Greenland Shark (Somniosus microcephalus)

Somniosus microcephalus, the Greenland shark, is a large, slow-moving elasmobranch of the deep, cold waters of the North Atlantic and Arctic Oceans. Radiocarbon dating of proteins locked in the eye lens nucleus has produced age estimates exceeding 400 years for a 4-metre individual, making the species the longest-lived vertebrate known to science. Its flesh is toxic to mammals, its swimming speed is the slowest recorded for any fish when adjusted for body size, and a 2026 whole-genome study uncovered molecular adaptations that may help explain how it survives to such an age. The combination of extreme longevity, remote habitat, and unusual biology has made it one of the most studied sharks of the past decade, while its conservation status has worsened: the IUCN elevated it from Near Threatened to Vulnerable in 2020.

Key facts

  • Scientific name: Somniosus microcephalus
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Elasmobranchii
  • Order: Squaliformes
  • Family: Somniosidae
  • Genus: Somniosus
  • Taxonomic rank: species

Physical description

The body is heavy and cylindrical, with a short, rounded snout, small eyes, and no anal fin. The skin is rough, covered with denticles that bear curved, pointed cusps. Coloration ranges from medium grey to brown and can display dark transverse bands, small dark spots, or small light spots on the dorsal surface.

The genus name Somniosus comes from the Latin somniosus, meaning ‘sleepy’ or ‘drowsy’, and microcephalus derives from the Greek mikros (‘small’) and kephale (‘head’), giving the full meaning ‘sleepy small-headed shark’. Marcus Elieser Bloch and Johann Gottlob Schneider, two German naturalists, assigned the scientific name in 1801, at which time they placed it in the genus Squalus as Squalus microcephalus.

Distribution and movement

The species ranges across deep, cold waters of the Arctic Ocean and the North Atlantic, with its southern limit reaching approximately the 32nd parallel north in the Atlantic. It is not confined to abyssal depths year-round: during the Arctic winter, individuals move inshore into shallow bays and river mouths. When water temperatures rise, they retreat to depths between 180 and 550 metres.

Although largely solitary, individuals aggregate temporarily around abundant food sources. Tracking and observation data show evidence of transient movements, recurring hotspots, and apparent seasonality in coastal-to-offshore presence.

Feeding

The Greenland shark uses a powerful inertial suction feeding mode, drawing prey into the mouth from distances of 25 to 35 centimetres. The upper teeth pin the prey in place while lower, blade-like teeth rotate and cut chunks of flesh free. Stomach contents have yielded polar bear jaws, reindeer remains, and a horse leg, which confirms that the species readily scavenges terrestrial mammal carcasses that enter the ocean. The diet is therefore far broader than that of a specialist deep-sea predator.

Locomotion

The Greenland shark holds the record for the slowest mean swimming speed (0.34 m/s) and the lowest tail-beat frequency (0.15 Hz) of any fish species, both figures adjusted for body size. Researchers attribute these values to the near-freezing water temperatures of its habitat, which limit the metabolic rate and muscular output available to the animal.

Age and longevity

Estimating the age of a Greenland shark is not straightforward. The method used for most bony fish and some other sharks, counting growth rings in calcified tissue, cannot be applied here because Greenland shark vertebrae are too soft to form readable growth bands. Age estimation instead relies on radiocarbon dating of the metabolically inert proteins in the eye lens nucleus. These proteins form before birth and do not turn over throughout the animal’s life, preserving a chemical record from the moment of development.

At a growth rate of less than 1 centimetre per year, a 4-metre individual would require well over 400 years to reach that size, placing the species firmly as the slowest-growing large vertebrate known. The implication is that sexual maturity arrives very late, which matters significantly for population recovery after depletion.

A 2026 study published in Aging Cell found biological signs of ageing in Greenland shark hearts, including fibrosis, oxidative stress, damaged mitochondria, and accumulated lipofuscin. The findings establish that extreme longevity in this species does not mean freedom from cellular ageing; it means the process proceeds at a rate that allows survival on a multi-century timescale.

Genomics and molecular biology

A 2026 study published in PNAS sequenced the first whole genome of a Greenland shark and identified expanded gene families associated with immune defense, DNA repair, and iron storage. The study also found unique amino acid substitutions in linker histone proteins; the authors proposed these may stabilize chromatin structure and reduce the accumulation of DNA damage over the shark’s exceptional lifespan. The genome work complements the radiocarbon age data by pointing to specific molecular mechanisms that could underpin multi-century survival.

The Greenland shark’s closest known relative is the Pacific sleeper shark (Somniosus pacificus). A full mitochondrial genome phylogenetic analysis placed the two as sister species and estimated their divergence at approximately 2.1 million years ago. Genetic evidence has also confirmed interspecific hybridization between the two: genetically admixed individuals have been recorded in the Canadian Arctic and sub-Arctic and in the temperate eastern Atlantic.

Toxicity and the flesh

The flesh of Somniosus microcephalus is toxic to mammals. The responsible compound is trimethylamine N-oxide (TMAO), an osmolyte the shark uses to stabilize its enzymes against the combined pressures of cold and depth. In mammals, TMAO ingestion causes symptoms that resemble severe intoxication; the toxin can be incapacitating or fatal to sled dogs.

Inuit communities historically hunted the shark through holes in ice using bait and lanterns. The hide provided material for boots, the teeth served as cutting tools, and the processed flesh was consumed as food. In Inuktitut the animal is called Skalugsuak.

Conservation status and threats

The IUCN reassessment of 2020 elevated the Greenland shark from Near Threatened to Vulnerable. In 2025, Canada’s Committee on the Status of Wildlife in Canada (COSEWIC) assessed the species as Special Concern. As of 2026, the species is not listed under CITES and has no comprehensive international trade protection.

The principal documented threat is bycatch. Deepwater trawl, longline, and gillnet fisheries targeting Greenland halibut, cod, and northern shrimp catch Greenland sharks incidentally in significant numbers. Given the species’ extremely slow growth, late maturity, and multi-century lifespan, any sustained increase in mortality has the potential to drive population decline over decadal or centennial timescales before it becomes apparent in standard stock assessments.

Did you know

  • The Greenland shark grows at a rate of less than 1 cm per year, meaning that a 4-metre adult took well over 400 years to reach that size, making it the slowest-growing large vertebrate known. (aaas.org)
  • Inuit legend explains the Greenland shark’s strong urine-like odour through the story of Skalugsuak: an old woman washed her hair in urine and the cloth she used to dry it blew into the sea, transforming into the first Greenland shark. (geerg.ca)
  • Despite being one of the world’s largest predatory sharks, the Greenland shark has never had a confirmed unprovoked attack on a human, and because of its depth and remote habitat it is considered non-threatening to people. (nationalgeographic.com)
  • A 2026 study published in Aging Cell found biological signs of ageing in Greenland shark hearts, including fibrosis, oxidative stress, damaged mitochondria, and accumulated lipofuscin, showing these exceptionally long-lived animals are not entirely immune to cellular ageing. (ibtimes.co.uk)

Data sources

Data updated: 2026-10-26