Sicklefin Weasel Shark

• Maximum lengthAbout 1.1 m (3.6 ft); most adults 0.8–1 m
• WeightUp to roughly 8–9 kg (18–20 lb)
• LifespanNot established; probably under 15 years
• Depth rangeMostly 10–100 m, down to about 170 m (560 ft)
• DietOctopus and squid, occasionally crabs and brittle stars
• IUCN statusVulnerable (assessed 2020)

How to recognise a sicklefin weasel shark

Start with the outline, because it is the giveaway. Every fin on this shark curves sharply backwards: the pectorals taper to points and sweep back, the first dorsal is clearly larger than the second, the anal fin is smaller than the second dorsal, and the tail is deeply notched. That uniformly falcate, scythe-like profile is what the English name is describing, and among the small grey sharks of Asian shelf waters it is the first thing to look for.

Then check the head. The snout is long and broadly rounded, the eyes are large, oval and horizontal, protected by the nictitating third eyelid that all ground sharks carry, and the nostrils have low skin flaps. The mouth is short and broadly arched, and it is genuinely small: microstoma means "small mouth", and the species is named for it. Inside, the upper jaw holds roughly 25 to 34 rows of broad, serrated teeth on each side and the lower jaw 37 to 43 rows of narrow, erect, smooth ones, a mismatch that suits a shark gripping soft prey rather than cutting through it.

Colour is a plain grey to bronze above and paler beneath, sometimes with scattered small white spots on the flanks. The most useful colour mark is the white edging on the trailing margins of both dorsal fins, sometimes extended to the upper lobe of the tail. Together with the small mouth, that white trim separates the species from the small requiem sharks it shares a market slab with, including the milk shark and the blackspot shark.

How big does the sicklefin weasel shark get?

The maximum is about 1.1 m (3.6 ft) in total length, and most adults you would see landed are between 80 cm and a metre. The earlier version of this page called 3.6 ft the shark's average length; it is the ceiling, not the average, and the difference matters when you are trying to picture the animal. A shark at the top of that range weighs somewhere around 8 or 9 kg, which is roughly the weight of a large domestic cat.

Maturity comes at three-quarters of maximum size. Males are mature by about 74 to 75 cm, females at around 75 to 78 cm, so the reproductive population is made up of sharks of two and a half feet upward. Pups are born at roughly 45 cm (18 in), which is unusually large relative to the mother: a newborn is already more than 40 per cent of adult length, a sensible strategy for a species that produces only a few young at a time.

There is no appreciable size difference between the sexes beyond females maturing slightly larger, which is normal in sharks that carry their young internally. Compared with the rest of its family this is a small animal: the snaggletooth shark, the giant of the weasel sharks, reaches well over twice the length. The bar below sets 1.1 m against a 1.8 m diver.

Where sicklefin weasel sharks live

The range runs across the warm shelves of southern and South-East Asia. Confirmed records come from India and Sri Lanka in the west, through the Bay of Bengal and the Andaman Sea to Thailand, Malaysia, Singapore, Vietnam and Cambodia, and on to Java, Borneo, Indonesia more widely, southern China and Taiwan.

One correction is worth making to almost every older account, including the previous version of this page. Australian animals were long called Hemigaleus microstoma too, but they were separated in 2005 as a distinct species, the Australian weasel shark. The true sicklefin weasel shark does not occur in Australian waters, so any Australian record you read predating that split belongs to its cousin.

The habitat is consistent: continental and insular shelves, close to the bottom, in water of roughly 10 to 100 m, occasionally down to about 170 m. It favours soft and mixed bottoms near reefs, which is where its cephalopod prey lives, and it does not enter estuaries or fresh water. This is a shark of the trawl grounds rather than the surf zone, which is why divers on Asian reefs almost never see one, while fish markets in the same towns can have dozens on the ice.

What sicklefin weasel sharks eat

Few sharks are as narrowly specialised. Stomach studies of this species turn up octopus again and again, with squid and cuttlefish second and almost nothing else of importance; crabs and brittle stars appear occasionally, and bony fish barely at all. For a requiem-shark relative that is a remarkable degree of focus, and the whole head is built around it.

The small mouth and comparatively weak jaws that gave the species its scientific name are not a handicap here. Octopus have no bones and no spines. What they have is eight arms and a tendency to jam themselves into crevices, so the useful tools are a strong grip and suction, not cutting power. The narrow, erect lower teeth hold the prey while the broad serrated upper teeth work through it, and a strongly muscled throat generates the suction to pull a reluctant octopus out of a hole. The old page's description of "weak jaws and small teeth built for holding and tearing into soft-bodied prey" gets this essentially right.

Hunting probably happens mostly at night and near the bottom, when octopus leave their dens. A shark searching for a cryptic, motionless, soft-bodied animal cannot rely on sight; the long rounded snout is packed with the electroreceptive pores of the ampullae of Lorenzini, which read the electrical signature of a hidden octopus through sand as easily as through water. Specialising on one prey type makes an efficient hunter and a fragile one: any collapse in cephalopod stocks hits this shark directly.

Behaviour and senses

The sicklefin weasel shark is a bottom-associated, mostly nocturnal animal, and that is about as far as direct observation goes. There has been no tagging programme and very little underwater footage, largely because the species lives on trawl grounds rather than dive sites.

Its build tells you it is a steady, manoeuvrable swimmer rather than a fast one. Falcate fins of this sort generate lift efficiently at cruising speed, and the moderately sized first dorsal and deeply forked tail suit an animal that patrols along the bottom for hours. There is no evidence of large schools; landings suggest loose aggregations of similar-sized animals, and pregnant females appear to concentrate seasonally, which points to pupping grounds that have never been mapped.

The senses are those of a bottom hunter working in dim, often turbid water. The eyes are large for the head, with a reflective layer behind the retina that multiplies what little light reaches 50 m down. Smell leads the animal to the general area, the lateral line registers movement close by, and electroreception does the final work; our page on shark anatomy sets out how those systems overlap. Nothing in its record suggests it treats a diver as anything other than an obstacle to swim around.

Reproduction and lifespan

This is where the species becomes genuinely unusual. Like all weasel and requiem sharks it is viviparous with a placental connection: the embryos consume their yolk, the emptied yolk sac fuses with the uterine wall, and the mother nourishes the pups directly for the rest of the pregnancy. What sets Hemigaleus apart is the pace. Gestation lasts roughly six months, and females produce two litters a year rather than one every second year as most sharks do.

Litters are small, usually two to four pups and occasionally a little more, born at about 45 cm. Two litters of three a year still means an output of around six young annually from every mature female, which is high by shark standards and well above what a great white or a basking shark manages. Combined with maturity at around 75 cm, probably reached in three or four years, this gives the species a genuine capacity to rebuild.

Age and growth have not been properly studied, so no lifespan figure can be quoted with confidence; a shark of this size, maturing this early, would be expected to live somewhere under fifteen years, in the same band as other small coastal sharks discussed on our page about how long sharks live. The productivity matters for conservation. The previous version of this page said the shark was listed as Vulnerable "due to its rarity" despite a high reproductive rate; in fact its listing has nothing to do with rarity and everything to do with the intensity of the fishing it faces.

Is the sicklefin weasel shark dangerous to people?

No, and it is worth being specific about why. Not one record in the SharkSider database names this shark, and no international attack file carries one either. The animal is about a metre long, it has a mouth small enough to have been named for it, and its teeth are sized for octopus flesh. It could not inflict a serious wound on a person if it tried.

Nor does it live where people swim. Sicklefin weasel sharks stay close to the bottom in 10 to 100 m of water, which puts them below the depth of almost all bathing, snorkelling and recreational reef diving in the region. The people who meet them are fishermen and market workers, and the hazard there is the abrasive skin and the ordinary risk of handling any shark on a deck. It sits with the genuinely harmless species on our list of the least dangerous sharks. If you want to know which sharks in these seas do deserve caution, the guides to Indonesia and India set them out.

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 lists the sicklefin weasel shark as Vulnerable. The species is not rare and it breeds faster than most sharks; what it faces is fishing pressure of extraordinary intensity across essentially its entire range. The shelf waters from India to Indonesia carry some of the densest concentrations of trawlers and gillnetters on Earth, and this shark lives on the bottom in exactly the depth band those fleets work hardest.

It is caught mainly as bycatch in demersal trawls and gillnets and is always retained: the meat sold fresh, dried or salted, the fins entering the fin trade, the rest going to fishmeal. A full account of that trade is on our page on shark fin soup and conservation. Landings of the species have fallen sharply in several Indonesian and Indian fishing ports over recent decades, which is the sort of evidence the assessment rests on. There is no targeted management for it anywhere in its range, and small sharks are rarely separated to species in catch statistics.

The encouraging part is biological. A shark producing two litters a year can respond to a reduction in fishing effort within a few generations, unlike the slow-breeding species covered on our page on why sharks are endangered. What it would take is basic trawl management on the shelves it occupies, gear that lets small sharks escape, and catch records that name species rather than lumping everything into one "shark" line.

Similar species and close relatives

The closest relative is the Australian weasel shark, which was treated as the same species until 2005 and is nearly identical in appearance; geography is the practical way to tell them apart, since their ranges do not overlap. Beyond the genus, the family Hemigaleidae holds the hooktooth shark, which shares the same Asian shelf waters but has a long mouth and protruding, hook-like lower teeth, and the snaggletooth shark, a much larger relative with a high, upright first dorsal fin. The weasel sharks of the genus Paragaleus are the family's other branch: the Atlantic weasel shark off West Africa and the whitetip weasel shark of the western Indian Ocean.

The confusion that actually happens is with small requiem sharks landed in the same nets. The milk shark is a similar size and colour but has a much longer snout, a bigger mouth and no white fin edging; the blackspot shark is marked with a dark blotch on the second dorsal fin. In both cases the check is the mouth: too small for the head, with every fin swept back like a blade, and you have a sicklefin weasel shark.

• Australian Weasel Sharkspecies profile
• Hooktooth Sharkspecies profile
• Snaggletooth Sharkspecies profile
• Atlantic Weasel Sharkspecies profile
• Whitetip Weasel Sharkspecies profile
• Milk Sharkspecies profile

Written and reviewed by

SharkSider Editorial Team

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 25, 2022 · Last updated September 22, 2026 · No incident attributed to this species in the SharkSider attack database, which is updated weekly.