Greenland shark

The Greenland shark (Somniosus microcephalus), also called the grey shark or gurry shark, is a large member of the sleeper shark family (Somniosidae), making it a close relative of the Pacific and southern sleeper sharks. It lives in the North Atlantic and Arctic Oceans and is famous for its extremely long life, though scientists know little about it because its habitat is deep and remote.

This species has the longest lifespan of any vertebrate, estimated at 272 to 510 years. It ranks among the largest living sharks, with a confirmed maximum length of 6.4 meters (21 feet) and a weight over 1,000 kilograms (2,200 pounds). Greenland sharks reach sexual maturity at about 150 years old, and females give birth to live pups after a gestation period estimated at 8 to 18 years. They are generalist feeders that eat a wide range of available food, including carrion.

The shark’s meat is toxic to mammals due to high levels of trimethylamine N-oxide, though a treated version is eaten in Iceland as the pungent dish kæstur hákarl. Because they live deep in remote northern waters, they are not considered a threat to humans. A possible attack on two British fishermen occurred in August 1936, but the shark species was never identified.

Adults typically grow to about 4 to 5 meters (13 to 16 feet). The largest confirmed specimen was 6.4 meters long and weighed around 1,023 kilograms (2,255 pounds). The International Game Fish Association record for the species is 775 kilograms (1,709 pounds). It rivals the Pacific sleeper shark (possibly up to 7 meters or 23 feet) for the largest in the family Somniosidae. Genetic data show that Greenland sharks split from ancestral sleeper sharks in the Canadian Arctic about 1 to 2.34 million years ago during the Pleistocene, likely due to glacial changes that isolated marine populations, driving adaptations for cold, deep water.

The shark has a thick body, a short rounded snout, small eyes, and small dorsal and pectoral fins. Its five gill openings are very small for its size. Females are usually larger than males, and males mature at a smaller size. Coloration ranges from pale creamy-gray to blackish-brown, usually uniform, though whitish spots or faint dark streaks sometimes appear on the back.

The shark is often infested with the copepod *Ommatokoita elongata*, a crustacean that attaches to its eyes. This copepod may glow, possibly attracting prey in a mutualistic relationship, but this idea is unconfirmed. The parasites can damage the eyes, causing ulceration, mineralization, and corneal edema, leading to near blindness. This does not seem to affect the shark’s lifespan or hunting ability, as it relies heavily on smell and hearing. The Greenland shark’s genome, published in 2024, is 6.45 billion base pairs long.

When feeding on large carcasses, the shark rolls its jaw. The 48 to 52 upper teeth are thin, pointed, and lack serrations, acting as anchors while the lower jaw cuts chunks. The 48 to 52 lower teeth are broad, square, interlock, and have short, smooth cusps pointing outward; teeth in the two halves of the lower jaw pitch in opposite directions.

Like other elasmobranchs, the Greenland shark has high levels of urea and trimethylamine N-oxide (TMAO) in its tissues, which aid buoyancy and act as osmoprotectants. TMAO also counteracts the protein-destabilizing effects of urea and deep-water pressure. Its presence increases with depth in both elasmobranch and teleost fish. The shark’s blood contains three main types of hemoglobin, each with two copies of alpha globin and two copies of three very similar beta subunits. These types have very similar oxygen and carbon monoxide binding properties, unaffected by urea. They show identical electronic absorption and resonance in Raman spectroscopy, suggesting identical or very similar heme-pocket structures. The hemoglobins have a lower affinity for oxygen than those of temperate sharks, an adaptation to deep water.

When hauled onto a deck, the shark thrashes its tail violently, making it dangerous to approach. Sailors typically kill it quickly. Cut pieces continue to contract for some time after death, making the shark extremely hard to kill and unsafe to touch near its mouth even after the head is cut off. According to Crantz, this movement can be seen three days later if the part is stepped on or struck.

The Greenland shark prefers cold water (−1.1 to 7.4 °C or 30.0 to 45.3 °F) and deep water (100 to 1,200 meters or 330 to 3,940 feet). As an ectotherm in near-freezing conditions, it is sluggish and slow, with the lowest swim speed and tail-beat frequency for its size of any fish, likely linked to its slow metabolism and extreme longevity. It swims at an average of 0.34 meters (1 foot 1 inch) per second, with a fastest cruising speed of about 0.74 meters (2 feet 5 inches) per second.