Hunting, trapping and poisons are the three most commonly used methods of mammalian pest control in New Zealand. Each method has benefits and limitations. Extensive research is focused on developing species-specific toxins, more efficient traps and the possibility of biological control through gene editing.
The Department of Conservation (DOC) works with the New Zealand Fur Council to support fur recovery as an option for possum control. However, DOC reports that hunting and trapping do not reduce possum populations enough to allow native species and forests to recover. In the 1950s, hunters were paid a bounty for possum pelts. It meant possums were killed in large numbers in easily accessible areas. Less-accessible forest regions were unaffected, and possums quickly reinvaded the cleared areas. Also, hunting does not target other mammalian pests like rats and stoats.
Trapping methods have improved considerably. New designs make them more efficient and humane and reduce the risk of bykill. Self-resetting traps reduce labour costs, and wireless systems mean that traps can be monitored remotely.
The Biological Heritage National Science Challenge is funding the development of super-lures to attract stoats to traps. Scientists have found that ferret odour is very attractive to stoats, and they are investigating how to create an identical artificial scent that will be easy to use.
Trapping can be an effective method for controlling possums and stoats in accessible areas, along forest edges, along rivers and in managed forests. DOC alone maintains 180,000 traps and spends more than $5 million each year on stoat and rat trapping. However, it is more costly than other forms of pest control. It is also not practical in isolated and rugged terrain.
In New Zealand, the National Animal Welfare Advisory Committee (NAWAC) provides advice on animal traps and devices, and they have approved certain traps as being more humane than others.
A number of poisons are available to control vertebrate pests. Often, a variety of poisons must be used to avoid the build-up of resistance and bait shyness (where animals start to avoid a particular bait, having learned that they don’t feel good after eating it).
Anticoagulants are poisons that work by stopping blood from clotting. In other words, the animals bleed to death. Usually, this bleeding is internal. Rats and possums die after eating the poison, while stoats (which are carnivores) die through secondary poisoning.
First-generation anticoagulants – like pindone – require multiple feeds for a lethal dose. Pindone is sometimes used in aerial operations for large-scale rabbit control. Second-generation anticoagulants – like brodifacoum – can kill pests with a single feed. It has been used aerially on off-shore islands.
Both types are used in bait stations. Anticoagulants are slow and painful killers. They also take a long time to break down in soil and water. Areas treated must not be used for hunting for 3 years after application – in comparison to 4 months for a 1080 application. There is a significant risk of bykill when using anticoagulants.
Cyanide is a highly lethal poison used in bait stations. It kills possums and rats but it breaks down too quickly to kill stoats through secondary poisoning. Cyanide is humane as it kills quickly. It does not leave residues in water and soil. High bykill has been reported in the past.
Recent New Zealand-developed poisons
The Biological Heritage National Science Challenge is developing new pest control tools, including poisons that are more humane and only harm the target species.
Para-aminopropiophenone (PAPP) is targeted at controlling stoats and feral cats. It acts rapidly and is considered to be humane. PAPP has low secondary poisoning risks and minimal residue risks to non-target species.
Sodium nitrate is a food preservative that is toxic at high doses. It is used for ground control of possums and feral pigs. It causes rapid death and is considered humane. There are no persistent residues, and it has a low risk of secondary poisoning.
Toxins from native plants have also been investigated. Natural toxins are more likely to be acceptable to Māori and other communities. Tuti, from the tutu plant, is toxic to rats. However, it is considered to be inhumane, causing extreme suffering, so its development may not be feasible.
Biocontrol and gene editing
Considerable effort was put into the biological control of possums. New Zealand scientists investigated limiting their fertility through the use of toxins and vaccines. The projects finished in 2010 due to concerns about the length of time required to produce results, risks associated with the biocontrol agents and potential controversy over genetic engineering.
However, new genetic technologies mean that gene editing may become a future possibility. It’s still not clear if genetic modification of pest species is possible or which genes or processes to target. Scientists working with the Biological Heritage National Science Challenge are sequencing the possum genome as a first step. International groups have already sequenced the genomes of rat and mice species.
The case for 1080
Alternative methods of pest control are effective for ground control operations in accessible areas.
Although most people would be relieved to see the end of aerial poison operations in New Zealand, there is currently no viable alternative to 1080. Extensive research shows that it is an effective, cost-effective way of managing pest populations, that it does not accumulate in the environment and that technological advances are reducing the chance of bykill.
Nature of technology
Pest control devices – including traps and toxins – continue to develop. Technological advances and the desire for more humane pest control are generating innovative products.
Learn more about 1080 and pest control in these articles:
- 1080 – an overview
- The chemistry of 1080
- 1080 and water quality
- 1080 and the risk to non-target species
- 1080 – a wicked problem
- 1080 and pest control – a timeline
This slide show presents some of the pros and cons of various methods of predator control.
Website 1080: the facts has information about alternatives to 1080, including a table that compares toxins.
Predator Free NZ has advice on trapping best practice for rats, stoats and ferrets.
Visit New Zealand’s Biological Heritage National Science Challenge website to read about the super-lure for stoats and find out more about close-to-market pest control tools and their strategic applications.
Bush Bay Action is a trapping-only operation in the Opua Forest. Read its position on the viability of wide-scale trapping as an alternative to aerial 1080 operations.
Manaaki Whenua – Landcare Research has information on the welfare performance of traps for capturing and/or killing small to medium-sized mammals.