Blue Zoo: Greenland Shark

Featuring one amazing marine animal per week.

The Greenland shark, also known as the sleeper shark, lives in and around the Arctic and spends most of its time in deep, cold water more than 6,000 feet (1.8 km) below the surface. Since it only rarely comes into shallow water, this shark is difficult to study, and very little is known about it. Here is some of what we do know!

The Greenland shark is the biggest fish in the Arctic, reaching over 20 feet long (6 meters). It’s also the second-largest carnivorous shark in the world, after the great white. It is difficult to gauge the age of a Greenland shark but, based on limited evidence, some believe they can reach more than 200 years old. If that’s true it would be the world’s longest-living vertebrate, but this hasn’t been confirmed.

The Greenland shark is usually a slow swimmer but it is also capable of sudden bursts of speed. They are thought to be primarily scavengers, eating whatever they can find, but also hunt opportunistically. Seaweed, jellies, and small fish have been found in the stomachs of these sharks, in addition to chunks of whale meat, entire seals, and even reindeer!

Greenland sharks sometimes acquire parasites in their eyes that cause blindness. The parasite is a copepod that eats the corneal tissue in the eye. However, this shark spends so much time in the pitch-black deep sea environment and it has such acute senses that it can easily survive even when blind.

The Greenland shark is entirely cold-blooded so its body temperature is the same as the water it in habits, which is almost always less than 33 ºF (1 ºC). To cope, it has a slow metabolism and compounds in its flesh that prevent it from freezing. Because of those anti-freeze compounds (which include urea and trimethylamine oxide) Greenland shark meat is toxic when eaten raw. Many fishermen therefore think of it as a trash fish. However, it was historically hunted for its oil, and a lengthy purification process can make it edible. In fact, fermented Greenland shark meat, or Hákarl, is even considered a delicacy in Iceland.

Photo courtesy moohaha, via Flickr creative commons.