How to stop herons eating pond fish
Here are some design considerations for your pond to prevent herons eating the fish inside.
What attracts herons?
1. Unimpeded access to water surface
Solution: Netting can provide a cost-effective heron-proof solution if carefully designed and maintained. A heron can put its neck through mesh that is 5cm knot to knot, and it has a reach of 60cm. The netting must therefore either have a small enough mesh size (2.5cm to make sure it is small enough not to trap the bird), or be at least 60cm above the water. The net also needs to be kept taut to prevent herons weighing it down.
Running a network of strings above the surface can also be used, but this is not likely to be as effective as netting.
A barrier (see Figure 1 in the downloadable diagram) made of chicken wire, two lengths of polypropylene twine, or an obvious ‘ribbon’ can be effective in the right situation. The barrier must be at the very edge of the pond or the heron will land inside the fence.
2. An area of water with a good all round view - herons need to be able to see danger coming
Solution: Consider growing tall shrubs or emergent plants at the edges of open ponds, or building a bank to make it more enclosed. Concentrate particularly on screening the edge(s) most often used by a heron for arrival and departure. The plants will benefit the fish and any wildlife using the pond.
3. Gently sloping banks - herons like to walk into the water from the bank and fish while wading
Solution: If building a pond from scratch consider making the sides vertical, but remember that these will need reinforcing or they will cave in. Also, a pond with vertical sides will be less attractive to other forms of wildlife. Hedgehogs can fall into straight-sided ponds, and unless there is a means of escape, they will drown, so careful consideration is needed before you build a straight-sided pond.
If changing the bank profile of an existing pond is impractical, position a chain of polyethylene floats, spaced less than 30cm apart, floating along the pool margin: herons are reluctant to feed between or over the floats (see Figure 2).
4. Water levels close to the top of the bank will make fishing from the pond edges easy
Solution: If you can control the water level, keep it at least 60 cm below the top of the bank. Combining low water levels with vertical sides to the pond can be effective (see Figure 3).
5. Calm and clear water makes the fish easier to see
Solution: A spray of water (as from a fountain) will make seeing fish difficult, but is unlikely to protect the entire surface of the pond (unless your pond is small and your fountain very vigorous!).
6. Water free from vegetation leaves fewer places for fish to hide
Solution: Vegetation provides natural cover for fish and helps to oxygenate the water. In ponds where this is not possible, or as temporary extra seasonal cover, consider using artificial lily pads that can be secured around the edges of the pond.
7. Fish at high densities
Solution: Apart from increasing the size of your pond or decreasing the number of fish, there is little you can do about this. Be aware that the more visible your fish are – such as at spawning time – the more irresistible they will be for herons. Fish weighing around 200g are just the size herons like – two roughly equal a heron’s daily food requirement.