- Scientific name: Somniosus microcephalus
- Also know as: Sleeper Shark, Gurry Shark
- Size: Up to 21 – 24ft in length and 2,500 – 3,000lbs
- UK minimum size: N/a
- UK shore caught record: N/a
- 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 United Kingdom, but can also occasionally be found elsewhere around the British Isles and 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. 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). However, it is a species which is rarely encountered by humans and many aspects of its life cycle are unknown, meaning that is is often referred to as the world’s most mysterious shark. Indeed, the Greenland shark was not observed and photographed by humans until 1995, and 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 – have never been viewed by humans and much of the information on this species is therefore made up of guess work and theories. Despite this the Greenland shark has been hunted for hundreds of years 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.
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 definitely extends into colder waters along the eastern coast of North America and in Europe they are found in Scandinavian and British waters – in 2013 an immature Greenland shark washed up on the Northumberland coast in North East England. However, due to the great depths that this species can live at the true range of the Greenland shark is unknown. 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 sharks are generally seen as a very deep water species as they will live and feed at immense depths of over 2000 metres where the water is extremely cold and little light penetrates. However, 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.
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 seals as they sleep in the water (most seals sleep on land but arctic seals have themselves 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, however, known that Greenland sharks were slow growing and lived to long ages 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 200 years old which would make Greenland sharks the world’s longest living vertebrate.
However, in 2016 a breakthrough was made when researchers at the University of Copenhagen found a way of accurately calculating the lifespan of a Greenland. 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.
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, as the skin of this species is too tough for the parasite to attach to. Once attached 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 that the Ommattokoita elongata and Greenland sharks live in a symbiotic relationship with the parasite feeding on the shark and simultaneously attracting prey towards the shark, possibly by using bioluminescence, allowing the shark to catch faster moving prey. At the time of writing, there is not yet solid evidence to back this up, and it remains a theory.
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. However, 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. However, individual fishermen from Iceland and Greenland still hunt this shark on a small-scale artisan 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, diarrhea 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 under sand 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.
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 by the IUCN (International Union for the Conservation of Nature), although this BBC article paints a more upbeat picture of Greenland shark numbers, stating that there may be healthy numbers of Greenland sharks in deep-sea areas which humans have yet to discover.