by Tony Orman
Back in 1917, the Auckland Acclimatisation Society in it’s annual report discussed possums saying “We shall be doing a great service to the country in stocking these large areas with this valuable and harmless animal.”
How things changed to the point in recent decades the possum has been demonised, vilified and subjected to cruel attempts by slow killing poisons to exterminate them. Primary schools have held “pest days” where youngsters were taught to inflict cruelty and heap disrespect on young possums. Some scientists hopping on the “pest” band wagon with its allocation of money have been monetarily moved to term the herbivore marsupial as a predator.
Back in 1961 I wrote in article in the “Auckland Weekly News” with the title “A query about the Possum – has it’s danger been exaggerated?”
Strangely the article drew no comment and I have not changed my views since, in fact probably only reinforced them.
For many years government and its department of Conservation proclaimed 70 million possums were ruining the forests and spreading bovine Tb among stock herds.
The weapon is 1080 poison, a toxin first developed as an insecticide in the 1920s but which knows no boundaries as far as living creatures go. It kills insects, birds and animals – anything that breathes oxygen. 1080 poison programmes are run by government departments on conservation grounds, and also the Animal Health Board on eradicating bovine Tuberculosis (Tb).
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 to dispute the mythical 70 million figure. Their estimates range 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.”
South Auckland possum hunter Wyn Hibberd was 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, big salaries at stake. They’ll prop up the myth with propaganda plus the government owns the 1080 factory.”
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.
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 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.
The Possum – demonised
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 harvesting 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 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.
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 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.
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 20 years ago and have been in a gradual decline for the last decade or more.
These realities seem ignored by DOC and AHB who frequently use the excuse to topdress with 1080 poison with the farcical “70 million possum” figure or “it’s remote country.” But if possum populations are low and stable, then the dropping of 1080 is pointless but at the same time, ecologically threatening – and a gross waste of valuable taxpayers’ money!
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 with in 2010, possum fur worth $110 a kilogram compared to $3 a kg for crossbred sheep wool.
There is interesting research and told of the work of botanist-hydrologist 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. Late last year in the Nelson Lakes National Park, defoliation of large tracts of beech forest were found to be naturally caused by caterpillars – not possums.
Possums are often berated as a spreader of bovine Tb in farmed cattle and deer herds. The Animal Health Board (AHB) is a major user of aerial 1080 poison.
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.
Treasury – “Tb spread by transport of infected stock”
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.”
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 %.
A 1995 study of 21 properties in Otago and Southland found that Tb infected cattle areas had significant populations of Tb infected ferrets. The study indicated tuberculosis ferrets probably transmit infection to stock. This study was outlined in the NZ Veterinary Journal -” The prevalence of bovine tuberculosis infections in feral populations of cats, ferrets and stoats in Otago and Southland.”
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 80 to 85 accurate. So that means one in 10 cattle can be Tb infected but give an erroneous “clear” of Tb reading.
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 2016 Agriculture Minister Nathan Guy told Parliament of 9830 possums tested, not one had Tb.
It is not only hunters who should be concerned at the widespread aerial topdressing of public lands with 1080. Conservationists should be too. The decline in native birds such as the kea is not due to predators. It is very probably due to the indiscriminate spreading of 1080.
A good percentage of deer are killed 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.
Mistaken belief that there is a possum problem is an excuse for OSPRI and DOC to dump more poisons.
Nathan Guy 2016 – 9830 possums autopsied – none had bovine Tb