Possum – Pest or Resource?

Opinion by Tony Orman

Quote – “We shall be doing a great service to the country in stocking these large areas with this valuable and harmless animal.”

Auckland Acclimatisation Society Annual Report 1917, in discussing possums.

“A query about the Possum – has it’s 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 probably only reinforced them.

Why should a deerstalker be concerned about whether or not the possums is a pest?

The answer is that the 1080 poison programmes run by government departments, on conservation grounds, and OSPRI, formerly the Animal Health Board, on eradicating possums bovine Tuberculosis (Tb) is indiscriminate.  It kills not only possums but other life from invertebrates to insects, native birds and wild game such as deer.

Why should a conservationist like me, challenge the mantra that the  possums is a pest?

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. The 70 million number was “calculated” by counting road kills on highways – a method that surely defies scientific credibility.

Let’s look at the assumptions one by one.

Experienced possum trappers I have spoken to over the years, all disputed the mythical 70 million figure. Their estimates ranged in the 20 million to 25 million figure. One very experienced trapper was the late George Spittal of Rai Valley. In an article in “NZ Hunting and Wildlife” Summer 1996 -97, he pointed out the fallacy of DOC’s thinking.

“Government departments say there were 70 million possums in the country in 1973-74. After spending $57 million (per annum) on possum controls, (they claim) there are still 70 million possums.”

Another possum hunter I spoke to was adamant about the flawed 70 million figure.

“It’s total bullshit. They’ve been quoting that for the last 30 years to justify their use of 1080,” he said.

And he is equally forthright on the corruption.

“There’s big money being paid out, 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,”  Wyn says.

“The claim of possums preying on birds and nests is greatly exaggerated. Possums are herbivores not carnivores. The biggest threat to native birds are stoats and especially wild cats – and 1080 poison. DOC aren’t aware because they’re in Cloud Cuckoo Land.”

BC P1010376.jpeg

South Island bush robin – 1080 kills birds

Possum browse

Several years ago, I came across details of a Department of Conservation workshop held in the mid-1990s on “Possums as Conservation Pests”.

A respected scientist Graham Nugent of Landcare Research, 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 further.

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 wîillows, 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.

Population Dynamics

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. Yet the Animal Health Board in conjunction with the Marlborough District Council aerial spread 1080 over the Manuka Island/Red Hills area despite a pre-drop trap line showing nil possums!

It is claimed aerial poisoning is only done in remote, rugged areas, but the instance quoted  above (Manuka Island/Red Hills) is adjacent to a state highway with some forestry access roads into relatively easy mountain country. Similarly, a DOC aerial drop in the historic Ship Cove, Cape Jackson area of the Marlborough Sounds, was very accessible by boat and again far from rugged country.

•  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 rigorous 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.

In addition, my observation is that possum numbers have naturally declined or are declining to a low stable level, which is a known characteristic of wildlife populations.

Thane Riney in his classic Fiordland Lake Monk study showed  how a deer population undisturbed and left to Nature, peaks and then falls to a low stable level.  Any wildlife population acts the same.

It’s Nature’s way.  Possums are no different.


A road killed possum

Many comment on a noticeable decline in road kills of possums, in areas that have not had 1080 distributed for two or three decades, such as  the Whangamoa Ranges between Nelson and Blenheim, as well as other highways. Twenty years ago, possums (dead or alive) were common on highways – today very few are seen.

Possums at an estimate, reached their peak 30 or 40 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 absurd. Possums are slow breeders with just one “joey” a year.

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 with possum fur worth $110  a kilogram – subject to fluctuations – compared to $3 a kg for crossbred sheep wool.

Ruahine Ranges

There is interesting research by botanist-hydrologist the late Dr Patrick Grant in the Ruahine Ranges. For decades in the 1950s-2000 period, government departments and the vociferous Forest and Bird Society have blamed possums and deer for tall dead spars of forest trees poking above the forest canopy in the Southern Ruahines. Dr Grant was intrigued when he read of early missionary explorer William Colenso’s travels in the ranges in the mid 19th century. Colenso told of forest damage and giant land slips long before any possums or deer were introduced.

Subsequently Dr Grant’s research pinpointed the major cause of forest damage as climatic. The dead tree spars were the remnants of a severe drought period 1909 -15. And such periods are cyclic. These periods of dry, windy weather were traced back by Dr Grant as far back as the 16th century.

Similarly Dr Grant compared photos taken in 1918 of the Waipawa upper reaches with the 1980s when he did his research and concluded the forest canopy had repaired itself despite the browsing of possums.

The seminar, “Moas, Mammals and Climate Change” in 1986 also featured papers by scientists on insect browsing such as grasshoppers on snow grass and beech roller caterpillars. In 2010 in the Nelson Lakes National Park, defoliation of large tracts of beech forest were found to be naturally caused by caterpillars – not possums.

A Treasury Working Paper “Coughing Up for Tb control” produced in 2000 raised serious doubts about the role of possums in bovine Tb infection.

It said on the likelihood of a trade ban from New Zealand’s export markets, that “the risk is probably very small,’ and that “the true risks are likely to be smaller and shorter in duration” than the Animal Health Board claimed.

The paper also addressed how the problem of Tb rose in the first place by saying “the root cause of the problem is not the presence of possums but rather their infection with Tb, as is clear from areas like Taranaki, which have possums but are still Tb free … suggest that Tb was spread by transport of infected animals.”


NZ is Tb Free!

In some areas, lowered Tb infection can also be attributed to greater awareness by farmers and transport operators and improved systems for stock movement.

Tb incidence rates show New Zealand’s 0.3% to be well below some other countries. In 2009, the bovine Tb rate  was  Wales 8.5%, over 5% in England, about 7% in Ireland and Spain over 1 %. 

In 2016 Agriculture Minister Nathan Guy disclosed in Parliament that 9,830 possums had been autopsied to assess the incidence of Tb infected possums. Not one possum of the 9,830 had Tb.

OSPRI uses the skin test to test farm stock for Tb. But the skin test is notoriously inaccurate with 25-30% error rate.      

In October 2001, Dr Frank Griffin of Otago University addressed 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.

After all, the skin test to detect Tb in stock, is widely acknowledged as being so inaccurate. In essence, it means one in 10 cattle can be Tb infected but give an erroneous “clear” of Tb reading. I know of four cases in Marlborough where farmers sick of getting positive reactors (Tb infected) got blood tests (95% accuracy) done. Animals that had tested as not Tb infected by the skin test, were carrying Tb. These animals are referred to as “sleeper animals”.

Scientists have been frustrated by the AHB’s and DOC’s dogmatism. Dr Frank Griffin of Otago saw the long term, logical solution for deer farming as selectively breeding genetically Tb resistant deer, but was refused funding while annually millions of dollars were spent by AHB and DOC  spreading 1080.

In any case, New Zealand’s low incidence of Tb.

Bill Benfield

Conservation researcher and author the late Bill Benfield wrote in any case total eradication to a zero incidence of disease is impossible. For that reason the World Organisation for Animal Health, an affiliate to the UN, sets the world standard for a country to declare “Tb free” at 0.2% for Tb infected herds and 0.1% for infected cattle. 

“What zero means is the impossible dream. It is like “infinity” – where is infinity? Where is zero? Like infinity, how do know you’ve reached it? Do you have to go on forever, even after 2055, seeking a holy grail of zero, which is what OSPRI spokespersons want. More cynically, OSPRI wants jobs for years, paid for by taxpayers and farmer levies?” he said.

WFB photo2.jpeg

The late Bill Benfield

A few years ago, Tasmanian scientist David Obendorf said figures obtained showed New Zealand rates of TB infection in cattle were slight, i.e. 0.0019% average over the past nine years. 

“It is so far below the 0.1% required by world standards for a TB-free declaration – that New Zealand must be one of the world’s most TB-free countries. By world standards, even possum are TB free! “ said David Obendorf

Conservationists should be concerned. Deerstalkers should also be concerned.

A good percentage of deer and most other life are killed by 1080 poison as is most other life. The poison  was first developed as an insecticide in 1917. It is non-selective, killing everything that takes in the toxin or if a sub-lethal dose, eliminating the species ability to reproduce.

In 2007 scientists Pat and Quinn Whiting O’Keefe challenged New Zealand’s widespread use of 1080 poison. The duo audited Department of Conservation scientific research and produced an 88-page monograph reviewing more than 100 scientific papers.  

There is now a familiar litany of scientifically insupportable claims about what great things aerial 1080, a universal poison, is doing for our forest ecosystems. The people of New Zealand have a right to know the truth about what the scientific evidence shows.” 

“The results are startling and belie most of the department’s claims.” 

“First, there is no credible scientific evidence showing that any species of native bird benefits from the dropping of tonnes of 1080 into our forest ecosystems, as claimed by the department and Forest and Bird. There is certainly no evidence of net ecosystem benefit.” 

The possum has been demonised to justify the use of 1080 poison. 

Belief that there is a possum problem is an excuse to dump more poisons.

Footnote; Tony Orman is a conservationist and outdoor sportsman and has had some two dozen books published.

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11 Responses to Possum – Pest or Resource?

  1. Jack Tuhawaiki says:

    On TB and possums you can add that in 2016 Minister of Primary Industries, Nathan Guy, stated in parliament, that over a ten year period, 124,000 autopsied possums showed an incidence of 0.04 per cent while as the opinion piece states, 9830 possums autopsied showed zero incidence.
    The possum generates “hate speech” from some official quarters (e.g. DOC) that has no fact and no credibility. Even Federated Farmers who one would suppose are intelligent and conversant with the countryside are anti-possum and pro-1080.

  2. Brer Possum says:

    Another good article by the author, plenty of research material to back up what he says.
    The possum is used as pet food and the fur used as well, why not turn it into more of a resource.
    Clean green NZ is a fallacy while we are still dumping this poison on our country.
    It needs to go, but I guess while corrupt DOC have control the gravy train will keep on rolling!

  3. Kathy White says:

    The possum has been vilified unjustly because the government wants people to hate them. In truth, they are marsupials, they don’t breed rapidly, and they mainly eat vegetation. Our trees and bush can sustain possums as long as their numbers are managed. We don’t need to go to extraordinary lengths to exterminate every last one of them. We can co-exist as can other wildlife. They can be used for meat in areas where their numbers are high, but only if they aren’t poisoned. It’s time we brought common-sense back to animal management, and also that we start to appreciate and care for our wildlife as a whole.

  4. Pete says:

    TB has been gone from NZ for many years now. No longer can we use this reason for the genocide happening in our forests. As for possums eating Kiwi and other native bird species eggs is just a joke. Recent admission that the greatest threat to Kiwi eggs was the common old Weka was yet another piece of evidence showing the possum to be rather harmless.
    However yes they do eat some of the young saplings coming thru and much prefer my fruit trees in spring than those even. I speak on a regular basis to pest control employees that work forests devoid of life. They say they could move through these forests using state of the art equipment at night eradicating way more possum but also utilising the carcass to other industries. They state they could achieve in 2 days what one month they are paid to do with poison. They also state no sacrificial wildlife such as birds would be accidentally killed using thermal and gun where as with poison they often kill the few remaining.
    Isnt it amazing that there are now only 5-7 Kea left inhabiting the Nelson lakes. DOC also admitting that their poison has been the highest factor in their demise. 40 Years ago there were many many 1000’s. So many that as a school child we could feed the cheeky ones that came into our town flying down from the heights.
    Do we really want to force many more species into extinction because of bureaucracy that has no real feel for what is happening in our forests. Money is the evilest of all and until we stop the people making fortunes spreading the vile 1080 to eradicate a possum that offers far less threat to species they supposedly target unfortunately this is what we will see.

  5. Bud jones JonesQSM says:

    It cannot be emphasized enough that these futile attempts of a war with nature with universal toxic nontarget poisons will not work. The great conservation writer,Bill Benfield points out that it is like pushing against a spring, it will always return to its default setting no matter the money/ effort thrown against it !!

  6. Stewart Hydes says:

    For how much longer is NZ going to “flog a dead horse” on possums?
    Or more accurately .. continue to squander millions of dollars of taxpayers’ money?
    I would venture to suggest that everybody involved in the anti-possum industry is just milking the situation .. sucking on the teat of taxpayers’ hard-earned dollars.
    And we are talking tens of millions of dollars, per annum .. over what has now been decades.
    It pays salaries .. helps to pay off helicopters .. and other mortgages.
    Some blood-suckers have managed to make a whole career out of it.
    And I can still find a possum just about as easily as I ever could.
    You’d think after all of this cost and effort .. they’d be practically extinct in one area or another.
    But they seem to be as widespread as they ever were.
    Which suits those milking the anti-possum industry just fine, I’m sure.
    You wouldn’t want your funding drying up now, would you?
    The whole fiasco fair gives me the sh#ts.

  7. Lew says:

    Years ago three of us when poisoning possums for 10 days yielded 1,200 possums the bird life was amazing but the kea found and followed our lines wrecking 15% of our skins. A few years later the same area was poisoned with 1080 the kea disappeared along with many other bird species. Possums never spread bovine tb it was cattle movements that spread it to possums and unfortunately possums were carriers of the disease and they were scapegoats for spreading tb leading to the use of 1080 poison. Never seen any bush destroyed by possums in fact their browsing encourages growth as the pruning of roses or other garden bushes and plants does.

  8. Charles Baycroft says:

    An outrageous lie told frequently and consistently becomes beleived to be the truth.

    Strongly entrenched irrational beliefs cannot be changed by logic and objective facts because of cognative dissonance.

    The Predator Free Ambition and false promotional narrative about saving the birds has been well constructed and promoted using the tax dollars of the people that are deceived by it but most are too well indoctrinated to question what they have been told.

    The 1080 deception is very much ike the 245T deception that polluting the ecosystems with toxic substances was absolutely necessary and could not cause any harm.
    The politically influential people involved in this deception seem to beleive that any collateral damage that occures is justified by achieving their biased and prejudiced personal goals.

    Unfortunately, the harmful effects of human exposure to 1080 are very difficult to identify and verify so people can be mislead to believe that ongoing exposure to such an extremely toxic substance will not harm them.

    The Predator Free by any extreme mneans avialable ambition is too politically imbedded in our system to be challenged by facts, logic or reason.

    The only way to stop this would be to convince enougbh people to stop voting for the political celbrites selected and prmoted by the influential elites of the National, Labour and Green political parties.

  9. Lew says:

    I think we better get used to the fact that possums and 1080 are going to be around according the AHB until 2050 the same time we are going to be pest free ?!?

  10. Mealie bug says:

    Well past 3 score years and 10 I am a mealy bug in a bunch of Chardonnay in the Nelson foothills. Mealy bugs are sapsuckers and have a few million years of history, 700 other plant hosts and are not that helpful to grape growers because they spread viruses that cause uneven ripening.
    Introduced fauna from weasle’s to wapiti’s and fish are pests at whatever population level according to the establishment – Ridiculous.
    If the people in charge were transported to a tent town at Williamsons flat in early winter and experienced that the peaks they were viewing extending in every direction are mearly one catchment in South Westland and one in Fiordland some reality might prevail
    ZIP Zero introduced preditors is an opportunity for extreme sucking on the Taxpayer tit
    Money is tight Few young people are interested in real work
    Management of introduced animals and fish would be self funding
    Only the blind totalitarians in charge can’t see it
    Meanwhile I’m looking forward to the ripe Chardonnay juice.

    Possum Response

  11. Bud jones JonesQSM says:

    I leave the final word on thispoison war with nature to Rachel Carson.
    “The more clearlywe can focus our attention on the wonders & realities of the universe about us, the less taste we shall have for destruction.

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