The Greenland shark prefers cold water temperatures () and deep water (). As an
ectotherm living in a just-above-freezing environment, this species is sluggish and slow moving, with the lowest swim speed and tail-beat frequency for its size across all fish species, which most likely correlates with its very slow metabolism and extreme longevity. It swims at an average of per second, with its fastest cruising speed reaching about per second. Because this speed is a fraction of the speed reached by seals (a well-established prey item), biologists are uncertain how the sharks are able to prey on the seals, though the sharks are thought to
ambush while seals are asleep. Like other sharks, the Greenland Shark has a well-developed lateral line system. This system is made up of fluid-filled canals that run beneath their skin, along the sides of their bodies, and over their heads. Small pores connect these canals to the water surrounding them, allowing them to detect vibrations and low-frequency pressure changes caused by movement in the water, such as prey swimming nearby. This is important, as Greenland Sharks live in deep, dark environments that provide no sunlight, where they cannot rely heavily on vision. Due to many Greenland Sharks experiencing eye damage from parasitic copepods, it is possible that vision is not their main, relied-upon sense. Instead, the lateral line, along with their sharp sense of smell, plays a key role in helping them locate prey and move through their environment, despite them being slow swimmers.
Genetics The Greenland Shark genome has roughly 6.5 billion base pairs, which is the largest genome of any shark sequenced. More than two-thirds of the genes found in the Greenland Shark genome are
transposable elements, commonly referred to as jumping genes, which are genes that can self-replicate. These genes often cause issues with normal gene function and lead to
mutations and other genetic complications. However, in Greenland Sharks,
DNA repair genes are hypothesized to be able to ‘jump’ like transposable elements, helping mitigate the damage caused by the other jumping genes. 81 genes that are unique to the Greenland Shark genome are suggested to be linked to DNA repair. Because of the
parasitic copepods that attach to the Greenland Shark’s eyes, along with the dark and visually obstructed environment, their vision may appear to be useless or impaired. However, the Greenland Sharks’ optic tectum (the brain region responsible for processing visual information) is a similar size to that of other
elasmobranchii. Greenland Sharks have a
tapetum lucidum, which enhances photon capture in low-light conditions. Greenland Sharks also possess rod-dominated retinas and rely on rod-specific phototransduction genes to be able to see in low-light conditions. The genes responsible for this rod-specific phototransduction include the
rh1, sag, gnat1, gucy2f, pde6a, pde6b, pde6d, pde6g, grk1, cnga1, gnb5, rcvrn and
gngt1 genes. Furthermore, only one set of cone-specific phototransduction genes (
grk7) is found in the Greenland Shark’s genome, confirming its reliance on rod-based vision. They primarily eat fish (
herring,
salmon,
smelt,
cod,
wolffish,
haddock,
halibut,
redfish,
sculpins,
lumpfish, and
skates) and
seals. Some Greenland sharks have been found also to eat
minke whale. The largest of these sharks were found having eaten
redfish, as well as other higher
trophic level prey. Because of their slow speeds and
low-twitch-speed muscle fiber, Greenland sharks are proposed to hunt marine mammals, such as seals and smaller cetaceans, that are
asleep, injured, or sick, as well as scavenging. Regarding most benthic prey, they use their cryptic coloration, approaching prey undetected before closing the remaining distance. Once they get close to their prey, Greenland sharks expand their
buccal cavity to
create suction, drawing in prey. This suction mechanism is the likely explanation for why the gut contents of Greenland sharks are often of whole prey specimens. Daily vertical migration between shallow and deep waters has also been recorded. Genetic evidence suggests that Greenland sharks historically inhabited deep-sea environments, ranging across panoceanic regions at depths greater than 1,000 m. During the
Quaternary period, global cooling influenced thickening sea ice and submerged Arctic landscapes, which likely severed connectivity between the local shark populations. Four previous records of Greenland shark were reported from Cuba and the northern Gulf of Mexico. A more typical depth range is , with the species often occurring in relatively shallow waters in the far north and deeper in the southern part of its range. In April 2022, a large
Somniosus shark was caught and subsequently released on
Glover's Reef off the coast of
Belize. This shark was identified as being either a Greenland shark or
hybrid; Greenland ×
Pacific sleeper shark. This observation is notable for being the first possible record of a Greenland shark from the
Western Caribbean, and being caught on a nearshore
coral reef (the only other record of this species from the Caribbean was made from a deep-water habitat off the Caribbean coast of
Colombia). The discovery indicates that Greenland sharks may have a wider distribution in the tropics, primarily at greater depths, than previously believed.
Life history The Greenland shark has the
longest known lifespan of all vertebrates. It is estimated that the species has a lifespan of at least 272 years, with the oldest individual estimated to be 392 ± 120 years of age. Estimates of age were made using
radiocarbon dating of crystals within the lenses of their eyes. One Greenland shark was tagged off the coast of Greenland in 1936 and recaptured in 1952. Its measurements suggest that Greenland sharks grow at a rate of per year. Efforts to
conserve Greenland sharks are particularly important due to their extreme longevity, long maturation periods, and the heightened population sensitivity of large sharks. There are also efforts to understand exceptional Greenland shark longevity on the molecular level. Several published works suggest that expansion of
transposable elements may play a crucial role. The longer duration and complexity of the female
maturation reflect sex differences in reproductive biology. Females undergo seven distinct maturation stages: immature, developing, ripening, early gravid, midterm gravid, late gravid, and postnatal. Males undergo three stages: immature, maturing, and mature. This extremely long gestation rate is crucial to understanding effective conservation strategies around the Greenland shark. Given the ongoing fishing pressures on Greenland sharks, their long gestation period and slow reproductive rate may severely limit their ability to recover from overfishing. Estimates of litter size have varied across studies. Some suggest that this species produces up to 10 pups per litter, each initially measuring some in length. Other studies, however, which take into account ovarian data and analysis of other squaliform shark species, have estimated that Greenland sharks may produce up to 10 pups per litter, each pup measuring from in length. The same study also confirms that Greenland shark embryos develop inside the uterus without a placenta. ==Threats==