How to help prevent herons eating your pond fish.

A common problem for many pond keepers is the loss of their much loved, and sometimes expensive fish stock to herons. Here in the UK the species involved is Ardea cinerea commonly known as the grey heron. These birds are efficient and increasingly common predators and can take surprisingly large fish - swallowing a 30cm koi would not be a problem and they can often damage larger fish in futile attempts to catch them. Once a heron has discovered that your pond is a source of brightly coloured, friendly food they will often return time and time again until all your precious fish have been devoured and they make no distinction between a £200 pound koi or a £2 goldfish. They have also been known to puncture pond liners with mistimed thrusts of their dagger like beaks. Apart from missing fish, other typical signs that a heron has decided your pond is it's new favourite 'all you can eat’ buffet are previously friendly fish suddenly becoming timid and hiding when you arrive beside the pond, wounds on the flanks of larger fish where a strike has been unsuccessful and scales left on hard surfaces such as paving around the pond. All this makes taking preventative defensive measures around your pond a good idea if you want to continue enjoying your fish.

One of the most effective anti-heron measures is a well positioned and maintained net covering. Ideally these should be installed at least 30cm above the waters surface. If the net is too close to the surface fish may become entangled and herons may still cause injury to fish while trying to catch them even though they are unable to pull the unlucky fish through the net itself. Nets will also help keep cats away from your fish as well as prevent leaves from overhanging trees and shrubs polluting the pond. They will need maintaining however as the weight of fallen leaves in autumn may break the net or push it into the water. Where possible it’s easiest to build removable frames to hold the netting to allow easy access for maintenance etc.
Many people consider nets unsightly and frames to hold them can be difficult to construct around naturally shaped or heavily planted ponds so a less intrusive option is an anti-heron fence. There are several versions of these available. A cheap version is an encircling ring of angled stakes strung with fine nylon line sometimes with small bells attached so when the heron approaches your pond it bumps into the line, the bell rings and scares the bird away. More sophisticated is a similar product that uses fine wires through which a low voltage current is passed via a transformer giving any approaching heron a harmless shock should it stray too close. More sophisticated still are electronic movement sensors positioned by the pond which when triggered flash lights and simulate bird of prey noises to chase of herons, or fire a jet of water. Make sure you switch these off when you decide to feed the fish though!
Other methods include traditional Japanese deer scarers known as ‘Shishi odoshi‘, reflective floating pyramids and plastic decoy herons which are believed to deter the somewhat territorial heron from visiting a pond it thinks is already ‘occupied’. To give the most realistic impression the decoy should be moved regularly but I have heard accounts of amorous herons attempting to mate with them...