The GBH by me has switched over to nighttime sampling of my pond fish only. I caught him last night in the pitch dark. I bolted out of the vehicle and ran at him/her arms waving hollering. He was so startled or couldn't see me well that I got quite close before he took off. I don't think you can win without a fence!
I too would wonder how many fish they eat. In the shallows they have to be getting the tiny fish I would think?
