The puma stories around sydney always turn into "big cat" stories.. THere was one in the local paper which showed a fuzzy photo of a beefed up cat... I'm guessing a feral. Occassionally people bring in scats and so forth, which they think is puma shit - turns out to be dingo or cat or dog. And therte's no evidence from hair or anything else either. I once talked to a person who was going on about how they saw a goat carcass that had been dragged up a tree by a puma... To which I replied, okay, where are the photos? Surely they could have walked back into the bush to get photos, i mean a goat up a tree is a big effort.
50 could establish a breeding population, but depends on over what geographical area and length of time... That's a damn small population.
As for the cats, their psycho things. Need a lot to wipe them out. Shooting, cutting off things, the list goes on.