Feral pigs (Sus scrofa) are classified as a potential pest problem in a number of regions and are monitored and controlled on a site-specific basis where necessary.
Pigs can reduce farm productivity by damaging pasture and young forestry plantings, preying on lambs, and spreading disease including Tb (bovine tuberculosis).
In natural areas, they can damage native vegetation, bird life and invertebrate life.
Below: Extensive pig rooting on a farm at Conway Flat, North Canterbury in 2003. With Biodiversity Condition Fund assistance, 18 landowners have been implementing a feral pig control plan prepared by Landcare Research. Photo: B MacFarlane
Landcare Research ecologist, Ivor Yockney, says the impacts of feral pigs in New Zealand are not well understood and have yet to be quantified, but there have been anecdotal reports of increasing feral pig populations throughout much of New Zealand.
‘It's unclear why pig numbers appear to have increased, but it may be in part due to farmers retiring pasture land for a range of reasons.
'Any increase in woody vegetation provides good habitat for feral pigs and makes them more difficult to control by hunters.’
Where numbers do build to problem proportions, an intensive knockdown programme is recommended using a combination of aerial shooting, intensive trapping, spotlight shooting and targeted ground hunting.
This should be followed by long-term sustained control using traps and hunting. Currently, there is no poison registered as suitable for pig control.
If well managed, pig traps can be an effective supplement to hunting.
Miles Giller, QEII North Canterbury Rep, says designs vary but the most effective can be dismantled and moved easily, are strong enough to require little maintenance and can catch several animals at once.
A suitable design
Below: A weld-mesh-panel trap with an inwards swinging door. The lure can be placed in a bag hanging overhead. Assembly of this trap takes about 15 minutes. Photo: Miles Giller
Set the door by propping it slightly ajar with a short stick. As animals enter, the door is lifted by their brushing back, the stick falls down, and the door will swing down and close.
Once inside, pigs cannot push their way out, but other pigs can push their way in.
Below: The inwards swinging door is hinged at the top. Photo: Miles Giller
Below: A family of pigs in a trap. With an inwards swinging door, multiple catches are common as one trapped pig lures another. Overnight catches of over 20 pigs in a single trap have been recorded. Photo: Ivor Yockney
Open SpaceTM Magazine No. 70, July 2007 © QEII National Trust