Yes hybrid bluegill could be dying out at 6 to 7 years old and/or rapid temperature changes or super cooling with the powerhouse could be stressing them, which I'm sure you've had this winter.

Are you sure the tails were eaten off or they succumbed to fungus. Seems a coon or other animal would do more than eat the tail.

How big is the pond?

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.