Blue swimmer crab
Fish · Last reviewed 2026-08-23
The swimming crab of Australian and Indo-Pacific sand and seagrass — raked, netted, scooped and caught by hand, and one of the most-taken recreational crustaceans anywhere.
Safety: injury while handling fish — can cause injury needing treatment. One more point applies here.
Catching Blue swimmer crab
Everything here on fishing for it. Each entry opens the page behind it.
- Ground
The blue swimmer is a portunid: the back pair of legs are flattened into paddles and it swims sideways, fast, which is the single fact that governs how it is caught. It cannot be lifted slowly off a bait the way a shore crab can, because it will simply leave.
So the fisheries built around it are all about closing off the escape. A drop or hoop net is lifted quickly from beneath. A scoop net is used on a crab seen in shallow water. A crab rake is dragged through sand to turn up buried animals. In South Australia people wade the shallow gulf sand and take them by hand and by rake in numbers, and in Western Australia they are netted from small boats over seagrass.
Males are the blue ones — bright blue legs and claws over a mottled shell — and grow larger than females, to around 22 cm across the carapace and a kilogram. It lives on sand, seagrass and estuarine bottoms from the shallows to moderate depth, across northern and southern Australia and through the Indo-West Pacific.
One rule is common to every jurisdiction whose rules were read for this page, and is worth stating on its own: a female carrying eggs goes back.
How it is caught
Identification
No photograph of Blue swimmer crab has passed identity review yet, so none is shown. A photograph is published only once somebody has checked the animal in it against the diagnostic features described on this page.
- Scientific name
- Portunus armatus
- Family
- Portunidae
- Water
- Saltwater, Brackish
- Conservation status
- Not assessed
- Regions
- Australia, Indo-Pacific, South-East Asia, South Asia
- The rear pair of legs flattened into swimming paddles — the feature that separates every portunid from the crabs that only walk.
- Long, spined claws and a carapace drawn out into a sharp spine at each side.
- Males bright blue on the legs and claws with a mottled shell; females duller, greenish-brown, and smaller.
- A broad rounded abdominal flap on the female, narrow and pointed on the male.
Size
- Typical
- 300–600 g (11 oz–1.3 lb)
- Large
- 700 g–1 kg (1.5–2.2 lb)
Exceptional: Reported to around 22 cm carapace width and about 1 kg in males, with females reaching a slightly smaller maximum
Lifecycle and reproduction
Lives on sand, seagrass and estuarine bottoms from the shallows into moderate depth. Commonly three to four years old, growing by moulting, with larger crabs moulting less often.
Spawns through the year in the warmer part of the range with a spring peak. A large female can carry several hundred thousand eggs and may spawn more than once in a season, which is the reason every jurisdiction whose rules were read requires an egg-bearing female to be returned.
Feeding and senses
An active predator and scavenger of small fish, molluscs and crustaceans over open sand and weed, and quick enough to catch prey rather than only find it.
Locates food by scent carried on moving water and by sight in the clear shallow water it is most often taken from — which is why a scoop net used on a crab that has been SEEN works at all, and why a bait in dead slack water does not.
Through the year
Warmer months concentrate the recreational fishery, when crabs move into shallow water where they can be raked, scooped and seen. In cooler water they move deeper and the shore methods stop working.
Distribution
Australia and New Caledonia: the south coast of Western Australia north to the Northern Territory, across Queensland and south the east coast to the New South Wales–Victoria border, including the South Australian gulfs. Part of a wider Indo-West Pacific species complex formerly treated as Portunus pelagicus.
This is a biological range — where the species occurs, not a prediction that you will catch one. To browse the fishing geography FishingHQ holds, start at fishing places.
Why anglers care
One of the most-taken recreational crustaceans in the world, and taken by more different methods than almost any other shellfish an angler meets: drop and hoop nets, scoop nets, crab rakes dragged through sand, hand gathering in the shallows, and snorkelling. Its significance is that it is a genuinely good crab caught in shallow water without a boat, which is why it is the object of a very large amateur fishery in Australia.
Handling and returning
The claws are long, spined and fast, and the animal uses them. Hold across the rear of the carapace between the swimming paddles, never by a claw or from the front, and use a measure rather than a hand.
Safety
Injury while handling fish — Can cause injury needing treatment
Long spined claws on a fast animal, frequently handled in shallow water by people who are barefoot and looking down. The carapace spines cut as well.
What reduces it: Grip across the back of the shell between the paddles, wear something on your feet when raking or wading, and never reach into a bucket or a keeper net by feel.
Fish welfare — Can cause injury needing treatment
Crabs held crowded in warm water die quickly, and a berried female returned after an hour in a bucket is not the same as one returned immediately.
What reduces it: Check for eggs and return females as they are caught rather than sorting later. Keep what is kept cool, shaded and uncrowded.
Where to go next
Where it lives
- EstuaryEstuarine sand and the gulf shallows, which is where most of the amateur fishery happens.
- Seagrass bedsSand and seagrass in the shallows, which is why it is raked and scooped rather than potted.
More fish
Not related to this page — just the rest of the section. There is little else joined to this subject yet, and a short page should still lead somewhere.
Sources and evidence
- FAO Species Identification Guides for Fishery Purposes and the FAO Species Catalogues — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Identification, distribution, habitat and fishery description for the crustacean species named here.States this directlyCitation checked — the work exists and is described correctly
- Australian state recreational crabbing guidance: gear, limits and berried females — Australian state fisheries agencies and Australian crabbing guidance (Credible secondary source)Relied on for: The Australian recreational crab gear vocabulary — drop nets, hoop nets, scoop nets, crab rakes and hand gathering — and the release of egg-bearing females.States this directlyCitation checked — the work exists and is described correctly
Why the 3 connections on this page are here, and the sources
How it is caught
An open question — 1 connection
FishingHQ looked into this and could not settle it. The open question is recorded here rather than being papered over.
Crabbing with a line and a drop net
Widely described as taken with drop and hoop nets, but no source read for FishingHQ covers this crab's fishery; an Australian state fisheries source is needed before this can be stated as practice.
- General angling website restatements of established technique — Various (Credible secondary source)Relied on for: The widely restated practitioner account of how swimming crabs are taken.Background and mechanism onlyCitation checked — the work exists and is described correctly
Where it lives
Backed by research — 2 connections
Supported by peer-reviewed research or fisheries science. The sources are listed and can be checked.
Estuary
Recorded from estuarine bottoms across its Australian range, including the South Australian gulfs where the shallow sand fishery is worked on foot.
- FAO Species Identification Guides for Fishery Purposes and the FAO Species Catalogues — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Identification, distribution, habitat and fishery description for the crustacean and reef species named here.States this directlyCitation checked — the work exists and is described correctly
Seagrass beds
Portunus armatus lives over sand, seagrass and estuarine bottoms from the shallows into moderate depth. Shallow ground is what makes hand gathering, raking and scoop-netting possible at all.
- FAO Species Identification Guides for Fishery Purposes and the FAO Species Catalogues — Food and Agriculture Organization of the United Nations (Scientific institute)Relied on for: Identification, distribution, habitat and fishery description for the crustacean and reef species named here.States this directlyCitation checked — the work exists and is described correctly
How FishingHQ labels evidence is explained in the evidence policy.