GW, you're right that snakes are very efficient, but turtles can eat quite a bit. 2 or 3 of each per acre shouldn't make much impact. Be careful what you wish for, because Turtles and snakes are sneaky.
I can walk around my pond and see maybe 1 snake and 8-10 turtles. Then I can drive around the pond mowing on my tractor, and see maybe 6 snakes and 25 turtles. Last time I mowed, I saw 3 huge diamondback watersnakes take off from the bank. I never knew they were there. While they're interesting and harmless, snakes that big can really eat a lot of medium size BG.
I have to figure out a strategy to thin them both out. I can chum the turtles and net 3 or 4 per week (I release them a mile away in a bayou), but that doesn't make much of a dent. I'm seriously wishing I had an alligator, which would keep them thinned and not eat many fish.