John Steffensen, a Danish marine biologist, spotted a local hunter on a small boat 15 years ago while fishing off Greenland's west coast. The boats edge was adorned by a large, dull-gray shark. Steffensen said that I was a little confused and thought, "Wow, I've never seen a Greenland shark." He then stated to Steffensen that he would love to catch one. The captain of our boat was laughing at me.
The captain must have wondered why anyone would want to catch a Greenland Shark. He said that one should not eat the meat of Greenland sharks. It is both toxic and foul tasting. It can, however, be fermented to create Iceland's famous hkarl. This is a safe dish, but not for the faint-hearted. It could also be fed to dogs in sleds, where it could cause shark drunkenness. In passing, the captain mentioned that Greenland sharks live for an extraordinarily long time.
Sharks can grow up to 15 feet, or slower. Photo: Julius Nielsen
Steffensen's interest was piqued by this last statement. He returned to Denmark as a professor at University of Copenhagen and began reading through scientific literature. A study that tracked the size of sharks over many decades revealed that size and age were closely linked in fish. One shark grew almost three inches in just 16 years. The sharks could grow half a centimeter per annum and can reach five meters (15 feet) or more. It doesn't take much math to figure that they are probably very old.
This was just the beginning of a remarkable scientific investigation that led to a study that suggested that Greenland sharks might be the longest-living vertebrate, surpassing the bowhead whales, koi fish and Galapagos tortoise. This discovery sparked an array of research on the current state of our understanding of longevity and the survival of this mysterious species.
Greenland sharks may seem strange at first, but they are not unusual. They are slow, awkwardly proportioned and have pinkish parasites hanging from their eyes. They can wander from the cold North Atlantic Ocean to the warm Gulf of Mexico, engaging in cannibalistic behavior.
Greenland sharks can grow old and long in cold waters of North Atlantic but they can also live in warmer waters. Photo: Julius Nielsen
Greenland sharks were commercially harvested for their oil-rich livers in the first half century. This was enough to kill hundreds of thousands of animals each year. They are considered a nuisance by fishermen who live on their land. They eat valuable halibut and can become entangled in nets. They can damage equipment and cause serious injury if they don't find a way out. Steffensen says that they absolutely hate these sharks. In part to offset the potential damage that they can do, many towns have offered bounties to Greenland sharks' hearts for decades. Around 5,000 were bought for $50 each in 1984. They are now worth a fifth of that price today, but they still attract hostility.
Steffensens fishing captain was therefore so puzzled. However, that didn't stop Steffensens curiosity, especially about the rumors of extraordinary longevity. How could he be certain? Without success, he tried to scan a vertebrae at a local hospital for signs and growth rings. Jan Heinemeier was a respected expert in radiocarbon dating and retired physicist at Denmark's Aarhus University. Heinemeier told him that the shark vertebrae could only be used to determine when a shark died and not how long ago it was. Heinemeier thought of another way. But what about eye lenses?
Eye lenses, unlike most tissues that grow new cells, are made at birth. They also remain extremely stable. Crystalline proteins within the lens can be carbon dated, as they do not have the ability to reproduce. Heinemeier actually used this exact approach to investigate a German child murder case.
The large eye of a Greenland shark's nucleus contains carbon dating back to when it was born. Photo: Julius Nielsen
Julius Nielsen was a doctoral student at the time and is now a scientist with Greenland Institute of Natural Resources. He helped to lead the study and had access to 28 female Greenland sharks that were caught by local fishermen. They ranged in length from three to 15 feet. They extracted the eyes and removed their outer layers. The lenses were then scraped using Heinemeiers method. Steffensen says that their eyeballs are the same size as oranges. He also said that he had some in his freezer at the time. Your eye lens looks almost like an onion. It is layered on the outside but the nucleus lies in the middle.
These results showed that Greenland sharks can live between 272 to 512 years. The results indicate that there could be Greenland sharks still alive today that were born in the Renaissance. Our first reaction was, "What did we do wrong?"," says Peter Bushnell, an Indiana University South Bend biologist who collaborated with Steffensen on the analysis.
Scientists from Dana, a Danish research vessel, corralled a 12-foot-long female Shark for tagging near Qaqortoq (Greenland) in August 2021. Photo by Kirstine Fleng Steffensen
One of the subtleties that they discovered was that older sharks grow exponentially slower than younger ones. A difference of four inches between the largest and smallest sharks could mean many decades of life. The study's largest shark measured more than 16 feet in length. Steffensen had personal knowledge that Greenland sharks can reach 18 feet. This could be a few more centuries. Bushnell and Steffensen will both admit that extrapolation can be a bit complicated.
Bushnell states that if sharks live for hundreds of years, it raises many questions about cell function, cardiovascular function, heart tissue, blood vessels, and everything else. How can something live so long?
Steffensen's colleagues published their research in Science in 2016. The spooky, cadaverous Shark became a huge sensation. The secret to this long life span has been a mystery for scientists around the globe. Holly Shiels is a senior lecturer at the University of Manchester in animal physiology. She has been focusing on their hearts which are approximately the same size as a small watermelon. She says that Greenland sharks might have an unusually sophisticated system for repairing damaged DNA.
Julius Nielsen, a scientist, up close and personal with a Greenland shark. Photo: Julius Nielsen
She says that the [cell] nucleus of a [Greenland shark] potentially 200-year-old [Greenland shark] appears like what we would consider a teenager in mammalian terms. We believe these could be renewing their hearts in a continuous way.
David Costantini (a conservation ecologist associated with the Museum of Natural History, Paris, France) has also focused on the oxidative stress found in Greenland shark blood. Kim Praebel from the Arctic University of Norway is searching for immune-related genes. He says that if you can live for three to four hundred years, then you should also avoid getting sick. It seems logical to me.
Bushnell finds the work fascinating, but it is misleading. He says genetics play a part, but lifestyle and environment are more important. Greenland sharks, large deep-sea animals, have evolved to survive in cold temperatures. This slows down their metabolism. They are extremely energy efficient thanks to their slow movements and ability to live on one seal for almost a year. Greenland sharks are free from predators, except when necessary. He says that to live long we would need to be like a Greenland shark.
There is one downside to longevity: prolonged periods of sexual maturation. Slowly reproducing animals is a sign that they live long. They can take up to 150 years before becoming sexually mature. This is why many sharks die before giving birth.
Nielsen conducted a recent study and found that Greenland sharks could produce up to 200 pups per year, which is 20 times more than was previously believed. Nielsen says that while this may help offset the difficulties of delayed sexual maturity, they also suggest that the survival of the species could depend on a small population of exceptionally fertile, centuries-old females. The entire species could be at risk if they leave.
He says that the loss of a mature Greenland shark sexually is extremely disturbing.
An ultrasound scan is used by researchers to examine a female measuring 12 feet in length to determine if she is pregnant and her heart rate. The resting heart beat was 810 beats per hour, which is among the slowest recorded in vertebrates. Photo by John Fleng Steffensen
Brendal Townsend is a shark researcher at Dalhousie University, Nova Scotia. He says that even though Greenland sharks appear to be abundant due to regular bycatch, they may still be in danger of disappearing. This wouldn't be the first. It happened again to Atlantic northwest cod in 1990.
Steffensen was only interested in the question of longevity when he first started studying Greenland sharks. As he continued to dig deeper, these questions seemed to have multiplied, creating paradoxes along his journey. Although they are predatory sharks, they are slow-moving and languorous. They are commercially ineffective, but could have a secret to a longer life span. They are everywhere fishermen see them. They may soon disappear, but they are everywhere fishermen look.
Steffensen reported back to the captain, who first ignited his passion for Greenland sharks many years later.
You were correct! He said that they are very old. How did you find out? Who did you hear?
The captain responded, "Oh, did you ever tell me that?" I had forgotten. We just know this.
