Greenland sharks: ocean's poisonous, half-blind monsters

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Greenland sharks are the longest-living vertebrates in the world.

In the Arctic and North Atlantic oceans, Greenland sharks (Somniosus microcephalus) are the longest-living creatures with a backbone and can live for up to hundreds of years. They belong to a family of sleeper sharks, which swim slowly and quietly.

Snatching dead creatures from the ocean floor, these sharks hunt a wide range of prey, including sharks and other marine species, seals, horses, and polar bears. Humans seldom come into contact with Greenland sharks, and scientists still have a lot to learn about their habits and behavior.

When it comes to sharks, how huge are the Greenland ones?

According to the St. Lawrence Shark Observatory, Greenland sharks can grow up to 24 feet (7.3 meters) in length and weigh up to 1,200 kilograms (2,645 pounds) (ORS). Even great white sharks (Carcharodon carcharias), which may grow up to 20 feet (6 m) long, are dwarfed by this creature. According to the Florida Museum of Natural History, they can grow up to 23 feet (7 meters) in length.

What you need to know

Up to 24 feet in length (7.3 m)

* The average lifespan is 272 years (estimate)

* Vulnerable conservation status

Dermal denticles are teeth-like scales on Greenland sharks' cylindrical bodies. According to the ORS, these unique scales help sharks swim more quietly by reducing drag. Sharks come in various hues and patterns, including black, brown, gray, or a combination of those colors.

The top jaw of a Greenland shark has 48 to 52 teeth, whereas the lower jaw has 50 to 52 teeth. According to the ORS, the bottom teeth are wide and curved sideways, so sharks can slice out round portions of flesh from prey by circularly moving their heads. The higher teeth are pointed to help sharks grip larger meals.

Are sharks in Greenland blind?

Greenland sharks can get blind from parasites called Ommatokoita elongata in the ocean. According to the Encyclopedia of Life, Ommatokoita elongata attach themselves to the eyes of Greenland sharks and can grow up to 1 inch (2.5 centimeters) long. The eye parasite normally lives in only one of the shark's eyes. Thus they don't usually go fully blind from it. According to the Florida Museum of Natural History, parasites don't affect sharks much because they rely more on their other senses in the dark ocean waters to catch prey.

How long are Greenland sharks known to last?

The lifespan of Greenland sharks is unknown. Greenland sharks have a maximum life span of at least 272 years, according to a study published in ScienceScience in 2016 based on eye tissue examination. Although the oldest Greenland shark in the study lived for 392 years and had a margin of error of 120 years, researchers speculated that the sharks might live for up to 512 years. There is no way to confirm the predicted range.

Julius Nielsen, a co-author of the 2016 article, previously told Live Science that the estimate was "rather unclear." Greenland sharks are the longest-living vertebrates known to ScienceScience, even if they live to a maximum age of 272.

Greenland sharks are considered slow swimmers at a peak speed of fewer than 1.8 miles per hour (2.9 kilometers per hour). According to the National Oceanic and Atmospheric Administration (opens in a new tab), they also grow slowly at less than 0.4 inches (1 centimeter) each year and have slow metabolisms (NOAA). Researchers don't know exactly why Greenland sharks live so long, but it may have something to do with the fact that they move at a leisurely pace.

The Greenland shark is found in what area of the island?

North America's Arctic and North Atlantic waters host a population of Greenland sharks ranging from Greenland to Portugal and the East Siberian Sea eastward (IUCN). It is estimated that sharks can be found at depths of 8,684 feet (2,647 meters), according to the International Union for Conservation of Nature.

Many questions remain unanswered about the life and reproduction of Greenland sharks. Puppy Greenland sharks are born from soft eggs that the mother sharks carry inside their bodies. It has been projected that Greenland sharks can produce 200 to 324 pups per pregnancy, depending on the shark's size, according to a study published in PLOS One in 2019. Pups of the Greenland shark range in length from 14 to 18 inches (35 to 45 cm). However, very little is known about the early life of Greenland shark pups or the overall survival rate.

Sharks in the Greenland waters feed on what exactly?

Fish, eels, and marine mammals such as seals are also part of Greenland sharks' diet. Animal Diversity Web at the University of Michigan says they've also been found with dead terrestrial animals like horses and reindeer in their bellies and that they've been sighted in big groups at the surface of the water eating on the carcasses of whales and fish killed by commercial whaling and fishing (ADW).

Taxonomy of sharks from Greenland

It belongs to the kingdom of animals.

This class of organisms belongs to the phylum Chordata.

The Chondrichthyes class

* Squaliformes is the order.

* The Somniosidae family

Somniosus microcephalus, genus, and species

* ITIS cites ITIS as the source.

Research published in 2008 by the news agency Reuters (opens in new tab) revealed that scientists discovered in the stomach of a Greenland shark the jaw of an immature polar bear, Ursus maritimus. However, most shark specialists concluded that the polar bear was likely already dead when the shark ate it. This makes sense, as sharks cannot handle eating live polar bears because of the risk they provide. In a research published in the journal Polar Biology in 2014, scientists discovered some polar bear muscle and skin in the stomach of another Greenland shark, and they determined that the bear was likely scavenged rather than hunted.

Do Greenland sharks get eaten by anything?

Sperm whales (Physeter macrocephalus) may prey on Greenland sharks at the top of the food chain. According to an article in Capeia, an online science communication journal, co-founder of the Greenland Shark and Elasmobranch Education and Research Group, Chris Harvey-Clark, recorded what appeared to be an escape attempt by a Greenland shark from the echolocation clicks of a foraging sperm whale.

One of those same echolocating sperm whales, which feed on Pacific sleeper sharks, was found dead with its teeth worn down to stumps, comparable to the orcas' (Orcinus orca) (Somniosus pacificus). As with Pacific sleeper sharks, Greenland sleeper sharks are closely related and share a similarly resistant coat. Harvey-Clark hypothesized that the sperm whale hunted Greenland sharks to explain the wear on the sperm whale teeth. No other sperm whales have been preying on these sharks in the wild.

Are Greenland sharks a threat?

According to official records, humans have never been attacked by a Greenland shark. On the other hand, anecdotal evidence points to the possibility of such attacks. A Greenland shark was seen "stalking" a group of GEERG divers. According to the ORS, scientists have also observed Greenland sharks scouting diver operations as if searching for seal prey. On Canada's Baffin Island, an unconfirmed claim stated that a Greenland shark had a human leg in its stomach in 1859.

Is the meat of Greenland sharks harmful to humans?

Humans are poisonous to ingest uncooked Greenland shark meat. According to a 1991 study published in Toxicon, their meat includes significant levels of trimethylamine oxide (TMAO), which breaks down into the toxic trimethylamine (TMA) molecule during digestion. TMA, like excessive alcohol intake, can cause serious gastrointestinal difficulties.

Only dried Greenland shark meat can be eaten. According to the Florida Museum of Natural History, the dried meat is fed to sled dogs in northern places like Greenland. People in Iceland, where the dish is known as Hákarl, also ferment the meat and eat it.

Are Greenland sharks in peril?

The International Union for Conservation of Nature (IUCN) has declared Greenland sharks critically endangered. Between the 13th and 20th centuries, humans hunted Greenland sharks for their liver oil in lamps and other items. Greenland sharks' population rebounded in the 1960s thanks to the halt of industrial fishing for their oil. Despite this, Greenland sharks continue to be killed as bycatch, or creatures that are hauled up by fishers alongside their intended catch, for example, in vast nets carried along the ocean floor meant to harvest large numbers of fish. Most Greenland sharks consumed by humans and fed to dogs are caught as bycatch, but a small number are intentionally targeted.

NAFO, an intergovernmental fishery scientific and management authority, restricts Greenland shark fishing directly and is attempting to limit the amount of bycatch. The North Atlantic Fisheries Organization (NAFO) governs most of the fisheries in the region, which includes the United States and Canada. But the International Union for Conservation of Nature (IUCN) advises greater protections for Greenland sharks, such as a bycatch policy.

In the last 450 years or three shark generations, the IUCN estimates that the Greenland shark population has decreased by 30% to 49%. Greenland sharks can live up to 150 years, which is conservative, but the decline might be much greater if they live longer lives and take longer to reach reproductive age, producing more sharks. The exact population size of Greenland sharks worldwide is unknown. The species is also being harmed by climate change, lowering Arctic sea ice, and making it easier for fishing fleets to reach the Greenland shark habitat.

supplementary materials

For further information on the habitats of these sharks, see the Encyclopedia of Life. An interactive map of Greenland shark sightings worldwide is available on the website. The NOAA Ocean Exploration website has more images and videos of Greenland sharks and other deep water critters. On this page, we don't go into great detail on the procedure of preparing Greenland shark meat for human consumption. Food Insider has put up a short YouTube video to explain the procedure in more detail.

Sharks of the World: A Complete Guide" is a good place to start if you're looking for information on Greenland sharks (Princeton University Press, 2021).

Reference : https://www.livescience.com/greenland-shark

Image source : https://pixabay.com/id/photos/hiu-ikan-laut-bawah-air-akuarium-164899/

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