Greenland Shark (Somniosus microcephalus): Facts and Age

What does a Greenland shark look like?

The Greenland shark is a heavy, thick-bodied shark with a short, rounded snout and tiny eyes. Its scientific name, microcephalus, means “small head.” The two dorsal fins are small and set far back, there is no fin spine, and the pectoral fins are small and rounded. The five gill openings are very small for an animal of its size, and the tail has a fairly short lower lobe.

Its color ranges from pale brownish-gray to almost black, sometimes with faint dark lines or pale spots on the back. The skin is covered in small, thornlike scales called denticles. Many Greenland sharks have a pale, ribbon-like parasite hanging from one or both eyes.

It belongs to the sleeper sharks (family Somniosidae), a group of slow, deep-water sharks. Its closest relatives are the Pacific sleeper shark of the North Pacific and the southern sleeper shark of the Southern Ocean, which look so similar that experts sometimes find them hard to tell apart.

How big is a Greenland shark?

The Greenland shark is one of the largest sharks in the world and by far the largest fish of the Arctic. Females grow larger than males.

Adults usually measure about 3–5 m (10–16 ft). Large ones weigh several hundred kilograms, and the heaviest reported are around 1,000 kg (2,200 lb) or more. Claims of sharks 7 m (23 ft) long exist but are not well documented.

These sharks grow extremely slowly. A shark tagged off Greenland in 1936 and caught again in 1952 had grown only about 8 cm (3 in) in 16 years, and studies suggest growth of about 1 cm (0.4 in) a year or less.

Where do Greenland sharks live?

Greenland sharks live in the Arctic Ocean and the North Atlantic, from Arctic Canada, Baffin Bay and Greenland to Iceland, the Faroe Islands, Norway, Svalbard and the Barents Sea. They also occur in the Gulf of St. Lawrence and off Newfoundland, and strays occasionally reach the North Sea and the British Isles.

They prefer very cold water, usually between about −1 and 7 °C (30–45 °F). In the far north, where the surface water is cold enough, they can be found in shallow water and even under sea ice, especially in winter and spring. Farther south they live deeper, on the continental slopes. A submersible filmed one at about 2,200 m (7,200 ft) off North Carolina, and in 2013 a Greenland shark was caught at about 1,750 m (5,740 ft) in the Gulf of Mexico.

Tagging studies show that Greenland sharks can travel long distances over months and often move up and down through the water column, but much about their movements remains unknown.

What do Greenland sharks eat?

Greenland sharks are both hunters and scavengers, and they will eat almost anything they can swallow. Their diet changes with size. Small sharks eat mostly squid and small fish, while large sharks eat bigger fish such as cod, Greenland halibut, redfish, wolffish and skates, as well as seals.

Remains of ringed, bearded and other seals are common in their stomachs. How such a slow shark catches seals is still a puzzle; one idea is that it ambushes seals while they sleep in the water. Greenland sharks also scavenge dead whales and other carcasses, and the remains of reindeer, horses and polar bears found in their stomachs probably came from animals that were already dead.

Their teeth are built for cutting. The upper teeth are narrow and pointed to hold prey, while the lower teeth are broad, square and interlocking, with blades angled to the side. By rolling its head and jaw, a Greenland shark can carve large chunks out of a carcass. It can also suck smaller prey into its mouth.

How slow is a Greenland shark?

The Greenland shark is the slowest-swimming fish for its size ever measured. In a 2012 study off Svalbard, tagged sharks cruised at an average of only about 0.34 m per second, roughly 1.2 km/h (0.76 mph), and their fastest cruising speed was about 2.7 km/h (1.7 mph). Their tails swept from side to side only about once every seven seconds.

Cold water slows the chemistry of muscles, and a big, cold-bodied fish saves energy by moving slowly. Learn more in How slow is a Greenland shark? and see where it ranks among the slowest animals.

How long do Greenland sharks live?

Greenland sharks have no hard bones with growth rings, so their age was a mystery until 2016. That year, scientists dated the oldest part of the eye lens, which forms before birth, using radiocarbon. Their results suggested that Greenland sharks live at least 272 years. The largest shark examined, a female about 5 m (16.5 ft) long, was estimated at 392 years, with a likely range of 272–512 years.

The same study suggested that females do not mature until they are about 150 years old. These estimates have wide uncertainty, but they make the Greenland shark the longest-lived animal with a backbone known to science. For details on the method and its limits, read How long do Greenland sharks live? or compare it with other longest-living animals.

Eye parasites and senses

Many Greenland sharks carry a parasitic copepod, a small crustacean called Ommatokoita elongata, attached to the cornea of the eye. It grows to about 3 cm (1.2 in) long and can scar the eye and damage vision. It was once suggested that the pale parasite might attract prey by glowing, but there is no evidence for this.

Partial blindness does not seem to stop the sharks from feeding. In the dark depths, Greenland sharks probably rely mainly on their excellent sense of smell, which draws them to carcasses from far away, and on the lateral line, a system of sensory canals that detects vibrations in the water. Studies of their eyes suggest that, when not damaged, they are well adapted to very dim light.

Reproduction

Very little is known about how Greenland sharks breed, because pregnant females are almost never caught. Like other sleeper sharks, they give birth to live young: eggs hatch inside the mother, and the pups develop there before birth. Litters have been estimated at up to about 10 pups, each about 35–45 cm (14–18 in) long at birth. How long pregnancy lasts is unknown, although scientists suspect it may be very long.

Because females appear to mature only at around 150 years of age and then produce small litters, a population takes a very long time to replace sharks that are lost.

Myths and facts

Myth: the Greenland shark is the oldest animal on Earth. It is the oldest known vertebrate, but not the oldest animal. An ocean quahog clam named Ming was aged at 507 years from its shell, and some deep-sea sponges and corals are thought to live for thousands of years.

Myth: Greenland sharks are known to be 500 years old. The often-quoted figure of around 400–500 years is the upper part of a wide estimate. The best-supported conclusion is that they live at least about 270 years.

Myth: all Greenland sharks are blind. Many carry eye parasites that damage vision, but not every shark is affected, and their eyes are adapted to see in very dim light.

Are Greenland sharks dangerous?

There are no confirmed attacks by Greenland sharks on people. They live mostly in cold, deep water where people rarely swim, and divers who have met them under Arctic ice describe them as slow and unaggressive. Old stories of human remains in Greenland shark stomachs have never been verified. As with any large wild predator, the safest approach is to watch from a distance and leave it alone.

The flesh is another matter. Fresh Greenland shark meat contains high levels of trimethylamine N-oxide and urea, which help the shark cope with cold and pressure but make the meat toxic to people and dogs. In Iceland, the meat is fermented and then hung to dry for months to make hákarl, a traditional dish famous for its strong ammonia smell.

Threats and conservation status

The IUCN Red List assessed the Greenland shark as Vulnerable in 2020, with a decreasing population. From the 19th century until the middle of the 20th, Greenland, Iceland and Norway ran large fisheries for its oil-rich liver, which faded as synthetic oils replaced it. Today the main threat is bycatch: Greenland sharks are caught by accident on longlines and in trawls and gillnets set for other fish, especially Greenland halibut, and some of those released are thought to die afterward.

Their extremely slow growth, late maturity and small litters make them highly vulnerable, since a shark killed today may have been born centuries ago. As Arctic sea ice shrinks, new fisheries and shipping are expected to expand into their range, so scientists are calling for better monitoring and ways to release sharks alive.