Only two sharks are genuine Arctic residents: the Greenland shark in the North Atlantic and the Pacific sleeper shark in the Bering and Chukchi seas. Everything else on the standard list visits sub-Arctic water seasonally and leaves.
Two strategies get a shark into cold water. The mackerel sharks — the salmon shark and the porbeagle — run a counter-current heat exchanger that holds the core well above the water outside. The sleeper sharks do the opposite: they run cold, load their tissues with urea and trimethylamine N-oxide, and move at a pace that costs almost nothing.
- Year-round Arctic sharksGreenland and Pacific sleeper
- Greenland shark cruising speedAbout 1.2 km/h
- Oldest Greenland shark datedEstimated near 400 years
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What cold water does to a shark
Cold slows chemistry. In an animal whose body temperature tracks the water around it, every muscle contraction, every nerve signal and every step of digestion runs at the rate the sea allows, and Arctic water sits between about −1.8°C and 4°C for most of the year. That is survivable, but it sets a ceiling on how fast a shark can move and how quickly it can process a meal.
A small number of sharks got around the ceiling. In the mackerel shark family, blocks of red swimming muscle sit deep inside the body rather than along the flank, and the blood serving them runs through a dense counter-current network called a rete mirabile: outgoing warm blood passes incoming cold blood and hands its heat across before it can be lost at the gills. The result is regional endothermy — a warm core inside a cold fish.
It is worth being clear about how rare this is, because the older version of this page claimed that many sharks are endotherms. They are not. The confirmed list runs to roughly eight species: the great white, the shortfin mako and longfin mako, the porbeagle, the salmon shark, and to a lesser degree the common and bigeye threshers. Out of more than five hundred described sharks, that is the whole of it.
The sharks that carry their own heat
The salmon shark is the extreme case. It works the sub-Arctic North Pacific from British Columbia to the Bering Sea, hunting salmon runs in water between about 6 and 14°C while holding its core around 25°C — usually 8 to 11°C above the sea outside, with elevations past 20°C recorded in animals working near-freezing water. Claims that it reaches 80 to 100°C, which the old version of this page carried, are a garbled transcription rather than a measurement, and the often-repeated top speed of 50 mph has never been verified by anyone. The best-supported burst figure for any shark belongs to the shortfin mako, at roughly 45 to 70 km/h.
The porbeagle does the same trick on the Atlantic side with a smaller margin, its swimming muscle measured 7 to 10°C above the surrounding sea. That buys it a wide vertical range: the deepest dive on record for a tagged porbeagle is 1,360 metres, made in winter off Nova Scotia, though the animals spend most days above 200 metres.
One species usually filed here does not belong. The basking shark is a mackerel shark and ranges far north, but direct measurement has shown it to be an ordinary ectotherm with no warm core at all. It reaches cold water by tolerating it, not by heating itself.
The two that actually live there
The Greenland shark took the opposite route and became the most committed cold-water shark there is. It runs at the temperature of the sea, cruises at roughly 1.2 km/h with the slowest tail-beat measured for a fish of its size, and has been recorded well past 2,000 metres. Radiocarbon dating of eye lens tissue gave the largest female in the study, an animal of 5.02 m, a best estimate of about 392 years within a range of 272 to 512 — the longest lifespan known for any vertebrate, and a figure that comes with wide error bars, as how long sharks live explains.
Its chemistry is frequently described as antifreeze, which is not quite what is happening. Greenland shark tissue is loaded with urea and trimethylamine N-oxide; the TMAO is there to counteract the destabilising effect of the urea and of deep-sea pressure on proteins. The by-product is that the meat is poisonous fresh, which is why Icelanders ferment and dry it for months before eating it as hákarl.
The Pacific sleeper shark fills the same role in the Bering and Chukchi seas and is built the same way. It is not a requiem shark, as the old text claimed — it sits in Somniosidae, the sleeper sharks, alongside the Greenland shark, and its nearest relatives are dogfishes rather than tiger or bull sharks. Its liver is enormous and rich in squalene, a light hydrocarbon that works as buoyancy rather than as protection against freezing.
The visitors that come north and leave
The blue shark is the great traveller of the group and reaches the northern edge of its range off Norway, Iceland and Newfoundland in the warmer months. Tagged individuals have crossed the Atlantic, with recorded journeys of several thousand kilometres, and litters are unusually large for a shark — commonly twenty-five to fifty pups, with an exceptional recorded maximum of about 135. What it does not do is live in the Arctic; it follows warm-water fronts north and retreats with them.
The spiny dogfish is the same story in miniature. It is one of the most abundant sharks in the world, rarely exceeds about a metre, carries a venomous spine in front of each dorsal fin, and has the longest gestation ever reliably measured in a vertebrate, eighteen to twenty-four months. Cool temperate water suits it; it pushes north in summer for the feeding and drops back south.
The bluntnose sixgill is often listed as Arctic and is better described as deep and cosmopolitan. It keeps the six gill slits of an older shark lineage, works down to around 2,500 metres in temperate and tropical water worldwide, and reaches the southern margins of the Arctic rather than the pole. Depth, not latitude, is what it is adapted to. The full set of cold-water species is in types of sharks.
What the incident record says about all of them
Neither of the two real Arctic residents appears in our incident database at all: no entry is attributed to a Greenland shark or a Pacific sleeper shark. That is not restraint on their part so much as arithmetic — almost nobody swims where they live, and one of them travels at walking pace in near-freezing water hundreds of metres down.
The visitors have short files. The salmon shark has four entries, none fatal, spanning 2000 to 2018, and they include a netted shark biting a researcher's leg and surf washing a dying juvenile against a wader's foot in California. The porbeagle has nine, also with no deaths, and most of them describe no injury at all — a bitten video camera off Maine, a bitten shoe on a boat off Islay. The sixgill has one, a minor foot and ankle injury to an abalone diver off Point Conception in 1985.
The blue shark is the only one with a serious record: 47 entries, of which 8 are logged as fatal, and just one of those has occurred since 2000 — a 2017 double boat capsize off Libya where the attribution is explicitly uncertain. Most of the fatal entries are from the 1950s. The full country files are under shark attacks, and the northern one worth reading is Iceland.
Frequently asked questions
Which sharks live in the Arctic all year?
Two: the Greenland shark in the North Atlantic and Arctic basin, and the Pacific sleeper shark in the Bering and Chukchi seas. Both are sleeper sharks, both run at the temperature of the water around them, and both stay in the region permanently rather than moving south for the winter.
Are any sharks warm-blooded?
About eight species are regionally endothermic, not warm-blooded in the mammal sense. The list covers the great white, both makos, the porbeagle, the salmon shark and, to a smaller degree, the common and bigeye threshers. They hold blocks of muscle and organs above water temperature using a counter-current blood network.
How does a salmon shark stay warm?
A dense network of blood vessels called a rete mirabile sits between the warm interior muscle and the cold blood returning from the gills, so heat is passed inward instead of being lost. A salmon shark holds its core around 25°C, usually 8 to 11°C above the sea, with elevations past 20°C recorded in near-freezing water.
Is the basking shark warm-blooded?
No. It is a mackerel shark, the same family branch as the porbeagle and the great white, and it ranges into cold northern water, but direct measurement showed it has no warm core. It is an ordinary ectotherm that simply tolerates cold rather than heating itself against it.
How old can a Greenland shark get?
Radiocarbon dating of eye lens tissue gave the largest female in the study, an animal of 5.02 metres, a best estimate of about 392 years within a range of roughly 272 to 512. The error bars are wide, but even the low end of that range makes it the longest-lived vertebrate known to science.
Why is Greenland shark meat poisonous?
Its tissues are loaded with urea and trimethylamine N-oxide, chemicals that stabilise proteins against pressure and against each other in deep, cold water. Eaten fresh, the meat causes severe illness. Icelanders deal with this by fermenting and air-drying it for months before serving it as hákarl.
Do Arctic sharks attack people?
Not in our records. No entry in the SharkSider database is attributed to a Greenland shark or a Pacific sleeper shark. The salmon shark has four non-fatal entries and the porbeagle nine, mostly describing no injury at all. Almost nobody is in the water where the resident species live.
How fast is a Greenland shark?
Around 1.2 km/h on average, which is slower than a person walking. Tracking work found the slowest tail-beat frequency recorded for any fish of comparable size. How it catches seals at that speed is still unsettled; ambushing sleeping animals is the leading explanation rather than pursuit.
References
A small team focused on researching sharks and making marine biology easy to understand. Every page is reviewed against current species records and the SharkSider attack database, and updated when new incidents or research appear.
Published November 2, 2016 · Last updated September 23, 2026 · Filed under Cool Shark Facts.
