I have now put fishing wire all the way around but I have heard that herons return to the same pond until they are sure there is no free meals left. I don’t feel confident enough to restock straight away – it is only thin wire after all! So how long is it the right time?

so sorry to hear of the Heron attack. Nature can be cruel sometimes, but the Heron would have truly enjoyed his meal. Will you continue and put more fish in the pond?
Have you the chance to get an ornamental heron as I have heard quite often that Herons will not come down if they see another Heron. You do need to move it round sometimes or they will realise it is not real.
Another thing is to cover the pond with a net, but I find them unsightly. They will do the trick though.
I am lucky and although Herons are always at a nearby RSPB reserve they haven’t stopped at my pond, but a Magpie did once eat my diamondback sturgeon.

Herons can also bring suprises !
My visiting Heron regurgitated a Black Comet from someone elses pond and has been living well in my pond for two years now.
Probably a good exchange for a couple of frogs.

Considered to be the world’s best fisherman, herons have an unmistakable shape and are superbly equipped for their lifestyle. This magnificently marked bird has a keen eye for ponds, however small and are particularly attracted by colourful ornamental fish in crystal clear water.
These offer a much easier proposition to a hungry heron which would otherwise spend its time waiting very patiently on the bank of a murky lake or river fishing for camouflaged coarse fish.

The incidents of heron predation on koi and garden ponds appears to be on the increase as they try to keep up with the continued rise in popularity of ponds and water features.

Heron Problems
Beside the obvious fish losses, there are other problems related to heron activity around garden ponds.

Spread of disease.
There is a real risk of the spread of disease through heron activity, as they move freely between natural and artificial water bodies. Just as a honey bee moves between flowers, picking up and transferring pollen wherever it goes, the same can be said of herons and disease. If a heron has recently left a wild fish population with typical levels of disease, then it is possible for such diseases to be transferred to a garden pond.

Stress
Perhaps the first sign that a heron has visited a pond is the sudden reduction in the tame behaviour of fish, remaining in deep water to avoid being taken by a heron. Some pond fish have been known to become so shy and reluctant to surface that their owner has believed that all the fish have been taken, only for them to reappear a week or so later from their sanctuary. Repeated heron visits will add further to your fishes’ stress.

Damage
Herons have been known to pierce liners through misguided stabs at fish. I have also seen fish that have been by skewered by a heron, but being too large to be eaten just left on the pond side. Finding your prized fish under these circumstances can perhaps be harder to bear than not finding them at all. Herons can also leave their calling card by making the tell-tale V notch scar across the back of fish that have escaped from the jaws of this avian predator.

Counter Measures
A real issue with heron predation is that if successful on a visit, a heron will return to a pond to fish again. The heron is a protected bird so no matter how protective we feel about our ponds and their contents, there is a limit to the counter measures we can take. So if we suspect or wish to prevent a problem, what options are open to us to prevent the problem?

The barrier method.
The only guaranteed method of preventing losses through heron predation is by covering the pond with tight netting that is fixed well above the pond. However, anti-predator netting detracts from the pond and seems to defeat the object of having an ornamental pond. A compromise is to erect a pergola above the pond, that may be well covered with shading or climbing vegetation. However, this will not prevent a heron from landing and walking up to the pond edge and fishing.

Lateral Thinking
a. Invisible lengths of fishing line

stretched around the perimeter of a pond will startle an unsuspecting heron if it strides across it, causing it to fly off. This method can complement a pergola and relies on the observation that herons will not land directly into a pond but walk into the water having landed on terra firma. However, some bereaved koi keepers will strongly dispute this theory.

b. Protective Drain Pipe

A couple of sections of drainpipe, placed horizontally on the pond bottom offer heron-proof cover for fish. It relies on the fish being quick enough and the heron not being patient enough to wait for the fish to leave their cover.

Heron Scarers
Traditional. Bamboo see-saw arrangement where water gradually feeds into a hollow open-ended section of bamboo, tipping the balance and causing the sudden movement and rush of water. It is also quite pleasing to look at and complements the Japanese feel of a koi pond.
Innovative. i. A trip-wire assembly where tight fishing line is stretched across the path of access for the heron. Upon touching the trip wire, a spring-loaded ‘cap’ is fired to startle the heron. Unfortunately, the system does not reset itself so the heron is free to revisit unchallenged.
An infra-red sensor, strategically positioned around the pond triggers a random jet of water, fired from the heron scarer. Also useful against cats.
Imitation
Herons. Imitation herons work on the principle that herons are territorial and will not fish together. However, I have seen a group of at least 14 herons sitting together in one corner of a field! Imitation herons have mixed reviews. I recall being at an aquatic shop, overhearing a disgruntled pondkeeper who had recently bought an imitation heron, only to be revisited by the real thing. I had a little smile to myself when I heard the retailers cute reply, "Well sir, you see I sell male herons, so you must have been visited by a female".

Predators. A heli-kite is similar to a helium filled balloon, but it is not as buoyant and has fins which help it to ‘hover’ and move around in the wind. If tethered well above a pond, it can intimidate a heron as it simulates a hovering bird of prey. They have been shown to be very effective over fishing lakes, even deterring cormorants. Home made versions can be put together using a foil helium balloon, so long as your neighbours don’t object to a permanent min Zeppelin hovering over your garden.

If there was a single reliable way of preventing herons from being a real threat to our fish then all of these devices and methods would be redundant. Some are more suited to specific situations and experimentation with various methods will show what works in your situation.

But by then it may be too late!