Possum – Pest or Resource?

   by Tony Orman

A query about the Possum – has its danger been exaggerated?
That was the title of an article I wrote for the “NZ Weekly News” back in 1961.  Strangely the article drew no comment and I have not changed my views since, in fact experience with observation and public discussions, in the back country over the next six decades has reinforced them.
Successive governments and more particularly the last two, i.e. National-led and Labour-led have top dressed public lands and some private lands with the 1080 poison aimed to kill possums. Government departments, claim conservation reasons for the poisons use and OSPRI (formerly the Animal Health Board) the reason of eradicating bovine Tuberculosis (Tb). But 1080 originally developed as an insecticide in the 1920s, kills not only possums but other life from invertebrates to insects, native birds and wild game such as deer.
The spreading of poisons is done on the erroneous assumptions that (a) there are 70 million possums spread evenly over New Zealand (b) possums are a rapacious consumer of foliage and (c) possums are the major vector (spreader) of Tb in farmed animals.
Let’s look at the assumptions one by one.
Experienced possum trappers I have spoken have long disputed the mythical 70 million figure. Their estimates range in the 20 million to 25 million figure. 
South Auckland possum hunter Wyn Hibberd  is adamant about the flawed figure.
“It’s total bullshit. They’ve been quoting that for the last 30 years to justify their use of 1080.”
And he is equally forthright on the corruption.
“There’s big money being paid out within bureaucracies, big salaries at stake. They’ll prop up the myth with propaganda plus the government owns the 1080 factory at Wanganui.”
The propaganda has exaggerated and perpetuated myths about possums such as the 70 million figure often quoted by DOC he says.
And he rejects the “tonnes” of vegetation DOC says possums gobble each night.
“That’s garbage. I get around the bush a lot and it’s in very good heart with possums present,”  Wyn says.
Herbivore Possums
“The claim of possums preying on birds and nests is a myth. Possums are herbivores not carnivores.”
Several years ago, I  came across details of a Department of Conservation workshop held in the mid-1990s on “Possums as Conservation Pests”.
A senior Landcare Research scientist Graham Nugent  spoke on the subject.                 
Assuming the oft-quoted figure of 70 million possums in New Zealand, the marsupials  “apparently consume about 21,000 tonnes of vegetation per day – presumably 300 g wet weight consumption multiplied by 70 million possums,” he said. “This oft-quoted figure is frequently used to depict possum as a rapacious consumer of all things green.”
 “But,” added Graham Nugent. “that implication ignores the trees’ daily foliage production of 300,000 tonnes for forests alone  – 7.5 million hectares x 15 tonnes wet weight of foliage per hectare per year.”
Let’s  explain that in simpler words – the fictitious number of 70 million possums would gobble only about 1/15th or 7 percent of the new foliage each night.
Indeed it would be less because most possums live near margins of forests adjoining paddocks rather than in the forest and a significant part of their diet is grass or spring and summer growth on farm trees like willows, growing outside the forest.
Graham Nugent termed the 70 million possum “guess-estimate” by DOC as a “back-of-a-cigarette-packet” calculation.  Recently DOC have tended to reduce the “estimate” of the total possum population down to about  35 million. Even that could be far too high.
And let’s take a more realistic figure of perhaps 10 million rather than 70 million possums. If a more realistic national possum population of 10 million is used, they would consume just one per cent, of the daily foliage production.
Is that a forest pest?  
Graham Nugent went on to say that possums do not threaten the total national forests by deforestation. For the bulk of New Zealand’s forest, the process is one of a change in individual species known as composition. There would be less of palatable vegetation species. So the change is merely a structural forest change.

DOC’s Ignorance

Seemingly DOC just does not understand basic possum population dynamics.

The realities are:-
•  Possum populations are not consistent. Some gullies may have high possum numbers, other gullies because of aspect, low or nil numbers.
•  Some areas by nature such as nutrients, hold low numbers of wild animals.
In Marlborough for example, the Richmond Range and the Red Hills area in the head waters of the Pelorus and Motueka Rivers have low populations. 
•  Possum numbers are much higher in marginal country and along lower bush edges where possums will “graze” pasture, than in forest. One study near Wellington suggested possum numbers were  400 percent higher (i.e. 4 times) that of numbers in the forest itself.
•  Possum numbers in rugged country are usually “controlled” by the rigourous environment especially climate. In inclement weather, natural mortality of possums may be as high as 40 percent.
•  The generally unpalatable nature of beech forest does not support high wild animal numbers.
Road Kill Evidence
Many comment on a noticeable decline in road kills of possums and in areas that have not had 1080 dropped. Twenty years ago, possums (dead or alive) were common on highways – today very few are seen. It is represented by the bell curve of a graph, where animal numbers on liberation increase rapidly, reach a peak as the carrying capacity is reached, and then fall to a low steady level of a stable population.
Possums at an estimate, reached their peak 20 years ago and  have been in a gradual decline for the last decade or more.
The alarmist supposition that possum numbers will explode if poison drops are stopped is regarded as most unlikely by competent wild animal biologists.  
In any case, if numbers were to increase, harvesting of possums by commercial fur trappers at no risk to other wildlife is the obvious option. 
Besides the possum is a resource.  In 2020, possum fur worth $140  a kilogram is about 10 times the price of merino wool and about 46 times the price of crossbreed wool.compared to about $4 a kg for crossbred sheep wool.
Bovine TB
Possums are often berated as a spreader of bovine Tb in farmed cattle and deer herds. The OSPRI ex-Animal Health Board is a major  user of aerial 1080 poison – blessed by DOC..
In 2016 NZ First MP Richard Prosser questioned Minister of Primary Products Nathan Guy on the incidence of TB in possums. Guy replied of 9830 possums autopsied, none had TB.
Skin tests are generally used to test stock for TB but skin tests have an error of about 25% more or less. That means an infected animal may not be detected. It remains in the farm herd to infect any other animals whose immune system is below par.
Some years ago, I heard, Dr Frank Griffin of Otago University address a Marlborough Deer farmers’ function. The scientist said that New Zealand’s pest management strategy focused narrowly on “killing possums and skin tests”  and  was not the solution to the TB problem.
The late Bill Benfield, conservationist and author of “The Third Wave” and “At War with Nature” said NZ’s bovine TB rates were so low that New Zealand must be one of the most TB-free countries in the world.
Insecticide 1080
The poison  was first developed as an insecticide in the earlier decades of the 20th century. It is non-selective, killing everything that takes in the toxin or if a sub-lethal dose, eliminating the species ability to reproduce.
So why does the possum-pest myth persist? 
It is public funded agencies like the Department of Conservation and OSPRI that want  empires and accompanying highly salaried jobs maintained.
It costs money, money from taxpayers and farmers to the tune of $110 million a year.
Worse still the ecosystem poison that 1080 is is endangering birds and the ecosystem.
Bird numbers from falcons to kea, kiwi, robins, tomtits and other species have fallen alarmingly under the 1080 regime which DOC has ramped up after the bureaucracy’s birth in 1987..
It’s bizarre that DOC blames predators and drops more 1080 poison to kill more birds, insects and invertebrates.
Suspect Science
What of the science which DOC claims supports their pro-poison policy?
The science is “paid” science commissioned by DOC or OSPRI. It lacks independence and in many cases credibility. Is it not unlike Monsanto commissioning a scientist to say Roundup is harmless?
An independent scientist Quinn Whiting-O’Keefe, a retired US scientist qualified in analytical science, spelt it out to a 2007 enquiry into 1080. Monofluoroacetate (1080) was originally developed and marketed as an insecticide.  —  It is therefore universally toxic to all animals, essentially every living thing except plants and some micro-organisms. The degree of toxicity of 1080 is extreme, but varies somewhat among species. It is categorised by the World Health Organization (WHO) as 1A, their highest rating, “extremely toxic”  — It can kill every air-breathing animal. 
New Zealand uses approximately 90% of the world’s supply of monofluoroacetate. It is banned in most countries in the world and severely restricted in every country except New Zealand .
Quinn Whiting O’Keefe continued “There is no credible scientific evidence that mass poisoning the forest ecosystems with aerial 1080 is of net benefit to so much as one native species. Considerable evidence exists that DoC’s aerial 1080 operations are doing serious harm, as one would expect, given that 1080 is toxic to all animals. It kills large numbers of native species of birds, invertebrates and bats.”  
©Possum poison (1080) cruelly kills birds like this inquisitive South Island bush robin

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