The mouse catshark (Galeus murinus) is a small deep-water catshark of the family Pentanchidae, reaching about 63 cm (25 in), that lives close to the bottom of the continental slope in the north-east Atlantic at depths of roughly 380 to 1,250 m. It is a uniform mouse-grey to grey-brown, without spots or saddles, with a blunt snout, oval cat-like eyes and a large, widely arched mouth.
It feeds mainly on deep-sea shrimp, along with small bony fish and cephalopods taken on or near the sea floor. Females lay eggs in golden, vase-shaped capsules covered in fine fibres, and the young hatch at about 8 to 9 cm. The IUCN assessed the species as Least Concern in 2023. It is entirely harmless: nobody dives to the depths where it lives.
- Maximum length63 cm (25 in)
- WeightNot recorded; well under 2 kg
- LifespanNot measured
- Depth rangeAbout 380–1,250 m (1,250–4,100 ft)
- DietDeep-sea shrimp, small fish, cephalopods
- IUCN statusLeast Concern (assessed 2023)
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Chondrichthyes
- Order
- Carcharhiniformes
- Family
- Pentanchidae
- Genus
- Galeus
- Species
- Galeus murinus
- Family (common)
- Deepwater catsharks
On this page
How to recognise a mouse catshark
The colour is the starting point, and the species is named for it. A mouse catshark is a flat, even grey-brown from snout to tail, a shade or two lighter on the belly, with no saddles, blotches, spots or pale fin margins of any kind. That plainness is diagnostic in its own right in the north-east Atlantic, where the catsharks it shares the slope with are almost all patterned: the blackmouth catshark carries a row of dark saddles, and the small-spotted catshark of the shelf above is peppered with fine dark dots.
The head is short and firm rather than soft. The snout is blunt and bluntly rounded in profile, the nostrils are partly covered by triangular flaps of skin, and the eyes are horizontal ovals with a rudimentary third eyelid, the nictitating fold that all ground sharks possess. Below them the mouth opens as a wide, low arch with long, well-developed grooves running back from each corner. The teeth are small and numerous, each with a narrow central point flanked by one or two cusplets.
Fins and skin complete the picture. Both dorsal fins are of similar size and shape, the first set above the rear of the pelvic fins and the second above the anal fin, the pectorals are broad and rounded, and the pelvic fins have gently rounded margins. The genus Galeus is known in English as the sawtail catsharks, after the crest of enlarged, saw-like denticles that runs along the upper edge of the tail in most of its members; on a plain grey specimen this is easier to feel with a fingertip than to see.
How big does a mouse catshark get?
The largest properly measured mouse catshark is 63 cm (25 in) in total length. That is the figure to use, and it is worth correcting the older claim that the species ranges from about 48 cm up to 84 cm. The very large specimens behind that upper number came from Icelandic waters and have never been confirmed as this species; the sensible reading is that they belong to another catshark of the same genus or were mismeasured, and repeating 84 cm as a maximum gives a false impression of the animal.
A 63 cm shark is roughly the length of a forearm and hand together. Sizes at which males and females become mature have not been firmly established for the species, and neither has any consistent difference between the sexes, which is unsurprising given how few specimens have passed through a laboratory.
Weight has never been published. Deep-slope catsharks have weakly mineralised skeletons, pale watery muscle and a large liver filled with low-density oil, which together keep them near neutral buoyancy, so a mouse catshark weighs far less than a coastal shark of the same length; well under two kilograms is a fair expectation. Hatchlings are much better documented, at about 8 to 9 cm. The scale bar below sets the maximum length against a 1.8 m diver.
Where mouse catsharks live
This is a north-east Atlantic species and nothing else. The core of the confirmed range is the slope around Iceland and the Faroe Islands, extending south along the banks, troughs and seamounts west of Scotland and Ireland, and north-east towards the deep water off Norway. It is a cold-water animal, and the deep Atlantic water it lives in sits somewhere between about 4 and 8 °C year round.
Two claims from the older version of this page should be dropped. Records attributed to the species off France and off Western Sahara almost certainly belong to the blackmouth catshark or the Atlantic sawtail catshark, both of which are common in those waters and both of which are members of the same genus.
Depths run from roughly 380 m to about 1,250 m, on or just above the bottom over the continental slope, with most catches from the middle of that band. The bottom there is soft mud and sand on a steady gradient; there is no daylight and no seasonal cycle to speak of, and food arrives mainly as material sinking from the productive surface layer above. Our overview of where sharks live puts this habitat alongside the shelves and reefs that most sharks occupy.
1 country list the mouse catshark in their species guide; the count is the number of incidents attributed to it there in the SharkSider database. Browse every guide on sharks around the world and sharks in the US.
What mouse catsharks eat
Shrimp come first. Stomach examinations put deep-sea shrimps and similar crustaceans at the centre of the diet, with small bony fish and cephalopods making up the rest. Everything is taken on or within a metre or two of the bottom; there is no evidence of this species feeding up in the water column, and its build argues against it.
The mouth suits that menu exactly. A wide, low arch opens quickly to draw in water and prey together, and the hundreds of small multi-pointed teeth hold a soft, slippery shrimp rather than cutting it. Nothing in the jaw is built for a struggle with large prey, and none of what the species eats puts up much of one.
Detection, not speed, is the hard part in permanent darkness. The pores of the ampullae of Lorenzini across the snout register the faint electrical fields given off by muscle and gills, which finds a shrimp sitting motionless in mud that no eye could pick out. The lateral line records the pressure wave of anything that darts away, and the sense of smell draws the shark along a scent trail towards carrion. The oval eyes, backed by a reflective layer, are still useful at the shallow end of the range where a trace of blue daylight survives.
How the mouse catshark lives
No mouse catshark has been filmed alive, kept in an aquarium or followed with a tag, so this section describes what the body implies rather than what anyone has watched. That distinction matters: most of the confident-sounding behaviour written about deep-sea sharks online is invention.
The build is that of an economical bottom cruiser. A large, oil-rich liver brings the animal close to neutral buoyancy, so it can hold station a few centimetres above the mud with almost no effort, and the pale, watery muscle suits slow continuous swimming rather than bursts of speed. Broad rounded pectoral fins give fine control in a small space.
Breathing does not depend on swimming. A bottom-living catshark draws water in through the mouth and spiracles and pumps it over the gills while lying completely still, which is what allows it to rest on the sediment indefinitely; our page on how sharks breathe contrasts this with the ram ventilation used by fast open-water sharks that must keep moving.
Beyond that the honest answers are short. Nobody knows whether mouse catsharks move up and down the slope with the seasons, whether they gather to lay eggs, whether males and females occupy different depths, or how far an individual travels in a year. Related shelf catsharks are known to rest in groups by day and separate to feed at night, but at 800 m there is no day and night to organise a routine around.
Reproduction and lifespan
The mouse catshark lays eggs, and its egg capsules are the most distinctive thing about it. Each is a golden-yellow, vase-shaped case roughly 5.3 to 5.6 cm long and 1.4 to 1.7 cm across, and the surface is covered in fine fibres that give it a curiously hairy, felted look quite unlike the smooth mermaid's purse of a shelf catshark. Those fibres tangle in sediment and on any hard object on the bottom, anchoring the capsule where the current would otherwise roll it away.
Females release the capsules in pairs, one from each oviduct. The embryo inside is supplied only by its own yolk and receives nothing further from the mother, the oldest and simplest of the strategies described on our page about how sharks reproduce. Development is slow because the water is cold: a capsule on a 5 °C slope can take many months to hatch, against six to ten months for a coastal catshark in warmer water. The young emerge at about 8 to 9 cm, already miniature versions of the adult and independent from the first minute.
How many eggs a female produces in a season, and whether there is a laying season at all, have not been established. Lifespan is a complete blank: no ageing study has been attempted, and the poorly calcified vertebrae of deep-water catsharks make growth bands hard to read even when someone tries. Small catsharks from shallow water generally reach ten to twenty-five years, and cold, slow-growing deep-sea relatives can be expected to live longer, but no measured figure exists for this species. Our guide to how long sharks live explains why.
Is the mouse catshark dangerous?
No, and there is no scenario in which it could be. The shallowest confirmed records sit at around 380 m, roughly ten times the depth limit of recreational scuba diving, and the species is most common far below that. It reaches 63 cm and its teeth are two or three millimetres long, built to hold a shrimp. The SharkSider database holds no incident attributed to it anywhere in the north-east Atlantic.
The only people who ever see one are the crews of deep-water trawlers working the slope off Iceland, the Faroes and the Hebrides, and the scientists who sort their catch. For them the worst the animal can manage is a graze from its sandpaper skin. The mouse catshark belongs with the other harmless deep-sea sharks on our list of the least dangerous sharks, and anyone wanting to know which species matter to swimmers in Irish or Icelandic water should read the country pages rather than this one.
The SharkSider database has no incident attributed to this species. The database draws on the International Shark Attack File, the Global Shark Attack File and verified local reports, and is updated weekly.
Conservation status
The IUCN Red List assessed the mouse catshark as Least Concern in 2023. The reasoning is depth and geography rather than any population estimate, because no estimate exists. The species occupies a broad stretch of the north-east Atlantic slope, a large part of its vertical range lies below the depths most fleets work, and there is no fishery anywhere that targets it.
Where the two do meet, mouse catsharks turn up as bycatch in deep bottom trawls and in longlines set for Greenland halibut, grenadiers and deep-water redfish around Iceland and the Faroes, and in the mixed deep-water fisheries west of Scotland and Ireland. The species has no market value and is discarded.
Two broader pressures deserve a mention. Deep-water trawling in the north-east Atlantic expanded rapidly from the 1990s and pushed gear into slope habitats that had never been fished, which is why European restrictions on fishing below 800 m were introduced; those limits happen to protect a good part of this shark's range. The second is climate: warming and changing oxygen levels in the deep Atlantic alter the band of water available to cold-adapted slope animals. Neither is an immediate threat to this species, and the honest qualification is that nobody is counting it. The wider picture is on our page on why sharks are endangered.
Relatives and look-alikes
The genus Galeus holds about twenty species of sawtail catsharks worldwide, and three of them share the north-east Atlantic with this one. The blackmouth catshark is the common slope catshark from Norway to West Africa and the Mediterranean, larger at about 90 cm, boldly marked with dark saddles and with a mouth lined in black. The Atlantic sawtail catshark is a smaller, southern species of the Alboran Sea and the Iberian and Moroccan slope. Both are patterned, which separates them from the plain grey mouse catshark at a glance.
The other deep catshark of the same northern waters is not a Galeus at all. The Iceland catshark, a member of the genus Apristurus, is similar in size and equally plain, but it has the soft, flabby body and the bell-shaped, flattened snout typical of its genus, and its skin tears easily. The white ghost catshark, from deeper water on the same slopes, is paler still.
Higher up, on the shelf rather than the slope, the two catsharks a British or Irish angler is likely to meet are the small-spotted catshark and the larger nursehound, both of them spotted and both living in water shallow enough to dive. Neither overlaps with the mouse catshark in depth or in appearance.
Blackmouth Catsharkspecies profile- Atlantic Sawtail Catsharkspecies profile
- Iceland Catsharkspecies profile
- White Ghost Catsharkspecies profile
- Small-Spotted Catsharkspecies profile
- Nursehound Sharkspecies profile
Frequently asked questions
What is a mouse catshark?
A small deep-water shark, Galeus murinus, of the family Pentanchidae. It grows to about 63 cm, lives near the bottom of the north-east Atlantic slope between roughly 380 and 1,250 metres, and is a uniform mouse-grey to grey-brown with no markings. The Latin name murinus simply means mouse-coloured.
How big do mouse catsharks get?
The largest properly measured specimen was 63 cm, about 25 inches, in total length. Older claims of specimens up to 84 cm from Icelandic waters have never been confirmed as this species and are best set aside. Weight has not been published, but these are light, soft-bodied sharks of well under two kilograms.
Where do mouse catsharks live?
In the north-east Atlantic only: around Iceland and the Faroe Islands, south along the banks and troughs west of Scotland and Ireland, and north-east into deep water off Norway. Reports from France and Western Sahara almost certainly refer to the blackmouth or Atlantic sawtail catshark, two relatives common further south.
What do mouse catsharks eat?
Mainly deep-sea shrimp and similar crustaceans, with small bony fish and cephalopods making up the rest, all taken on or just above the sea floor. In total darkness the shark locates prey using the electrical sense of the ampullae of Lorenzini on its snout, backed by the lateral line and a good sense of smell.
Why is it called the mouse catshark?
Because of its colour. The Norwegian zoologist Robert Collett, who described the species in 1904, gave it the name murinus, Latin for mouse-coloured, after its plain grey-brown body. Catshark refers to the narrow, oval, cat-like eyes shared by the whole group, and sawtail to the crest of denticles along the tail.
How do mouse catsharks reproduce?
They lay eggs. Each embryo develops inside a golden, vase-shaped capsule about 5.3 to 5.6 centimetres long, covered in fine fibres that give it a hairy appearance and help anchor it to the bottom. The young live on their yolk alone and hatch at about 8 to 9 centimetres, fully formed and independent.
Are mouse catsharks dangerous to people?
No. The shallowest records lie around 380 metres, roughly ten times deeper than recreational scuba diving reaches, and the shark grows to only 63 cm with teeth a couple of millimetres long. No incident has ever been attributed to the species and the SharkSider database holds none. Only trawler crews and researchers see one.
Are mouse catsharks endangered?
No. The IUCN assessed the species as Least Concern in 2023. No fishery targets it, much of its depth range lies below the gear that works the north-east Atlantic slope, and European limits on fishing below 800 metres cover part of its habitat. It appears occasionally as discarded bycatch in deep trawls and longlines.
How long do mouse catsharks live?
It has never been measured. No ageing study has been carried out, and the weakly calcified vertebrae of deep-water catsharks make growth bands very hard to count. Shallow-water catsharks generally live ten to twenty-five years, and cold, slow-growing deep-sea relatives are expected to live longer, but no figure can be given with confidence.
How do you tell a mouse catshark from a blackmouth catshark?
By the markings and the mouth. The mouse catshark is a plain, even grey-brown with no pattern at all. The blackmouth catshark carries a conspicuous row of dark saddles along its back and tail and has a mouth lined with black skin, and it grows larger, to about 90 cm. Their depth ranges overlap widely.
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 October 29, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.
