The Greenland shark is the largest member of the Somniosidae family. It is the second largest* carnivorous shark after the great white and it is the largest Arctic fish. Its range extends from the Arctic Ocean and Northern Europe to the 32nd parallel north in the Atlantic Ocean. It reaches an enormous size and despite its lethargic appearance, it is a predator capable of short bursts of speed, and under certain conditions may hunt seals and even larger mammals including the beluga whale. The Greenland shark is very rarely observed because of its bathybenthic environment that is inaccessible to divers. The first underwater photos of a live specimen were taken in the Arctic in 1995, and the first video images of a shark swimming freely under natural circumstances were filmed by the current GEERG team in 2003 in the St. Lawrence Estuary. *(equal length)
NAMES Scientific Name: Somniosus microcephalus* (Bloch & Schneider, 1801)
somniosus : from the latin [somnus] + [osus] = sleep (full of)
microcephalus : micro + greek [kephalē] = small head
Greenland shark, sleeper shark, ground shark, grey shark, gurry shark, requin du nord (Fr.), requin du Groenland (Fr.), laimargue (Fr)., requin noir (Fr.), skalugsuak (Inuktitut), iIqalugjuaq (Inuktitut), requin dormeur (Fr.), requin de fond (Fr.), requin de glace (Fr.) The Greenland shark is often called the «Bottom shark» by St. Lawrence and Saguenay fishermen in Quebec.
SIZE AND APPEARANCE Maximum length: Up to 7.3m (24')
Average length: 2.5m to 4.5m (8' to 15')
Weight: Up to 1,200kg (2,645 lbs) (Koefoed 1957)
The Greenland shark has a cylindrical body. It has no anal fin. There is a distinct caudal keel on the caudal base. Its head is small compared to the rest of its body. There are two large spiracles above and slightly behind the eyes. The shark's skin can be black, brown, grey, or a spotted mix of all three. Its whitened rostrum (snout) (see photo below) is a sign of repeated abrasion resulting from the foraging sharks' quest for food on the sea floor.
Its 2 dorsal fins are small and spineless. The base of the dorsal fins is shorter than their lengths. The caudal fin is assymetrical. Its eyes are round and small and are usually host to a parasitic copepod, except in the case of the St. Lawrence specimens observed by GEERG which rarely have parasites.
The Greenland shark's dentition determines its feeding technique. The upper teeth, pointy but not serrated, enable the shark to pin its food into position. The bottom teeth, wide and curved sideways, serve to cut the food item by swinging the head in a circular motion. By doing so, the shark cuts out a round "plug" of flesh from its victim when it is too large to swallow whole. This behaviour was recorded on film by Dr. George Benz on Baffin Island. The upper teeth number 48 to 52 while the lower teeth number 50 to 52. Small prey items that fit into the shark's mouth whole are simply sucked off the bottom.
The documented plug-like wound mentioned above is not to be associated with the so-called "corkscrew" wound which has been reported by the media and in a documentary film in 2010. The corkscrew wound on seals has not been definitively associated with the Greenland shark and we believe that it may in fact not be caused by any shark species. See the section below for more details: CORKSCREW CONTROVERSY
The distribution of the Greenland shark extends from the Arctic Ocean and Northern Europe to the 32nd parallel north in the Atlantic Ocean, including the St. Lawrence Estuary and Saguenay Fjord. In fact, this is the only shark that can tolerate Arctic temperatures yearround. Its presence has been recorded in every season in the Saguenay Fjord, not only in winter as is widely believed. Considering the cold temperatures and the depth of the fjord (close to 300 m) this is entirely plausible.
Water temperature is a crucial factor for this shark's comfort zone. It prefers very cold water (-0.6°C to 10°C) and seasonal variations determine its migration up or down the water column. In the summer, the shark is normally found at great depth where the water is coldest. In winter, it rises to the surface layer, which is colder than the water on the sea floor.
GEERG observations of the Greenland shark since June 2003 put into question many of the long accepted theories about the Greenland shark's seasonal and daily migrations throughout the water column.
Provisional distribution map for Somniosus microcephalus based on research by GEERG. Details on observations (other than year) are available. Map does not include data from the U.S. or Europe. To submit additional sightings or captures, please contact us at: firstname.lastname@example.org
DEPTH RANGE The Greenland shark has been visually recorded from the surface (0 m) to 2,200 m (Observed from a submersible on the wreck of the SS Central America in 1988). Unidentified specimens of the genus Somniosus - possibly S. microcephalus - were recorded on camera swimming by oil rigs at deeper depths in 2007 (2,200 m / Gulf of Mexico) and 2012 (2,774 m / Brazil). The pressure at the site off Brazil was 4,050 PSI (277 BAR), which is beyond the rupture point of a SCUBA tank. For the sake of comparison, the pressure inside the tires of most passenger cars is between 32 to 35 PSI.
SWIMMING SPEED The Greenland shark is one of the slowest swimming sharks in the world and we have often observed Greenland sharks that were almost immobile. However, based on our hundreds of visual observations of free-swimming Greenland sharks, and having carefully analysed hours of video images as well as several months of acoustic telemetry data, we have determined that the average swimming speed of the Greenland shark in the St. Lawrence Estuary is 0.3 m/s. GEERG telemetry data from 2005 has also allowed us to calculate a long-distance average speed of 0.3 m/s for a single shark over a period of 29 hours and a distance of 26 km (Gallant et al. 2013). We have also observed the Greenland shark reaching or exceeding bursts of speeds of 1 m/s, which is a common occurence during tagging operations by divers. Reports of a top speed of 0.7 m/s (1.6 mph) for this species are therefore false. Reports of the Greenland shark requiring "a full seven seconds just to move its tail back and forth" are also false as can be clearly observed in our video sequence at the top of this page.
WORLD'S SLOWEST SHARK?
Having ourselves swum alongside dozens of Greenland sharks, we know that it is often very slow-moving. However, we do not claim that it is the world's slowest shark. On what basis does one make such an assertion? Some shark species remain motionless (0 m/s) for long periods while they use their spiracles to extract oxygen from the water. Other shark species have no spiracles so they have to constantly swim to force oxygen through their gill openings. Greenland sharks have unusually large spiracles that allow them to take in oxygen while swimming at reduced speed in order to conserve energy in their near-freezing environment, or to hunt by stealth. However, they are entirely capable of bursts of speed, possibly to hunt, but certainly to evade attack and to escape from GEERG divers equipped with tags and spears! Studies have shown that Pacific angel sharks covered distances of no more than 30 to 75 km over a period of three months while one Greenland shark that we tagged in 2005 covered 26 km in just 29 hours. Both species use their spiracles - at least in part - to breathe and both species have shown site fidelity over a period of months - even years - as is the case at our study site. So how does one define world's slowest shark?
The Greenland shark is by no means a race car, but there have been many occasions when physical overexertion has prevented us from keeping pace with one for more than 1-2 minutes while diving.
Few people in the entertainment industry or in the media have shown interest for this allegedly characterless shark. In the absence of definitive proof or a clear scientific definition, the title of 'World's Slowest Shark' may therefore be an attempt at attracting media attention to this much overlooked species. Scientific rigour precludes us from making such a bold statement.
PREY The Greenland shark is an opportunistic predator that will eat just about anything that comes across its path, either dead or alive. However, we believe that it is primarily a scavenger.
Mammals: beluga, narwhal, porpoise, seals, and other animals including a dog, horse, reindeer and white (polar) bear remains.
Invertebrates: crustaceans, gastropods, jellyfish, octopus, sea stars (sun stars & brittle stars), squid, urchins, whelk and other snails.
Others: Bird remains, kelp.
Mammals: The Greenland shark has reportedly been seen by scientists, hunting caribou in the manner of a crocodile ambush at rivermouths in the Canadian Arctic. Note: This much-publicised anecdote - although plausible - has never been substantiated. More than likely, the Greenland shark feeds on drowned caribou that fell through the ice while migrating.
According to GEERG researcher Jeffrey Gallant, "There is little chance that a Greenland shark could predate a live adult white (polar) bear unless it were injured or seriously ill." Contrary to what was reported by the media in 2008, global warming is also unlikely to help the Greenland shark catch bears. "The Greenland shark simply cannot afford the risk of injury nor the expenditure of energy required to kill such a large and dangerous animal, with or without the help of global warming. There is far easier prey to be found."
PREDATORS The only confirmed predator of the Greenland shark is the sperm whale (Physeter macrocephalus). GEERG has recorded two occurrences of a sperm whale exhibiting predatory behaviour while in the presence of the Greenland shark in the St. Lawrence Estuary. Unfortunately, the same whale - known as Tryphon - died of entanglement in fishing apparatus in 2009. Further investigation by GEERG researcher Jeffrey Gallant (2009) led to the discovery of another potential indicator that this particular sperm whale could have been feeding on Greenland sharks for several years. Photo analysis revealed that Tryphon's teeth were severely eroded from abrasion. The same dental anomaly was observed in a pod of orcas (Orcinus orca) feeding on Pacific sleeper sharks (Somniosus pacificus) off British Columbia in 2008.
The Pacific sleeper shark is practically identical to the Greenland shark. Orcas and sperm whales are believed to feed on sleeper sharks mostly for the large quantity of oil found in their livers. However, the hunters must first tear apart their prey with their teeth which are eroded by the sharp denticles that cover the shark's skin. Feeding on sharks in this fashion over a period of several years would likely accelerate tooth wear thus transforming the predator's normally sharp teeth into rounded stubs.
Video: Sperm whale known as Tryphon clicking in the presence of Greenland sharks. The sperm whale may have been using echolocation to hunt Greenland sharks.
Greenland sharks are also cannibalistic in the presence of other sharks that are either dead, injured, or caught on a line.
REPRODUCTION Little research has been done on the Greenland shark's reproduction. It is ovoviviparous: its eggs develop and hatch inside the female. The female gives birth to at least 10 pups at a time each measuring approximately 40 cm. Mating and birth have never been observed.
Females observed by GEERG in the St. Lawrence mostly have mating scars on their caudal area. When the male decides to mate, it bites the female into submission. Fortunately for the female, its skin is twice as thick as the male's.
LIFE EXPECTANCY Aging a Greenland shark is practically impossible since it does not have vertebral growth rings as do many other species. Therefore, determining the age of a Greenland shark would require the capture and measurement of a newborn pup followed by periodical recapture and measuring until the end of its natural life. Doing so in captivity* would not reflect the natural growth rate of a shark in its natural environment, and a study in the wild over a long period, say 200 years, would require several generations of researchers as well as an extreme range tracking system, the likes of which does not yet exist.
Very limited research (a single science paper) has shown that the Greenland shark grows by about 0.5 to 1 cm per year. A shark that was captured and tagged off Greenland in 1936 was recaptured in 1952. In 16 years, the shark's length had only increased by 6 centimetres. Assuming its growth rate is constant (no growth spurts), one can thus hypothesize that a mature seven-metre specimen could be over 200 years old, making the Greenland shark the longest-living vertebrate on the planet.
* No Greenland shark has ever been kept in captivity
for more than a month.
PARASITES The parasite most commonly associated with the Greenland shark is the copepod Ommatokoita elongata. It latches itself to one or both of the shark's eyes which causes lesions to the cornea and can render the shark partly blind. However, even if it was completely sightless, the Greenland shark could easily survive using its other senses to detect and localise prey.
Also, since the shark lives at great depth and often under ice, its habitat is normally devoid of light rendering its eyes useless. Certain researchers believe the copepod is bioluminescent and serves to attract prey to the shark but this has never been proven. It is interesting to note that while over 90% of Arctic populations of the Greenland shark parasited by the copepod, less than 10% of the sharks encountered by GEERG researchers in the St. Lawrence are hosts of Ommatokoita elongata.
In 2004, GEERG researcher Jeffrey Gallant observed a sea lamprey (Petromyzon marinus) parasiting a Greenland shark near Baie-Comeau, in the St. Lawrence Estuary. (See science paper* in Publications section)
* Gallant, J., C. Harvey-Clark, R.A. Myers, and M.J.W. Stokesbury. 2005. Sea lamprey (Petromyzon marinus) attached to a Greenland shark (Somniosus microcephalus) in the St. Lawrence Estuary, Canada. Northeastern Naturalist. 2006 13(1):35–38.
TOXICITY AND TRIMETHYLAMINE (TMAO) Water and dissolved solutes, including various salts, calcium chloride and sulphates, pass through a fish’s body (cells, tissues, and organs) in a process known as osmosis. Larger molecules inside the blood and tissue fluids of fishes and sharks, including proteins and trimethylamine oxide (TMAO*), also exert a contributory osmotic effect but they are too large to pass through the channels that govern salt balance.
* By-product of the metabolic breakdown of proteins and amino acids.
If the salt concentration in a fish’s tissues is lower than that of the surrounding water, its body will absorb salt from the environment until both levels become equal. If a marine fish swims up a freshwater river, the reverse phenomenon will occur and it will diffuse salt into the environment via specialised sodium secreting cells located primarily in gill tissue. In both cases, too much or too little salt is detrimental to most fish species because they can only survive within a specific range of salt concentrations. Fish that are thus restricted to either freshwater or seawater are known as stenohaline. Some species, such as salmon, are able to osmoregulate in varying levels of salinity. These fish are called euryhaline.
When salt and other solutes enter a fish’s tissues, they force water out of the body. Since salt levels in marine fishes are lower than those of the surrounding environment, they must continually take in water and excrete salt through their gills. Salt levels in sharks are also lower than that of sea water but sharks manage osmosis differently. In order to maintain a stable amount of water in its body, the Greenland shark will retain a high concentration of urea in its blood, thus compensating for lower salt concentrations. However, because high levels of toxic urea will damage its body by destabilizing protein, the Greenland shark also retains even higher levels of trimethylamine oxide to counter the damaging effects of the urea. When the trimethylamine oxide and urea are combined with the salt in the shark's tissues, the osmotic pressure of the shark's body fluids is higher than that of the surrounding water. In other words, the shark is ‘saltier’ than seawater. Unlike bony fishes that must constantly take in water to replace water lost through osmosis, the Greenland shark does not need to expend energy to maintain life-sustaining water levels in its body.
In addition to contributing to the shark’s osmotic pressure, trimethylamine oxide and high levels of urea also serve as a natural antifreeze by stabilizing the enzymes and proteins in the Greenland shark’s tissues. When the shark encounters extremely deep and cold conditions, this prevents the formation of ice crystals that disrupt cell walls and cause the leakage of cellular contents, which results in tissue and organ damage, then death.
When Greenland shark flesh is consumed, the digestive process turns trimethylamine oxide (TMAO) into trimethylamine (TMA), a substance that smells like ammonia and rotting fish. In addition to causing intestinal discomfort, trimethylamine also has adverse neurological effects akin to consuming excessive quantities of alcohol. Death may ensue in extreme cases when too much shark flesh has been consumed. Greenland shark flesh is nonetheless considered a delicacy in Iceland. See ‘Fisheries’ section below.
Attacks on humans attributed to the Greenland shark are extremely rare. However, it is important to realise that it lives in water so deep and inhospitable to humans that most will never encounter a swimmer or diver. It would thus be very imprudent to label the shark as harmless to man based solely on the few existing statistics. During natural encounters in the St. Lawrence Estuary, at least one shark was observed swimming by the boat tender. Even more alarming, a shark stalked a team of divers all the way to the surface. The latter could be indicative of visual reconnaissance by an experienced live seal predator. Further demonstration of the shark's ability to ambush live prey was experienced firsthand by GEERG researchers Harvey-Clark and Gallant during a frighteningly close encounter in zero visibility and shallow water (5 m) in June 2004.
(1) In 1940, a wildlife officer was stalked by a Greenland shark while walking on pack ice at Basques Island in the St. Lawrence. The shark's behaviour is consistent with that of an experienced seal predator.
(2) Around 1859, a human leg was reportedly found in the stomach of a Greenland shark caught at Pond Inlet, on Baffin Island.
(3) A frequently told story is that of a native family being attacked by a Greenland shark during a canoe excursion on the St. Lawrence in 1848. They only survived the attack by throwing an infant child overboard to distract the shark. Another version of the same story takes place aboard a kayak in the Arctic, which leads us to believe that both stories are more legend than fact.
Although the following are by no means attacks, the victims having already died, thousands of victims of shipwrecks and torpedoings in the North Atlantic and the St. Lawrence - including the Empress of Ireland - over the last centuries have no doubt been scavenged by the Greenland shark as it hovers just over the sea floor in search of food.
More and more research is being conducted on the Greenland shark. In Canada, GEERG and SRI Canada are pursuing various research projects in the St. Lawrence Estuary and the Saguenay Fjord. The Canadian Shark Research Laboratory conducts research on Greenland shark specimens captured by the fishing industry in the Maritimes.
GEERG researchers are particularly interested in the Greenland shark's movements and distribution in the St. Lawrence and Saguenay systems as well as in its behaviour under natural conditions (no captures or use of attractants).
The cost of mounting expeditions to conduct field studies is very high, and funding for such endeavours is extremely rare since this species has practically no commercial value, hence it generates little interest. GEERG thus relies on the support of the diving community, the coastal population, active and retired fishermen, and our institutional partners which include the Musée du Fjord, the Aquarium du Québec, the Biodôme de Montréal, the University of British Columbia, Dalhousie University, and the Université du Québec à Trois-Rivières.
In certain countries, the Greenland shark is still hunted commercially for its oil. Between the latter half of the 19th century and 1960, fishermen in Greenland and Iceland caught up to 50,000 sharks annually. The oil contains Vitamin A and was used to light lamps.
Because its flesh is non-edible, the carcass was dumped overboard into the ocean where it fed other sharks. The shark's flesh contains so much urea and TMAO (trimethylamine oxide) that it must undergo a long and unpleasant process before it can be fed to sled dogs. Foregoing the process makes the dogs enter a drunken-like state called « shark sick » . High levels of intoxication lead to convulsions, or even death.
In Iceland, shark meat is processed to perfection, buried in gravel for 6 to 12 weeks and then hung to dry for 2 to 4 months. It is then cut into bite-sized cubes, and served as an hors-d'oeuvre called hakárl or kæstur hákarl. A more modern technique is to simply compress the meat in a large perforated container to remove the toxic fluids.
The tasty treat is traditionally downed with a shot of Brennivín, the local firewater. All right then: "Bottoms up!"
(Below) Hakarl drying near Bjarnahöfn, Iceland. Image : Creative Commons
Sable Island (Nova Scotia) and now the North Sea (England & Scotland) are ripe with controversy surrounding the Greenland shark. It has long been suggested that Sable Island is a hunting ground for sharks based on the regular appearance of mutilated seal carcasses. Many of the victims present a corkscrew-like cut that twists around the length of the seal's body. This particular wound is believed by many to be the result of a Greenland shark attack. Similar reports began to emanate out of the UK in the summer of 2010. After much analysis and debate, we do not believe that the Greenland shark is responsible for these so-called "corkscrew" kills. The environmental and behavioural evidence put forward simply does not concur with our own findings that are based in part on telemetry data and on firsthand observation of the Greenland shark underwater. Certain environmental conditions normally associated with the Greenland shark's distribution also do not exist at either location.
Under certain conditions, seal carcasses that wash up dead on Sable Island without the distinctive corkscrew wound
may still have been scavenged or killed by the Greenland shark. Missing heads and flippers are typical of a Greenland shark feeding, but the only confirmed bite wound pattern for the Greenland shark is circular. The Greenland shark bites into its victim and then twists itself repeatedly until a 'plug' of flesh is torn out. It may even be possible for a large seal - or even a cetacean - to survive such an attack. The corkscrew wound simply does not fit with the known feeding pattern of the Greenland shark: a pattern that has been observed and filmed. The culprits are more than likely dynamic positioning thrusters used by vessels associated with offshore drilling or construction.
Note: Some of the more mangled dead seals that wash up at Sable Island may have been
killed by the white shark, Carcharodon carcharias, which appears to be making a comeback in the North Atlantic.
RELATION WITH MAN
Unlike the god-like reverence for sharks prevalent in the South Pacific, Westerners hold little appreciation for these toothed monsters. Generally perceived as indiscriminate killing machines, this isn't usually the case for the Greenland shark, at least not by certain fishers that mockingly call it the « bottom shark » and consider it to be completely harmless.
Even worse, certain fishers consider it a pest that damages their nets and that contributes to the decline of fish stocks. Pity the shark that is caught by these fishers who cut off their caudal fin and toss the shark overboard to a certain and pointless death.
The overall public perception on sharks isn't much better. Thanks to sensationalistic documentaries and movies such as « Jaws », which largely prevailed until recently, few people have any sympathy for sharks although most gaze in awe at the sight of the beast hanging from a hook at the local wharf. Like them or not, few animals generate so much media frenzy and genuine fascination. GEERG aims to reverse this baseless and destructive trend with ground-breaking research and public-awareness.
INUIT LEGEND SKALUGSUAK
The Greenland Shark's tissue has a high urea content, which gave rise to the Inuit legend of the shark's origin: An old woman washed her hair in urine and dried it with a cloth. The cloth blew into the sea and there it became Skalugsuak, the first Greenland Shark.
When a young Inuk girl told her father she wanted to marry a bird, he killed her fiancé and threw his daughter into the sea from a kayak. When she hung on to the side, he cut off each of her fingers until she let go. Sedna slid into the depths where she became the goddess of the sea. Each of her fingers turned into a sea creature, including the Greenland shark. The shark was entrusted with the duty to avenge the goddess and one day, it capsized the father's kayak and ate the man while he was fishing. When an Inuk dies in this fashion, the locals say the shark was sent by Sedna.
In 1922, the crew of a Newfoundland sealer stuck in the ice captured over 30 Greenland sharks after attracting them to the surface by emptying the bilges of seal fat and blood. The sharks hauled out of the water with gaffes measured between 3.7m and 4.9m (12' to 16'). Many other stories tell of similar experiences.
When beluga whales were still hunted on the St. Lawrence, dozens of Greenland sharks were drawn to the killing grounds at high tide where the whales were gutted and bled to death in towns such as Bergeronnes. As the tide went down, the sharks became beached on the shoals and they too were sliced open by the fishermen in order to extract their livers for oil. When the tide came up again, some sharks, still alive and much to the surprise of their executioners, managed to swim back to the ocean where they survived for a short while longer.
The Greenland shark is not listed as a threatened species by COSEWIC (Committee on the Status of Endangered Wildlife in Canada). However, its numbers in the St. Lawrence and Saguenay are still unknown.
The Greenland shark is listed as Near Threatened by the IUCN Red List (International Union for the Conservation of Nature and Natural Resources).
Click HERE to go to the IUCN Red List web page on the Greenland shark.
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Les nouvelles du large, (Bulletin no. 7) - GREMM, 18.06.1999
Les nouvelles du large, (Bulletin no. 8) - GREMM, 24.06.1999