We just put in a 3/4 acre pond, and blue herons have been coming regularly to eat the growing frog population. I once owned small Koi pond and know too well what these things will do to a small garden pond, but do I need to be concerned they will consume my fish in a pond this large and deep? Thanks!
I was very concerned about Blue Heron until I faced a much more deadly enemy the "water turkey" / Anhinga.
I have concluded for me the Herons are a minor nuisance eating frogs, snakes, minnows, and a few small fish vs the Water Turkeys in relatively large groups diving under the water and eating lots of small to medium size fish.
As far as the herons I have had moderate luck with the alligator decoys.... I still use the gator decoys and think my problem with herons would be worse without them. In my experience the herons are much more afraid of humans than the water turkey. Although water turkey tend to be seasonal and herons are around pretty much year around.
However, they probably have no real positive effect on your pond. They can introduce parasites. They can also eat some of your fish, and/or damage them by 'spiking' them. You may see some LMB with puncture-type wounds, and that would be due to a Heron.
It really comes down to the level of 'damage' that you observe due to Herons that form your view on letting them coexist peacefully, or making life more difficult for them.
Finally, I view the Great Blue Heron as a creature with prehistoric roots almost like a Pterodactyl. So, in my mind, I feel they have deep instincts. We've heard stories of Herons taking a fish from one body of water and dropping it in another body of water; if true, I view that as the bird creating a new food source by stocking a pond. When you see a large LMB with puncture wounds, that fish is usually too large for the Heron to eat; in that case, I think the Heron is trying to eliminate a competitor for the same food base.
Excerpt from Robert Crais' "The Monkey's Raincoat:" "She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."
My friend pulled a 6.4 lb LMB out of our 1 acre pond last fall, and a neighbor removes 50-60 eating size BG out per year, all with regular visits from a nearby blue heron rookery. I used to worry about all the coyotes eating newborn deer too. It seems that there are enough of both fish and deer to go around in my neck of the woods.
I have herons standing in front of my feeder and whenever the feeder goes off the water is alive with fish, GS and BG among others, only baitfish in the pond so far, but they sure get rid of a bunch of fish in a hurry. I had one that got caught in a coon trap set just under water in front of the feeder, I relocated it a little ways off.
All the really good ideas I've ever had came to me while I was milking a cow.
Electro survey at my place surprised me at how many fish had been injured by herons. Maybe ten to fifteen percent had beak marks, some quite recent. Cormorants left a while back, so I know recent attacks were herons.