duck population

I'm also curious about the ducks at the arboretum. I'd like to focus on the population fluctuations of the ducks there. How is their population maintained? What has been done in the past or present to maintain the population? I read in an article that the ducks were overpopulating due to peopl releasing pet ducks there, etc. and so to solve the problem people were starting to kill them. Animal activist people step in and started relocating the ducks in order to stop the murder of the arboretum ducks. I want to know what else these ducks have gone through.