Department of Fisheries have put this on their website very recently: http://www.fish.wa.gov.au/About-Us/News/Pages/Look-Out-For-Pest-Crabs.aspx
Fact Sheet is here: www.fish.wa.gov.au/Documents/biosecurity/asian_paddle_crab.pdf
This includes info on what to do if you think you have seen one of these crabs.
