ARTICLE : THE CASE FOR 1080

 September 2002 – The case for 1080

It’s that time of year again when the choppers take to the skies with their cargoes of 1080 and opponents take to the media channels with their increasingly vociferous complaints against the forest “carpet bombing”.

Amidst the claims and counter-claims being made by the various groups involved with the issue, it has become difficult to separate fact from fantasy.   Little wonder, when headlines shout warnings about 1080 poisoning water supplies or causing foetal abnormalities, that some thinking New Zealanders have become uneasy about the use of the toxin.

Matters will come to a head next year (2003) when the Environmental Risk Assessment Authority intends to re-evaluate the use of 1080.   The hearings will become the focal point for opposition but also provide the Department of Conservation (DOC) and the Animal Health Board (AHB) with a public forum to state their case for continued use.   Both agencies have compelling evidence that 1080 is producing results, not only in halting the decline in biodiversity but also in checking the spread of bovine Tb.

Why aerial 1080 works

One faction of the opposition to 1080.   Hunters are not in fact hostile to the poison itself but the way in which it is applied.   When 1080 is dropped from the air, not only possums die but so do deer.   The hunters argue that the poison should be used by teams on the ground, which would place it out of reach of deer, or that possums should be trapped.

Against that, DOC and AHB argue that in about one week a helicopter can cover the same area as hunters take in a year, thus avoiding problems of possums re-infesting areas that have been dealt with.   Not only is it a cheaper option (up to 10 times in some areas), but aerial 1080 kill rates are as high as 95 percent.   A successful aerial operation allows a conservation manager to quickly get on with other jobs.

The by-kill that comes from a poison operation is another plus.   Rats, mice, hedgehogs, feral cats and stoats either eat 1080 directly or feed on possum carcasses that are infected.   Since deer, goats and pigs are pests, their incidental kill is a conservation benefit.

Despite the rhetoric about how trappers should be used to catch possums, in practice they are not always up to the job.   Not only can they not access many of the remote, difficult-to-reach spots in the country, nor are there always the people available to do the work in, say, deepest South Westland.

Flourishing forests

One of the complaints from 1080 advocates has been that, while there has been a lot of anecdotal evidence that 1080 works, there have been too few scientific studies to back this up.   Says Cam Speedy, an animal control expert from the Tongariro / Taupo conservancy:   “We can certainly show results visually.   If we fly over areas of forest that we have been managing for eight or nine years, the bits of it that we couldn’t afford to get to are dead.”   But in the last few years, that lack of hard proof has changed as robust studies have documented a transformation in 1080-treated areas.

Tui and bellbirds find mistletoe a valuable source of nectar, and in fact play a vital role in pollination.   Coincidentally, one of the possum’s favourite foods is the mistletoe, which has steadily disappeared from throughout New Zealand.   Since the mid-90s, when aerial 1080 possum control operations began in the Tararuas, various mistletoe species have increased radically.   Similarly in the Landsborough Valley of the West Coast, there has been a three-fold jump in the amount of foliage on mistletoe plants since 1080 operations began in 1993.   Before an aerial 1080 operation in the Waihaha catchment in Pureora Forest in 1994, scientists had searched for signs of mistletoe plants but found nothing. A year after the operation, the first plants were observed, most likely sprouting from leafless haustoria (gall-like growths).¹

At Motatau, near Whangarei, half of 50 kohekohe trees surveyed in 1997 were almost totally stripped of their vegetation.   But by 1999, after 1080 and brodifacoum were used to kill 90 percent of the possums, only one tree had died and most of the rest had foliage cover in the normal range.   Landcare Research scientist Graham Nugent said this was a “spectacular recovery” and showed the value of possum control.   In an adjacent area, Okaroro, with no control, the increase in the kohekohe canopy was only 6 percent.

Northern rata, a favourite possum food, has improved in areas treated with 1080 in Tararua Forest.   Northern rata trees growing in sites that had received possum control two growing seasons before assessment were in better condition than those that were located in areas that had not received possum control.²   A 30-year possum control programme in the Otira Gorge using 1080 has shown spectacular results.   Giant southern rata, once threatened through defoliation, now flower regularly and possum-vulnerable fuchsia trees, along with other native plants, are thriving.

In 1999 the Department of Conservation carried out an aerial 1080 operation on a 5086-hectare area in the Pembroke Ranges, north of Milford Sound.   At risk was the rata / kamahi / totara forest from possum browsing.   Using “foliar browse index scores” (the amount of vegetation browsed in a specific study area), conservation staff recorded lush new growth on Hall’s totara the year after the operation, with some trees increasing their foliar cover by 40-50 percent.³

The birds are back

As forests have been restored, the positive effects on native bird species have been remarkable.   Kapiti Island provides one of the best examples.   There, possums were finally eradicated in the mid-80s with the help of 1080 dropped on the steep western cliffs.   In the six years between 1982 and 1988 the density of birds doubled, from about 15 per hectare to about 30.   This happened even while rats (now also eradicated) were still present.

1080 has been applied aerially in the Waipapa Ecological Area, part of Pureora Forest Park, in 1984, 1991, 1995, 1996 and 2001.   In two of these operations (1991, 2001) the entire Ecological Area was treated aerially.   It is no coincidence that the Waipapa Block contains the largest population of kaka on mainland New Zealand.   The estimated kaka population at Waipapa at October 2001 was 729 (with a confidence interval of between 533 - 999); by March 2002 this had jumped to 975 (confidence interval 717 - 1324).   Of 20 female kaka monitored at Waipapa until 2001, none had died.   However, at nearby Waimanoa Forest, at least five of nine nesting females were killed by stoats.   Without a doubt, these figures show the benefits of pest control, both through aerial 1080 and poison baits in bait stations.⁴

At Mapara Reserve in the King Country, there were only five breeding pairs of the North Island kokako in 1989 when conservation managers began a programme of intensive poisoning using aerial 1080 and other toxins in bait stations.   By 1997 the number of breeding pairs had increased markedly from five to 44, and during those years 180 chicks were fledged.   Nesting success at Mapara during this period was 40 percent, whereas by contrast in Rotoehu Forest, where no 1080 was applied, nesting success was only 15 percent. ⁵

Following a 1080 operation in Pureora Forest in 1996, 72 percent of North Island robin nests in the area treated with 1080 were successful.   This compares with 11 percent nesting success in an adjacent area where 1080 was not used.   One year after the 1996 poison operation, the robin population in the area that received 1080 control had increased by 28 percent, in contrast to the area that did not receive 1080 where the increase in numbers was only 3 percent.⁶

Although significant numbers of tomtits died during a 1080 operation at Pureora Forest, the overall tomtit population had recovered a year later to 75 percent of its pre-poison level.   They were able to rear two broods in a season, and even three on occasions. ⁷

Like a number of toxins in the environment, the active ingredients of 1080 (sodium fluoroacetate) occur naturally.   Around 40 plants in Australia, South Africa and South America contain the compound in their leaves, some of them at levels considered hazardous.   The toxin is produced by the plants to deter browsing animals.

In essence, then, 1080 can be summed up as:
• an “organic” herbal extract although, for reasons of cost, an artificially synthesised version with the same chemical molecule as the herbal active ingredient;
• something which is regularly consumed in trace amounts by a large proportion of the community in a “herbal infusion” form (namely tea), so accepted as being safe at low concentrations and not “inherently evil”;
• a water soluble product but of very low toxicity in its diluted form when found in water and the general environment;
• something which biodegrades within days in soils and water;
• is readily metabolised and excreted in sub-lethal doses, so
• non-accumulative in the food chain and general environment.
• able to be delivered in ways that selectively kills high proportions of pest animals, but very low proportions of native animals, and the selective removal of pests enables native species to thrive as a consequence.

Gerard Hutching
Freelance writer

¹ Sweetapple et al. 2002: Mistletoe (Tupeia antarctica) recovery and decline following possum control in a New Zealand forest.   New Zealand Journal of Ecology Vol 26, No 2.
² Phil Brady, TSO DOC, pers comm.
³ Pembroke possum control programme Stage 2 John O’Groats River to Kaipo River.
⁴ Terry Greene (in press)
⁵ Williams, Des, from article Microscope on Mapara
⁶ Powlesland et al (1999), “Costs and benefits of Aerial 1080 Possum Control Operations using carrot baits to North Island Robins (Petroica australis longipes), Pureora Forest Park in New Zealand”, Journal of Ecology, Vol 23, No 2.
⁷ ibid