Greenland sharks (Somniosus microcephalus) are the longest-living animals with a backbone, and survive for up to hundreds of years in the deep, cold waters of the Arctic and North Atlantic oceans. Greenland sharks belong to a family called sleeper sharks, which move slowly and stealthily through the water.
These sharks sneak up on live prey and scavenge a variety of dead animals, including other sharks, seals, drowned horses and polar bears. Greenland sharks rarely encounter humans and scientists still have much to learn about their lifestyles.
Key facts
Size: Up to 24 feet (7.3 m)
Life span: 272 years (estimate)
Conservation status: Vulnerable
Greenland sharks have cylindrical bodies covered in teeth-like scales, called dermal denticles. These specialized scales reduce drag and help the sharks move more silently through the water, according to the ORS. The sharks can be black, brown, gray or a mixture of all three colors, and they may have spots.
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.
Related: Ancient Greenland shark reveals its age in eerie underwater video
"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.
Related: No, scientists haven't found a 512-year-old Greenland shark
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 females carry inside their bodies. In a 2020 study published in the journal PLOS One, researchers estimated that Greenland sharks can 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. However, little is known about how Greenland shark pups spend their early lives or how many survive to adulthood.
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 by commercial whaling and fishing, according to the University of Michigan's Animal Diversity Web (ADW).
Greenland shark taxonomy
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Order: Squaliformes
Family: Somniosidae
Genus and species: Somniosus microcephalus
Source: ITIS
Scientists have even 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.
Upon its death, that same echolocating 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). Greenland sharks are closely related to Pacific sleeper sharks and have similarly tough skin. To explain the sperm whale tooth wear and a fleeing Greenland shark, Harvey-Clark theorized that the sperm whale hunted Greenland sharks. Scientists have yet to observe sperm whales hunting these sharks elsewhere.
Related: Sperm whales outwitted 19th-century whalers by sharing evasive tactics
Untreated Greenland shark meat is toxic to humans. Their meat 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 meat is also fermented and consumed by people inIceland, where the food, called Hákarl, is considered a delicacy.
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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. But thee IUCN recommends the development and enforcement of further protections, such as bycatch policy, for Greenland sharks.
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 and thus take 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.
There aren't reliable books on Greenland sharks specifically, but for a general guide to the world's sharks, check out "Sharks of the World: A Complete Guide" (Princeton University Press, 2021).
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