Caught crab is an Asian pest
A KEEN-EYED crab fisherman identified the Swan River’s fourth confirmed pest Asian paddle crab near Matilda Bay, Crawley on December 22.
However, Department of Fisheries Department of Fisheries marine biosecurity officer Marion Massam said there was no indication the pest was spreading in the estuary, after three of the poisonous invaders were netted about 7km downstream at Mosman Bay in 2012.
“These are just the odd individuals who have tried to colonise an area, and the fact that the department has developed a good information network, receives fishers’ intelligence, means it can respond to a catch and get the animal identified straight away, and mount a response,” Ms Massam said.
Australia has no Asian paddle crab breeding populations but numbers in Auckland Harbour are enough for the species to be reported in commercial catches, after an initial discovery in the late 1990s.
The Mosman Park catches prompted Fisheries’ netting and public education, and follow-up trapping three, six and 12 months later, which caught no Asian paddle crabs, 1139 native blue swimmers, 273 four-lobed swimmers and one example each of a threespot and coral crab.
Ms Massam said larvae in a ship’s ballast, individual crabs inside hulls or larvae drifting from the north on the Leeuwin Current were the most likely sources of Asian paddle crabs but it was almost impossible to identifying a culprit among hundreds of vessels visiting or moving around WA each year.
Finding a female would change Fisheries’ response to the threat, which she said was presently suspected to be “isolated males dropping off a boat”.
Since 2013, Fisheries has received about 400 calls from crabbers with suspect crabs but many were the native four-lobed swimming crab that has no spines between its eyes, while the Asian paddle crab has sharp spines between the eyes and six spines down each side
Officer Marion Massam with the caught Asian paddle crab and (below, left) an Asian paddle crab and (right) a native fourlobed swimming crab.