The Greenland shark can live 400 years and was swimming before the US existed

In the cold, dark waters of the North Atlantic and Arctic swims a shark that may be the longest-lived vertebrate on Earth. Slow, sluggish, and rarely seen, the Greenland shark can survive for centuries, meaning individuals alive today could plausibly have been swimming the seas before the United States declared independence. Its extraordinary longevity, only firmly established in recent years, has reshaped how scientists think about aging in the animal kingdom.

A vertebrate that measures its life in centuries

The Greenland shark is a large, heavy-bodied predator that can grow to more than 20 feet in length. It lives in frigid, deep water, often near the freezing point, and moves so slowly that it has been described as gliding rather than swimming. That unhurried existence appears to be central to how it lasts so long.

NOAA Fisheries describes the species as living an estimated up to about 400 years, a figure that would make the oldest individuals older than the country whose waters some of them patrol. Even the more conservative ends of the estimate place the shark’s lifespan well beyond that of any other backboned animal known to science.

How scientists dated a fish that has no bones to count

Establishing the age of a Greenland shark posed an unusual problem. Many fish can be dated by counting growth rings in hard structures such as ear stones or bony spines, much as one counts rings in a tree. Sharks, however, have skeletons made of cartilage rather than bone, and the Greenland shark lacks the calcified fin spines that allow some other sharks to be aged.

The breakthrough came from an unlikely part of the body: the eye. The lens of the shark’s eye contains proteins that form before birth and are never replaced, preserving a chemical snapshot of the era in which the animal was born. By analyzing radioactive carbon in those lens proteins, tied to fallout signatures from mid-twentieth-century nuclear testing, researchers were able to estimate the ages of individual sharks and arrive at the centuries-long figures that stunned the field.

Growing up almost impossibly slowly

Extreme longevity comes paired with extreme slowness in nearly every part of the shark’s biology. The species grows only about a centimeter a year, so reaching its full adult size is itself the work of many decades. That glacial pace of growth is one reason the animal can persist for so long: a body that builds and replaces its tissues slowly may accumulate the damage associated with aging at a correspondingly slow rate.

Reproduction is equally unhurried. Females are thought not to reach sexual maturity until they are roughly 150 years old, meaning an individual can spend more time simply becoming an adult than most animals spend alive. A shark that must survive a century and a half before it can breed is exquisitely vulnerable to anything that raises mortality among the young, because replacements arrive so rarely.

A diet, and a passenger, as strange as the shark

The Greenland shark is an opportunistic feeder, taking fish and squid and scavenging carcasses on the seafloor. Remains of seals and even land mammals have turned up in the stomachs of some individuals, though scientists debate how much of that reflects active hunting versus scavenging animals that had already died.

Many of the sharks also carry a peculiar hitchhiker: a parasitic crustacean that attaches to the eye and can impair the animal’s vision. Given that the shark hunts in near-total darkness at depth, where eyesight is of limited use anyway, the impairment may matter less than it would for a surface predator. The shark appears to rely on other senses to find food in the lightless water it calls home.

The flesh of the Greenland shark carries a further oddity. Its tissues are laced with compounds that help the animal cope with the pressure and cold of the deep, but those same substances make the raw meat toxic to eat, capable of sickening anyone or anything that consumes it fresh. In Iceland the fish has traditionally been made edible only through a lengthy process of fermentation and drying that neutralizes the toxin, a practice that speaks to how thoroughly the shark’s biology is tuned to an environment hostile to most life.

Why a slow shark is easy to lose

The same traits that make the Greenland shark remarkable also make it fragile in the face of human pressure. An animal that takes 150 years to reproduce cannot rebound quickly from population declines, whether caused by fishing, bycatch in nets set for other species, or changes to its cold-water habitat. Once numbers fall, recovery would unfold over timescales that dwarf a human lifetime.

Because the species lives so deep and so far from shore, much about its life remains poorly understood, from how many exist to how they navigate and mate across the vast, cold expanses they inhabit. Historically the sharks were hunted for the oil in their livers, and even today they are caught unintentionally in fisheries targeting other species, a persistent drain on a population that can barely afford to lose breeding-age adults.

What is clear is that the Greenland shark represents a rare natural experiment in longevity, an animal that has quietly turned the ordinary limits of a vertebrate lifespan into something measured not in years but in centuries. Each individual that survives is, in effect, a living archive of the ocean it has drifted through, carrying in its slow-built body a record of conditions stretching back generations of human history.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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