Russ ... I had a similar experience a few years ago, but on a much smaller scale ... Had 6 koi in a small pond... went on vacation and my b-i-l was going to feed the fish ... first day out he calls and says there are only two koi in the pond and there was no sign of any of them ... a few days later there was only one ... I get home and about a day or two later I go to feed the one and it is GONE! ... I look around and find half a fish on my lawn ... talking to some neighbors I find out that there was a heron spotted in different locations in the neighborhood...

Some pond owners have taken to stringing fishing line about six inches to 10 up across their ponds ... if the heron hits it they just fly off ...
Ironically, in this case the fishing line is SAVING the fish ...