If the cats are a big a problem as they say, a few hundred Ruger 10/22 rifles, and a boatload of ammunition will produce a huge number of dead cats. If that doesn't work fast enough, add in a bounty and there will be too many dead cats to properly dispose.
I spent all of 1978 in Australia. Weekends were at a family farm. Shot 75 - 100 Rabbits every time we were there with 22lr. We didn’t even bother to pick them up. Thing is it didn’t even seem to ever put a dent in the population and the people there the other 5 days a week also were killing them. Cats like Rabbits are a non-native species in a ecosphere without enough large predators to balance things out. I can definitely can see a need to control the population. Problem is, unlike the 70’s I doubt there are as many people out shooting in the bush these days.
Shooting them would be a lot cheaper, also.
I like cats, but people who enable the proliferation of feral cats are not thinking. And they usually seem to be the type of people who don’t give a jump about the lives of humans.
About 1973, after DROS, I was back at Ft. Eustis, VA. The post’s wildlife control officer organized feral cat hunts and supplied the .22LR ammunition.
Bet they don’t do that anymore.