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Greenland sharks (Somniosus microcephalus) may live for several centuries, but the famous “400-year-old shark” is an estimate with wide uncertainty—not a precisely dated birthday. A 2016 radiocarbon study estimated that the largest female it examined, 502 cm long, was 392 ± 120 years old (a 95.4% probability range). The same study estimated sexual maturity at 156 ± 22 years. Such slow growth and late reproduction mean that sharks removed by fishing can take generations to replace. Incidental capture in fisheries is the clearest documented direct threat; climate-driven habitat change is an additional concern whose population effects are not yet quantified.
How long do Greenland sharks live?
The best-known estimate comes from Nielsen and colleagues’ 2016 study, indexed by PubMed. The researchers estimated that a 502 cm female Greenland shark was 392 ± 120 years old. The plus-or-minus value is not a normal measurement error around a known age: it describes the study’s 95.4% probability range. In practical terms, the estimate supports a lifespan of centuries while leaving substantial room around the headline number.
The study inferred that the species reaches sexual maturity at 156 ± 22 years and concluded that its lifespan is at least 272 years. These are model-based age estimates, not observations of a shark living from a recorded birth date. Canada’s 2025 assessment by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) notes that the estimates have not been validated with an independent aging method and that uncertainty in deep-ocean radiocarbon affects birth-date calculations.
The original abstract described the result this way: “Our results show that the Greenland shark is the longest-lived vertebrate known, and they raise concerns about species conservation.” That statement should be read together with the study’s uncertainty range and the later Canadian assessment, rather than as proof that every Greenland shark reaches 400 years.
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The key numbers
| Measure | Reported value | What it means |
|---|---|---|
| Largest shark sampled | 502 cm total length | The longest individual in the radiocarbon sample |
| Estimated age of that shark | 392 ± 120 years | 95.4% probability range from the 2016 model |
| Estimated age at sexual maturity | 156 ± 22 years | Model estimate, not a directly observed birthday |
| Minimum lifespan inferred by the study | At least 272 years | A conservative conclusion from the study’s age model |
How scientists estimate the age of a shark without annual rings
Why ordinary shark aging methods do not work well here
Many sharks can be aged by counting growth bands in vertebrae or other hard structures, somewhat like counting rings in a tree. Greenland sharks are a poor fit for that approach. They lack fin spines, and their vertebrae are too soft to provide the usual, clearly countable bands. A different biological clock was therefore needed.
Radiocarbon in the eye lens
The 2016 study measured radiocarbon in the nuclei of eye lenses. Lens proteins form before birth and then persist, so the radiocarbon signature in that tissue can preserve information about the period when the shark was born. By comparing the measured signal with known changes in ocean radiocarbon over time, the researchers modeled a likely birth date and age.
The sample contained 28 female sharks measuring 81 to 502 cm in total length. The method is powerful because it uses a tissue that retains its original proteins, but it is still an indirect estimate. Deep-ocean radiocarbon does not follow a perfectly uniform timetable, and assumptions about that history feed into the resulting age range.
What the uncertainty changes
It is accurate to say that the largest sampled shark was estimated at 392 years old, provided the 120-year uncertainty and the 95.4% probability range travel with the number. It is not accurate to turn that estimate into “Greenland sharks all live 400 years” or to present 392 as a precise maximum. COSEWIC specifically says no alternative method has yet validated the ages. Future validation could narrow, shift or otherwise refine the estimate without changing the evidence that the species is exceptionally long-lived.
Why Greenland sharks may live so long
Cold, deep-water ecology
Greenland sharks inhabit cold northern waters and are often associated with deep environments. NOAA’s National Ocean Service presents a slow metabolism adapted to cold water as one theory for their longevity. That is a plausible biological explanation, not a proven single cause. Cold conditions, low metabolic rates and the species’ broader physiology may work together, but scientists have not established one mechanism that accounts for every year of the estimated lifespan.
A careful summary is that the sharks’ cold-water ecology is associated with slow life processes and longevity. It would overstate the evidence to claim that cold water definitively causes a four-century lifespan.
Growth of less than a centimetre per year
NOAA reports growth of less than 1 cm per year. COSEWIC cites a limited mark–recapture estimate at or below 1 cm annually. This is an approximate reported rate, not a guarantee for every individual, region or life stage. Growth can vary with body size, food availability and local conditions, and the underlying data are limited.
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Even with those qualifications, growth below 1 cm per year helps explain why the species cannot quickly replace large adults. A shark that takes many decades to reach a substantial size has fewer opportunities to recover from an episode of elevated mortality than a fast-growing fish.
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Very late maturity and long generation time
The estimated maturity age of 156 ± 22 years is central to the conservation problem. If a shark does not reproduce until well over a century old, removing mature animals can affect reproduction for a very long time before replacement individuals reach breeding age. The same slow life history that may protect the species from age-related wear also limits its demographic speed: population growth and recovery are inherently gradual.
What threatens Greenland sharks?
Threats differ in how directly they have been observed and how confidently their population effects can be measured. COSEWIC’s 2025 assessment identifies fisheries interactions and climate-related habitat change as key concerns, while emphasizing that the overall population impact remains difficult to quantify.
Fisheries bycatch: the clearest documented direct threat
Greenland sharks are caught incidentally in trawl, demersal longline and gillnet fisheries throughout their range. COSEWIC estimates that at least 3,500 sharks are caught as bycatch worldwide each year. For Canadian fisheries, its estimate is 1,688 to 2,208 sharks annually. The assessment cautions that bycatch records are poor and may undercount the true total.
| Fishing interaction | Evidence and scale | What is established |
|---|---|---|
| Global incidental capture | At least 3,500 sharks per year, according to the 2025 COSEWIC assessment | Bycatch occurs across the species’ range; the estimate may be low because reporting is incomplete |
| Canadian fisheries | 1,688–2,208 sharks per year, according to COSEWIC | These are estimated annual captures, not a complete census of all mortality |
| Trawl, demersal longline and gillnet gear | All are reported as sources of bycatch | Incidental capture is documented in several major gear types |
| Small-scale fisheries in Iceland and Greenland | Greenland sharks are also targeted in these fisheries | Not all fishing mortality is accidental |
Capture does not automatically equal death, but the outcome after release is poorly documented. COSEWIC says post-release survival of discarded bycatch is largely unknown. That gap matters: a release requirement can reduce retained catch while still leaving unanswered questions about injuries, handling time, depth-related stress and delayed mortality.
Climate-driven habitat change
Arctic climate change may alter sea-ice extent and other habitat conditions used by Greenland sharks. COSEWIC identifies possible effects on distribution, fitness and population dynamics. Those pathways make climate change a credible additional pressure, but the assessment does not provide a quantified climate-driven decline or a measured change in abundance attributable to warming.
The distinction is important. Fisheries bycatch is directly observed, even though its totals are incomplete. Climate-related habitat change is a recognized potential threat whose consequences for the species’ numbers, reproduction and survival have not yet been quantified.
Why a precise global decline is not available
There is no population estimate for Greenland sharks in Canadian waters in the COSEWIC assessment. Global decline estimates vary widely because key inputs—including life-history rates and mortality—are uncertain. Without reliable abundance, age structure and survival data, scientists cannot responsibly convert the annual bycatch estimates into a single percentage decline for the entire species.
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Canada’s Special Concern designation
In May 2025, COSEWIC designated the Greenland shark Special Concern in Canada. The assessment says Canadian fishery rules and licence conditions prohibit retention and require sharks to be released alive with as little harm as possible. This is a Canadian measure; it should not be presented as a worldwide rule. Enforcement, handling practices and regulations can differ in other jurisdictions.
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Global context
COSEWIC reports that the species was assessed as Vulnerable by the International Union for Conservation of Nature (IUCN) in 2020. That is a global assessment cited by the Canadian report, not a substitute for current abundance monitoring in every part of the range.
Why bycatch reduction is a priority
NOAA’s public explainer states: “Reducing bycatch is critical in conserving this unique species.” The logic is straightforward: a shark with growth near or below 1 cm per year and maturity estimated around 156 years cannot rapidly replace adults lost to fishing. Better identification of hotspots, accurate reporting, careful handling and survival studies would all improve the ability to judge whether release rules are preventing mortality rather than merely changing where it is recorded.
What scientists still need to learn
The longevity result is striking, but several uncertainties shape how it should be used.
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitches- Independent age validation: COSEWIC notes that the eye-lens radiocarbon estimates have not been confirmed by another aging technique.
- Deep-ocean radiocarbon history: Uncertainty about past radiocarbon conditions affects inferred birth dates.
- Abundance and trends: Canadian waters lack a population estimate, and global trend calculations depend on uncertain inputs.
- Post-release survival: The fate of discarded bycatch is largely unknown.
- Climate responses: Habitat, distribution and fitness may change as Arctic conditions shift, but population-level effects are not yet quantified.
These are not reasons to dismiss the centuries-long estimate. They define its proper limits and show why conservation planning should use precaution: even the lower end of the reported age range implies an animal that matures late and recovers slowly.
How to interpret the “400-year-old shark” headline
When a headline says Greenland sharks live for 400 years, the defensible interpretation is that radiocarbon modeling places at least some individuals in the multi-century age range. The most cited individual was estimated at 392 ± 120 years, and the study inferred a minimum lifespan of 272 years. The result identifies an extraordinary longevity record while retaining a wide probability range.
It also explains the conservation warning. A species does not need a precisely known global decline to be vulnerable when each generation spans centuries, growth is roughly a centimetre or less per year, and fishing removes animals faster than recruitment can replace them. For Greenland sharks, the strongest immediate evidence points to fisheries bycatch; climate-related habitat change deserves monitoring but still carries major uncertainty about its ultimate effect.
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