Predator Free Stewart Island talks begin

Feasibility studies on options for the Predator Free Rakiura Halfmoon Bay Project are now out for the Stewart Island/Rakiura community to consider.

The Predator Free Rakiura Governance Group has published three technical reports covering options for predator removal, details of a proposed predator fence, and biosecurity requirements to keep the island predator-free. A summary paper has also been published providing a concise overview of the three technical reports and indicative costs of the project, and touching on possible key issues.

Predator Free Rakiura Governance Group member and Stewart Island resident Sandy King says the scenarios discussed in the reports represent an assessment of the most likely to succeed and realistic options for the removal of predators from the Halfmoon Bay Project area and are designed to stimulate discussion among all communities of interest and stakeholder groups.

“None of the options in the technical reports are set in stone – no decisions have yet been made. These reports have been prepared to support public discussion and are by no means a final project plan,” Sandy said.

“Members of the Governance Group care deeply about this special place and realise that achieving our vision is only possible if all the communities involved also commit to making it a reality.”

The Governance Group is holding drop-in sessions on October 5-6 at the Stewart Island Community Centre. Sessions will run from 2pm to 5pm and 7pm to 10pm on 5 October, and 9am-12 noon on 6 October. Authors of the reports will be attending to answer questions and listen to feedback.

Anyone who can’t make these sessions can ask questions and make comments on the Q&A page of the Predator Free Rakiura website, or talk to any Governance Group members.

At the same time discussions are beginning on the island, the Governance Group will canvas the views of other communities with an interest in Rakiura via newsletters, meetings and email, and encourage them to read the reports and provide feedback.

Copies of the reports can be obtained from the Four Square supermarket on Stewart Island, or downloaded from the Predator Free Rakiura website.

Get the reports


Governance Group members:

Sandy King 03 2191102 after 4pm or 0278679011
Jill Skerrett 03 219 1069 or 03 219 1417


The idea of making Rakiura predator-free has been around for many years. This project is exploring how the community can work towards this goal. The community is leading the project, with advice and support from the Department of Conservation (DOC).

The indicative project cost is estimated to be between $11 million and $32 million. This figure will depend on the size of the project area and predator removal methods, which are both factors the community will have input into. It also depends on research to determine the density of bait stations or traps for the three rodent species present on Stewart Island.

The project is currently funded by DOC and the Morgan Foundation, and the Governance Group is investigating future funding options, including ongoing costs.

These reports focus on the first step of the project – predator elimination around Halfmoon Bay. If successful, the second step will be predator elimination of the rest of the island.

Predators to be eliminated will be rats, possums, feral cats and hedgehogs.

The Governance Group is made up of representatives from communities and organisations that share an interest (be it cultural, legal and/or a personal connection) in Stewart Island including local residents, Ngāi Tahu, Tīitī Islanders and the Rakiura Māori Land Trust, Southland District Council, Environment Southland, fishers, hunters and business owners.

The technical content in these reports was developed by a group of practitioners with experience in removing predators from islands and mainland islands around New Zealand and overseas. This group included representatives from Environment Southland, DOC, independent contractors and local technical expertise from Stewart Island. Independent technical peer review was also undertaken by reviewers from three different organisations and represents some of the most highly regarded expertise in this field.




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Message from Predator Free Rakiura Governance Group

The Predator Free Rakiura Governance Group met for the 7th time on Thursday May 14th in Invercargill.

As most of you know, the Governance Group asked for detailed options to be prepared on how any removal of predators from the Halfmoon Bay area might be achieved. This work has been concluded and the papers will be published and distributed as soon as possible. They will be released alongside a series of public workshops. Dates and details will available in the next SIN.

Despite the research, some uncertainties remain. In particular one big unknown is the home range size of kiore on Stewart Island Rakiura and how this might change when more dominant rat species are removed. More research is needed into their behavioural patterns to ensure that any ground-based operation could be guaranteed to remove them. This research could make a huge difference to the potential cost of the project, and therefore its chances of going ahead.

The costs of implementation are still being refined, and can vary depending on the different options. Some of the options will not be affordable, but they will allow a good conversation . Further work is required on the costs to ensure an accurate estimate is achieved.


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Acoustic Recorder Forest Bird Survey

When talking about the concept of a predator free Rakiura, one of the comments that we often hear is that there is no need for this work as the birds are doing fine.  For those who spend a lot of time visiting sites outside of Halfmoon Bay, they would be well aware of just how incorrect this statement is.  For most of the island, the birds are disappearing.  In fact, my experience would be that if you exclude Halfmoon Bay and Ulva Island, then Stewart Island has less birds than most forested mainland sites.

To try to demonstrate this dramatic loss of birds, an acoustic survey of forest birds was completed at five sites about Stewart Island over the last month.  The survey was completed for the Predator Free Rakiura Governance Group.

Five sites were selected for survey.  Ulva Island represented a pest free environment.  The Dancing Star site represented a fenced and predator controlled environment.  Ackers Point represented the township, while Port William and North Arm represented areas where no long-term predator control has occurred.

Ten digital acoustic recorders (ARs) were deployed at each of the five sites between January 19 and 21.   They were then collected approximately 10 days later.   The ARs were programmed to run for 10 hours each day from 04:30 to 14:30.  They were deployed at > 200 m intervals along predator control network tracks for ease of retrieval.  In three instances (Port William, Dancing Start and Ackers Point) we sampled most of the available habitat.  At the other two larger sites (North Arm and Ulva Island) the recorders were deployed in similar clusters to the three small sites.  There was a five day period that all ARs we simultaneously recording (22nd – 26th) and we analysed 5 minute sessions after the dawn chorus (06:30 – 07:30), giving a total of 2580 samples.

Initial results analysed for kakariki indicated that over a five consecutive morning period kakariki were significantly more likely to be detected at the Dancing Star and Ulva Island Sites where pests are either absent or maintained at very low densities.

These are preliminary results only.  The large number of samples will take a while to work through and full results will be detailed in the next SIN.






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Bird call analysis using Acoustic Recorders


In last months SIN, I described how we were using digital recorders to look at the abundance of birds at a variety of sites.  The aim was to see if areas that had received long term pest control had higher numbers of birds than other areas.  It would also give an indication of the change in bird numbers that we could expect if we removed predators from around the township.  The sites selected were Ackers Point, Dancing Star Foundation and Ulva Island as areas that had received long term predator control, and Port William and North Arm as sites that haven’t had this control.


The following graph really speaks for itself.




Ulva Island is setting the standard for what we would expect from an island that has been pest free for almost 20 years.  The rat invasion and eradication a few years ago has obviously had little long term negative impact.  The other outstanding feature is the high level of birdlife at the DSF site, with about twice as many birds as the other sites.  This clearly shows the benefit of the predator fence and seven years of ensuring that any invading predators are removed.


If we set Ulva Island as the level that birds should be at in our forests, then you can see how poorly these native birds are doing in sites without any control of rats, cats and possums.  Perhaps also it suggests how much we have to gain should we follow through with the predator free Stewart Island concept.

Brent Beaven

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February 2015 SIN Update from Predator Free Rakiura Governance Group

The Predator Free Rakiura Governance Group met for the 6th time on Tuesday 10 February in Invercargill. It was quite an eventful meeting and the Governance Group felt it was worth providing an update.

As most of you know, the Governance Group has asked for detailed options to be prepared on how any removal of predators from the Halfmoon Bay area might be achieved. Drafts of these papers were discussed at the meeting. The detail of those options is still being refined, but at this stage all options being looked at involve a ground-based approach for the Halfmoon Bay project.

The indicative costs for implementation looked were significantly higher than initial estimates. The Governance Group had concerns whether this level of funding could be raised. Further work is required on the costs to ensure an accurate estimate is achieved.

Other issues also need to be explored further. For example, one big unknown is the home range size of kiore on Stewart Island Rakiura and how this might change when more dominant rat species are removed. More research is needed into their behavioural patterns to ensure that any ground-based operation could be guaranteed to remove them. This research could make a huge difference to the potential cost of the project, and therefore its chances of going ahead.

The Governance Group has requested further work on all three of the papers that will unfortunately delay their release, including exploring different options for any fence and the removal of predators.

If you have any specific questions you can contact any of the Governance Group or contact the project team via the Q&A section on the site.


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By Phil Bell (for the Predator-free Rakiura Governance Group)

Following on from the article in this month’s SIN (October), here are more details on each of the toxins outlined (with a table of pros and cons at the bottom). The majority of the information below has been adapted from the ‘Pesticide Information Review’ for each toxin – these are available via DOC on request if you would like even more detail.



Registered for what target species on Rakiura: possums

Registered for use: in bait stations; in bait bags; hand laying in paste form. Operators require a Controlled Substances License to use it in all formulations.

Trade names: Feratox™;Cyanara50 Cyanide Paste; Cyanide Paste for Possum Destruction; Trappers Cyanide Paste


Track record

Cyanide has been used in New Zealand for killing possums since the 1940’s.


How does it work?

Cyanide disrupts energy metabolism by preventing the use of oxygen in the production of energy, leading to respiratory failure and death.


Fate in the environment

Cyanide (in all formulations) is potentially hazardous until broken down and unrecognisable, likely to take several months depending on environmental conditions. Cyanide is rapidly lost from soil through volatilization, chemical reactions with other compounds, and biodegradation by microorganisms. Leaching of cyanide into water will occur. Cyanide is highly soluble in water.


Effects on non-target species

Cyanide appears to be toxic to a range of vertebrates and invertebrates. There is limited data on the toxicity of cyanide to reptiles and amphibians, though it would appear that cold-blooded animals such as frogs are less susceptible.


There are no LD50 values (the individual dose required to kill 50 percent of a population of test animals within a set timeframe) available for native New Zealand species. Native species found dead after pesticide operations using cyanide include kiwi, kea, tomtit, robin, silvereye, tui, weka and short-tailed bats. Most of the non-target deaths have been reported after handlaying of cyanide paste.


Accidental dog and cattle deaths have also been reported during pest control operations using cyanide. Cyanide is not accumulated or stored in any mammal studied, and cyanide biomagnifications (accumulation) in food webs has not been reported.


Time to death

Cyanide is seen as one of the most humane pesticides available for possum control, with death occurring within a matter of minutes (averaging 10-20). However, the rapid onset of toxicosis means that possums can become bait shy if they receive a sub-lethal dose of cyanide.



Registered for what target species on Rakiura: rats and possums

Registered for use: aerial application and hand broadcast (for island or ‘behind fence’ eradications); in bait stations

Trade names: Pestoff™


Track record

Brodifacoum has been used successfully in predator eradication programmes around the world, including the majority of island (e.g. Taukihepa/Big South Cape) and ‘behind a fence’ projects (e.g. Maungatautiri) in New Zealand. Brodifacoum in bait stations has also been used on the mainland to control brushtail possums and rodents, including on private farms. Many households throughout the country use brodifacoum to kill rodents that become a nuisance pest in their homes.


How does it work?

Brodifacoum is a second generation anticoagulant (meaning it is more potent and has a much longer action). It acts by interfering with the synthesis of vitamin K-dependent clotting factors. This increases the clotting time of blood and leads to death from haemorrhaging.


Fate in the environment

Soil type, temperature, and the presence of soil micro-organisms capable of degrading brodifacoum will all influence the degradation time, with baits potentially remaining toxic for months in certain conditions. As baits disintergrate, brodifacoum is absorbed into the soil where it is slowly degraded over weeks to months.


Brodifacoum has a very low solubility in water. The only residues of brodifacoum to have been detected in water bodies following pest control operations in New Zealand comes from a single sample of stream water collected 24 hours after bait application and within 20cm of baits in the streambed.


Effects on non-target species

Most terrestrial vertebrate species are likely to be susceptible to brodifacoum if enough is eaten either through primary (eating the bait directly) or secondary (eating poisoned animals or carcasses) poisoning. There is only limited information, principally for birds, on the toxicity of brodifacoum to native New Zealand species. All NZ trials to date have failed to show an effect on invertebrates that have fed on brodifacoum baits. Native non-target individual deaths, and residues, have been reported in a wide range of species after the use of brodifacoum.


The benefits of using brodifacoum to eradicate rats from offshore islands are also apparent. In all cases, any short term losses of individuals of native species are offset by the longer term benefits of removing the rats (e.g. successful breeding and juvenile recruitment).


Feral and domestic non-target deaths (cats, pigs, deer, and sheep) have been reported following brodifacoum use. Surveys of feral animals have shown that contamination (in both sub-lethally and lethally poisoned animals) has occurred where there has been sustained use of brodifacoum. Brodifacoum is not readily metabolised and is stored in the liver of sub-lethally exposed animals, where it can remain for many months.


There is an effective antidote (Vitamin K) for domestic animals poisoned with brodifacoum. However, long term treatment is required.


Time to death

The mean time to death of brushtail possums is 20.1 days and Norway rats is 7.2 days after ingestion of a lethal dose. This long latent period (time from consumption to death) means that bait shyness is unlikely to develop in animals receiving a sub-lethal dose.



Registered for what target species on Rakiura: rats

Registered for use: in bait stations

Trade names: Pestoff 50D™; RatAbate™; D-Block for the Control of Rats


Track record

Overseas use report successful rodent eradications on small islands up to 72 ha. More recent attempts to eradicate rats on small islands in Hawaii and Japan by aerial application of baits containing diphacinone have had mixed success (for multiple reasons). Successful rat control was recorded at some DOC mainland islands using bait station networks containing diphacinone.


How does it work?

Diphacinone is a first generation anticoagulant (meaning it is less potent than Brodifacoum). Like other anticoagulants, diphacinone inhibits the formation of vitamin K- dependent clotting factors in the blood, leading to multiple haemorrhages causing death.


As with all first generation anticoagulants, diphacinone is readily metabolised and rodents are far more susceptible to poisoning through multiple feeds than a single dose, meaning it is best used as a toxin within bait station operations.


Fate in the environment

Diphacinone is practically insoluble in water and slow to break down in the environment (taking weeks to months). It binds tightly to soil and is not readily leached or likely to be taken up by plants.


Effects on non-target species

The only information available for NZ native species relates to an estimated 25% mortality of short tailed bats in 2009 following the use of diphacinone paste in biodegradable plastic bags. Birds appear relatively tolerant of diphacinone, although birds of prey may be more vulnerable than others, particularly if they are exposed to regularly repeated doses.


Mammals are highly variable. Although dogs and cats will likely survive secondary doses received from scavenging single rat carcasses, they may be at risk from baits and multiple doses of contaminated food. Aquatic species are unlikely to be exposed to diphacinone if used correctly within bait stations. Invertebrates appear to be highly resistant to anticoagulant poisoning.


Residues in terrestrial living animals and carcasses can be expected and secondary poisoning has been demonstrated. Elimination time in the livers of moderately dosed deer and pigs were about 12 and 28 days respectively.


Time to death

Diphacinone baits at 3 mg/kg will kill rodents in 5–8 days. It is most effective in multiple doses where rodents can feed freely for 10 days or more without running out of bait.  The latent period means that bait shyness is unlikely to develop in animals receiving a sub-lethal dose.


Sodium monofluoroacetate (1080)

Registered for what target species on Rakiura: rats, possums, and feral cats

Registered for use: aerial application; hand broadcast; in bait stations; in bait bags; in paste form. Operators require a Controlled Substances License to use it in all formulations.

Trade names: Pestoff Exterminator Paste™; 1080 Pellets; 1080 Rodent Pellets; 1080 Feral Cat Bait; Pestoff Professional 1080 Possum Paste; No Possums 1080 Gel Bait


Track record

1080 is the most widely used poison for rat and possum control in New Zealand for situations where numbers need to be reduced rapidly over large areas. It is the main tool being used by DOC in the current ‘Battle for our Birds’ rat and possum control programme, in response to the widespread beech mast event. Of note for the Rakiura context, vertebrate pesticides containing 1080 are also registered for the control of feral cats.


Manufactured 1080 is chemically identical to the toxic compound found in some plants, including in black tea leaves (grown in India and Sri Lanka).


How does it work?

Monofluoroacetate is converted within animals to fluorocitrate, which inhibits the tricarboxylic acid cycle. This results in accumulation of citrate in the tissues and plasma, energy deprivation, and death. In other words, 1080 results in accumulation of citrate in the tissues and plasma, energy deprivation, and death.


Fate in the environment

1080 in baits may take several weeks to degrade depending on the environmental conditions but it breaks down into harmless substances. It does not accumulate in the soil.


Sodium monofluoroacetate is highly water soluble so leaching out of soil will occur. Water samples have been collected from streams following numerous pest control operations using 1080, and 96.6% of these samples contained no residues of 1080. Where residues were found most of these had less than 1 µg l1 1080.


Effects on non-target species

1080 is likely to be toxic to most native animals. There is wide variation in sensitivity between taxonomic groups with mammals more sensitive than birds and invertebrates (on a weight for weight basis). The risks 1080 operations pose to aquatic species is considered very low. There are records of a range of individual native birds found dead after aerial poisoning operations and many of these individuals have contained residues of 1080; however the populations have all survived and benefited.


Dogs are especially vulnerable and highly likely to die if they eat 1080 baits or scavenge animals killed by 1080. Feral deer population mortality from aerial poisoning operations targeting possums is highly variable and does not appear to be consistently influenced by toxic loading, sowing rate, prefeeding, or bait type. Most estimates of deer kill range between 30 and 60%. 1080 has a relatively short half-life in sub-lethally dosed animals and it is metabolised and eliminated from living animals within days – it does not accumulate in the food chain. However, 1080 can persist in carcasses for months.


Time to death

Most deaths of pest species occur 8 – 48 hours after ingestion of a lethal dose. The short latent period means that bait shyness can develop in animals receiving a sub-lethal dose.


4-aminopropiophenone (PAPP)

Registered for what target species on Rakiura: feral cats

Registered for use: in bait stations. Operators require a Controlled Substances License to use it.

Trade names: PredaSTOP™.


Track record

PAPP is a newly registered toxin, and as such it does not yet have the track record to illustrate its effectiveness. Trials in Australia have used it in feral cat eradications on small islands.


How does it work?

PAPP induces methaemoglobinemia by rapidly oxidising haemoglobin to methaemoglobin in red blood cells. Methaemoglobin blocks the blood’s ability to carry oxygen, resulting in the brain, heart and other muscles being starved of oxygen. This leads rapidly to unconsciousness and death due to heart failure. It is similar in effect to carbon monoxide poisoning


Fate in the Environment

There is limited information on its fate in the environment.  PAPP is soluble in water and will leach through soils.


Effects on Non-target Species

Weka are the only native species for which an LD50 has been estimated (~ 568 mg/kg). Overseas studies indicate that most species of bird appear to be relatively tolerant to PAPP. However, ducks are known to have a relatively low LD50 compared to other avian species. Reptiles may be vulnerable to PAPP. No non-target deaths were reported during field trials to gain registration for PAPP.


The metabolic pathways involved in the detoxification and excretion of PAPP vary between species. As a result, the toxicity of PAPP varies significantly between species, with mammalian carnivores being particularly sensitive.


PAPP and its metabolites are rapidly excreted so most of a sub-lethal dose will be cleared within 24 hours. There is no available information on residue levels in carcasses of poisoned animals.


If PAPP is used inappropriately, it could kill companion animals such as cats and dogs. An effective treatment for PAPP poisoning is available (methylene blue). However, the rapid of onset of symptoms in acute PAPP poisoning may limit the efficacy of treatment.


Time to death

The onset of symptoms and death is rapid after ingestion, within 246 minutes for feral cats.


Table 1. The pros and cons of each toxin described above


Toxin Pros Cons
  • Considered a fast acting, humane toxin for possums
  • Less risk to pet dogs
  • Short caution/withholding period (for hunting and consuming deer) of only 2 months required
  • Requires prefeeding to gain acceptance of the toxic bait
  • Fast acting toxin can result in bait shyness (which can last for 2 years in possums)
  • Significant non-target risks to wildlife (especially weka)
  • Risk of secondary poisoning to feral cats considered to be low
  • Bait is relatively expensive
  • Has successfully eradicated rats from some islands
  • Readily metabolised so they have a shorter persistence time in living tissue (than second generation anticoagulants)
  • Antidote available (Vitamin K)
  • Requires rodents to consume more bait over a longer time period to receive a lethal dose (at least 5 consecutive nights)
  • Possums are relatively resistant to first generation anticoagulants
  • Less effective as secondary poisoning for feral cats (than second generation anticoagulants)
  • Significant non-target risks to wildlife and pets
  • Caution/withholding period (for hunting and consuming deer) of 8 months usually required
  • Proven track record in successful eradications around the world
  • Registered for use for rats and possums
  • Slow acting so can enable secondary poisoning of feral cats
  • Well known effects enable better mitigation planning to minimise non-target impacts
  • Registered for aerial application in areas enclosed within predator-proof fence
  • Antidote available for pets and humans
  • Policy restricts use of brodifacoum on DOC managed land – exemptions can be applied
  • DOC policy prohibits the use of brodifacoum targeting possums – exemptions can be applied
  • Significant non-target risks to wildlife and pets
  • Can remain in the liver of sub lethally poisoned animals for months (including deer)
  • Would require a 36 month caution period for deer hunting and consumption
Sodium monofluoroacetate (1080)
  • Less risk to non-targets and people as it degrades quickly and is metabolised rapidly
  • Registered for aerial application
  • Registered for use on rats, possums, and feral cats
  • Very well studied with a large knowledge base of impacts and effects developed
  • Well known effects enable better mitigation planning to minimise non-target impacts
  • Deer repellent available
  • Likely to achieve secondary poisoning of feral cats
  • Fast acting toxin can result in bait shyness (which can last for 3 years in possums)
  • Can be detected and avoided by some individual rats so it is not suitable for eradication (where no individuals can be left)
  • Significant non-target risks to pets (dogs are highly susceptible)
  • Deer repellent will not result in zero deer deaths
  • Requires prefeeding to gain acceptance of the toxic bait
  • Caution/withholding period (for hunting and consuming deer) of 9 months usually required
Para aminopropiophenone (PAPP)
  • Single feed toxin – only one bait needs to be eaten for a lethal dose
  • Reduced non-target impacts compared with other toxins
  • Highly toxic to mammals – carnivores are particularly susceptible, so ideal for feral cats
  • Veterinary treatment for PAPP poisoning available (Methylene blue)
  • Short caution/withholding period (for hunting and consuming deer) of only 1 month required
  • New toxin – never been used in eradication or long term control programmes
  • Requires prefeeding to gain acceptance of the toxic bait
  • Must be encased in raw minced meat
  • Bait station used must exclude non-target animals
  • Pets are at risk if they ingest the bait
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Response to Ron Morrison letter in September SIN

In the September Stewart Island News, Ron Morrison reiterated his idea of delaying the eradication until the technology for eradicating the rest of the island is perfected, as it might circumvent the need to use a predator fence.

We have responded to similar questions on the website and in the August issue of SIN, so we will briefly revisit those responses before we look at the couple of new points Ron has raised. The Governance Group has previously responded to Ron’s suggestion, which we will summarise below:

  • Buffers/ zones are unproven technologies for an eradication. We don’t know if using a buffer or zones would work in a large-scale eradication, let alone their cost. The Governance Group doesn’t think it makes sense to wait for a technology that we don’t even know will work – a fence may still end up being needed. Sandy King’s article in the September SIN reinforced the difficulties in using a buffer as opposed to a barrier given current technology.
  • We do have the technology to complete the Halfmoon Bay project, so why delay those benefits? The Governance Group has discussed the economic, social & ecological benefits of the Halfmoon Bay project extensively. We have conservatively estimated the benefits at $10m in annual tourism revenue, an additional 88 jobs and an increase of 119 people to the population of Oban (including 9 extra children in the school). Waiting for an unproven technology would mean delaying these benefits and possibly putting them permanently at risk – as by then funders may have moved on to other projects.
  • There is a need for significant investment to make Predator Free Rakiura a reality – why make that investment without the community on side? The answer is it won’t happen without the community onside, meaning the island, many native species and greater NZ would miss out. An eradication over the whole of Rakiura and surrounding islands could cost around $50 million. Even before this can be done, a massive investment needs to be made in research and development to work out how such an eradication would be undertaken. The government and other funders are unlikely to fund this work if it was unclear that the Oban community was behind the project.

Ron raised a few new points in his letter to the September SIN.

Firstly he pointed out that Predator Free Oban does not have the same marketing appeal as Predator Free Rakiura. This is a fair point, but it overlooks the points made above. A Predator Free Oban would spur investors to fund the research needed to advance a Predator Free Rakiura. Without a Predator Free Oban, it is unlikely the investment needed for a Predator Free Rakiura would be made. Funders with an interest in predator free New Zealand are likely to focus on other projects, such as Great Barrier Island, the Chatham Islands, or peninsula based projects on the mainland (such as a possum-free Coromandel or Northland).

Secondly, Ron criticised the Economic Appraisal because it did not “encourage the community to develop a strategy that will capitalize on the opportunity being offered by Predator Free Rakiura.” A strategy would certainly be a good idea if the Predator Free Rakiura proposal proceeds. As the report mentions, the benefits will only be realized by those willing to take the opportunities a project of this scale presents. However, preparing such a strategy doesn’t make sense until all partners are in agreement to move ahead with the Predator Free Rakiura proposal.

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Response to Vicki Coats letter in September SIN

In the September SIN, Vicki Coats asked what impact the proposals for a predator free area in Bluff and reducing the visitor fees on Kapiti Island might have on the projected outcome of the Predator Free Rakiura project. She also asked if the new self-resetting traps could be used for any eradication in the place of a fence and poison. She also asked if her survey results could be published on the website.

As well as posting her question to the September SIN, Vicki also posted her questions on the Predator Free Rakiura website at the same time. So on August 25th well before the SIN was published the results of Vicki’s survey were published on the Predator Free Rakiura website. And we also answered Vicki’s more detailed questions at that time on the Q&A page, which are re-printed below:

Thanks for your questions. Your survey is up on the site.

If the Bluff project proceeds (it is early days), it will be a one of a number of similar small fenced areas on the mainland – like Zealandia and Maungatautari. This is nothing on the scale of Rakiura/ Stewart Island – even the Halfmoon Bay project is many times larger than these mainland sanctuaries. It would however provide a great safe haven for birds migrating between a predator free Rakiura and the mainland.

There are a number of factors which make Kapiti unique, which is why we didn’t include it in our study of predator free tourism. With no wharf or airstrip on the island, travel there is difficult and sporadic. Overnight stays are expensive and capacity is small, so it is only really of interest to small groups going kiwi spotting. DOC dropping its fees is mostly of relevance to visiting school groups.

As to your question on Goodnature traps, DOC is undertaking work to test the concept of defence zones or buffers consisting of traps (including single action, and Goodnature resetting devices) and toxin in bait stations to prevent rat and possum reestablishment into predator free areas; however it is still very early days. Validation of this technique is not expected for a number of years. While the results to date are promising, the technique is not proven to be effective or ready to be rolled out at the scale required for the Stewart Island context.



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Buffer or Barrier?

Article by Sandy King

Following the article about “The Fence” from the PFR Governance Group in August’s SIN I thought I’d take a closer look at the difference between a buffer zone and a physical barrier, and the relative effectiveness of each when dealing with invasive predators. Conveniently, there are easily accessible examples of each – found in the work SIRCET are doing from Ackers Point to Golden Bay Road vs a low key DOC project on adjacent Native Island.

The GG article began with these statements:

One of the key principles for undertaking any eradication is that reinvasion can be managed. Some sort of barrier is needed to slow reinvasion, but so far the only barriers that have been shown to work are water (which is why eradications have happened on islands) and predator fences.

The important word to note here is “slow” – the idea that a barrier such as a fence will completely stop all reinvasion is outdated and unrealistic, we now know to expect some reinvasion in most cases (except perhaps where the barrier is extensive, such as the expanse of Southern Ocean surrounding Campbell and Macquarie Islands), and that the systems in place to manage reinvasion are essential and the key to a successful project.

The SIRCET project has no physical barrier, instead the project area has been divided into 3 zones, the Core, the Buffer, and the Community zone – effectively a buffer for the Buffer. I think every local is aware of the persistent hard work and dedication that has gone into the SIRCET trapping programme over the winter months. The Core area, from Ackers Point to Leask Bay/Evening Cove, and the Buffer now have lines 75m apart with a rat trap every 25m along those lines – a 75x25m grid. During an intensive trapping session those traps were checked daily for about 10 days in early autumn, every second day until June, and subsequently twice weekly. 623 rats were caught in the Core and Buffer zones between April and June.

Native Island, on the other hand, does have a physical barrier – albeit a bit “leaky”. The narrow stretch of water separating Native Island from the mainland is easily within swimming distance of rats and reinvasion is a certainty. The question is whether this leaky barrier is enough to slow reinvasion so that occasional re-invaders can be caught faster than they can breed.   Regular SINers might recall an article in January 2014 in which the Native Island project was explained – testing whether Goodnature self-resetting traps would get rid of rats and possums. Locals were invited to join the team on their monthly checks, and recently I took up the invitation and spent a morning with the guys checking traps and chatting about what they’d achieved. They have 146 Goodnature self-resetting rat traps set on lines 100m apart with a trap every 50m (a 100x50m grid), checked and serviced monthly. It is impossible to tell how many rats have been killed, most carcasses are either removed by weka or decompose in the interval between checks. However, they monitor progress using tracking tunnels (tunnels with inkpads and tracking paper, baited for one night each monitoring period. The results are presented as percent of tunnels showing rat tracks). They monitored rat numbers before traps were first set in November 2013 and got 84% tracking, which is “quite high”, and have since been monitoring rat numbers frequently.

The same monitoring technique has been used by SIRCET to monitor rats remaining in the project area for a number of years. In spite of huge numbers of rats killed monitoring still shows high tracking index results. More specifically, the intensified trapping effort in the Core area hasn’t decreased the tracking index to below 10% – a prerequisite target for the introduction of sensitive bird species such as robins (a core goal of SIRCET’s Halfmoon Bay Habitat Restoration Project). The following table compares tracking results for the SIRCET Core and Buffer zones with Native Island.

SIRCET – Core SIRCET – Buffer Native Island
November 2013 No data No data 84%
January 2014 No data No data 46%
March 2014 25% 30% No data
April 2014 12% 70% 17%
June 2014 15% 40% 30%
August 2014 No data No data 6%
Sept 2014 42% 56% No data


It would appear from this that even a “leaky” barrier is enough to slow rat reinvasion to Native Island to the point where it can be managed; even with a wider trap grid, less frequent checking and an unproven type of trap, although it remains to be seen whether the downwards trend continues and is maintained.

SIRCET has achieved a lot over the past 12 years as a result of its trapping effort; during annual bird call counts numbers have consistently been higher inside the project area than out, and monitoring shows improvements in the vegetation. However one of their aims is to reintroduce some of our rare, precious and vulnerable species – to have saddleback/tieke resident in our gardens, and to do this the rat tracking index needs to be consistently 0%, i.e. rat numbers are so low they are undetectable. Saddleback and rats cannot co-exist and there are plenty of examples to prove this. When I talked to Trustees their frustration at not yet being able to attain their ultimate goal was palpable.  The question of whether a barrier would serve their purpose better than a buffer was met with wistful looks and muttered comments about the cost of a fence. However in the long term the initial cost to erect a fence may be comparable with, or even less than, the cost of maintaining the effort that went into trapping from April till June which resulted in an encouraging decrease in rat abundance in the Core zone, not to mention the unquantifiable costs of having your ultimate goal always somewhere beyond the horizon.

Thanks to SIRCET for sharing their data and thoughts, and for their efforts to enhance our local environment, and thanks to DOC for the data.


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Kia ora koutou katoa, Stewart Bull is my name and the natural environment is my game. As part of the Predtor Free Rakiura Governance Group I am representing the Rakiura Titi Island Community which has a membership of approximately 16,000 people.

I am currently a representative on various bodies and committees, Chair of Rakiura Titi Committee, Te Runanga O Ngai Tahu representative on the Rakiura Titi Island Administering Body and a Member of Southland Conservation Board, member of Whenua Hou Committee, Kaitiaki Roopu (Iwi liaison) with Department of Conservation, Te Ao Marama (Murihiku Resource Management Group), Chairman of Oraka Aparima Runaka, member of Coal Island Trust, member of Fiordland Marine Guardians

I have made myself available as it allows me influence for the betterment of the environment and the activities that take place in and around the natural world.

The Rakiura Titi Island community in conjunction with the Department of Conservation undertook a pest eradiation exercise on Taukihepa (Big South Cape) approximately 6 years ago.

We used helicopters to distribute Brodificom all over the island as well as manual distribution in caves and under houses, etc.

It is with pleasure that I can state this was a successful exercise.

Although some of the birds such as weka took a bit of a hit, they have recovered to such a state as to become a nuisance. The recovery of the tui, bellbird, robin, parakeet, morepork etc., has steadily increased as each year passes.

The insects and plant life have also made a noticeable recovery.  The weta had all but disappeared but now on a still night it sounds like rain on the leaf litter as the weta ping about.

I just wanted to share these thoughts as it is a prime example of the positive outcome that can be achieved by removing pest species.

If we apply cost and benefit analysis then benefit definitely wins, therefore imagine the outcomes that we will see as a consequence of ridding Rakiura (Stewart Island) of pest species that are predating our bird life. I have no doubt it will be similar to that we are seeing on the Titi Islands.

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