I don't surf so you're kinda asking the wrong guy - the risks from wildlife are overstated - you're far more likely to die at the hands of a 20-something male.
Bikes and parts are expensive in Oz though so if you already have a bike somewhere, I'd ship it there.
Is it even worth buying a bike when I get to Aus or should I get a surfboard and chance it with the sharks, jellyfish and rays?