The Pacific sleeper shark has the largest reported deep-sea-associated size: deep-water photographs have been interpreted as showing an animal about 7 metres (23 feet) long. That is an estimate, not a confirmed capture. The largest directly measured Pacific sleeper in the 2024 review was a 4.65-metre female. Greenland sharks may reach 5.5 metres according to a 2025 Canadian assessment, while an older NOAA guide records a 4.82-metre bluntnose sixgill shark.
There is no perfectly certain, universal ranking because “deep sea” has no shared depth cutoff in the available sources and the biggest animals are rarely sampled. The fairest comparison keeps measured specimens, photographic estimates and literature-reported maxima separate.
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What “largest deep-sea shark” actually means
“Deep sea” is often used as shorthand for sharks that spend much of their lives in cold, dark, deep water. It is not a single scientific zone applied consistently to every species in this comparison. Pacific sleeper sharks occur from relatively shallow water to depths beyond a mile, Greenland sharks have been recorded diving to 2,200 metres, and bluntnose sixgills also occupy deep habitats but can move vertically. A shark that uses deep water but also visits the continental shelf may still appear on a deep-sea list.
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Maximum length is also an evidence problem. A fish measured on a deck provides a different kind of evidence from one photographed beside an object of known size. The largest-looking animals are difficult to land, and large adults are especially scarce in fishing and survey records. A responsible ranking therefore labels each figure by evidence type instead of presenting every number as an equally verified record.
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Deep-water sharks compared
| Species | Best size figure in the cited sources | Evidence type | What the source establishes |
|---|---|---|---|
| Pacific sleeper shark (Somniosus pacificus) | About 7 m (23 ft) estimated; 465 cm directly measured | Submersible photographs and a landed specimen | Largest candidate, but the 7 m figure is an estimate. The strongest confirmed landing in the 2024 review was a 465 cm female. |
| Greenland shark (Somniosus microcephalus) | 550 cm possible for females; 510 cm reliably measured in the review literature | Assessment maximum and measured record | One of the largest confirmed deep-water-associated sharks. The Canadian figure is a potential maximum, not a measurement of every large female. |
| Bluntnose sixgill shark (Hexanchus griseus) | 482 cm (15.8 ft) | Record reported in an older NOAA-hosted guide | A large historical record, explicitly attributed to that guide rather than treated as a newly updated global record. |
| Goblin shark | Not stated in the reviewed sources | Natural-history description | The FAO describes it as one of the deepest-dwelling and least frequently encountered sharks, but the available material does not provide a comparable current maximum. |
| Megamouth shark | Not stated in the reviewed sources | Natural-history description | The FAO describes it as a very large deep-water shark, while emphasizing how little was known about it in that overview. |
Pacific sleeper shark: the leading size candidate
The Pacific sleeper shark is the species most often associated with the very largest deep-water estimate in this evidence set. It lives throughout the Pacific and has been observed in both shallow and deep habitats. NOAA reports sightings from submersibles more than a mile underwater. Its range and depth flexibility mean that it belongs on a deep-water list without being restricted to the deepest ocean trenches.
What has actually been measured
A NOAA-hosted 2024 review identifies a 465-centimetre (4.65-metre) female as the largest confirmed landed Pacific sleeper in its account. The shark was caught in the eastern Aleutians in October 2021 and measured by a trained fisheries observer. This is the strongest physical measurement cited for the species here: the animal was available for direct measurement rather than inferred from an image.
Why reports reach about 7 metres
The same review discusses deep-water photographs that imply substantially longer animals. A Suruga Bay submersible observation was estimated at roughly 660–720 centimetres by comparing the shark with an object of known size. The authors considered that estimate credible, but they still distinguish it from a measured landing. NOAA’s 2024 feature similarly says that very large Pacific sleepers have been estimated from submersible cameras at up to 23 feet, while noting that none longer than 14 feet had been measured from fishing or survey vessels at the time of publication.
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchThose statements are not contradictory. They describe two evidence classes: a maximum suggested by imagery and a smaller maximum verified on a specimen. Until a comparably large animal is physically measured, “about 7 metres” should be written as an estimate, not as the confirmed length of a captured shark.
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Why the uncertainty is unusually large
Large Pacific sleepers are rarely represented in catch records, and cameras cannot always provide a reliable scale, angle or view of the entire body. NOAA Fisheries research biologist Beth Matta summarized the knowledge gap: “Yet we still know little about even its most basic biology.” The absence of large measured animals does not prove that the photographic estimate is wrong; it shows why the estimate cannot be given the same status as the 465-centimetre landing.
Greenland shark: the largest measured rival
The Greenland shark is a second major contender and has a more clearly documented large-adult range. Canada’s 2025 COSEWIC assessment says males reach up to 375 centimetres and females may attain 550 centimetres total length. In the literature discussed by the NOAA-hosted 2024 review, the largest reliably measured Greenland shark is 510 centimetres. The two figures should be kept with their source labels: 5.5 metres is an assessment-level potential maximum for females, while 5.1 metres is the reliably measured value cited in the review.
Typical size and identification limits
Common lengths in the Canadian assessment’s cited literature are 200–400 centimetres. That range describes where many reported sharks fall; it is not a ceiling. The assessment also warns that large Somniosus sharks can be difficult to distinguish by external morphology because traits overlap. A photograph or brief observation may therefore support a size estimate without making species identification completely certain.
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Depth and extraordinary longevity
NOAA says Greenland sharks are known to dive as deep as 2,200 metres. They are also famous for extreme longevity, but the age number requires careful wording. NOAA reports a carbon-dating estimate of 272–512 years for a 5-metre female in the cited study. Carbon dating produces an estimated interval, not a definitive birthday or exact age. The result is best understood as evidence of an exceptionally slow life history rather than a precise age claim for every large Greenland shark.
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Bluntnose sixgill shark: a documented 4.82-metre record
The bluntnose sixgill is another large deep-water shark and is easier to identify from a distinctive feature: six gill slits rather than the five found in most sharks, plus a single dorsal fin. An older NOAA-hosted identification guide reports the largest sixgill on record as a 482-centimetre (15.8-foot) female.
That number remains useful as an attributed record, but the guide is older (circa 2007). It should not be presented as proof that no later or larger specimen exists, nor should it be blended with the newer Pacific sleeper and Greenland figures as though all three came from one standardized survey. The sixgill’s 4.82-metre value is a guide-reported record, not a newly updated global maximum.
Where goblin and megamouth sharks fit
The goblin shark and megamouth shark belong in a broad overview because both are strongly associated with deep water and are seldom encountered. The FAO describes the goblin as one of the deepest-dwelling shark species. Its long snout and protrusible jaws make it unmistakable in a close specimen, but the reviewed material does not provide a current, directly comparable maximum length.
The FAO also describes the megamouth as a very large deep-water shark and emphasizes how little was known about it in that historical overview. “Very large” is not a measurement, so it cannot be used to place megamouth above a 5.5-metre Greenland shark or a 7-metre photographic Pacific sleeper estimate. Including either species in a list is reasonable; assigning it a precise rank from the available evidence is not.
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How to compare maximum lengths without being misled
Use four questions whenever a source claims a record-sized deep-sea shark:
- What is the total length? Check whether the figure is in metres or centimetres and whether it means total length measured in a standard position.
- How was it obtained? A trained observer’s measurement of a landed specimen is stronger for a confirmed record than a camera estimate. A literature-reported maximum needs the original context attached to it.
- Was “deep sea” defined the same way? The reviewed sources do not establish one depth threshold for all species. A shark that regularly uses 2,200-metre water and one seen beyond a mile may both be deep-water-associated, even if their habitats overlap only partly.
- How well are large adults sampled? Fishing gear, survey routes and camera deployments do not sample every depth or size class. Rare large animals can be missing from catch records while still appearing in occasional imagery.
Applying those tests produces a qualified result rather than a forced single-number leaderboard. The Pacific sleeper has the highest reported estimate, at about 7 metres, but the Greenland shark has a larger source-specific female potential maximum than its best reliably measured value. The sixgill has a substantial older record at 4.82 metres. None of these figures proves that one species is always larger than every individual of the others.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How large are these sharks in practical terms?
| Figure | Approximate scale | Qualification |
|---|---|---|
| 465 cm | 4.65 m | Directly measured Pacific sleeper female from the eastern Aleutians, October 2021, as reported in the 2024 review. |
| 510 cm | 5.1 m | Largest reliably measured Greenland shark cited in the 2024 review. |
| 550 cm | 5.5 m | Female Greenland shark may attain this length in Canada’s 2025 COSEWIC assessment. |
| 660–720 cm | 6.6–7.2 m | Pacific sleeper estimate from a Suruga Bay submersible photograph beside a known-size object. |
| 23 ft | About 7 m | NOAA’s camera-based upper estimate for very large Pacific sleepers. |
| 482 cm (15.8 ft) | 4.82 m | Largest bluntnose sixgill reported in an older NOAA-hosted guide. |
The table shows why unit conversion alone does not settle the ranking. A 7-metre estimate is longer than every directly measured value listed, but it is also less precise than a measurement taken from a landed shark. The evidence label belongs beside the number whenever the figure is quoted.
Why giant deep-water sharks are difficult to study
Deep habitats are expensive and technically difficult to survey. Submersible cameras may encounter an animal only briefly, often at an angle that hides the tail or exaggerates perspective. Fishing records are biased toward places and depths where vessels operate, and large adults may avoid gear or occupy habitats that are rarely sampled. For Pacific sleepers in particular, NOAA notes that large individuals are rarely encountered and that limited data complicate management.
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Species identification adds another complication. The COSEWIC assessment says large Somniosus species can share overlapping morphological traits. A size estimate attached to a photograph may therefore be more secure than the species label unless the image, location and diagnostic features are all clear.
Conservation stakes behind the record claims
Size is not just a curiosity. Large, slow-growing sharks generally replace lost adults slowly, so removing a few mature animals can matter even when no precise population total is available.
Pacific sleeper shark
NOAA says most Pacific sleeper mortality in Alaska waters comes from fisheries bycatch. The agency describes the species as poorly studied, slow-growing and low in productivity. When large adults are rarely seen, managers have less information about the part of the population that contributes the most to reproduction. NOAA scientist Cindy Tribuzio put the problem in broader terms: “A large portion of the population remains unseen and unsampled.”
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Canada’s 2025 COSEWIC assessment identifies Greenland sharks as incidental bycatch in several fishing gears. Slow growth, late maturity and exceptional longevity increase the risk from overfishing because recovery can take a long time. The shark’s estimated lifespan should not be turned into a precise age claim, but it does support the conclusion that this is a low-productivity animal.
A useful comparison, not a harvest rule
Tribuzio notes that sustainable fishing rates for long-lived sharks can be very low, giving the spiny dogfish—a Pacific sleeper relative with a lifespan of about 100 years—as an example that may tolerate harvest rates of only about 3 percent. That comparison illustrates the sensitivity of long-lived sharks; it is not a specific allowable catch rate for Pacific sleeper or Greenland sharks.
The clearest answer
If “largest” means the biggest reported deep-water-associated shark, the Pacific sleeper leads with a photographic estimate near 7 metres (23 feet). If “largest” means a directly measured animal, the available figures are closer: a 5.5-metre potential female Greenland shark in the 2025 Canadian assessment, a 5.1-metre reliably measured Greenland shark cited in the 2024 review, and a 4.65-metre measured Pacific sleeper. The bluntnose sixgill’s 4.82-metre record remains an important, older comparison.
Those distinctions are the answer, not a technical footnote. Deep-sea sharks are hardest to observe at the sizes that attract record claims, so the most honest description pairs every length with its source, date and evidence type.
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