Greenland Sharks

Greenland shark (omniosus microcephalus)

Greenland sharks are the longest-living shark and also the longest-living vertebrate (all mammals, birds, reptiles, amphibians and fish). They have been known for a long time to live for a really time. 2016 research that dated the layers in the sharks' eye lenses found that the sharks were between 272 and 512 years old. [Source: Stephanie Pappas, Live Science, July 25, 2022]

Greenland sharks (Scientific name: omniosus microcephalus) are also known as sleeper sharks, ground sharks, gray sharks, and gurry sharks. They are known as ekalugssuak in Greenland, hakarl in Iceland, and hakjerring in Norway. The Greenland Shark is known for being the primary ingredient of the infamous Icelandic dish “Hakarl,” By some reckonings it is the second largest carnivorous shark in the world, after the great white shark. They are the only sharks that can survive the cold of the Arctic Ocean all year. They have extremely slow metabolisms and grow only about a centimeter (0.39 inches) a year. Over their long lives they can reach lengths of six meters (19.7 feet). [Source: Live Science, Patrick Mills, Animal Diversity Web (ADW) /=]

Greenland sharks are are found in the North Atlantic, from the coast of New England and Canada to waters off the Scandinavian countries and have been spotted as far south as the mouth of the Seine River in France and Belize. They live in temperate, polar, saltwater and marine environments and are found in coastal areas and in the open ocean far from land as well as in estuaries and intertidal areas. They are typically found at depths of 145 to 1200 meters (475.72 to 3937.01 feet) at an average depth of 180-550 meters (feet). Greenland sharks were spotted at at a depth of 2,195 (7,200 feet) by a submersible that was investigating the wreck of the SS Central America./=\

Greenland sharks live mainly on continental and insular shelves and come into intertidal regions, some river mouths and shallow bay areas during the winter months. During the warmer months they often move to depths from 180 to 550 meters. They have been observed as deep as 1200 meters. One one occasion one was observation at a depth of 2200 meters off the coast of Georgia. In northern parts of their range, Greenland sharks have been observed from zero to 1200 meters in waters from one to 12 degrees Celsius (32 to 54 degrees F) . In southern parts of their range, they may occur at greater depths. /=\

Websites and Resources: Shark Foundation shark.swiss ; International Shark Attack Files, Florida Museum of Natural History, University of Florida floridamuseum.ufl.edu/shark-attacks ; Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems

Do Greenland Sharks Really Live to Be 400 — And How Can This Be

Greenland shark range

Scientists estimate the Greenland shark lives at least 250 years. They may live over 500 years. According to the 2016 study, one female Greenland shark was estimated to be 400 years old. Researchers found that, on average, Greenland sharks have a lifespan of about 272 years. The largest ones measured 4.9 meters (16 feet) and five meters (16.5 feet) long and had lifespans of 335 and 392 years, respectively. One tool used to measure the species’ lifespan — which may also be secret behind its longevity — is its slow growth rate. [Source: Zoë Miller,Azmi Haroun, Business Insider, December 25, 2022]

The age of other shark species can be estimated by counting growth bands on fin spines or on the shark’s vertebrae, much like rings on a tree. Greenland sharks, however, have no fin spines and no hard tissues in their bodies. Their vertebrae are too soft to form the growth bands seen in other sharks. Scientists could only guess that the sharks lived a long time based on what they knew — the sharks grow at a very slow rate (less than 1 centimeters per year) and they can reach over 6 meters in size. [Source: NOAA]

But recent breakthroughs allowed scientists to use carbon dating to estimate the age of Greenland sharks. Inside the shark’s eyes, there are proteins that are formed before birth and do not degrade with age, like a fossil preserved in amber. Scientists discovered that they could determine the age of the sharks by carbon-dating these proteins. One study examined Greenland sharks that were bycatch in fishermen’s nets. The largest shark they found, a 5-meter female, was between 272 and 512 years old according to their estimates. Carbon dating can only provide estimates, not a definitive age. Scientists continue to refine this method and may provide more accurate measurements in the future. But even at the lower end of the estimates, a 272-year lifespan makes the Greenland shark the longest-lived vertebrate.

Greenland shark size

One theory to explain this long lifespan is that the Greenland shark has a very slow metabolism, an adaptation to the deep, cold waters it inhabits. A NOAA remotely operated vehicle doing a dive off New England encountered a Greenland shark at a depth of 783 meters, but these sharks are known to dive as deep as 2,200 meters. They’re also the only shark that can withstand the cold waters of the Arctic Ocean year-round.

The slow metabolism could explain the shark’s slow growth, slow aging, and sluggish movement — its top speed is under 2.9 kilometers per hour. Because the sharks grow so slowly, they aren’t thought to reach sexual maturity until they’re over a century old. That means removing mature Greenland sharks from the ocean affects the species and the ecosystem for many decades. Though the Greenland shark used to be hunted for its liver oil, the majority of Greenland sharks that end up in fishing nets and lines now are caught by accident. Reducing bycatch is critical in conserving this unique species.

Greenland Shark Physical Characteristics

Greenland sharks are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature), heterothermic (have a body temperature that fluctuates with the surrounding environment) and have bilateral symmetry (both sides of the animal are the same). [Source: Patrick Mills, Animal Diversity Web (ADW) /=]

Greenland sharks are large sharks. They range in length from 40 centimeters to 6.4 meters (15.75 inches to 21 feet), with their average length being 2.4 to 4.4 imeters (8 to 15 feet). They range in weight from 700 to 1000 kilograms (1542 to 2203 pounds). Females are larger than males and the two sexes have different shapes.

According to to Animal Diversity Web: Most of the body is a medium grey or brown in color and sometimes exhibits dark transverse bands or small spots or blotches that are lighter or darker than the base color. The snout is short and rounded, and the body is heavy and cylindrical in shape with small precaudal fins. They have relatively small dorsal and pectoral fins for their size. No spines are present in the two equally-sized dorsal fins, and the ventral lobe of the caudal fin is slightly elongated. No anal fin is present. The skin is quite rough, exhibiting denticles with curved pointed cusps. Teeth in the upper and lower jaws differ in shape; upper teeth are spear-shaped while the lower teeth are shaped with high roots and low bent cusps for slicing.

images of a Greenland sharks from 1884

Greenland Shark Behavior and Feeding

Greenland sharks have been described as sluggish. They spend much of their time hovering near the sea floor in search of food but are capable of pursuing prey. Most Greenland sharks migrate every year, but they do so based on depth rather than over distances. During the winter they move to relatively shallows depths and then return to deeper waters in the summer.

According to Animal Diversity Web: These sharks have been observed exhibiting the behavior of animals that often prey on seals, even stalking a camera operator in one rare instance. However, no attacks on humans by this species have been confirmed. Greenland sharks are solitary, outside of the mating season or when large groups occur to exploit carrion, such as that produced by the commercial fishing industry. [Source: "Greenland Shark and Elasmobranch Research and Education Group", Compagno and Fowler, 2005, Patrick Mills, Animal Diversity Web (ADW) /=]

Greenland sharks sense using touch, vibrations, electric signals and chemicals that are detected with smell. Like all sharks, Greenland sharks has a lateral line which aids in the detection of movement in the surrounding waters. Sharks also have especially keen chemical perception. No communication has been observed within the species.

Many of these sharks have copepod parasites attached to the corneas of their eyes. A single, female copepod will attach itself to one of the corneas, resulting in corneal damage and blindness in one eye. This does not seem to negatively effect the shark, as they do not rely on their vision. It has been suggested that the bioluminescence of these parasites helps lure prey, thus resulting in a mutualistic relationship, but there is no evidence to support this. /=\

Greenland shark in 2008

Greenland sharks feed mainly on fish, marine mammals, and carrion. Fish include species commonly found in northern latitude waters such as herring, salmon, smelt, cod, pollock, haddock, halibut, redfish, sculpins, lumpfish and skates. Seals and small whales are also consumed. Drowned horses and reindeer have been found in the stomachs of captured specimens. Greenland sharks has been observed feeding in great numbers on carrion produced by commercial whaling and fishing operations. There are no known predators of adult Greenland sharks other than humans because of their very large size. /=\

Greenland Shark Mating, Reproduction and Offspring

Greenland sharks are ovoviviparous (young are produced from eggs that hatch within the body of a parent) and iteroparous (offspring are produced in groups). They engage in internal reproduction, in which sperm from the male fertilizes the egg within the female, and are polygynandrous (promiscuous), with both males and females having multiple partners. The average number of offspring is 10. [Source: Patrick Mills, Animal Diversity Web (ADW) /=]

Mating by of Greenland sharks has never been observed, but females have been found with mating scars on their caudal fins. Therefore, it is inferred that, as is the case with most sharks, males bite females until they submit.

There is no specific information on parental Investment in Greenland sharks. However, most sharks are independent immediately after birth. During the pre-fertilization and pre-birth stages provisioning and protecting is done by females. Females provide developing embryos with rich food sources to support their development. The size of fully grown young at birth has not been confirmed but is thought to be around forty centimeters. Most adults grow to between two and four meters in length. /=\

Greenland Sharks, Humans, Conservation

hakari in the drying shed

Humans utilize Greenland sharks for food; their body parts are sources of valuable materials. The sharks are commonly fished by people in the Arctic regions, particularly Norway, Iceland, and Greenland, for its liver oil and meat. Unless properly washed or dried, Greenland shark meat is toxic to humans. Inuit people have also been known to use the fish’s skin to make boots and its teeth as knives. [Source: Patrick Mills, Animal Diversity Web (ADW) /=]

The International Shark Attack Files at Florida Museum of Natural History list no unprovoked attacks for the Greenland shark. According to the International Union for Conservation of Nature (IUCN) Red List Greenland sharks are near Threatened; They have no special status according to the Convention on the International Trade in Endangered Species (CITES).

The status of the Greenland shark populations is not well understood. They support a fishery for liver oil in Greenland, Norway, and Iceland, but some researcher suspect that populations have diminished. They have an estimated population doubling time of 14 years. Their slow growth means that if they are overfished it could take a long time for them to recover.

Hákarl

Hákarl(fermented shark in English) is a national dish of Iceland consisting of a Greenland shark or other sleeper shark that has been cured with a particular fermentation process that includes burying it in a hole in the ground to putrefy and then hung to dry for four to five months. It has a strong ammonia-rich smell and fishy taste — definitely an acquired taste. Hakarl is sold at shops and supermarkets and is eaten throughout the year but has traditionally been associated with with þorramatur, a selection of traditional Icelandic food, served at the midwinter festival þorrablót. [Source: Wikipedia]

hakari ready to eat

Hákarl comes in two varieties: chewy and reddish glerhákarl ("glassy shark") from the belly, and white and soft skyrhákarl ("skyr shark") from the body. It is often served in cubes on toothpicks. Those who try for the first often gag and throwing up is not unusual because of the high ammonia content. First-timers are often told to pinch their nose while taking the first bite, as the odor is much stronger than the taste. It is often eaten with a shot of the local spirit, a type of akvavit called brennivín.

The meat of the Greenland shark is poisonous when fresh because of its high urea and trimethylamine oxide content. However, when properly processed, it can be consumed safely. The traditional method for making hakarl begins with gutting and beheading a shark and placing it in a shallow hole dug in gravelly sand, with the cleaned cavity resting on a small mound of sand. The shark is then covered with sand and gravel. Stones are placed on top of the sand in order to press the fluids out of the body. The shark ferments in this fashion for six to twelve weeks, depending on the season. Following this curing period, the shark is cut into strips and hung to dry for several months. During this drying period, a brown crust will develop, which is removed prior to cutting the shark into small pieces and serving. The modern method is simply to press the shark's meat in a large plastic container, into which drain holes have been cut.

People make jokes about hakarl and challenges are made to as is the case with eating live squid in South Korea, skewered scorpions in China, duck blood cubes in Vietnam or haggis in Scotland. The late TV travel chef Anthony Bourdain described hakarl as "the single worst, most disgusting and terrible tasting thing" he had ever eaten. Chef Gordon Ramsay challenged James May to sample three "delicacies" (Laotian snake whiskey, bull penis, and fermented shark) on The F Word. After eating fermented shark, Ramsay spat it out, but May was able to keep his down. May even offered to eat it again. In an episode of the Simpsons, Homer threatened native Icelander Carl with the dish, saying, "Give us some answers or you'll get a mouthful of rotten shark fermenting in its own urine!", to which Carl exclaims, "No, no! Anything but the inedible, repulsive food of my native land!"

Conservationists don’t look kindly on hakarl as Greenland shark reproduce very slowly and take decades to reach maturity. It is believed that hunting and fishing of Greenland shark for food has led to declines in their numbers. Once they are overfished it will take them a long time to recover if ever. Associations, such as the Northwest Atlantic Fisheries Organization, an intergovernmental fishing science and management body, wants a ban of the hunting and killing of Greenland shark.

Image Source: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated March 2023