Oh Mal so sorry to hear this, I know your feeling.
I've had the heron eat some of mine before.
A new predator has arisen, one that I liked but now move as soon as I see them move in. I'm not so upset when Gert the Snake decides to make a meal out of this predator. The Bull Frog. Wondered Why after the long winter these frogs were very fat, I now know. I float a heater on my pond in the winter. All winter these frogs made me laugh. On a bright sunny day they would be out sitting on the rocks. Probably digesting fish. Never knew these frogs that were named, Vaughn, (he crooned a lot) Smiles and Happy. Were 'Fish Eaters' well they are and I caught one with a fish in it's mouth. They arose from their winter slumber with 'Big Fat Bellies' and my baby fish population was down.
One of the girls I work with was so excited last year when her DH spent the week-end making a pond for her. She add fish and some plants, soon the frogs moved it. How exciting! I think not! She covered her pond for the winter with the frogs, when spring rolled aroung she uncovered her pond all that was left was 'ONE BIG FAT FROG' he spent the winter eating her fish and the other frog.