Sleeper Shark Discovery in Antarctic Waters Challenges Scientific Assumptions

Sharks can be found off the coast of every continent on earth, except for Antarctica—or so we thought. Last week, scientists with the Minderoo-UWA Deep-Sea Research Centre released footage of a massive sleeper shark cruising by one of their underwater cameras, in frigid waters long thought to be too cold for shark survival. We were all kind of scratching our heads, going, ‘I don't think you're supposed to get sharks in Antarctica’, recalls Alan Jamieson, a professor at the University of Western Australia and director of the Minderoo-UWA Deep-Sea Research Centre. According to Jamieson, this shark is the first of its kind to be found in Antarctic waters. The sleeper shark was seen swimming near the South Shetland Islands at a depth of 1,640 feet (around 500 meters) in near-freezing waters. If you’re wondering how this shark was able to survive in the coldest waters on earth, you must first consider that this wasn’t any shark; as it turns out, sleeper sharks are built different. Sleeper sharks, a group that includes the iconic Greenland shark, are big-bodied, slow-moving sharks found in cold, deep waters, especially in the Arctic and North Pacific. Rarely seen, these sharks have a super-sluggish metabolism that forces them to live life in the slow lane. Greenland sharks, for example, have a top speed of less than two miles per hour and grow less than one centimeter per year. This leisurely lifestyle allows sleeper sharks to conserve energy, which is needed to stay warm in cold water. It also allows them to live extraordinarily long lives, with some estimates suggesting they can endure for over 400 years. Another cold-water survival trick of sleeper sharks: their tissues are loaded with urea and trimethylamine N-oxide (TMAO). Urea, a common compound also found in our urine, helps sharks maintain osmotic balance with the surrounding seawater, but it also destabilizes their proteins. TMAO solves this problem by reinforcing the shark’s proteins, so much so that they can function at near-freezing temperatures. While all sharks have TMAO in their bodies, sleeper sharks have far more than most. These are true polar sharks, says Dave Ebert, a shark scientist at San Jose State University. Ebert, who was not involved with the discovery, says it was exciting but not unexpected to see a sleeper shark in Antarctica. For his part, Jamieson was still surprised when he saw a sleeper shark pop up on his Antarctic camera. In my 25-year career, I've only seen four, says Jamieson. The sleeper shark he saw in the deep Antarctic ocean, whose exact species is unknown, was one of the larger ones he’s seen, stretching somewhere between 6 and 9 feet (2-3 meters) in length. Sleeper sharks are extremely cryptic. They lead solo lives and spend much of their time in deep water. The rarity of seeing one anywhere, especially in a place they’d never been seen before, was not lost on Jamieson. There are different types of rarity in the world, and this type is absolutely astronomical, he says. He believes his camera, which he and his colleagues had set to measure the biodiversity of the area, was able to pick up a sleeper shark because it happened to be placed in a patch of warmer water. There might be a little hot water corridor there that allows them to penetrate further south than they normally would, Jamieson says. Whether it was a fluke or proof of residence remains to be seen. Nevertheless, the discovery of a sleeper shark in Antarctic waters suggests that there really isn’t anywhere in the ocean where sharks can’t eke out a living. It’s also a testament to how much we still have to do, says Jamieson. Are there other sharks in Antarctica? Are they all the way around? Are they just in this particular spot? There’s so much we don’t know.