At the range you would be bowhunting from (assuming a boat, dock, or close range from shore), a quality crossbow will do the trick. You would want the traditional bolt tip that is a plain sharp point with the retractable barbs so that the barbs do not hinder shell penetration.

That said, turtles are not bad for a pond given there are not too many. And, one has to ask why there would be so many? There may be enough dying older fish to support a larger population and the clean up crew would be desired. Turtles can do some substantial damage to vegetation, however. I can tell when a snapping turtle is in my pond due to the sudden destruction of the lilies that I am trying to get established.

The only turtle attacks on people I have heard of were accompanied by the words..."watch this"...lol