Occasionally, we catch sight of them. The very first underwater photos of Greenland sharks were snapped in 1995. Thick, torpedo-like bodies. Surprisingly small fins. A short round snout and little eyes.

These sharks belong to the sleeper shark family, and they can grow to sizes—21 feet long—that match great white sharks. They cruise through chilly waters in the Arctic and North Atlantic at just about 0.76 miles per hour, reports Wired. When they want they can push to a maximum of 1.7 miles per hour.

But all this—everything that we thought we knew about Greenland sharks—doesn’t account for the animal that an undersea vehicle recorded in the depths of the Gulf of Mexico. The strange encounter, the deepest any shark had been seen in the Gulf, was definitely with a sleeper shark, though the researchers couldn’t be sure if it was a Greenland shark. But in 1995, another group reported a Greenland shark off the coast of Savannah, Georgia.

The problem with spotting these sharks is that they like staying deep. These odd sightings might indicate that they don’t just hang out in the Arctic. Reports of Greenland sharks off the coast of Canada, Portugal, France, Scotland and Scandinavia start to tell a story of a fish whose world is wider than we thought. "They may be everywhere that's cold enough and deep enough," Aaron MacNeil of the Australian Institute of Marine Science told the BBC.

Fisherman used to pull tens of thousands of Greenland sharks from the sea up until the 1960s, which seems to indicate abundance. The harvest stopped not because of declining numbers but because there wasn’t no longer much reason to continue it. The sharks' liver oil had been used as industrial lubricant and lamp oil; Greenland shark meat is toxic and only edible if fermented for weeks. As you might expect, this traditional Icelandic dish isn’t in high demand.

As a result, Greenland sharks have remained largely mysterious. We know they eat fish, but some have turned up with seals, reindeer, horses, moose and even polar bear parts in their stomachs. These sharks probably fed on already dead carcasses that had fallen into the water: with their slow movement, it's not clear how how they could nab seals, which are much faster swimmers. While dead seals with strange spiral lacerations have also turned up and some people proposed Greenland sharks as the killer, researchers remain very skeptical. (Propeller injuries seem more likely.)

Still, one of their reasons was that Greenland sharks wouldn’t be in the waters of the United Kingdom, and that assessment might deserve a second look.