Thanks for the ID Loritx. I've seen pictures of herons but none that look like this one.
Now that I know what it is, I'm at a loss for what to do. I guess I can try putting up more fishing line, but now I'm wondering what's the point. The bird was already on the other side of the fishing line that was there. That means he flew over it despite the fact that conventional wisdom says herons don't fly that close to the pond so that they don't scare the fish. What gives?
The fish have plenty of places to hide, but they only know to hide after one has been eaten. Only four left, of the seven (or nine - depending on when I started counting them). So it may be just a matter of time before they're all gone. I had 8 heron free years to enjoy my pond. Now the fun seems to be over...