Management Information
Preventative measures: Harbouring and releasing brushtail possums (Trichosurus vulpecula) in New Zealand was made illegal in the 1940s (Cowan, 2005)
Cultural: Bounties were offered for possums in New Zealand between 1951 and 1962. In this 11 year period about 8.2 million bounties were paid but the bounty system probably encouraged the illegal spread and release of possums (Cowan, 2005).
Physical: Possums are trapped for fur throughout New Zealand but pelts from the South Island are worth more. In periods of high fur prices trappers may have a significant impact on possum populations but this control is limited to accessible areas (Cowan, 2005; Marks, 2006). Possums were eradicated from Rangitoto and Motutapu islands using a combination of methods including aerial 1080 drops (estimated to kill 93% of the population), trapping using leg hold traps and ground based shooting with dogs. Helicopters fitted with forward looking infra-red cameras were used to identify areas of possum activity at night. The eradication of possums from both islands (joined by a small causeway) took 6 years (Mowbray, 2002). Possums have been removed from a number of areas surrounded by predator proof fences (e.g. Karori Sanctuary in Wellington) although the fences need constant monitoring for breaches that would allow possums and other introduced mammals back into the fenced area. Chemical: Possum control in New Zealand using poison is coordinated by three main groups: the Animal Health Board (to minimise the Tb risk to domestic stock); the Department of Conservation (to protect forests and native wildlife); and the Regional Councils (for Tb control and conservation reasons). 1080 in carrots or cereal baits is spread using helicopters to treat large areas. Smaller areas are generally treated using ground based poisoning utilising toxins such as 1080, cyanide (in paste or capsule form), cholecalciferol, and various anticoagulants. Ground based poison control is often backed up with physical methods such as trapping and shooting (Cowan, 2005). Biological: Two methods of biological control are being investigated: immunological interference with fertility and disabling the normal hormonal control of reproduction (Cowan, 2005). Tompkins and Ramsey (2007) investigated different methods of distributing fertility control vaccines through bait stations and concluded that the delivery method would not affect success of fertility control operations. Instead, the success depends on vaccine characteristics, namely: “its expense relative to existing tools, its longevity in the field, and its efficacy at reducing female breeding success”. Integrated management: Possum control using poisons (particularly aerial drops) frequently controls rodent species and in turn predators such as mustelids and feral cats through secondary poisoning.
Location Specific Management InformationAllports Is. (New Zealand)
Brushtail possums (Trichosurus vulpecula) were eradicated from Allports Island in conjunction with a mouse eradication programme, using a brodifacoum bait. Codfish Is. (New Zealand)
Brushtail possums (Trichosurus vulpecula) were eradicated from Codfish Island using a combination of traps, cyanide poison and dogs. Eradication was completed in 1987. Kapiti Is. (New Zealand)
The control of brushtail possums (Trichosurus vulpecula) on Kapiti Island began by trapping in 1920, and continued until 1969 when a moratorium was placed on trapping when the value of this control was disputed. An eradication programme was initiated in 1980. There were three main phases to eradication. From 1980 to 1982, possums were killed by seven trappers commercially harvesting possum skins, using gin traps. Between 1983 and January 1985, four trappers worked on the island for wages, as opposed to selling skins, trapping at a more intense level. The final phase was from March 1985 to March 1987, where two trappers worked at a high level, and three dog handlers with teams of dogs also worked intensively searching the island for any remaining possums. In August 1984, the northern end of the western cliffs of the island were sown by helicopter with 1080 (mono sodium fluoroacetate) poison. During these years, 19,500 possums were killed by gin traps, 1500 by 1080, and a further 32 were caught by dogs toward the end of the programme. Possums were declared to be eradicated in October 1986, and since then stringent quarantine measures have remained in place to ensure reinvasion does not occur. Karori Reservoir (New Zealand)
Brushtail possums (Trichosurus vulpecula) have been eradicated from the area enclosed by a predator-proof fence at the Karori Reservoir, using a combination of poison and trained dogs. Motutapu Is. (New Zealand)
An eradication programme began in 1990, in conjunction with that taking place on Rangitoto Island. Bait stations containing cyanide paste were laid out, supplemented with ground shooting using dogs. Victor soft catch traps were used along the buffer zone between Rangitoto and Motutapu Islands. The final possum was caught in the 1993/1994 season. Following eradication, rapid recovery of the canopy and understorey was evident. There was also an increase in weed species. Nelson (New Zealand)
Brushtail possums (Trichosurus vulpecula) are designated as 'Regional surveillance pest' by the the Tasman-Nelson Regional Pest Management Strategy. The strategy has its effect over the combined area that lies within the administrative boundaries of the Tasman District Council and Nelson City Council. The objective of the strategy is to promote the control of possums and improve the public understanding of their impact. The councils provide significant funding to the Animal Health Boards for the control of possums. Please see Hierarchy of Plant Designations for an explanation of designation terminology. Rangitoto Is. (New Zealand)
An eradication programme began in 1990, in conjunction with that taking place on Motutapu Island. An aerial 1080 drop achieved an estimated 93% kill rate. Bait stations containing cyanide poison were laid out in 1991, as well as Victor No. 1 soft catch traps. These were later changed to steel jaw traps. Dogs were used to locate possums which had become bait or trap shy. Monitoring was carried out and included the use of Forward Looking Infra-Red cameras to identify animals at night from the air. The final possum was killed in 1996. Rapid recovery of the canopy and understorey was evident. There was also an increase weed species. Tasman District (New Zealand)
Brushtail possums (Trichosurus vulpecula) are designated as 'Regional surveillance pest' by the the Tasman-Nelson Regional Pest Management Strategy. The strategy has its effect over the combined area that lies within the administrative boundaries of the Tasman District Council and Nelson City Council. The objective of the strategy is to promote the control of possums and improve the public understanding of their impact. The councils provide significant funding to the Animal Health Boards for the control of possums. Please see Hierarchy of Plant Designations for an explanation of designation terminology. Wenderholm Regional Park (New Zealand)
Intensive control of brushtail possums (Trichosurus vulpecula) began in 1982, by poisoning using sodium cyanide, and trapping using wire cage and Timms kill-traps during a two week period each year. The park was closed to the public during each operation. More recently, Victor No. 1 leg-hold traps and brodifacoum poison have been used. During 2000, a 500 ha buffer area inland from Wenderholm was also trapped and poisoned. Possum numbers have been reduced to below a 5% residual trap catch index. The control of possums has been followed by improved productivity in bird species such as the The 'near threatened' New Zealand pigeon (see Hemiphaga novaeseelandiae in IUCN Red List of Threatened Species), improved forest health and an increase in invertebrate numbers. It should be possible to maintain possum numbers permanently at very low levels.
Management Resources/Links
5. Cowan, P.E. 2005. Brushtail possum. In. C.M. King (Ed.) Handbook of New Zealand Mammals, Second Edition, pp56-80. Oxford University Press, Melbourne. 6. Lovegrove, T. G., C. H. Zeiler, B. S. Greene, B. W. Green, R. Gaastra, and A. D. MacArthur., 2002. Alien plant and animal control and aspects of ecological restoration in a small 'mainland island': Wenderholm Regional Park, New Zealand. In Turning the tide: the eradication of invasive species: 155-163. Veitch, C.R. and Clout, M.N.(eds). IUCN SSC Invasive Species Specialist Group. IUCN. Gland. Switzerland and Cambridge. UK.
Summary: Eradication case study in Turning the tide: the eradication of invasive species. 7. Montague, T. L. 2000. The brushtail possum: Biology, impact and management of an introduced marsupial. Manaaki Whenua Press, New Zealand.
Summary: An account (by several authors) that outlines the breadth and complexity of the possum problem in New Zealand. The book explores current and potential future management techniques, and measuring the benefits of controlling possums. 10. Tompkins, D.M. and Ramset, D. 2007. Optimising bait-station delivery of fertility control agents to brushtail possum populations. Wildlife Research 34: 67-76. Results Page: 1
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