Greenland sharks are arguably the slowest sharks in the ocean. While great whites and mako sharks dash around at over 50 kph, Greenland sharks idle along at barely 1 kph.
It’s highly unlikely you’ll ever see a Greenland shark, as these huge creatures live deep in the frigid Arctic waters, far below the depths usually accessed by scuba divers.
Only recently, a human laid eyes on a living Greenland shark, and the first footage of this intriguing fish only emerged in 1995.
Since then, researchers have been doing their best to study Greenland sharks, but their living conditions make it challenging.
Nevertheless, scientists have managed to put together a few fascinating facts about the Greenland shark, including remarkable information about its lifespan. We’ll share that information with you here, along with some other insights and observations.
The Greenland shark is a slow-moving species of shark that is found in the Arctic Ocean and North Atlantic.
These sharks are one of the longest-living vertebrates on earth, with a lifespan of over 400 years.
Greenland sharks are considered a vulnerable species due to hunting by humans for their liver oil and low reproductive rate.
What do Greenland Sharks Look Like?
If you ever encountered a Greenland shark in the ocean, you’d be forgiven for thinking you’d seen a submarine. These huge sharks measure up to 23 feet long and have a cylindrical shape similar to a submarine.
They are usually gray or brown, with a white snout. Scientists believe this pale coloration is caused by “repeated abrasion” resulting from the shark using its snout to forage for food on the seafloor.
The Greenland shark’s pectoral fins are small compared to its body, giving it a rather awkward appearance. It also has a small head and small, round eyes that are often parasitized by long pinkish copepods known as Ommatokoita elongata.
These parasites permanently attach themselves to the shark’s cornea, causing “severe, visual impairment.” This isn’t thought to bother the Greenland shark unduly as it doesn’t rely on its eyesight for survival.
Behind their eyes, Greenland sharks have distinct openings known as spiracles. They use these to force water over the gills so they can breathe even when moving very slowly, which is something Greenland sharks tend to do.
Greenland sharks often swim with their mouths gaping open, making them seem rather dim-witted.
Greenland Sharks Taxonomy
Greenland sharks bear little resemblance to other sharks, but they are related. Like other sharks, Greenland sharks have cartilaginous skeletons and belong to the Chondrichthyes class.
Within this class, it belongs to the subclass Elasmobranchii, along with all other sharks, skates, and rays.
The Greenland shark is the largest member of the sleeper shark family and one of the largest species of shark in the world. Like other sleeper sharks, it’s a non-aggressive species that swims lethargically and rarely exerts itself.
The Greenland shark’s closest living relatives are the Pacific and southern sleeper sharks.
Although Greenland sharks do occur in the waters around Greenland itself, their habitat ranges far beyond that. It’s also known as the gurry shark, ground shark, and gray shark, while the Inuit call it “Eqalussuaq, which means shark or big fish.”
Greenland Shark Characteristics
Most Greenland shark measure between 6.5 and 13 feet in length, although they can get up to 23 feet long.
They are very slow-moving creatures that usually move at an average pace of around 0.3m per second. If they’re in a hurry, they may accelerate to around 3kph!
The Greenland shark has sharp, pointed teeth in its upper jaw, which it uses to hold onto its prey. Its bottom teeth are much wider and curve sideways. By moving its head in a circular motion, it uses these bottom teeth to carve chunks of flesh out of its prey.
Greenland sharks are one of the few poisonous shark species, and their skin is toxic to humans. Eaten fresh, it “can cause symptoms in humans similar to severe inebriation.”
The Greenland shark’s toxicity is caused by chemicals in its skin that act as a kind of antifreeze, protecting the shark “against the debilitating effects of severe cold and high water pressure.”
Another curious characteristic of the Greenland shark is its phenomenal survival capability. The longest-living vertebrate on Earth, the Greenland shark can live for 400 years or more! Not only that, but it also appears to have an “extremely low risk for cancer and infectious diseases.”
Greenland Shark Life Cycle
Although we know that Greenland sharks probably live for between “252 and 512 years,” we don’t know much else about their lives.
Some scientists have estimated that female Greenland sharks are pregnant for anywhere between 8 and 18 years, but there’s little evidence to support this theory.
We do know a few things about the Greenland shark’s reproduction, namely that it occurs via internal fertilization, as with most other shark species. The Greenland shark is ovoviviparous, meaning it lays eggs inside its body before giving birth to live young.
Greenland sharks produce an average of 10 pups per pregnancy. At birth, these pups measure approximately 15 inches in length.
Although researchers are unsure of the level of parental care these pups receive, they suspect that they’re completely independent from the moment they’re born.
Not only is the Greenland shark slow-moving, but it’s also slow-growing. Scientists believe they only reach sexual maturity when they’re around 13 feet, which takes approximately 150 years.
Where do Greenland Sharks Live?
As far as Greenland sharks are concerned, the colder, the better. As a species of polar shark, they enjoy cold-water environments where the temperature ranges between 29 and 60℉.
Greenland sharks have a surprisingly wide global distribution despite their love of frigid waters.
They are most commonly found in the Arctic Ocean and North Atlantic but also occur as far south as the North Sea and the waters around the Eastern Seaboard in the United States.
In April this year, researchers caught a Greenland shark off the coast of Belize. This discovery has led some scientists to theorize “that the Greenland shark can be found across the globe if one knows where to look.”
Greenland sharks dive deeper than almost any other species of shark, accessing water that never gets warmed by sunlight. This ability could allow them to travel much further than the confines of their preferred Arctic environment.
In 1988, a Greenland shark was spotted by an unmanned submersible close to the wreck of the SS Central America, which lies some 7,200 feet below the surface. Some years later, a Greenland shark was seen off the coast of Brazil at a depth of over 9,000 feet!
The Greenland shark is the only species known to inhabit such cold waters throughout the year. In the summer, they descend even deeper to avoid the heat, while in winter, they’re more commonly seen close to the surface.
Greenland Shark Behavior
The Greenland shark is a top predator, even though it moves so slowly. It relies on stealth rather than speed for its kills and won’t turn its nose up at the occasional piece of rotting flesh either.
Although largely solitary, Greenland sharks will occasionally congregate if a particularly large carcass needs cleaning up.
Greenland sharks have very poor eyesight, and many are believed to be completely blind due to the parasitic copepods in their eyes. Instead of using sight to find something to eat, it relies on its superior sense of smell and ability to sense electrical fields.
Like most other sharks, Greenland sharks have a network of sense organs, known as the ampullae of Lorenzini, that enables them to hunt in total darkness.
Despite the Greenland shark’s considerable size, scientists have found they need very little food to survive.
A research project led by Eric Ste-Marie of the University of Windsor in Canada “found that these large predators only require only 61-193 grams of fish or marine mammal prey daily.”
It seems the lethargic Greenland shark requires very little energy to sustain itself in its frigid environment.
What do Greenland Sharks Eat?
Greenland sharks are opportunistic ambush predators and scavengers. They will eat almost anything they come across from fast-moving fish to rotting carcasses.
Greenland sharks employ some intriguing hunting techniques to compensate for their lack of speed.
In 2012, researchers struggled to figure out how Arctic ringed seals were ending up in the stomachs of Greenland sharks, given that they travel at much faster speeds.
With an average speed of 10 kph, Arctic ringed seals are too fast for a Greenland shark to capture and yet form a significant portion of the shark’s diet.
By monitoring a select group of Greenland sharks, researchers concluded that they use “camouflage and slow speed to ambush seals” while they’re sleeping.
Other studies indicate that the diet of juvenile Greenland sharks consists primarily of squid. It’s only as the sharks mature that their tastes become more diverse. As adults, they appear to eat almost anything, including caribou.
Scientists have reportedly seen Greenland sharks “hunting caribou in the manner of a crocodile ambush at river mouths,” although this report has never been substantiated. Experts suspect that the sharks just eat the carcasses of caribou drowned during migration.
There have been no reports of Greenland sharks attacking humans, probably because they rarely come into contact with one another.
The only indication of the Greenland shark showing aggression towards a human dates back to 1859, when “it was reported that a Greenland shark was caught containing a human leg in its stomach.” The story was never investigated or substantiated.
What Hunts Greenland Sharks?
The Greenland shark has no known natural predators, probably due to its considerable size. The only marine predator to take on large sharks is the orca which rarely dives deep enough to see a Greenland shark, let alone kill one.
Humans have probably had the biggest impact on the Greenland shark population, hunting them primarily for their liver oil. One adult Greenland shark can yield around 30 gallons of liver oil, making it a highly lucrative catch.
Although the meat of the Greenland shark is toxic, causing symptoms similar to those of being heavily intoxicated, it’s considered a delicacy in Iceland.
To make it edible, the meat is first cured using a nine-week fermentation process before being hung to dry for four to five months.
The result tastes a little like very strong cheese “with an aftertaste of urine,” so it is something of an acquired taste!
The demand for Greenland shark meat may be small but the numbers taken by the commercial fishing industry are still high enough to negatively impact the population, which the IUCN considers “to be vulnerable to extinction.”
We still have much to learn about the Greenland shark, and the information we have acquired has only made scientists and researchers more curious.
How does the Greenland shark survive in such cold waters? What is the secret to the Greenland shark’s longevity, and how long is it pregnant?
We may not have the answers to those questions yet, but we do know that the Greenland shark lives longer than any other vertebrate on Earth.
It is also likely to have one of the longest gestation periods and only reaches sexual maturity at the great age of 150 years old!
As we discover more about the Greenland shark, so we should do more to protect this unusual species.
As a top predator and scavenger, it plays a critical role in our marine ecosystem and could “hold the key to cardiac health and long life.”