I have seen Great Blue Heron's, (I have a resident one that hopefully soon I will make non-resident), eat fairly large numbers of fish and up to the 8" range... I am sure they can eat even larger.
My stocked fish were in the 4-8" range when he started to visit... unfortunately.
Beyond eating stocked fish they are also a major link in the fish infection/grub chain.
What I have heard about decoys is that they have to be moved often to be effective and that eventually the heron will get used to it and land anyways.


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