Greenland sharks (Somniosus microcephalus) belong to a family of sharks called sleeper sharks, which move slowly and stealthily through the water. They are the longest-living vertebrates, or animals with backbones, surviving for up to hundreds of years in the deep, cold waters of the Arctic and North Atlantic oceans.
These sharks sneak up on live prey and scavenge dead animals, including other sharks, seals, drowned horses and polar bears. Scientists are learning more and more about these mysterious sharks that rarely encounter humans, but there are still many unknowns surrounding their lifestyles.
How big are Greenland sharks?
Greenland sharks are among the biggest sharks in the world; they grow up to 24 feet (7.3 meters) long and weigh up to 2,645 pounds (1,200 kilograms), according to the St. Lawrence Shark Observatory (ORS). That's longer than great white sharks (Carcharodon carcharias), which are estimated to grow up to 20 feet (6 m) long, with unconfirmed reports suggesting they can reach 23 feet (7 m) in length, according to the Florida Museum of Natural History.
Size: Up to 24 feet (7.3 m)
Life span: 272 years (estimate)
Conservation status: Vulnerable
Greenland sharks have cylindrical bodies that can be black, brown, gray or a mixture of all three colors, and they may have spots. These sharks also have teeth-like scales, called dermal denticles, covering the surfaces of their bodies. The scales reduce drag and help the sharks move more silently through the water, according to the ORS. A Greenland shark's mouth contains 48 to 52 teeth in its upper jaw and 50 to 52 teeth in its lower jaw. The upper teeth are pointed, to help the sharks hold on to larger food, while the lower teeth are wide and curved sideways so the sharks can carve out round chunks of flesh from prey by moving their head in a circular motion, according to the ORS.
Ocean parasites called Ommatokoita elongata are often attached to the eyes of Greenland sharks. The parasite tends to live in just one of the shark's eyes, but this can still render the shark partially blind. Because the sharks rely more on their other senses to catch prey in the dark ocean waters, the parasites don't seem to affect the sharks much, according to the Florida Museum of Natural History.
How long do Greenland sharks live?
Greenland sharks' exact life span is unknown, but they are considered the longest-living sharks, and the longest-living vertebrates, in the world. A 2016 study of the sharks' eye tissue published in the journal Science estimated that Greenland sharks have a maximum life span of at least 272 years. Researchers estimated that the oldest Greenland shark in that study was about 392 years old, but the estimate had a large margin of error of 120 years, which led to speculation that Greenland sharks could live to 512 years old. The estimated range hasn't been verified.
"It's important to keep in mind there's some uncertainty with this estimate," Julius Nielsen, co-author of the 2016 paper, previously told Live Science. "But even the lowest part of the age range — at least 272 years — still makes Greenland sharks the longest-living vertebrate known to science."
Greenland sharks live in the slow lane, with a top swimming speed of less than 1.8 mph (2.9 km/h). They also grow slowly at less than 0.4 inch (1 centimeter) per year and have slow metabolisms, according to the National Oceanic and Atmospheric Administration (NOAA). Scientists don't yet know how Greenland sharks live so long but it may be linked to their slow way of life.
Where do Greenland sharks live?
Greenland sharks live in the Arctic and North Atlantic oceans from North America to Greenland and from Portugal to the East Siberian Sea, according to the International Union for Conservation of Nature (IUCN). The sharks have a large range and can be found swimming from the surface down to depths of 8,684 feet (2,647 m), the IUCN says.
Scientists still have much to learn about how Greenland sharks live and reproduce. Female Greenland sharks give birth to live young, called pups, that hatch from soft eggs that the females carry inside their bodies. In a 2020 study published in the journal PLOS One, researchers estimated that Greenland sharks give birth to between 200 and 324 pups per pregnancy, depending on the size of the shark. Greenland shark pups are just 14 to 18 inches (35 to 45 centimeters) long when they're born.
What do Greenland sharks eat?
Greenland sharks have a varied diet that includes fish, other sharks, eels and marine mammals, such as seals. They have also been found with drowned land animals, including horses and reindeer, in their stomachs, and have been seen in large numbers at the sea surface, feeding together on the remains of whales and fish killed during commercial whaling and fishing, according to the University of Michigan's Animal Diversity Web (ADW).
Genus and species: Somniosus microcephalus
Scientists found a Greenland shark with the jaw of a young polar bear (Ursus maritimus) in its stomach, Reuters reported in 2008. The researchers were unsure how it got there; but most shark experts believed that the polar bear was likely already dead when the shark ate it, as live polar bears are too dangerous for the sharks to take on. Researchers also found some polar bear muscle tissue and skin in the stomach of another Greenland shark during a 2014 study published in the journal Polar Biology, and they concluded that the bear was likely scavenged rather than hunted.
Greenland sharks are near the top of the food chain, but sperm whales (Physeter macrocephalus) may hunt them. Chris Harvey-Clark, co-founder of the Greenland Shark and Elasmobranch Education and Research Group (GEERG, now the ORS), wrote in Capeia, an online science communication magazine, about recording a Greenland shark seemingly fleeing from the echolocation clicks of a foraging sperm whale. Upon its death, that sperm whale was found with its teeth worn down to stumps, similar to those of orcas (Orcinus orca) that feed on Pacific sleeper sharks (Somniosus pacificus), which are closely related to Greenland sharks and have similarly tough skin. As such, Harvey-Clark theorized that the sperm whale hunted Greenland sharks. Scientists are yet to observe sperm whales hunting these sharks elsewhere.
Are Greenland sharks dangerous?
There are no verified reports of a Greenland shark attacking a human. However, some anecdotal evidence suggests that such attacks could occur. GEERG divers observed a Greenland shark "stalk" a team of divers. They have also seen Greenland sharks investigate diver activities as if they were scouting seal prey, according to the ORS. A Greenland shark was reportedly found with a human leg in its stomach off Canada's Baffin Island around 1859, but this report was not verified.
Untreated Greenland shark meat is toxic to humans, as it contains high levels of trimethylamine oxide (TMAO), which breaks down into the poisonous trimethylamine (TMA) compound during digestion, according to a 1991 study published in the journal Toxicon. TMA can cause severe intestinal problems and produces similar effects to excessive alcohol consumption. Greenland shark meat is edible only when dried. The dried meat is fed to sled dogs in northern regions such as Greenland, according to the Florida Museum of Natural History. The shark is also fermented and consumed as a delicacy in Iceland.
Are Greenland sharks endangered?
The IUCN considers Greenland sharks to be vulnerable to extinction. Humans killed Greenland sharks for their liver oil to use in lamps and other products between the 13th and 20th centuries. The commercial fishing of Greenland sharks for their oil ended by the 1960s, which helped their population. However, Greenland sharks continue to be caught and killed as bycatch, or animals that get pulled up by fishers alongside their intended catch, for example, in large nets dragged along the bottom of the ocean intended to catch a large number of fish. Most of the Greenland sharks eaten by humans and fed to dogs come from bycatch, although some sharks are targetted on a small scale.
The Northwest Atlantic Fisheries Organization (NAFO), an intergovernmental fishing science and management body, prohibits the direct fishing of Greenland sharks and seeks to reduce bycatch. The NAFO applies to most fisheries in the Northwest Atlantic ocean and includes countries such as the U.S. and Canada. The IUCN recommends further protections, such as bycatch policy, be developed for Greenland sharks and enforced.
The IUCN estimates that the Greenland shark population has declined by 30% to 49% over the past 450 years, or three shark generations. However, this decline was estimated based on a conservative Greenland shark life span of 150 years; the decline could be much higher if the sharks have longer life spans, as it would take them longer to reach reproductive age and produce more sharks. The global Greenland shark population size is unknown. Climate change is also hurting the species — for example, by reducing Arctic sea ice, which gives fishing fleets easier access to Greenland shark habitat.
- See photos and videos of a Greenland shark and other deep sea creatures encountered during the NOAA Northeast U.S. Canyons Expedition in 2013.
- Watch this short video on YouTube about how Greenland shark meat is prepared and consumed in Iceland, from Food Insider.
- Learn more about where Greenland sharks live with an interactive map, from the Encyclopedia of Life.