The sleeper shark is a family of sharks known by its scientific name somniosidae. There are many different species of sleeper shark but two most well-known are the Pacific sleeper shark and the Greenland shark. Other sleeper sharks are commonly referred to as dogfish.
The Pacific sleeper shark has a wide habitat range and has been spotted in seas around the arctic, Japan, Australia and throughout most of the pacific. It is large, with specimens at least 23 feet (7 meters) having been seen in the wild. Not much is known about the shark, as it is a deep sea shark rarely spotted near the surface. Like many other fish who live on the ocean floor, it is slow-moving and has adapted to survive in extremely cold weather, as low as 40 degrees Fahrenheit (4 Celsius). It hunts live prey, and has a mouth that is specially designed to tear large chunks of flesh to devour whole. The stomach contents of deceased pacific sleeper sharks show a diverse palette; dolphins, snails, crabs and seals all seem to be prey for the massive fish. There is also evidence to suggest that the pacific shark even hunts giant squid, making them and the sperm whale the only known predators of that giant creature.
The Greenland sleeper shark is closely related to the pacific variety, and is similar in size. It too can grow upwards of 20 feet (6 meters) in length, and often weighs more than 2,200 pounds (1,000 kilograms). It too is also comfortable in extreme weather and depths. It has been found at depths as low as 7,200 feet (2,200 meters). Like its name suggests the Greenland sleeper shark is native to the Greenland area, and is also found along the shores of upper North America and in parts of Europe. Stomach contents of captured or beached Greenland sharks have been found to contain the remains of polar bears, seals, horses and squid.
While it was once believed that the shark was primarily a scavenger eater that feasted on the remains of dead animals, researchers have since witnessed firsthand the massive shark attacking live caribou and other large animals.
Greenland sleeper shark is considered to be a delicacy in both Greenland and Iceland, but it must be prepared carefully as the flesh of the shark is poisonous. Typical preparation of Greenland shark involves it being boiled several times over until the poison is removed. It is also often left hanging in barns for months, where it can dry and ferment. This process can last several months. The final result is a dish called hakari, which is known for its incredibly strong taste that has caused violent reactions in those not used to it.