6.1 Non-toxic control techniques
What are the alternatives to 1080 for killing possums or reducing the effects of possum damage?
Traps
Commercial possum operators and some of the management agencies have used traps for many decades. Public pressure in the 1970s to ban leg-hold traps led to research on the capture efficiency and humaneness of the wide variety of traps commercially available. Research showed that the available kill traps were relatively ineffective at catching possums, compared to leg-hold traps. However, welfare aspects were improved by using a leg-hold trap called Victor No.1, which reduced injuries to possums while still being effective at catching them. The Victor No.1 is now the most widely-used trap. By legislation, all leg-hold traps must be checked within 12 hours of sunrise on the day after they are set.
Poorly set traps can kill or injure birds. Surveys of trappers in 1936 and 1946 showed that the native birds most commonly caught were harriers, moreporks and kiwis. A 1984 survey of only 66 trappers reported catching 141 kiwis. Catches of other native species were not reported. Currently DOC requires that traps used in areas of kiwi or weka habitat be set well above ground level, so that these birds are not placed at risk.
The Timms trap kills possums humanely and quickly, and is widely used in urban situations, but is not capture-efficient compared with leg-hold traps. It is too large and cumbersome for use in the back country. Other kill traps that are effective and small enough for use in large-scale control operations have recently been introduced. Four trap models have been developed specifically for possums over the past two years (Warrior, Sentinel, Master and Holden) and they are now commercially available.
Shooting
Shooting possums is labour-intensive and there is little evidence to suggest that shooting alone is an effective technique for controlling possums over large areas. Shooting can be effective in small areas such as orchards and stands of trees surrounded by pasture. Possum populations may become wary of spotlights if they are shot at over an extended period of time.
Repellents
Researchers have developed a number of repellents designed to deter possums and other herbivores from damaging young trees. Egg and paint formulations are used by forestry contractors because they are relatively cheap. These repellents can significantly reduce damage to young seedlings, but don't provide total protection. They are not practical to use for Tb control or in the protection of native forests.
Tree guards and bands
Tree guards are physical barriers used to keep possums from damaging seedlings. Tree bands or sheaths have proven to be highly successful at preventing possum browse to saplings and older trees, by presenting an impassable barrier to climbing possums. They have been used to protect isolated pohutukawa growing in coastal areas and individual rata trees. Pole guards are used routinely to prevent possums from climbing power poles and affecting electricity supplies.
Fence barriers
Predator-proof fences can be constructed to exclude possums and other pests, the most notable example to date being that at the Karori Wildlife Sanctuary. However the cost of such barriers can be prohibitive. A "floppy top" fence that rolls over to the outside causing climbing possums to fall off has been trialled, and an operational fence installed at Warrenheip, to exclude pests from an area to be used as a nursery for kiwi chicks. A local conservation trust also intends to install a predator-proof fence around Maungatautari, in the Waikato, and is currently fundraising for the project.
Various designs of electric fence have been tested. Electric fences can exclude possums effectively, but maintaining them requires continual vigilance, especially in summer when vegetation is growing vigorously and may fall on the fence, shorting the electrical circuit.
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