Alien  Earthlings

The Greenland shark (Somniosus microcephalus) is the world’s longest-living vertebrate, capable of living over 400 years, inhabiting the cold, deep waters of the Arctic and North Atlantic.

Overview

The Greenland shark is a massive, slow-moving shark of the sleeper shark family (Somniosidae), closely related to Pacific and southern sleeper sharks. Adults typically range from 2 to 4 meters (6.5–13 feet) in length, but can reach up to 7.3 meters (24 feet) and weigh over 1,400 kilograms (3,000 pounds). Females are generally larger than males, reaching sexual maturity around 150 years of age. The species is ovoviviparous, giving birth to live young after an estimated gestation of 8–18 years, with litters averaging 10 pups. 

Lifespan and Longevity

Greenland sharks are the longest-living vertebrates, with radiocarbon dating of eye lens proteins estimating lifespans between 272 and 512 years. Their extreme longevity is attributed to a very slow metabolism, sluggish swimming speed (less than 3 km/h), and adaptation to frigid, deep-water environments. This slow pace of life allows them to conserve energy and reduce cellular damage over centuries. 

Habitat and Distribution

These sharks inhabit the North Atlantic and Arctic Oceans, from Baffin Bay to the Barents Sea, occasionally extending south to the North Sea and the Eastern Seaboard of the U.S. They prefer cold waters between −1.1 and 12 °C (30–54 °F) and depths from 100 to 2,200 meters (330–7,200 feet). Greenland sharks migrate vertically and seasonally, moving to shallower waters in winter and deeper waters in summer. 

Diet and Behavior

Greenland sharks are generalist predators and scavengers, feeding on fish, squid, seals, and occasionally terrestrial mammals like reindeer or horses that enter the ocean. They often ambush sleeping or slow-moving prey due to their low swimming speed. Their sense of smell and lateral line system compensate for poor vision, which is often impaired by parasitic copepods (Ommatokoita elongata) attached to their eyes. 

Physiology and Adaptations

Greenland sharks have high concentrations of trimethylamine N-oxide (TMAO) in their tissues, which increases buoyancy and protects proteins under high pressure. Their slow metabolism, low tail-beat frequency, and cold-water adaptations contribute to their longevity. Despite eye parasitism, their visual system is functional and adapted to dim light, with rod-dominated retinas and DNA repair mechanisms supporting retinal integrity over centuries. 

Human Interaction and Conservation

Greenland sharks are not considered a threat to humans due to their remote habitat. Their flesh is toxic to mammals unless properly processed, as in the Icelandic delicacy kæstur hákarl. Historically hunted for liver oil, they are now primarily caught as bycatch. The IUCN lists them as vulnerable due to slow growth, late maturity, and susceptibility to overfishing and climate change. 

Notable Facts

• They can live over 400 years, making them the longest-living vertebrate. 

• They grow extremely slowly, about 1 cm per year. 

• Greenland sharks have been found with unusual prey, including polar bears and reindeer, indicating scavenging behavior. 

• They are sluggish swimmers, relying on ambush tactics and keen olfactory senses. 

• A Greenland shark recently washed up on the Irish coast, highlighting their rare appearances in shallow waters. 

Greenland sharks remain one of the most enigmatic and fascinating marine species, offering insights into longevity, deep-sea adaptations, and Arctic ecosystem dynamics.