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.
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.
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.
DID YOU KNOW?
This mysterious shark is not often seen by cameras: The first photograph of a live Greenland shark wasn’t taken until 1995.— National Geographic
Some have speculated that Greenland shark sightings could be behind the Loch Ness monster myth.— Oceana
A Greenland shark was spotted off the coast of Belize in spring 2022, raising the possibility the sharks are more widespread than previously thought.
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Greenland sharks can live for centuries. We’re finally learning their genetic tricks.
A first-ever analysis of the whole Greenland shark genome gives researchers a couple of clues to their longevity.
For humans, puberty hits after around a decade. But Greenland sharks have to wait well over 100 years. A century-long childhood might seem like science fiction, but Greenland sharks are the longest-living vertebrate on Earth, with lifespans thought to stretch to around 400 years. These fish spend centuries diving deep into frigid Arctic and Northern Atlantic waters, where they reach massive sizes by growing roughly a centimeter a year. The largest fully grown Greenland sharks can be longer than a Toyota Prius and weigh over 2,000 lbs.
Normally, an animal can’t grow so old. Over time, declining bodily functions and illnesses like cancer accumulate and take their toll. Yet the Greenland shark seems to defy this pattern, meaning it must have evolved genetic tools to stave off age-related diseases.
Recently, scientists have gotten some new genetic clues to their longevity. And while the new findings won’t translate to humans living to age 400, they are giving scientists tantalizing blueprints for how we might maintain health longer into our lives.
How to catch an enormous Greenland shark
In 2021, Arne Sahm decided to hunt for clues behind the sharks’ long life; not just to learn about the shark, but also to potentially compare them to the biology of other long-lived animals, like the naked mole rat.
“It’s good to learn whether there are some common tricks of evolution to make very long-lived species even more long-lived,” says Sahm, a bioinformatician at the Leibniz Institute on Aging – Fritz Lipmann Institute in Germany.
“You put 10 hooks on a long line,” says John Steffensen, a marine biologist at the University of Copenhagen in Denmark who worked with Sahm on the project, and has spent the last two decades catching these sharks for research. “They’re called shark hooks, they’re huge.” Onto those hooks goes chunks of stinky, rotten meat. A combination of heavy-duty ropes and chains lower the smelly snack down hundreds of feet, then haul it back up with a shark, or possibly multiple, in tow.
For Sahm’s research, Steffensen and other fishers caught sharks in the southern fjords of Greenland and sent the team brain samples. Researchers then extracted DNA from the samples to compile and inspect the sharks’ genome. They published their findings on a preprint server in September.
Two genetic clues point to the source of the sharks’ long lives
If a genome were a book of instructions, DNA would be the words and genes would be paragraphs. For the first time, the team put together the Greenland sharks’ entire book –– their chromosomal genome. They found the book is about twice as thick as a human’s, clocking in at 22,634 genes and around 6.45 billion base pairs. Base pairs form the rungs of a DNA strand’s double helix structure—the individual letters on a ‘page’ of DNA.
But these transposons might play a more beneficial role in the Greenland shark. Many of the Greenland shark’s duplications included genes that were linked to DNA repair. So instead of creating a disruption, they may have created additional helpful genes, which could hypothetically slow down aging. If DNA is left damaged, it can contribute to problems within cells, including cancer. Researchers think the better a genome is maintained, the longer lifespan an organism could have.
(These sharks have rare earth metals in their organs. Is your old cell phone the culprit?)
A gene called TP53 also caught the teams’ attention. Heralded as the ‘guardian of the genome,’ TP53 is vital for cancer prevention. Many animals have it, including humans, elephants and whales. TP53 contains instructions for the protein p53, which aids in tumor suppression and DNA repair. It works by either stopping cells with damaged DNA from dividing further until it’s repaired, or causing them to die. That ensures the cell’s growth doesn’t snowball uncontrollably, becoming a tumor.
In Greenland sharks, a portion of its TP53 gene sequence is altered from how it typically functions in other animals. Using an AI model, the researchers predicted that the mutation could impact p53’s structure and how it handles DNA repair, possibly leading to a longer life. But Sahm notes these are only predictions—to further understand the alteration, they would need to experiment with it in cells in the lab.
The keys to a Greenland shark’s long life can help scientists understand longevity in other animals and could be beneficial to humans, too. But it isn’t going to help us live for centuries.
Sharks are too distant from humans and our systems are too different to make direct comparisons, Sahm says. Instead of providing a proverbial fountain of youth, the shark’s genome adds to other genomic data of long-lived animals. Scientists can make comparisons between those animals and humans to learn more about the aging process. For example, they can look for genes present in long-lived animals and absent in short-lived ones that could aid in staving off age-related diseases.
“The goal isn’t to make people live longer, the goal is to keep people healthier for longer,” says Paul Robbins, a molecular biologist at the University of Minnesota who was not involved with the study. Human longevity research mainly aims to improve people’s healthspans, the length of time someone spends in good health throughout their life. For example, one aspect of longevity research is how to balance long life with cancer prevention. Because there are some overlaps in our longevity-related genes –– like the importance of TP53, for example –– the shark’s genome could help reveal targets for developing healthspan therapies, like pharmaceuticals or gene therapies, Robbins says.
(It’s not your life span you need to worry about. It’s your health span.)
And because there are other animals studied for longevity, the results can help inform that research as well, Bodnar adds. For example, scientists can compare the Greenland shark to short-lived species like mice to look for differences. On the flip side, their genome can be compared to other sharks, or to other long-lived marine species like the bowhead whale, to look for similarities.
More studies are needed to confirm the function of the proteins found in the Greenland shark’s genome. Looking at gene expression would be one next step, which can be done using cell cultures or by inserting genes in other model animals.
“It’s fantastic to have a genome, it’s an essential resource for future studies,” Bodnar says. “But it really is just the beginning.”
