First, turtles are cold blooded, which means they don't eat as much because they don't expend calories on staying warm. example, large snakes and alligators are known to eat about one large meal each month. 500 hundred fish in 210 days seems to me like a lot of eating for a turtle. Also they are not completly meat eating, I did a few quick searches and found thier diet donsists of everything, even algae. I bet that she did get a few of your fish, but she ate alot of other things, some of which you didn't want in your pond anyway.
Warning: The following is my sappy opinion.
I bet a turtle that big is at least 30 years old or more. They CAN get up to 150lbs. Do you know why you never see any that big? Because they all get killed by people, they don't have any other natrual predators. Now would you rather tell your kids and grandkids about the big snapping turtle you killed once or show them the oldest biggest snapping turtle in the state? Personaly I would rather save something like that to share with the next generation of pond masters.
