Asian paddle crab

Charybdis japonica

Asian paddle crab

Asian paddle crab

Legal Status: No Status
Status in New Zealand: Established
Organism: Water snails, crabs, shellfish, starfish, and other aquatic

This pest is in New Zealand. It is widespread in the Hauraki Gulf and has been detected in Whangarei Harbour and Opua/Waitangi in Northland.

If you suspect you have found this crab in any other location in New Zealand, report it to: 0800 80 99 66.

If you are the owner/operator of a moored vessel, you can help prevent the spread of this marine pest by ensuring your boat’s hull is clean and well antifouled.

Description

The Asian paddle crab (Charybdis japonica) is a swimming crab native to South East Asia. It is normally found in the waters of Japan, Korea and Malaysia. It is typically found in estuaries where there is firm sand or muddy fine sand.

Charybdis japonica is a relatively large crab with paddle-like hind legs. Adults have a shell width of around 12cm. The adults also have six distinct spines or spikes on each side of the eyes.

The crabs range in colour from pale green through olive green, to a deep chestnut brown with purplish markings on the carapace (shell). Most of the crabs found in the Waitemata tend to have yellow-orange and brown-orange markings on the shell and legs. They have white tips on the claws.

Impact

This aggressive crab has the potential to compete with native crabs for space and food. It is a potential threat to marine farming as it preys on shellfish and other aquaculture species. It is also known for its aggressive temperament and can inflict a vicious bite if disturbed.

It is not, however, reported to be a pest in its native habitat or in other countries.

It was first reported in New Zealand in Auckland in late 2000. It is now widespread in the Waitemata Harbour and wider Hauraki Gulf. A single specimen was found in Whangarei Harbour in 2003 and in 2009, two further specimens have been found in this harbour.

How the paddle crab spreads

Adult paddle crabs can produce hundreds of thousands of offspring. The larvae can float in the water for three to four weeks, during which time they can be moved large distances by tides and currents. Adults are also capable of swimming large distances.

Human activities associated with boating, shipping, fishing and marine farming could increase its rate and distance of spread – either as a hitchhiking pest on a dirty boat bottom or marine equipment, or as larvae in ballast water or bait tanks.

How you can prevent its spread

Operators of ships, barges, yachts and other moored vessels should:

  • Keep the hull clean and antifouling paint in good condition.
  • Carry out cleaning in a facility that captures all removed material and disposes of it away from the sea.
  • Avoid uptake of ballast water from the north eastern North Island coastal region – especially in spring/summer when crab larvae are likely to be present. If uptake is necessary, avoid discharging into other coastal areas.

Commercial fishers

  • Keep nets and traps clean and flush live bait tanks, bait buckets and containers with freshwater before moving between sites.
  • Avoid moving seawater in bait tanks from the north eastern North Island coastal region.

Marine farmers

  • Ensure stock and equipment being transferred to other sites is free from unwanted hitchhikers.
  • Freshwater wash or thoroughly air dry equipment before moving it to new areas.

Recreational fishers and divers

  • Check your boat and gear for unwanted hitchhikers.
  • Do not move water from the north eastern North Island coast to other areas.
  • Keep nets clean and flush bait buckets and containers with freshwater before moving sites.
  • Rinse your dive gear with freshwater after use.

Page last updated: 21 October 2013