Deep in the freezing waters of the North Atlantic, the Greenland shark moves at a glacial pace, growing just one centimeter per year. This slow-motion lifestyle gives them an astonishing lifespan. By radiocarbon dating the proteins in their eyes, scientists discovered these sharks routinely live for hundreds of years, making them the longest-lived vertebrates on Earth.
A Giant in the Arctic Depths
The Greenland shark, Somniosus microcephalus, is one of the largest extant shark species, comparable in dimensions to the great white shark. Thriving in the frigid waters of the North Atlantic and Arctic Oceans, these massive elasmobranchs regularly inhabit temperatures hovering near freezing, often between minus one and ten degrees Celsius. They routinely descend to significant depths, frequently found hundreds or even thousands of meters beneath the surface, where sunlight cannot penetrate.
Unlike many apex marine predators that rely on bursts of explosive power and rapid development, the Greenland shark operates on a radically stretched biological timeline. Field measurements and tagging studies indicate that these animals expand their body length by as little as half a centimeter to one centimeter per year. Reaching lengths exceeding four to five meters, individuals spend multiple generations of human history merely reaching physical adulthood in the dark ocean basins.
Reading History in the Eye Lens
Determining the age of elasmobranchs is notoriously difficult because sharks have skeletons made of soft cartilage rather than hard, calcified bone that forms annual growth rings. While some shark species possess calcified bands along their fin spines or vertebrae, the Greenland shark has extremely soft vertebrae that do not develop readable annual markers. For decades, biologists could only speculate about the true lifespan of these colossal, slow-growing animals based on estimated growth rates.
The breakthrough came through the biochemical analysis of the shark's eye lenses. The core of the vertebrate eye lens contains specialized proteins called crystallins, which are synthesized during embryonic development and remain metabolically inert throughout the animal's life. Because no new protein turnover occurs in this innermost core, the carbon trapped within it reflects the radiocarbon levels present when the shark was born.
By applying radiocarbon dating to the eye lens nuclei of sharks caught as bycatch, researchers established that the Greenland shark is the longest-lived vertebrate known to science. The largest shark in the landmark study, measuring over five meters, was dated with an estimated age of approximately 392 years, with an uncertainty range spanning from roughly 272 to more than 500 years. The same analysis revealed that females likely do not reach sexual maturity until they are roughly 150 years old.
The Physiology of Extreme Slowness
The extraordinary longevity of the Greenland shark is inextricably linked to its extreme physiological adaptations to cold water. The species is one of the slowest-swimming sharks ever recorded, with a typical cruising speed of just over one kilometer per hour and maximum burst speeds rarely exceeding three kilometers per hour. Their tail beats move with a languid, deliberate rhythm that conserves metabolic energy in an environment where calories can be scarce.
Cold ambient temperatures fundamentally suppress biochemical reaction rates, lowering overall metabolic demand and slowing tissue degradation. Enzymes and cellular machinery in the Greenland shark operate at a fraction of the pace observed in warm-water fishes. This depressed metabolic rate, combined with efficient cellular repair mechanisms and low oxidative stress, appears to protect tissues from the wear and tear that typically drives senescence in shorter-lived vertebrates.
Sensory Adaptations and Opportunistic Feeding
A large portion of the Greenland shark population carries a notable parasite: the pinkish-white copepod Ommatokoita elongata, which permanently attaches itself to the shark's corneas. These crustacean parasites feed on corneal tissue, frequently resulting in severe scarring and partial blindness. However, in the pitch-black depths of the Arctic waters, visual acuity offers little advantage, and the sharks rely primarily on acute olfactory senses and lateral line systems to navigate and locate food.
Despite their sluggish movement, stomach content analyses show that Greenland sharks consume an astonishingly wide variety of prey. Their diet includes bottom-dwelling fish such as halibut, skate, and cod, as well as marine mammals like seals. Researchers suspect they ambush sleeping seals or scavenge carcasses that sink from the ice above. In rare historical dissections, remains of terrestrial animals, including reindeer and horses that fell through sea ice, have also been retrieved from their digestive tracts.
Chemical Armor and Cultural Utilization
To survive the crushing hydrostatic pressure and freezing temperatures of the deep northern seas, the Greenland shark accumulates high concentrations of urea and trimethylamine N-oxide (TMAO) in its bodily tissues. These compounds act as natural antifreeze and osmolytes, stabilizing proteins against structural collapse under cold and pressure. However, these high chemical levels make the fresh meat highly toxic to humans and other mammals, inducing symptoms similar to severe alcohol intoxication or neurotoxic poisoning when ingested raw.
Indigenous Arctic peoples and historical northern communities developed specific methods to process the meat safely. In Iceland, the meat is traditionally cured through months of fermentation and wind-drying to produce hákarl, a process that breaks down and expels the toxic compounds. Historically, the species was also heavily targeted for its massive, oil-rich liver, which was processed into lamp fuel and industrial lubricants across northern Europe until synthetic and mineral oils replaced marine oils in the mid-twentieth century.
Conservation in an Era of Changing Oceans
The sheer length of the Greenland shark's life cycle creates acute vulnerabilities to modern human activities. Because an individual shark may need to survive for a century and a half before producing its first offspring, population replacement is exceptionally slow. Decades of heavy commercial liver exploitation in the nineteenth and early twentieth centuries likely removed large cohorts of reproductive adults, leaving population scars that may take centuries to fully heal.
Today, the primary threat to the species comes from commercial fishing bycatch, particularly in deep-water bottom trawling and longline fisheries targeting valuable species like Greenland halibut. Although many sharks are released when caught, post-release mortality and the loss of mature breeding individuals remain conservation concerns. As warming Arctic waters alter sea-ice dynamics and open the far north to increased industrial fishing, protecting these ancient animals requires monitoring a species whose generational timeline vastly exceeds our own.
Key takeaways
•The Greenland shark is the longest-lived vertebrate on Earth, with lifespans estimated to reach up to four centuries or more.
•Scientists determined their age by radiocarbon dating the crystalline proteins inside their eye lenses, which are formed during embryonic development and never replaced.
•Their slow-motion lifestyle—including a swimming speed of around one kilometer per hour and growth of under a centimeter per year—is adapted to near-freezing Arctic depths.
•Because females do not reach sexual maturity until roughly 150 years of age, populations are exceptionally slow to recover from historical hunting and modern bycatch.