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Asian paddle crab (Charybdis japonica)

The Asian paddle crab is a non-native, aggressive swimming crab that has been detected sporadically in South Australia and Western Australia, but is not considered established in Australia. It is a potential biosecurity concern because it preys on a range of marine animals and established populations occur in northern New Zealand.

Key facts

Type: Pest animal, invertebrate.

Native to: Coastal western Pacific, from China to Thailand.

Established in: SA.

Identification

  • It is a swimming crab with a broad carapace that can reach up to 120 mm wide.
  • The rear pair of legs are flattened into paddles.
  • Colour varies from mottled cream and purple or pale green and off-white to olive-green with purplish markings.
  • Some specimens have yellow-orange markings.
  • It is known for aggressive behaviour.
  • Look-alike: Other swimming crabs may look similar; seek expert identification if you are unsure.

Where it lives

In Australia, individuals have been found near ports in large estuaries, including areas with soft sediments, rocky shores, artificial structures and seagrass meadows.

Why it matters

  • It is an aggressive marine predator that feeds on crustaceans, cephalopods, echinoderms, molluscs and some fish.
  • Established populations could affect marine communities through predation; the species is considered established in northern New Zealand.
  • It is not considered established in Australian waters, where detections have been sporadic.

How it spreads

  • Its planktonic larvae can be dispersed by ocean currents.
  • Females spawn multiple times, with hundreds of thousands of eggs per clutch, and larvae develop into juveniles after at least 17 days.

Control methods

  • Report suspected sightings to the relevant state or territory biosecurity agency; in South Australia, sightings can also be reported to PIRSA Fishwatch.
  • Do not release a captured crab or move it to another waterway, and avoid handling it directly because it can behave aggressively.
  • Targeted trapping and eDNA surveillance are used to monitor the species in Western Australia and South Australia; coordinate any trapping or removal with the relevant authorities.
  • Photograph the crab and record the location and date if it is safe to do so, and follow instructions from biosecurity officers about specimen handling.

Site hygiene and welfare

  • After working in marine waters, inspect and clean boats and fishing gear, and drain and dry equipment before moving to another waterway.
  • Do not transfer water or live marine animals between sites.
  • Use methods set out in the national model codes of practice and standard operating procedures for the species.
  • Coordinate control with neighbours and the local government biosecurity plan, as isolated effort is quickly undone by reinvasion.

Classification by state

  • Australia (national): National priority exotic pest. On the National Priority List of Exotic Environmental Pests, Weeds and Diseases, so any new detection should be reported straight away.
  • Queensland: Prohibited matter. Report it to Biosecurity Queensland on 13 25 23 within 24 hours and do not move or deal with it. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Prohibited matter. It is an offence to deal with it, and you must notify NSW DPIRD as soon as you become aware of it.
  • Victoria: Noxious aquatic species. Declared a noxious aquatic species under the Fisheries Act 1995, so it must not be brought into Victoria, kept, sold, moved or released into waters. Report any sighting to the Victorian Fisheries Authority on 13 FISH (13 3474).
  • South Australia: Noxious species. Declared a noxious species under the Fisheries Management Act 2007, so it must not be brought into South Australia, kept, sold or released, and it must not be returned to the water alive. Report any sighting to PIRSA FISHWATCH on 1800 065 522.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Not a declared pest. Not a declared pest or prohibited matter in Tasmania. Importing animals is still controlled by Biosecurity Tasmania.
  • Northern Territory: Not a declared pest. Not on an NT declared or prohibited list. Check with the NT Government before keeping, moving or releasing it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • South Australia: Landscape South Australia Act 2019 (SA), administered by the regional landscape board

Sources