GREENLAND SHARK: CHARACTERISTICS, HABITAT, BEHAVIOR - BIOLOGY - 2025

The Greenland or boreal shark (Somniosus microcephalus) is a cartilaginous fish that is part of the Somniosidae family. This species has the longest lifespan among all living vertebrates, and can last between 260 and 512 years.

Its body is large, measuring up to 7.3 meters long. In relation to the fins, the dorsal and pectorals are small. The boreal shark's coloration varies from gray to brown, and may have dark transverse stripes.

Greenland or Boreal shark. Source: Couch, Jonathan; Lydon, AF

Somniosus microcephalus is distributed in the North Atlantic and Arctic oceans. This fish makes annual migrations. In winter, it congregates in deep waters, up to 80 ° N, to inhabit warmer areas. On the contrary, during the summer, it goes further south, at a much greater depth.

As for their diet, they are carnivores. Its diet is made up of eel, Atlantic salmon, cod and herring, among other fish. Likewise, it eats crustaceans, seabirds and small mammals, such as the seal. Also, it is a scavenger animal, which eats the meat of reindeer, horse or other cetacean carcasses.

characteristics

Despite having a small head, the Greenland shark is robust and large. It has a short, rounded muzzle and the eyes are tiny.

In relation to the fins, the pectorals are small and the tail lobe is slightly elongated. As for the dorsal fins, they are reduced and do not have spines. On the other hand, this species lacks a tail fin.

As for the gill openings, they are relatively small, compared to the large size of the fish. These are located on both sides of the shark head.

- Adaptations

The boreal shark lives in very cold waters, whose temperature averages 4 ° C. Due to this, your body has undergone various adaptations, which allow it to develop and survive in that environment. Among these are:

Large amounts of trimethylamine oxide and urea

This shark needs to maintain the volume of water and salt in the body, which implies a huge energy expenditure. However, the fact that it has a high level of urea means that it can achieve this balance without wasting energy.

An unfavorable aspect is that the high concentration of urea destabilizes the proteins. To counteract this, the fish has the compound trimethylamine oxide in its blood chemistry. This element also contributes to buoyancy, besides acting as an antifreeze agent.

Excellent sense of smell

The presence of eye parasites causes Somniosus microcephalus to have a highly developed sense of smell. In this way, it can locate its prey, as well as the carrion of other marine species.

Dermal denticles

Like the other sharks, all the skin is covered by denticles. These are projections, in the form of small teeth that reduce resistance to water, while the shark swims. The denticles are spread evenly throughout the body, forming separate longitudinal columns. They are conical and curved towards the tail fin.

Large spiracles

Behind the eyes, the Greenland shark has two holes, which correspond to the vestiges of the gill slits. These structures allow the animal to obtain more oxygen from the water, while it performs its slow swim.

- Size

Microcephaly somniosus is a large, slow-swimming shark. The males of this species are smaller than the females. Thus, it measures an average of 6.4 meters, although it can be up to 7.3 meters long. As for its weight, it varies from 1 to 1,400 kilograms.

- Coloring

The boreal shark has a gray, brown or black body. However, it may have white spots or dark lines on the back of the body or on the sides of the body.

- Teething

The upper and lower teeth differ in shape. Thus, the upper ones are thin, have no striations and have the appearance of a spear. These can vary between 50 and 52 pieces in each jaw.

In relation to the lower ones, they are square, wide and with short cusps, which are directed outwards. In total, they can add 48 to 52 teeth.

The teeth of the upper jaw act like an anchor, while those of the lower jaw cut prey into pieces. When feeding on the carrion of large animals, the boreal shark makes a twisting motion on its jaw.

In this video you can see a specimen of this species:

Evolution

The common ancestor between the Greenland shark (Somniosus microcephalus) and the Pacific sleeper shark (Somniosus pacificus) lived in deep waters, probably with a pan-oceanic distribution.

Furthermore, experts suggest that the divergence of these two species occurred 2.34 million years ago. This fact is probably not linked to a single event, such as the emergence of the Isthmus of Panama. It can also be associated with the cooling of the planet, which happened during the Quaternary.

The earliest appearance of S. pacificus occurred around 100 million years ago. Some of these fossils correspond to the Miocene, and were found in Italy and Belgium. This suggests the presence of these species before the late Miocene cooling and the beginning of the Pleistocene glacial period.

As a result of various investigations, scientists confirm the existence of genetically mixed sharks in the sub-Arctic, Canadian Arctic and temperate eastern Atlantic regions.

This suggests a hybridization between S. pacificus and S. microcephalus, product of the contact that occurred after the initial divergence between the species.

Life expectancy

The boreal shark has the longest lifespan ever known in all vertebrate species. Due to the fact that its annual growth is approximately ≤1 centimeter, the experts consider very probable that the longevity of this shark is exceptional.

The specialists are unable to use in this species the established chronologies that evaluate the growth. This is because the shark lacks calcified tissues. This is why, in a study carried out in the Arctic seas, specialists estimated the age of the shark using another method.

In this case, they used a chronology obtained from the cores of the ocular lenses. The data are obtained by applying radiocarbon dating techniques.

The results indicate that the total length varies between 504 and 588 centimeters. In relation to age, it is in an estimated range of 260 to 512 years.

Likewise, considering that the female sexually matures to a length of approximately 400 centimeters, the corresponding age is 134 to 178 years. Taking into consideration the findings of this research, the lifespan of a boreal shark that measures more than 500 centimeters in length is 272 years.

Taxonomy

-Animal Kingdom.

-Subreino: Bilateria.

-Filum: Chordata.

-Subfilum: Vertebrate.

-Infrafilum: Gnathostomata.

-Superclass: Chondrichthyes.

-Class: Chondrichthyes.

-Subclass: Elasmobranchii.

-Superorden: Euselachii.

-Order: Squaliformes.

-Family: Somniosidae.

- Genus: Somniosus.

-Species: Somniosus microcephalus.

Habitat and distribution

Distribution

The Greenland shark is distributed in the northern Atlantic Ocean and in the Arctic regions, in a range between 80 ° N and 55 ° S. However, sightings have been reported south, near Portugal and France, in the Gulf of San Lorenzo, in Carolina of the North and in Cape Cod.

Thus, in the Arctic and the North Atlantic it extends from the coast of New England and Canada to the Scandinavian maritime waters. In this way, it covers Iceland, Greenland, Cape Cod, the island of Spitsbergen (Norway), the Gulf of Maine.

In addition, it lives from the White Sea (Russia) and Norway, to the North Sea and from the Gulf of Saint Lawrence to the Ellesmere Islands. In the South Atlantic and the Southern Ocean, it is located in Macquarie, the Kerguelen Islands and in South Africa.

Habitat

Somniosus microcephalus is an epibnthic and pelagic fish, which lives near the continental and island shelves and on the upper slopes, located at a depth between 1,200 and up to 2,200 meters. This species is found in waters whose temperature ranges from 0.6 to 12 ° C, although it usually prefers those that are below 5 ° C.

The Greenland shark makes long migrations. During the colder months, in the boreal Atlantic and in the Arctic, it lives in the intertidal area and on the surface, on the coast, the mouths of rivers and in shallow bays.

In the spring and summer, in the regions of lower latitude, such as the North Sea and the Gulf of Maine, it inhabits the continental shelves.

The experts conducted a follow-up study in late spring in the region off Baffin Island. This investigation showed that the sharks remained in deep areas during the morning, gradually moving to shallower areas in the afternoon and at night.

State of conservation

The Greenland shark is threatened with extinction, mainly due to its poaching. This situation has caused the IUCN to include this species within the group of animals in danger of extinction.

Historically, the Greenland shark has been the target of liver fisheries in the waters of Iceland, Norway and Greenland. This species is valued primarily for its liver oil. A large specimen can supply approximately 114 liters of liver oil.

In 1857, in Greenland, the annual catch was 2,000 to 3,000 sharks, but in the 1910s these figures increased to 32,000 sharks annually. Due to conservation policies, this fishing ceased in 1960.

Currently, this species is caught incidentally in gillnets, fish traps, and in shrimp and halibut trawl fisheries. In addition, it is caught by artisanal fishing carried out in the Arctic.

In the following video you can see the hunting of a specimen of this species:

Feeding

Somniosus microcephalus mainly feeds on pelagic and bottom fish. These include herring, capelin, Atlantic salmon, redfish, cod, eel, Greenland and Atlantic halibut. It also eats other sharks, squid, seabirds, snails, crabs, starfish, jellyfish, and sea urchins.

Boreal sharks, despite having a slow swim, often catch small marine mammals, such as porpoises and seals. In addition, they usually feed on carrion, which includes carcasses of reindeer and horses.

To capture their prey, the Greenland shark often congregates in large groups around fishing boats.

Reproduction

The female of this species is sexually mature when her body measures around 400 centimeters, which corresponds to an age between 134 and 178 years.

Experts point out that the scars on the female's tail fins could correspond to courtship or mating behaviors. Therefore, it is inferred that the male bites her into submission.

Due to the limited information on the reproductive process of the Greenland shark, it was previously presumed that the female deposited the eggs on the seabed. However, thanks to studies carried out in 1957, it was found to be an ovoviviparous species.

Thus, the fertilization of the eggs occurs internally, and these remain inside the uterine cavity until they are mature. The embryos feed on the yolk sac. In relation to the size of the litter, it is between 5 and 10 young.

At birth, the young shark measures 38 to 42 centimeters. This is completely independent, which suggests that there is no type of parental care.

Behavior

Somniosus microcephalus is an ectothermic animal, which lives in waters close to 0 ° C. Its swimming speed is very low, considering its large size. This makes it one of the slowest cartilaginous fish.

It usually swims at 1.22 km / h, although at times it could reach 2.6 km / h. Because this speed is less than that used by a seal to move, biologists hypothesize that, to hunt this marine mammal, the shark attacks it unawares while it sleeps.

The boreal shark spends much of its time near the bottom of the sea, searching for food. However, it can also chase and capture its prey.

This species has solitary habits. However, on certain occasions it is even. One of these occasions is during the reproductive stage, where it is temporarily grouped with the female.

In addition, it can massively congregate around fishing boats, in search of carrion produced by the commercial fishing industry.

Relationship with

Some Greenland sharks frequently have copepod Ommatokoita elongata parasites attached to the cornea of ​​their eyes. This causes damage to this structure, which can lead to loss of vision.

However, this situation does not seem to seriously affect the shark, since it does not depend on sight to capture its prey.

Experts suggest that the bioluminescence of these parasites contributes to the animals getting closer to the shark, which could represent a mutualistic relationship between these two animal species.

References

1. Nielsen, Julius, Hedeholm, Rasmus, Bushnell, Peter, Brill, Richard, Olsen, Jesper, Heinemeier, J., Christiansen, Jørgen, Simon, Malene, Steffensen, Kirstine, Steffensen, John. (2016). Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Recovered from researchgate.net
2. Kyne, PM, Sherrill-Mix, SA & Burgess, GH 2006. Somniosus microcephalus. The IUCN Red List of Threatened Species 2006. Recovered from iucnredlist.org.
3. Wikipedia (2020). Greenland shark. Recovered from wikipedia.org
4. Dane Eagle (2020). Greenland Shark. Recovered from floridamuseum.ufl.edu.
5. Marinebio (2020). Greenland Sharks. Recovered from marinebio.org.
6. John P. Rafferty. (2020). Greenland shark. Recovered from britannica.com.
7. Mills, P. (2006). Somniosus microcephalus. Animal Diversity Web. Recovered from animaldiversity.org.
8. Walter RP, Roy D, Hussey NE, Stelbrink B, Kovacs KM, Lydersen C, McMeans BC, Svavarsson J, Kessel ST, Biton Porsmoguer S, Wildes S, Tribuzio CA, Campana S, Petersen SD, Grubbs RD, Heath DD, Hedges KJ1, Fisk AT. (2017). Origins of the Greenland shark (Somniosus microcephalus): Impacts of ice-olation and introgression. Recovered from ncbi.nlm.nih.gov.