Eradication Methods

Possum eradication techniques and information:

There are many different methods of controlling the brush-tail possum currently employed within New Zealand. They all vary in effectiveness and can pose potential toxicity threats to humans, animals and biota in general.

The pros and cons of all current methods, and detailed information on available poisons and trap types are outlined in detail below.

Control methods:

 

1) Shooting:

  • Can be quick, effective and humane.
  • Can be effective in smaller open areas such as orchards and more sparsely foliated areas of pasture.
  • Uneconomic for larger areas as the sole method of control due to high labour costs.
  • Only an option in rural areas of the peninsula.
  • Licensed, responsible shooters required. Some members of the public have concerns with the use of firearms.

2) Trapping:

  • Known to be the best method for urban areas due to poison and shooting not being appropriate (domestic animals etc).
  • May be effective when bait aversion has built up within populations.
  • Kill traps and live traps relatively humane, leg hold traps less so.
  • The use of some trap types is restricted by city and regional councils in urban areas.
  • Higher maintenance and labour than poisons but less than shooting.

3) Poisons:

  • Generally considered to be the cheapest and most effective method of control.
  • Certain poisons have a high degree of health risks associated with their use and can pose risks to stock, pets and birds through primary and secondary poisoning.
  • Poisons vary in their efficacy, bioaccumulation (build-up in various organisms) and length of time to kill the intended target species.
  • Public perception and concerns with certain poisons can be an issue.

 

Please note: For various reasons including the relative ease of access to control sites and proximity to populated areas; the use of sodium fluoroacetate (1080) will not be considered as part of a control regime for the Otago peninsula.

LINKS:

National Animal Welfare Advisory Committee (NAWAC): for assessing the welfare performance of restraining and kill traps can be found here: http://www.biosecurity.govt.nz/animal-welfare/nawac/policies/guideline09.htm

Landcare research trap test results from NAWAC standards can be found here (updated May 2008): http://www.landcareresearch.co.nz/research/pestcontrol/trapdesign/welfare_performance.asp

 

Comparisons and implications of trap types:

 

Note: Not all trap types available for possums are mentioned here. Also used, although now less commonly, are BMI 160 (Conibear type traps USA) and LDL 101 (Canada) traps among others. Both these traps have passed NPCA tests (2005) as per NAWAC guidelines. This summary is not intended as a recommendation of trap types to be used.

1) Kill traps:

Trap type: “Timms”.

Advantages:

  • Instant kill (unlike leg holds)
  • Good around gardens/houses
  • Yellow attracts possums
  • Highly unlikely to trap other/domestic animals if appropriate bait used (i.e. fruit)
Disadvantages:

  • Bulky/heavy (1.25kg)
  • Less effective than leg holds (Victor #1)
  • Not appropriate for large areas
  • Fails independent tests if not baited very specifically. Version 3 trap know to be an improvement.
Trap type: “Warrior/Bulldog”.

Advantages:

  • Compact
  • Instant kill (unlike leg holds)
  • Ground or tree set
  • Unlikely to capture domestic animals if used correctly
  • Good for large areas
  • Passes independent tests for kill time and escapes
Disadvantages:

  • Heavy (0.890kg)
  • Less traps can be carried than leg holds
  • Less effective than leg holds (Victor #1)
Trap type: “Sentinal”. (Developed from LD 101)

Advantages:

  • Lightweight (0.550kg)
  • Instant kill (unlike leg holds)
  • Designed for remote areas
  • Ground or tree set
  • No setting handle required
  • Can also be used as bait station
  • Passes independent tests for kill time and escapes
  • Shown to be almost as effective as leg hold traps (Landcare Research)
Disadvantages:

  • Bulky; less traps can be carried than leg holds
Trap type: “Possum master”.

Advantages:

  • Lightweight (0.5kg)
  • Tree and ground set
  • No setting tools required
  • Passes independent tests (recommended to be tree set vertically)
Disadvantages:

  • Poor performance in tests, both possums and ferrets
  • Must be set vertically (trees only)
  • Less effective than leg holds (Victor #1)

2) Live traps:

Trap type:

“Colapsable/Holden” etc (various models).

Advantages:

  • Appropriate for urban areas
  • Animal is not killed so can be released if not target species (e.g. domestic cat or flightless bird)
Disadvantages:

  • Bulky/heavy.
  • High labour costs, animals must be killed promptly after capture and trap reset.
  • Only appropriate in urban areas or where non-target species are present.

3) Leg hold traps:

 

 

Note: Leg-hold traps have been used in New Zealand for many years to trap pest animals, such as possums, ferrets, stoats and feral cats, to protect our native plants and animals and control bovine tuberculosis. The traps have metal jaws and are designed to catch and hold an animal by a limb, including the foot. Internationally and within New Zealand, concerns have been raised over the humaneness of leg hold traps. The main animal welfare concerns are injury and distress associated with being trapped, potential for escape of injured animals, and animals suffering if they are held in the trap too long. In addition, leg hold traps set around residential dwellings and in other areas such as public walkways and picnic areas increase the risk of injury to pet cats and dogs.

Note: All leg-hold traps must be set above ground on a tree or post at approx 70cm when there is a likelihood of ground dwelling birds being caught.

After consultation the Government has decided to restrict the sale and use of leg-hold traps in New Zealand. New regulations come into effect on 1 January 2008.

From 1 January 2008: No leg-hold traps can be used within 150 metres of a dwelling without the express permission of the occupier or in any area where there is a probable risk of catching a pet animal.

From 1 January 2009: no long-spring leg-hold traps of size 1 ½ or larger and no double-coil leg-hold traps larger than size 1 ½ can be used.

Source: http://www.biosecurity.govt.nz/regs/animal-welfare/stds/traps

Trap type: “Victor No1”

Advantages:

  • Light and small.
  • Easy to place and set in remote areas.
  • More effective that other trap types in catching possums (re
  • Fast reset compared to kill traps (1min vs over 2 min).
Disadvantages:

  • Can be viewed as inhumane causing undue suffering to animals (see above).
  • High risk of injury to domestic animals if used in urban areas.
  • Risk of injury to other non-target (native) species.
  • Must be checked and reset each day by law.

Note: padded leg-hold traps are now commonly used as a way to reduce injury to non-target species and reduce suffering of target species. Padded leg-hold traps, however, can lead to unacceptable escape rates and can still injure non-target species unnecessarily.

 

Poisons and Toxins:

 

There are 5 poison types most commonly used for possum control in New Zealand by the public: brodifacoum, pinedone, cyanide paste baits, encapsulated cyanide and cholecalciferol.

1080 or sodium monfluoroacetate (as previously mentioned) is a controlled substance and is not being considered for use on the Otago peninsula.

The main methods of deploying baits and poisons are:

1) bait stations must be elevated on trees or posts away from ground animals by law to avoid primary and secondary poisoning of non-target species. Stations are filled with cereal based and/or wax coated pellets. Dogs are particularly sensitive to these two anticoagulants – requiring only a 200gm dose to be lethal. Stations provide protection from rain and moisture. The two most common types are the Philproof and the Kilmore which hold up to 2kg of bait. Smaller stations are also available.

2) bait bags must be stapled to a tree, post or similar. They provide a cheap, weatherproof method of elevating bait away from ground animals. Bags are stapled approx 25cm up a tree and typically a “blaze” of flour and icing sugar is smeared on the trunk above the bag to act as an attractant.

3) paste form cyanide can be legally applied directly at ground level. Paste is usually applied on a stone, piece of wood or in a station near known possum trails after “pre-feeding”.  Paste should be removed or overturned after 2 nights to reduce gas emissions during break-down which can encourage shyness. Removal also reduces chance of harm to non-target species.

Note: Cyanide is the only poison legally allowed to be applied at ground level.

 

 

Brodifacoum/Pindone

(anticoagulants):

Trade names: Talon ®, Pestoff ®.

(bait station filled with brodifacoum)

Characteristics

Advantages

Disadvantages

Anticoagulant toxicants act by interfering with the normal synthesis of vitamin K-dependent clotting factors in the liver of vertebrates. This results in an increase in blood-clotting time until the point where no clotting occurs i.e. blood is thinned to the point of haemorrhage which leads to death.
  • Generally available to public with no license required
  • Less toxic to invertebrates than mammals and birds
  • Effective against possums that have

developed poison/bait shyness

Pinedone:

Residues in sublethally poisoned animals

(particularly liver) are less persistent than

brodifacoum

 

  • High risk of secondary poisoning of non-target species
  • 2-4 weeks for possums to die
  • Expensive with high possum densities

Brodifacoum:

Persistent (> 1 year) in liver of vertebrates. Can put meat for

human consumption at risk.

Pinedone:

Large amount of bait required to be eaten (1-2kg/possum)

Cyanide (sodium and potassium) paste and encapsulated pellet baits:

Trade names: Feratox ®

(Feratox ® tablets or capsules)

Characteristics

Advantages

Disadvantages

Cyanide is a HIGHLY TOXIC “asphyxiant” which causes a rapid decrease in O2 and an increase in CO2. Animals’ are unconscious within seconds and die within minutes. Available in paste and pellet formulations containing 475-600 g/kg cyanide.

Cyanide does not accumulate in soil or food chain and is not mutagenic or carcinogenic.

.

Paste:

  • Cheapest option available
  • Most humane poison, rapid kill (minutes)
  • Low secondary poisoning risk
  • Low environmental persistence

 

Feratox ®:

  • Safer to handle than paste.

Low hazard to non-target species.

 

Paste:

  • Limited to licensed contractors
  • “bait-shyness” can develop, leads to ineffectiveness
  • Highly toxic and can kill ground birds e.g. kiwi and weka

 

Feratox ®:

  • Limited to licensed contractors
  • Can persist in environment for 2-3 months

 

Cholecalciferol:

Trade names: Campaign ®, Feracol ®.

Characteristics

Advantages

Disadvantages

Feracol is a peanut butter flavoured bait, highly palatable to possums. The active ingedient is Cholecalciferol (vitamin D3) in a concentrated form. This is very toxic to some animals in particular, POSSUMS. Feracol eliminates in a humane way by elevating plasma calcium levels resulting in heart failure.
  • Generally available and no license required
  • Lower toxicity to birds than mammals reduces

primary poisoning risk to birds

  • Low risk of secondary poisoning (dogs/birds)
  • Does not persist in soil or water
  • Residues in sub-lethally poisoned animals do not

have prolonged persistence

  • Fate and persistence in the environment not

well understood

  • Treatment for accidental poisoning available but complex
  • Most expensive type of bait, however pre-feeding can make it cost effective

 

 

 

Sources: Weblinks and Publications.

1.       http://www.biosecurity.govt.nz/regs/animal-welfare/stds/traps

2.       http://www.pestcontrolresearch.co.nz/traps.htm#3

3.       http://www.landcareresearch.co.nz/research/pestcontrol/trapdesign/Traps_tested.asp

4.       http://www.ew.govt.nz/environmental-information/Plant-and-animal-pests/Animal-pests/Possums/Poisoning-possums/

5.       http://www.biosecurity.govt.nz/animal-welfare/nawac/policies/guideline09.htm

6.       http://www.landcareresearch.co.nz/publications/infosheets/possums/traps.pdf?traps

7.       Thomas, Malcolm and Sessions, Laura (NPCA) Private landowners’ guide to possum control; practical tools and techniques for controlling possums on private land. Produced by the National Possum Control Agencies. ISBN 0-9583736-3-9

8.       Warburton, Bruce (Landcare Research) 2005. A guideline for using kill traps to trap small mammals. National possum control agencies, Ministry of agriculture and forestry.

Published Papers.

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**MSDS sheets (poisons)

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