Common names: Sleeper shark, ground shark, grey shark, gurry shark.

Inuktitut names: Skalugsuak, Ekalugssuaq, Iqalugjuaq.

French common names: Requin du nord, requin noir, requin dormeur, requin de fond, requin de glace.

Scientific Name: Somniosus microcephalus* (Bloch & Schneider, 1801) — Somniosus: from the Latin [somnus] + [osus] = sleep (full of); microcephalus : micro + Greek [kephalē] = small head; Meaning: *Smallheaded sleeper

In spite of its appellation, the Greenland shark is not endemic to Greenland, nor is it unusual to find it elsewhere. It is just as home in the St. Lawrence and the Saguenay as it is in the Arctic Ocean.

Greenland sharks have been visually recorded from the surface (0 m) down to 2,200 m¹ near the wreck of the SS Central America (recorded by an unmanned submersible 260 km east of Cape Hatteras) in 1988². The pressure at the location off North Carolina was 3,203 PSI (221 BAR), which is beyond the safe operating limit of many scuba tanks. For the sake of comparison, the pressure inside the tires of most passenger cars is between 32 to 35 PSI. A sleeper shark—species unknown—was observed at the depth of 2,774 m off the coast of Brazil in 2012.

¹ The species of sleeper shark observed at 2,200 m (1998) is unconfirmed although it is generally assumed to be a Greenland shark due to the location.
² Herdendorf, C. E., and Berra, T. M. (1995). A Greenland shark from the wreck of the SS Central America at 2,200 meters. Trans. Am. Fish. Soc. 124, 950–953.

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 scuba diving. Unless the Greenland shark is only compared to other shark species or fish of the same size, and for all of the reasons stated above, we thus do not believe that it is the world’s slowest shark, let alone the world’s slowest fish.

As for other species vying for the title of the world’s slowest shark—and discounting burst speeds—a study¹ demonstrated that Pacific angel sharks, Squatina californica, covered distances of no more than 30 to 75 km (19 to 47 miles) over a period of three months, or at most 7.3 km (4.5 miles) in a single night, while one Greenland shark tagged by GEERG in 2005 covered 26 km (16 miles) in just 29 hours². Both species use their spiracles³ to assist with breathing and both species have exhibited site fidelity (philopatry) over a period of months, or even years. Granted, angel sharks don’t migrate and they aren’t the most active swimmers so it may be an unfair comparison. So what about the other sleeper sharks and deep-sea dogfishes such as the dwarf lanternshark and gulper sharks? Any one of them could win—or should it be lose?—by a snout!

Until recently, few people in the entertainment industry or in the media have shown interest for the allegedly characterless Greenland 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.

¹ Fouts, W.R. & Nelson, D.R. (May 7, 1999). “Prey Capture by the Pacific Angel Shark, Squatina californica: Visually Mediated Strikes and Ambush-Site Characteristics”. Copeia. American Society of Ichthyologists and Herpetologists. 1999(2): 304–312.
² Gallant, Jeffrey J., Marco A. Rodríguez, Michael J. W. Stokesbury, and Chris Harvey-Clark. (2016). Influence of environmental variables on the diel movements of the Greenland Shark (Somniosus microcephalus) in the St. Lawrence Estuary. Canadian Field-Naturalist 130(1): 1-14.
³ Unlike the many shark species that must constantly swim to force oxygen through their gill openings, some sharks can remain motionless for long periods while they use their spiracles to extract oxygen from the water. Among these, the Greenland shark has unusually large spiracles that allow it to take in oxygen while swimming at reduced speed either to hunt by stealth or to conserve energy in its near-freezing environment.

Little research has been done on the Greenland shark’s reproduction although it is believed to reach sexual maturity at the age of 156 ± 22 years¹. Since the female gives birth to at least 10 pups at a time, some researchers believe that it is viviparous: Its eggs develop and hatch inside the female where the pups are fed by a placenta. The Greenland shark is believed by others to be ovoviviparous (aplacental viviparity): Its eggs also develop and hatch inside the female but there is no placenta. The pups thus feed on each other so few survive until birth. Although mating and birth have never been observed, newborn pups are believed to measure approximately 40 cm.

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.

¹ Nielsen, J., Hedeholm, R. B., Heinemeier, J., Bushnell, P. G., Christiansen, J. S., 2815 Olsen, J., et al. (2016). Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Science 353, 702–704.

The Finnish proverb stating that “Age does not give you good sense, it only makes you go slowly,” may hold some truth with the Greenland shark. With an average cruising speed of 0.3 m/sec (1 ft), the Greenland shark is indeed a very relaxed swimmer. Its unusually slow metabolic rate may be attributed in part to its frigid living environment, which may also help explain the latest discovery¹ on this mysterious northerly predator.

Until recently, aging a Greenland shark was impossible since it does not have vertebral growth bands—counted like rings on a tree—as do many other shark species. Therefore, determining its age 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 under controlled conditions—no Greenland shark has ever been kept in captivity for more than a month—would not reflect the natural growth rate of a shark living in an oceanic 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 and ongoing tracking system, the likes of which does not yet exist.

Even today, very limited information exists on recaptured sharks, and the only science paper with reliable recapture data is over fifty years old. In that study¹, 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 eight centimetres (3 in), or 0.5 cm (0.2 in) per year. Two less reliable reports in the same paper obtained from sharks recaptured after two and 14 years suggest growth rates of no more than 1.1 cm (0.43 in) per year, or approximately 0.3 m (1 ft) per 30 years. Assuming the rate is constant—no growth spurts—a fully-grown Greenland shark could theoretically be well over 500 years old.

The Greenland shark’s suspected yet hypothetical longevity was apparently confirmed in a study² released in August 2016 by a science team led by Julius Nielsen at the University of Copenhagen. According to the article published in the journal Science, the scientists used radiocarbon dating to establish the age of 28 Greenland sharks. The age ranges of sharks born before atomic bomb testing in the 1950s—which nearly doubled the amount of carbon-14 in the atmosphere—revealed a life-expectancy of at least 272 years, that sexual maturity may not be reached before 156 ± 22 years, and that the largest shark (5.2 m / 17 ft) was 392 ± 120 years old. Considering that the largest known length for the Greenland shark is over seven metres (23 ft), there may be living specimens that were swimming in the St. Lawrence when Jacques Cartier laid claim to New France in 1534. Although scientific debate on this discovery may linger for years—radiocarbon dating of deep-dwelling marine organisms is not very precise—, it is safe to say that even with the most conservative margin of error, the Greenland shark is currently and by far the longest-living vertebrate on the planet.

¹ Hansen, P. M. (1963). Tagging experiments with the Greenland shark (Somniosus microcephalus (Bloch and Schneider)) in subarea 1. Int. Comm. Northwest Atl. Fish. Spec. Publ. 4, 172–175.
² Nielsen, J., Hedeholm, R. B., Heinemeier, J., Bushnell, P. G., Christiansen, J. S., 2815 Olsen, J., et al. (2016). Eye lens radiocarbon reveals centuries of longevity in the Greenland shark (Somniosus microcephalus). Science 353, 702–704.

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 stabilising 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.

According to the Canadian Shark Attack Registry, the Greenland shark has been involved or suspected in four confirmed incidents with humans in Canada. As of 2023, most confrontations have involved stalking people by the shore, in boats or diving. None have resulted in an attack or injury.

It is important to note that the Greenland shark is found in water so deep and inhospitable to humans that most will never encounter a swimmer or diver during their entire lifetime. It would thus be very imprudent to label the shark as harmless to man based solely on the few existing statistics. During encounters by GEERG in the St. Lawrence Estuary, sharks have been observed leaving the bottom to investigate diver activities at the surface. In one instance, a shark stalked a team of divers all the way to the surface at the end of a dive. Both circumstances 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, 15 ft) in June 2004.

Although the following are by no means attacks, thousands of victims of shipwrecks and war in the North Atlantic and the St. Lawrence—including the Empress of Ireland—may have been scavenged by the Greenland shark as it hovers just over the sea floor in search of food.

¹ Gallant, J. (2022. July 26). Canadian Shark Attack Registry (1st ed.). St. Lawrence Shark Observatory. https://geerg.ca/en/shark-attacks

Fallen Empress (Oil on canvas) © Jean-Louis Courteau. Courteau’s painting depicts how the Empress of Ireland may have appeared a few weeks after her sinking. Such a wide view of the wreck would in fact require extraordinary environmental conditions since visibility on the Empress of Ireland is usually poor, rarely exceeding six metres. The opportunistic Greenland shark homing in on the smell of death was likely a frequent visitor to the wreck in the months that followed the disaster.

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.

The Inuit long dried the Greenland shark’s skin to make boots and they used its teeth to cut hair. Sailors used its denticle-covered skin under their boots to prevent slipping on wet wooden decks.

To this day, 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. The St. Lawrence Shark Observatory aims to reverse this baseless and destructive trend with ground-breaking research and public-awareness.

We have found numerous documented references of Greenland sharks in the St. Lawrence and the Saguenay Fjord dating as far back as the early 1800’s.

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 3.7 m and 4.9 m (12 ft to 16 ft). Many other stories tell of similar experiences.

When beluga whales were still hunted on the St. Lawrence, dozens of Greenland sharks were often 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.