Greenland shark

The Greenland shark is the world’s longest living vertebrate. It can live for 400 years—twice the age of the longest-living land animal, the giant tortoise. There could be an individual in the ocean today that was alive during the 1665 Great Plague of London and George Washington’s presidential inauguration in 1789.

Despite its name, the Greenland shark is not only found in Greenland; it has been spotted as far away as the western Caribbean. Also known as the gray, ground, gurry, or sleeper shark, this animal lives in incredibly cold, deep waters, so it is much less studied than many of the more than 500 other shark species. It is one of the slowest sharks, too: Its scientific name, Somniosus microcephalus, roughly translates to “sleepy small-head.” Yet these rare animals may be a top predator.

The world’s longest-living vertebrate

 Many shark species can be aged by counting growth bands on their vertebrae, like rings on a tree. The Greenland shark’s soft vertebrae do not have these bands, however. Instead, its age is determined by removing the layers of the lens of its eye—which continues growing throughout its lifetime—and radiocarbon dating the tissue in the center.

Using this method, scientists discovered Greenland sharks have a life expectancy of at least 272 years and could reach 392, give or take about 120 years. What’s more, these slow-growing creatures don’t reach reproductive age until around 150 years old.

Measuring the Greenland shark’s growth rate is challenging because individuals are rarely recaptured. However, one shark tagged in 1936 had only grown 2.3 inches when it reappeared 16 years later.

Life in the cold

The largest fish in the Arctic Ocean—and the only shark found there year-round—the Greenland shark also inhabits the North Atlantic and Russian high Arctic. Infrequently observed at the surface, it can live in waters 7,200 feet deep and between 28.4 to 44.6 Fahrenheit (minus 2 to 7 degrees Celsius).

Specially adapted for cold water, this shark’s tissues contain high levels of chemical compounds that act like anti-freeze and prevent ice crystals forming in the body. These sharks conserve energy by swimming very slowly—about 1.12 feet per second—but can exhibit short bursts of speed to ambush prey.

Appearance, diet, and behavior

Dark gray, brown, or black with a cylinder-shaped body, small eyes, rounded snout, and no anal fin, Greenland sharks resemble a submarine and can reach 23 feet long and may weigh 1.5 tons. In comparison, the great white shark grows to 15 to 20 feet but is significantly heavier, weighing 2.5 tons or more.

Greenland sharks have narrow, pointed upper teeth and broader, squared teeth on the lower jaw. Holding large prey in position with their upper teeth, they roll their head in a circular motion, using the lower teeth like a blade to tear off circular chunks of flesh. Smaller prey is eaten whole.

Primarily scavengers, Greenland sharks are not fussy eaters and consume a variety of fish, squid, and carrion. Stomach contents of  sharks have even included polar bears, horses, and reindeer. Evidence suggests they may be opportunistic hunters capable of ambushing seals in stealth attacks. They have been linked to the discovery of nearly 5,000 mutilated seal corpses in Nova Scotia between 1993 and 2001: The victims’ pelts were ripped off in a spiral shape—like a peeled orange—giving the shark the gruesome, but debated, nickname of the “corkscrew killer.”

Vision

Arctic Greenland sharks often have poor vision because of a parasite called Ommatokoita elongata. This tiny crustacean latches onto the shark’s eye, damaging the cornea and leaving scar tissue with each infection. The shark is not debilitated by its blindness as it relies heavily on other senses in its dark habitat far beneath the ice.

Human threats 

There’s no proof of Greenland sharks attacking humans: An 1859 report of a Greenland shark found with a human leg in its stomach was never corroborated. However, the animal’s flesh is poisonous; eating it can cause diarrhea, vomiting, stumbling, and convulsions, also known as getting “shark drunk.” To make it safe for consumption, the meat must be left to rot, compressed to remove toxic fluids, then dried out for months, diced, and served—an Icelandic delicacy known as kæstur hákarl.

Humans do pose a threat to Greenland sharks: The International Union for the Conservation of Nature lists the Greenland shark as vulnerable to extinction. The animal’s slow growth rate, late maturity, and low reproduction rate make it vulnerable to threats such as fishing, pollution, and climate change. Until the 1960s they were hunted for the oil in their livers, which was used as industrial lubricant or for lamp oil. Although they are no longer targeted by fisheries, Greenland sharks are still caught accidentally and often become entangled with fishing gear.