Feebullet, My uncle emigrated to Oz in 85, doing very well he is too!
Back to the point, even though I'm a Carp angler in the UK I can see the reason why you hunt to kill. Carp and the ecology of Oz just don't mix, they spawn too successfully, invade and/or destroy the habitat of your native species and generally make bloody nuisances of themselves. Germany also have a catch and kill policy on Carp (might even be all coarse fish) which is generally ignored by anglers over there.
Carp aren't as big a problem in the UK yet, they've been in our waterways since about 1400, could be earlier. Originally stocked into land locked "stew ponds" for eating purposes. They've become fashionable as a recreational species in the last twenty or so years because they're easy to catch, readily available, to the point that land owners actually dig a hole in a spare field, fill it with Carp and charge "anglers" (I use the term loosely) about a quid an hour to fish for them.
I don't fish such places myself, preferring older, mature lakes and rivers for other species. I do however have the odd Carp session as much for the camping and relaxation as the actual fishing. They do pull well when hooked which is another bonus.
I take my hat off to the way that your nation is trying to preserve it's heritage and wish the Uk would take a stamp out of your book.
We have, off the top of my head, American signal crayfish which are destroying the native white crayfish, with, I believe, a parasite they host (I've just been reading another thread, it seems it's a disease or plague). They're also damaging coarse and game fish stocks by making a meal of their eggs.
Motherless minnows, Chinese mitten crabs, some alien form of shrimp, grey squirrels, coastal cormorants moving inland (that's another story altogether). There's plenty more that don't spring to mind and there seems to be very little being done about any of them. All of which are slowly but surely killing off our native species.
Sorry, I seem to be rambling