institute of Water and Atmospheric Research and is chair of the deep water chondrichthyans working group for the IUCN Species Survival Commission Shark Specialist Group. She was also awarded the prestigious Eugenie Clark Award in 2021.
Twitter: @BritFinucci
Instagram: @britfinucci
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