Blue herons are extremely territorial. If you shoot one another will come and take it's place. You would probably have to shoot 50 or 100 to solve your problem, but only temporarily. There are many things you can do to drive them away short term. They will return. The problem is they are smart and eventually find ways to avoid your latest trick or learn that there is no real danger to them. They love automatic feeders. If you feed your fish in deep water it will help. If you stay until the feed has been eaten it will help. There are no effective permanent solutions. Take it from someone who has raised fish commercially and I currently have 9 fishing ponds. I have tried all the tricks and then some to no avail.
