ADF&G tried capture, neuter & release on Wolves to save Caribou way back when. Of course it didn't work.
   Whether its wolves or feral cats, the bottom line is - living ones have to eat - & what they eat should concern us all. If feral cats are not fed by humans, & even if they are given food regularly, they will follow their instincts & predate on small mammals, birds, etc. 
   So, do you prefer screeching cats over melodious songbirds?