For decades, divers and scientists alike believed that sharks roamed every ocean on Earth—except one. The icy waters of Antarctica were thought to be simply too cold, too extreme, for any shark to survive. But the ocean, as it so often does, has revealed yet another surprise.
Illustration of a sleeper shark
In January 2025, researchers from the Minderoo-UWA Deep-Sea Research Centre captured extraordinary footage: a large sleeper shark gliding silently past a deep-sea camera in Antarctic waters. The sighting took place near the South Shetland Islands, at a depth of around 500m, in water hovering near freezing.
Even for seasoned scientists, the moment was startling. As marine researcher Alan Jamieson later admitted, seeing a shark there felt almost impossible. Until now, no sleeper shark had ever been recorded in these southernmost seas.
Built for the cold
This was no ordinary shark encounter. Sleeper sharks are among the ocean’s most mysterious and slow-living predators. Closely related to the legendary Greenland shark, they inhabit deep, cold waters in regions such as the Arctic and North Pacific.
Everything about them is adapted to extremes. They move slowly—rarely exceeding a gentle cruising speed—and grow at an almost unimaginable pace of less than a centimetre per year. This unhurried existence allows them to conserve energy in environments where every calorie matters.
It also contributes to one of the most astonishing traits in the animal kingdom: longevity. Some Greenland sharks are believed to live for centuries, possibly over 400 years, making them among the longest-living vertebrates on Earth.
The chemistry of survival
Surviving in near-freezing water requires more than just a slow lifestyle. It demands remarkable internal chemistry.
Sleeper sharks are packed with compounds such as urea and trimethylamine N-oxide (TMAO). Urea helps balance their internal fluids with the surrounding seawater, but it can destabilise proteins. TMAO counteracts this effect, stabilising proteins so they continue to function even in the coldest conditions.
All sharks possess TMAO, but sleeper sharks carry it in especially high concentrations—one of the keys to their success in polar environments. As shark expert Dave Ebert explains, these animals are true specialists of the cold, perfectly adapted to life at the edge of what is biologically possible.
A rare encounter
Encounters with sleeper sharks are rare anywhere in the world. They are solitary, elusive, and spend much of their lives in deep, dark waters far beyond the reach of most divers.
The individual captured on camera—estimated to be between two and three metres long—was a remarkable sight. Even more remarkable is how seldom such encounters occur. In a career spanning 25 years, Jamieson himself has only seen a handful.
What drew this shark so far south remains uncertain. One possibility is the presence of slightly warmer water currents—a kind of hidden corridor through the deep sea—allowing these cold-adapted sharks to venture into Antarctic territory.
Expanding the map
Whether this sighting represents a lone wanderer or the first glimpse of a hidden population is still unknown. But it challenges long-held assumptions about where sharks can live.
For divers, explorers and ocean lovers, it is a powerful reminder that the ocean still holds secrets in even its most remote and inhospitable corners. And perhaps most exciting of all, it suggests that Antarctica—long thought to be shark-free—may yet reveal more silent cruisers moving through its icy depths. The question now is not if sharks can survive there, but how many are waiting to be discovered.
