Retorts

Possum Corrections

Regarding the recent article [Discovery, July 1993] "From furry friend to fatal fiend" by Louise Shaw: Although it is good to see this magazine supporting potential journalists, the article in question makes some statements which are not quite correct. This probably does not reflect on the student's ability, as access to information is generally poor for secondary school students.

There is no evidence that the fur trade has ever kept the possum population of New Zealand in check. Skin exports peaked in 1980, with 3.2 million skins being exported. This would equate to a total of approximately 4.5 million possums killed assuming a discard rate of one in three. A conservative estimate of New Zealand's possum population is 70 million, so harvesting by the fur trade represented only 6.4% of the total population annually, which can easily be maintained as possums have an natural rate of increase of 20% to 30% annually.

It is difficult to accurately assess the national expenditure on possum control. The Department of Conservation was allocated $3.3 million last year for conservation possum control. This will increase to $6.6 million this year. Conservation possum control is only part of the possum control scene however. Control of possums in bovine tuberculosis endemic areas attracted $4.6 million from the Animal Health Board last year, while Regional Councils spent approximately $1.8 million. Regional Councils also control possums for other reasons such as forestry and conservation protection.

This year farmers and other peripheral industries are expected to contribute $16 million, whilst the Government's total annual contribution will increase by $11 million to $24.5 million.

There is no real evidence that possums are developing a significant immunity to 1080 nationwide, although this may be true in isolated cases. There is potential for this to occur in the long term.

Birds are not placed at "high risk" at all by control techniques used today. Following the eradication of possums from Kapiti Island in the mid 80s, both fauna and flora values increased dramatically. 1080 was aerially applied during that eradication campaign. Other research data also indicates that 1080 aerial operations have minimal effects on native bird life. These bird populations actually benefit from the removal of possums which are both a significant competitor and predator as Louise quite rightly pointed out.

The comment that 1080 endangers non-target species via food chains in the ecosystem is a common fallacy that has been long since laid to rest. 1080 is fully and rapidly biodegradable, and where animals receive a sublethal dose, the 1080 in their bodies is quickly eliminated (usually within a week). 1080 does not persist in soil, water, or any life forms. Therefore the "biomagnification" effect observed with some toxins does not occur.

D. Meenken, Surveillance Officer for Manager, Operations, Wellington Regional Council

We hope you saw link-textDavid Morgan's article in the August issue which looked at possum control strategies.