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The fastest reliable field assessment
Start with the fins rather than color or apparent size. If the shark has an anal fin between the pelvic and caudal fins, it is not a Greenland shark. If there is no anal fin, inspect the two dorsal fins: Greenland sharks have two small, approximately equal-sized fins without conspicuous spines. The first dorsal fin begins well behind the pectoral-fin base, around the middle of the body, and the second begins near the pelvic-fin insertion.
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- Anal fin: absent.
- Dorsal fins: two, small, similar in size, and spineless at their origins.
- First dorsal position: clearly behind the pectoral-fin base, not immediately behind the head or shoulder.
- Second dorsal position: close to the pelvic fins.
- Body: large, heavy, and cylindrical, with a rounded, relatively short snout and small mouth.
- Tail: asymmetrical, with a short upper lobe and a noticeable subterminal notch.
This combination is much more useful than a single feature. A dark shark is not automatically a Greenland shark, and a small-looking individual in a distorted photograph is not automatically a different species.
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1. Establish whether an anal fin is present
Look along the underside between the pelvic fins and the tail. The anal fin, when present in a shark, is a separate fin on the centerline ahead of the caudal fin. Greenland sharks lack it, leaving an uninterrupted space behind the pelvic fins. This is the first split in Fisheries and Oceans Canada’s Atlantic Canadian key, which covers 19 shark species.
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Do not mistake a pelvic fin, a fold of loose skin, or the lower edge of the tail for an anal fin. In a side-on image, trace the fin back to its attachment on the belly. A true anal fin has its own base and stands apart from the paired pelvic fins.
2. Count and inspect the dorsal fins
Greenland sharks have two dorsal fins on the back. They are relatively small and roughly equal in size, with no conspicuous spines at their origins. Spines may be hard to see in a blurred, distant, or damaged photograph, so record the feature as “not visible” rather than assuming it is absent.
Spiny dogfish and black dogfish also lack an anal fin, but each has obvious dorsal spines. In the Atlantic Canadian key, those spines direct the identification away from Greenland shark. A visible spine is therefore a strong exclusion clue; an unseen spine is not proof that none exists.
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3. Locate the first dorsal fin against the paired fins
Use the pectoral fin as the front reference point. On a Greenland shark, the first dorsal fin starts well behind the pectoral-fin base, approximately at mid-body. The second dorsal fin is much farther back, near the pelvic-fin insertion. This spacing is more informative than simply saying that the shark has “rear” dorsal fins.
Perspective can shift apparent positions. A shark viewed from above, bent in a net, or photographed with a wide-angle lens may make the first dorsal fin look closer to the head. Compare the fin bases with the body axis, not with the image edges.
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4. Check the overall profile
The body is heavy and cylindrical rather than slender. The snout is rounded and relatively short, and the mouth is small in proportion to the head. The pectoral fins are small and rounded. The tail is asymmetrical, with a short upper lobe and a noticeable notch near the subterminal portion.
These traits are supporting evidence. A juvenile, a partially obscured carcass, or a shark seen at an angle may not show the profile clearly. Record which traits are actually visible instead of filling gaps with assumptions.
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Color can range from grayish brown to blackish, sometimes with dark or pale spots. Lighting, depth, water quality, and decomposition can alter the apparent shade. The eyes are relatively small and are often partly covered by the ectoparasitic copepod Ommatokoita elongata. The parasite can be conspicuous, but it is not a stand-alone species mark: an image may omit the eyes, and related sleeper sharks can create similar impressions.
6. Record location and depth without treating them as proof
Greenland sharks occur primarily in the North Atlantic and adjacent Arctic waters, including Atlantic Canada, Greenland, Iceland, and the wider Northeast Atlantic. They are cold-water, deep-dwelling sharks; a Fisheries and Oceans Canada profile gives an Arctic and subarctic temperature context of approximately −2 to 7 °C and says they are commonly found below 200 m, with seasonal variation.
Those conditions make a sighting more plausible, not definitive. Other large sleeper sharks, and possible hybrids, can occur in overlapping environments. A location outside the usual range deserves careful documentation rather than an automatic rejection or acceptance.
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External features in detail
Head, snout, and mouth
The head tapers into a rounded, relatively short snout. The mouth is small compared with the massive body. In a clear lateral view, this gives the shark a blunt, compact front rather than a long, pointed rostrum. Do not press the snout shape beyond what the image supports: foreshortening can make any shark look shorter-headed.
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The dorsal fins are low, small, and approximately equal in size. Their origins do not show the conspicuous spines characteristic of spiny dogfish or black dogfish. The first fin is set far behind the pectoral base; the second is near the pelvic-fin insertion. When documenting a specimen, photograph both fin bases and the adjacent skin, because a fin tip alone cannot establish whether a spine is present.
Anal-fin region
The absence of an anal fin is often the most useful quick mark. Photograph the underside or obtain a clear side view that includes the region between pelvic and caudal fins. If that area is hidden, state that the anal fin could not be assessed; do not infer absence from a cropped image.
Pectoral fins, tail, and body
Small rounded pectoral fins contrast with the broad, muscular trunk. The tail is asymmetrical, with a short upper lobe and a distinct subterminal notch. These features help separate a bulky sleeper shark from more streamlined sharks, but they should follow the fin-count assessment rather than replace it.
Teeth: useful only when already visible and safe
Greenland shark upper teeth are slender and thorn-like. Lower teeth are broad and carry strongly oblique cusps. Tooth form can help with a safely documented, already deceased specimen, but it is not a reason to handle a live shark or place hands near the mouth. A closed mouth, damaged jaw, or poor image should be recorded as “teeth not assessed.”
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Comparison with common regional look-alikes
The following distinctions are drawn chiefly from the Fisheries and Oceans Canada key for Atlantic Canadian waters and the NOAA-hosted shark identification guide. They are regional aids, not a universal key for every Arctic shark.
| Shark or group | Anal fin | Dorsal-fin clues | Other useful distinction | Confidence limit |
|---|---|---|---|---|
| Greenland shark (Somniosus microcephalus) | Absent | Two small, approximately equal fins; no conspicuous spines; first well behind pectoral base; second near pelvic insertion | Heavy cylindrical body, rounded short snout, small rounded pectorals, asymmetrical tail | Large sleeper sharks can overlap in appearance; species-level certainty may require genetics |
| Spiny dogfish | Absent | Dorsal spines are present | DFO key describes quadrangular teeth with a laterally directed cusp | Tooth examination is unnecessary and unsafe on a live shark |
| Black dogfish | Absent | Dorsal spines are present | DFO key describes teeth with several triangular cusps | Use the spine mark first; teeth are a secondary feature |
| Prickly or bramble sharks | Comparison guide does not establish every field character | NOAA guide places the first dorsal fin over or behind the pelvic-fin origin | Squaloid sharks that may resemble one another in general form | NOAA’s comparison coverage is limited; treat this as a useful distinction, not an exhaustive key |
| Pacific sleeper shark (Somniosus pacificus) | Not stated in the cited comparison | Morphologically similar to Greenland shark | Geography can inform an assessment | External characters overlap; genetic work may be needed |
| Southern sleeper shark (Somniosus antarcticus) | Not stated in the cited comparison | Morphologically similar to Greenland shark | Southern distribution can provide context | External characters do not guarantee separation |
“Not stated” in the table means that the cited material does not establish that comparison, not that the feature is unknown to science. A regional key should not be expanded into a global identification claim.
Why sleeper-shark identifications can remain uncertain
The Pacific sleeper shark and Southern sleeper shark are close morphological look-alikes. The May 2025 COSEWIC assessment says no taxonomic character currently provides unequivocal separation among species within the large Somniosus group. Proposed measurements, including interdorsal space and prebranchial length, vary and overlap.
Some genetic analyses support Greenland and Pacific sleeper sharks as distinct sister species, while the assessment describes unresolved species-level questions elsewhere in the group and evidence of hybridization. Consequently, a photograph or a single external measurement should not be presented as definitive when the record matters for science, management, publication, or a legal investigation.
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When a provisional identification is appropriate
Use “probable Greenland shark” when the anal fin is absent, the two dorsal fins are small and spineless, the first dorsal position fits, and the body profile is consistent, but the image does not resolve all competing species. Explain which marks were visible and which were not assessed. This is more informative than assigning false precision.
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When to seek genetic confirmation
Consider tissue-based or other approved genetic confirmation for an unusual range record, a specimen that could alter a regional species list, a possible hybrid, or any identification with regulatory or conservation consequences. Preserve chain-of-custody information and follow the receiving laboratory’s sampling instructions. Do not remove tissue from a live animal or handle a shark solely to improve an identification.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A safe workflow for field observers
- Keep distance and follow local wildlife rules. Observe a live shark without touching, restraining, feeding, or placing yourself near its mouth or tail.
- Capture context first. Record date, coordinates or a defensible location description, depth if known, water temperature if measured, and whether the observation was from a vessel, shore, submersible, or bycatch event.
- Photograph the diagnostic zones. Obtain a full side profile, the underside or pelvic-to-tail region, both dorsal-fin bases, the head and eye, and the tail. Take several angles rather than relying on one frame.
- Annotate visibility. Mark each character as present, absent, or not visible. “Not visible” is essential when glare, gear, darkness, or cropping hides a fin.
- Apply the fin sequence. Check anal-fin absence, dorsal-fin number and spines, first-dorsal position, then body and tail form.
- Compare only with appropriate references. The DFO key is specifically for Atlantic Canadian waters. The NOAA guide is a useful supplemental reference, not a guarantee that every Arctic species is covered.
- Escalate uncertain records. Contact a qualified fisheries agency, museum ichthyologist, or laboratory when the sighting is unusual or consequential. Keep original files and metadata.
Size, age, and life history: useful context, not identification marks
COSEWIC’s 2025 Canadian assessment cites common lengths of 200–400 cm total length, adult males up to 375 cm, and females up to 550 cm in the records it reviewed. These figures overlap with the sizes of other large sharks and should not be used as a species test. Perspective, sex, posture, and an unknown reference scale can make length estimates especially unreliable.
The same assessment gives late maturity at approximately 150 years. NOAA Ocean Service’s explainer, last updated September 23, 2026, reports that carbon dating estimated the largest female in the cited study at 272–512 years old. Carbon dating can provide estimates, not a definitive age, and that range applies to the largest examined female rather than every Greenland shark.
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| Figure | What it describes | How to use it |
|---|---|---|
| 200–400 cm | Common total lengths cited by COSEWIC from Compagno (1984) | Background only; not diagnostic |
| Up to 375 cm | Adult male length in cited COSEWIC records | Record-specific maximum, not a universal ceiling |
| Up to 550 cm | Adult female length in cited COSEWIC records | Record-specific maximum, not a field cutoff |
| Approximately 150 years | Approximate age at late maturity in the Canadian assessment | Conservation and life-history context |
| 272–512 years | Carbon-dating estimate for the largest female in the NOAA-cited study | An estimate for that examined animal, not a definitive lifespan for all individuals |
Conservation context in Canada
COSEWIC assessed the Greenland shark as Special Concern in Canada in May 2025. The designation is Canadian; it is not a statement of global conservation status. The assessment cites incidental capture in trawl, benthic longline, and gillnet fisheries, an estimate of at least 1,700 Greenland sharks bycaught annually in Canada, slow growth, late maturity, longevity, and possible effects from accelerated climate change.
These facts explain why careful identification matters, but they are not identification marks. Do not infer a conservation category from a shark’s apparent size, color, or the presence of an eye parasite. If a bycatch or stranding is involved, follow the relevant reporting and release requirements rather than attempting an extended examination.
Common identification mistakes and corrections
- Mistake: identifying by black color. Correction: color ranges from grayish brown to blackish and may include spots; begin with fin arrangement.
- Mistake: treating the eye parasite as proof. Correction: Ommatokoita elongata is a useful observation to record, not a species-level test.
- Mistake: calling every large, spineless shark a Greenland shark. Correction: sleeper-shark species overlap; document uncertainty and consider genetics.
- Mistake: using location as a verdict. Correction: North Atlantic or Arctic context raises plausibility but does not exclude similar species or hybrids.
- Mistake: inferring a missing fin from a cropped photograph. Correction: use “not visible” unless the relevant body region is clearly shown.
- Mistake: handling a live shark to inspect teeth or spines. Correction: rely on remote images and qualified personnel; teeth are optional evidence, never a justification for unsafe contact.
- Mistake: treating a measurement as conclusive. Correction: interdorsal and prebranchial measurements can overlap among Somniosus species.
A concise reporting template
A useful report states the evidence and its limits in the same paragraph. For example: “The animal is provisionally identified as a Greenland shark because no anal fin is visible, two small dorsal fins without conspicuous spines are present, the first dorsal begins well behind the pectoral-fin base, and the body is heavy with a rounded snout. Color is gray-brown and the eye appears partly occluded, but those traits are supportive only. The image does not resolve all Somniosus species, so genetic confirmation would be needed for a definitive unusual record.”
Attach the original photographs, observation conditions, location, depth, estimated scale, and the name of the person or agency making the assessment. This format lets another reviewer reproduce the reasoning instead of relying on an unsupported species label.
Source notes for readers
The regional fin key is Fisheries and Oceans Canada’s Key to shark ID, modified March 22, 2022, and its scope is Atlantic Canada. The agency’s Greenland shark profile was modified November 23, 2018. NOAA’s hosted identification guide contains a Greenland shark entry and is dated circa 2008 in search metadata. COSEWIC and Environment and Climate Change Canada published the Canadian assessment and status report in 2025. NOAA Ocean Service’s longevity explainer was last updated September 23, 2026.
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