Greenland Shark

Greenland Shark

  • Scientific name: Somniosus microcephalus
  • Also know as: Sleeper Shark, Gurry Shark
  • Size: Unknown, but at least 24ft in length and in excess of 2000lbs.
  • UK minimum size: N/a
  • UK shore caught record: N/a
  • IGFA world record: 1,708lbs
  • IUCN status
    • Global: NT (Near Threatened)
    • Europe: NT (Near Threatened)
  • Distribution: Wide distribution throughout the cold waters of the northern hemisphere, with the range of this species spanning the east coast of North America to European waters. Found in very deep waters around the British Isles and the rest of Europe.
  • Feeds on: Very slow-moving nature of this species means that it is thought to be a scavenger rather than hunter and will feed on any kind of animal matter which it finds.
  • Description: Very large shark species. The body is broad and cylindrical and usually greyish in colour. Head is small and eyes are tiny, and mouth is filled with very small, but sharp teeth. Fins are small in relation to the size of the body. Gill slits are also small and located low down on the body.

The Greenland shark is the second-largest species of carnivorous shark (after the great white shark). It is a species which is rarely encountered by humans and many aspects of its life cycle are unknown, meaning that is often referred to as the world’s least-understood shark species. Indeed, footage of a Greenland shark swimming in its natural environment was not captured until 2003. Many aspects of the life of this species – such as its growth rate, gestation period and feeding habits – are little studied by humans and much of the information on this species cannot be definitively confirmed. Despite this, the Greenland shark has been hunted for hundreds of years by indigenous peoples on a small-scale basis and is a culturally important food source in some Nordic countries.

In 2016 new research revealed that Greenland sharks were the longest living vertebrate in the world, with a lifespan of at least 272 years, and possibly much longer.

Distribution

As the name suggests Greenland sharks are found in the highest concentrations in the cold waters around Greenland, Iceland and in Arctic waters. Their range extends into colder waters along the eastern coast of North America and in Europe they are found in Scandinavian and British waters. They have been reported as far south as the Portuguese coast, and it is believed that this species’ range could extend well into the Atlantic Ocean in deep water areas which remain unexplored by humans.

Greenland Shark Distribution

Worldwide distribution of the Greenland shark.

Greenland sharks are generally seen as a very deep water species as they will live and feed at immense depths down to several thousand metres where the water is extremely cold and little light penetrates. Greenland sharks can also happily live and feed at the surface of the sea as well and can come into relatively shallow waters, although it is thought that this only happens in Arctic regions where the water is still extremely cold at the surface. Very occasionally Greenland sharks have been sighted close to land and even in estuaries and other shallow areas. It is unknown why Greenland sharks are found in these areas but one theory is that Greenland sharks may become lost and confused once they are out of their deep-sea habitats and end up inadvertently near to land when they cannot find their way back to deep water.

A Greenland shark was found by dog walkers washed up at Embleton Bay in Northumberland in 2013. Despite being three metres long the female shark was a juvenile. The Greenland shark was taken to Newcastle University where it was frozen and then donated to the Natural History Museum in London where it was examined and then preserved in alcohol where it remains to this day.

Feeding Habits

The bulky size and small fins of the Greenland shark mean that it is one of the slowest moving fish in the oceans, with scientists calculating that its top speed is around 1.6 miles per hour – about half the speed the average adult walks. For this reason Greenland sharks are thought to mostly scavenge food from the seabed, using their strong sense of smell to locate food sources. All types of animals will be consumed with dead fish, squid and marine mammals being consumed, but Greenland shark have also been found with the flesh of animals such as reindeer and polar bears in their stomachs – presumably from animals which had died and fallen into the sea. However, there is evidence that Greenland sharks can hunt to a limited extent as relatively fresh seal flesh has been found in the stomachs of this species. One theory is that Greenland sharks have learned to quietly approach and kill sleeping seals (most seals sleep on land but arctic seals have adapted to sleep in water to avoid polar bear attacks), although this hypothesis has yet to be proven. Another theory is that Greenland sharks have learned to wait near to holes in Arctic ice and ambush seals who use these holes to access the surface to breathe. In 2013 a Greenland shark was found on the Canadian coast apparently choking on a two foot long chunk of flesh from a moose. It was unknown how the Greenland shark came to be feeding on this animal. Due to their size fully grown Greenland sharks are not commonly preyed upon, although it is thought that large sperm whales and groups of killer whales may attack and kill Greenland sharks on rare occasions.

A Lifespan of Hundreds of Years

The Greenland shark is thought to be an extremely slow-growing and long-lived species. For many years it was not possible to accurately gauge the age of Greenland sharks as the age of fish is estimated by studying a bone structure in the inner ear known as the otolith, but as sharks have skeletons made of cartilage, not bone, this was not possible. It was known that Greenland sharks were slow-growing and long-living as Greenland sharks which were caught, tagged and then re-captured years later were found to have only grown a few centimetres in length. Based on this growth rate a fully-grown Greenland shark would be around two hundred years old which would make Greenland sharks the world’s longest-living vertebrate.

Greenland Shark Size

Size comparison between a fully grown Greenland shark and a human.

In 2016 a breakthrough was made when researchers at the University of Copenhagen found a way of accurately calculating the lifespan of a Greenland shark. The researchers used a radiocarbon dating technique to examine proteins which were found in the lens of the eyes of twenty-eight Greenland sharks and calculated that the largest shark was between 272 and 512 years old, with its most likely age being 390. This makes Greenland sharks easily the longest living vertebrate in the world and means they may have to be around 156 years old before they are capable of breeding.

Parasites

Greenland sharks and other sleeper shark species are often affected by a parasitic copepod known as Ommattokoita elongata. This parasite is around 5cm long and attaches itself to the eye of Greenland sharks. Once in place it will feed on the cornea of the shark and will severely damage the eyesight of the shark, often resulting in complete blindness if the shark has Ommattokoita elongata attached to each eye. However, due to their adaptations to living in deep, dark water and the sensory information which they can gain from their sense of smell and lateral line the Greenland shark can continue to live and feed even when they have lost most, or even all, of their sight.

There is also a theory put forward in the scientific journal Nature in the 1960s that the Ommattokoita elongata and Greenland sharks live in a state of mutual dependence. It was proposed that while Ommattokoita elongata feeds on the Greenland shark the movements of the parasite attracts smaller fish who see it as prey, allowing the shark to catch these fish easily. Despite the theory being proposed many decades ago, it has still not been established if such a symbiotic relationship exists.

Catching Greenland Sharks

Unsurprisingly this is not a species which is often caught on rod and line and there is no British shore or boat caught record for this species. There is an International Game Fish Association all-tackle rod and line caught record. This is listed as a huge Greenland shark of 1,708lb captured by Terje Nordtvedt at Trondheimsfjord, Norway in October 1987 on a herring bait. Greenland shark have been featured in an episode of Robson’s Extreme Fishing Challenge broadcast on Channel 5 in 2014 and in two episodes of River Monsters broadcast in 2013 and 2017 respectively. In these episodes artisanal Greenland fishermen are seen catching Greenland sharks from holes cut into ice using simple handlines, and the species is also caught by rod and line anglers from boats in Norwegian waters.

Human Consumption

Hákarl

Hákarl hanging to dry as part of the process to make the flesh safe to eat.

Greenland shark were heavily hunted in the first half of the twentieth century with up to 30,000 sharks caught by fishermen every year. The Greenland shark was commercially valuable as the liver oil of this species was used for lamp oil and as an industrial lubricant, and the rough skin could be used to make boots and shoes. As modern manufacturing processes have developed the commercial value of the oil and skin has plummeted and there is currently no large-scale commercial fishery for this species. Individual fishermen from Iceland and Greenland still hunt this shark on a small-scale artisanal basis. If eaten fresh the flesh of the Greenland shark is highly dangerous to humans as it contains high levels of toxins and can produce sickness, nausea, diarrhoea and in extreme cases can lead to death. Despite this, the flesh of the Greenland shark used in the Icelandic national dish of Hákarl. This is made by burying the shark underground for several weeks and then cutting sections of the flesh away and hanging these to dry for several months. After this process the flesh is safe to eat, although Hákarl is described as having an ammonia-like smell and an extremely fishy taste.

Conservation

Although Greenland sharks are no longer caught on a large scale there is concern over how many are taken as bycatch by trawlers and then discarded at sea. Due to the extremely slow growth rates and low reproductive capacity it would be extremely difficult for this species to recover from any decline in numbers. For this reason, Greenland shark is classed as Near Threatened in Europea and globally by the IUCN (International Union for the Conservation of Nature), although this BBC article paints a more positive picture, stating that there may be healthy numbers of Greenland sharks in deep-sea areas which humans have yet to discover.

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