My guess is that 3-4 turtles per acre are probably just as beneficial as they are harmful. Problem is, (here in the South for sure!)they don't stop coming.

I have dozens, and although I absolutely hate to do it, I have been shooting a few. I tried chumming them with fish pellets, to see if I could get them within netting range. Well, I netted 4 one day, and drove them to a small bayou. The next day, the other turtles wouldn't come within 100 feet of us! I guess word travels fast in a small pond. \:D