This is very unfortunate and I'm sorry for your loss. As others have said this is all too common. I'm right by an inland pacific bay here in Costa Mesa and we have GIANT birds here frequently. I think nets and covers are ugly and take away a lot of the appeal of having a pond but there would be no other way to have one here.
There was a lady back in the 90's that I read about. She had a lot of property with a nice pond and stocked it with some high $$ koi. Then a bald eagle decided to eat her fish and not only would fish and game not do anything about the bird (she wanted it killed or removed.. funny I know.. national bird.) they also told her since it was a natural pond on the property she couldn't cover it because it was a natural food source for the eagle. She had to deal with losing thousands of dollars worth of fish!
That's horrible I feel her pain my fish wernt cheap either): koi that big are very valuable the ones I lost were the small ones too and they were thicker than my arms
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