‘While we didn’t catch any more after the initial discoveries, we can only assume it’s a very small population or they are trap-shy,’ biosecurity section leader Victoria Aitken said.
WA’s first confirmed asian paddle crab capture was in Mosman Bay last October. Two more specimens were netted in November and during the Christmas holidays.
But several trapping programs by Fisheries failed to find more of the invaders, which could have arrived in the river as larvae in weed on the bottom of uncleaned boats or in ships’ ballast water.
The asian paddle crab can carry a virus and will compete with native crabs.
Ms Aitken said a public awareness campaign about the invader resulted in more than 200 reports that were investigated and two confirmed captures of the rare non-pest species called the banded-leg swimming crab in Kalbarri at Christmas.
Fisheries will complete follow-on trapping for the asian paddle crab in May and October in Mosman Bay and adjacent parts of the Swan River.
‘The two main native crabs that we catch, blue swimmers and four-lobed swimming crabs, will both be moving down river and out of the river mouth at this time of year so catches will decline,’ she said.
‘With the asian paddle crabs, unfortunately we can’t know what they are doing as they are new in this environment, so there are no predictions on their current behaviour.’
Asian paddle crabs have six spines from their eyes to the outer edges of their carapaces.
Fact sheets are at www. fish.wa.gov.au and sightings must be reported to Fishwatch on 1800 815 507.