Have you seen this crab?

Andrew Hosie's blog | Created 5 years ago

The Western Australian Department of Fisheries has issued an alert after the Asian Paddle Crab, Charybdis japonica, was caught by a recreational crabber near Mosman Park on 19 October. Fishers and divers in the Swan and Canning Rivers as well as the greater Cockburn Sound area are urged to report any unusual crabs to FishWatch reporting line on 1800 815 507 or email biosecurity@fish.wa.gov.au.

Male specimen of the Asian Paddle Crab, Charybdis japonica

Male specimen of the Asian Paddle Crab, Charybdis japonica, collected from near Mandurah in early 2010
Photo by Andrew Hosie
Image copyright WA Museum

Fisheries are undertaking a comprehensive trapping survey to determine if there is an established population in the region. So far only many hundreds of native crab species have been caught. In 2010 Fisheries undertook a similar survey of the Peel-Harvey Estuaries after a single male was caught near Mandurah and identified by the Western Australian Museum. As no further specimens were found it was concluded that the species had not established in the estuary. Prior to this the only other record for this species in Australia is of a single male from Port River, Adelaide in 2000.

The Asian paddle crab is an aggressive predator that has become established in northern New Zealand where it is spreading and potentially driving out the local swimming crab species. This species is also known to carry the white spot virus that could potentially harm native prawns, crabs and lobsters. This nationally notifiable disease is yet to be found in wild crustacean populations in Australia.

Like the Blue Swimmer, Portunus armatus (was P. pelagicus), and related species like the Mud Crab, Scylla serrata, the Asian paddle crab has a pair of flattened, paddle-like hind legs. The Asian Paddle Crab is smaller than both the Blue Swimmer and Mud Crab, reaching a carapace width of 120 mm. Asian Paddle Crabs are six spines or teeth on each side and eight spines between the eyes. Blue swimmers and mud crabs have nine spines on each side (the last being extremely long in Blue Swimmers) and only six spines between the eyes. Fisheries have prepared a factsheet to aid in identification.

Should you come across an unusual crab that you suspect may be the invasive Asian paddle crab then note where it was caught and take photos and contact FishWatch 1800 815 507 or email biosecurity@fish.wa.gov.au.

Further information can be found here:
http://www.fish.wa.gov.au/About-Us/Media-releases/Pages/Pest-crab-warning-after-Swan-River-discovery.aspx