Scoping the potential to eradicate rats, cats and possums from Stewart Island / Rakiura

Transcription

1 Scoping the potential to eradicate rats, cats and possums from Stewart Island / Rakiura Quotes of note Southland mayor Frano Cardno on visiting Sirocco the kakapo on Ulva Island (Southland Times, 2 Sept 2006). It was a truly magical experience walking through the bush on Ulva Island. The lush undergrowth, the sounds of kiwi and kaka s call and you can t help reflect and say a quiet thankyou to the Ulva Island Trust in partnership with DOC, who have eradicated all pests from this beautiful island. The birds and bush are being restored to what we had in the past, what an investment for the future. Andy Roberts, Southern Islands Area Manager (Campbell Island Eradication Scoping Paper 2000). We only got to this position by doing what others believed was impossible! Contact details Brent Beaven PO Box 124 Stewart Island / Rakiura Ph: Fax: Brent@sircet.org.nz Page 1 of 55

2 Summary This document is only a draft. It is intended as a basis for debate and discussion. None of the ideas listed in here are decided, set in concrete or in any other way formalised. They are simply an initial series of thoughts that form a basis for us to have a discussion on. In other words your feedback will help shape this document!! There is no set timeframe for an eradication. We are simply exploring if it would ever be possible and what the issues are that would need to be addressed. Page 2 of 55

3 Contents Hyperlinks...Error! Bookmark not defined. Quotes of note...1 Summary...1 Contents...3 Stewart Island / Rakiura...5 Climate...6 Land Status Why do it? The path to now Potential Benefits Why is Stewart Island / Rakiura important? Why is getting rid of rats, cats and possums important? Getting to know the enemy Why eradication instead of control?...15 CONTROL...15 ERADICATION Can it be done? All individuals can be put at risk by the eradication technique(s)...16 What has worked before?...16 Eradication success by species...19 BAIT DISTRIBUTION OPTIONS...21 THE TOWNSHIP They can be killed at a rate exceeding their rate of increase at all densities. 26 TRAPS VRS BIOLOGICAL CONTROL VRS TOXIN CHOICE...26 WHICH TOXINS AND BAITS SHOULD BE USED?...26 Significant non-target risks to wildlife and pets, most of which can be mitigated, but some may not The probability of the pest re-establishing is manageable to near zero...31 Biosecurity...31 Contingency The project is socially acceptable to the community involved Benefits of the project outweigh the costs Ecological...35 Social...36 economic...37 Carbon Credits What will it take? COMMUNITY ENGAGEMENT...39 Diverse resource ownership issues Institutional issues Toxin Issues...40 RODENT CONTROL; PAST AND PRESENT...40 NON TARGET BYKILL...41 DEER HUNTING...43 Page 3 of 55

4 Water quality...43 Public safety How will we know if it has worked?...44 Result Monitoring...45 Outcome monitoring Knowledge gaps Timeframe Cost...48 Comparable costs...49 Bibliography...50 Appendix...51 Native birds...51 Lizards:...52 Freshwater fish:...52 Marine fish:...52 Invertebrates:...53 Pets...53 Stock...54 Page 4 of 55

5 Stewart Island / Rakiura [need photos of these sites and map of location] Stewart Island / Rakiura is the third largest of New Zealand s main islands, located approximately 30km to the south of the South Island (Lat. 46º 39 S to 47º 16 S and Long. 167º 20 E to 168º 14 E.). It is a large island, measuring 64km by 40km, with a land area of ha. Rakiura is composed of igneous rocks that form the large granite formations of Mt Anglem / Hananui (the island s highest point at 979m), the Ruggedy Mountains in the north of the island and the Tin Range and peaks of the South, including the exfoliating granite domes of Gog and Magog. Other significant features include Paterson Inlet, with the Freshwater and Rakeahua Rivers at its head. These two rivers drain from large, significant wetland systems. The eastern coast is characterised by bays and inlets such as Paterson Inlet, Port Adventure and Port Pegasus in the south eastern corner. The rugged western coastline features Mason Bay, a 12km stretch of ocean pounded sand. The island is surrounded by over XX small islands and rock stacks, including pest free Whenua hou, Taukehepa, Bench and Ulva Islands. There has been relatively little human settlement or development. Many alien species that are wrecking havoc elsewhere in the country (e.g. stoats, ferrets, pigs, goats, mice, etc), are not present. The only alien mammalian vertebrates present on Stewart Island / Rakiura are rats, cats, possums, deer and a small isolated population of hedgehogs. Because of these factors, Stewart Island / Rakiura is still predominated by large areas of relatively intact forest cover and a large array of rare plant and animal species. Rimu (Dacrydium cupressinum) is the most common tree, along with kamahi (Weinmannia racemosa), southern rata (Meterosideros umbellata), miro (Prumnopitys ferruginea) and totara (Podocarpus hallii), in what are the southernmost podocarp forests in New Zealand. Rimu and kamahi dominated forest covers about 60% of the land area. Manuka (Leptospermum scoparium), leatherwood (Olearia colensoi), inaka (Dracophyllum longifolium) scrublands make up a further quarter, with the remainder composed of grasslands, alpine turf, wetlands or bare rock. Page 5 of 55

6 CLIMATE 1 Any other climate graphs available?? Rainfall 1580mm Rain days per year 290 Sunshine hours 1700hrs Average summer max 16.6 Average winter max 9.9 Prevailing wind direction West Average wind strength 10 km/hr Calm days 73 LAND STATUS The land status of Stewart Island / Rakiura is shown below (figure). Approximately, 90% of the island is public conservation land, administered by Southland Conservancy of the Department of Conservation (DOC). Of this, ha (85% of total land area) is National Park. The next biggest land manager is the Rakiura Maori Land Trust, that is responsible for about 8% of the island. The last 2% comprises one small township (approx 400 people), located on the the Northern side of Paterson Inlet, extending around to Halfmoon and Horseshoe Bays. 1 data taken from SI tourism strategy Page 6 of 55

7 1. Why do it? This section covers the why questions, setting a context for why we should pursue the goal of eradicating possums, rats and cats from Rakiura. 1.1 The path to now Stewart Island / Rakiura has the potential to be the jewel in the crown of New Zealand s conservation and eco-tourism activities, as well as a leader in protection of forests and wetlands for their intrinsic value, for peoples enjoyment and as Carbon sinks. Management of alien animals on Stewart Island / Rakiura has been a contentious issue in the past, but DOC s current philosophy of talking with people, openness and allowing people to have input into managing their backyard has led to a productive, collaborative working relationship between DOC and the Stewart Island / Rakiura community. A key step in this has been the formation of a liaison group (comprised of community members, deerstalkers, Forest and Bird and Tangata Whenua) to advise and work with the Department to find solutions to managing alien animal species on Stewart Island/Rakiura. Some of the outcomes of this process have been: 1. A joint approach to the Minister of Conservation from the community, New Zealand Deer Stalkers Association (NZDA), Game and Forest Foundation and Forest and Bird, for more money to complete island wide possum management. 2. The local branch of the NZDA adopting 300ha of coastal forest at Mason Bay for ongoing rat and cat control to compliment DOC s possum control operations. 3. The group requesting that we look at the possibility of eradicating rats and cats from Stewart Island / Rakiura. This perceived benefit of conservation has been further developed by the formation of the Halfmoon Bay Habitat Restoration Project (see This project has captured the community s heart by trapping possums, rats and wild cats right around their houses, with a resultant increase in bird numbers. Not only has this community group more than quadrupled tui and bellbird numbers, they have reintroduced Stewart Island weka to the township area. This has all been achieved by a local trust with a band of dedicated volunteers. Subsequent to a visit from Trevor Gray (CEO of the Tindall Foundation), the community (via a range of formal and informal forums) were canvassed to get their ideas on where the Tindall Foundation could make a difference on Stewart Island / Rakiura. The idea of scoping out the possibility of removing rats, possums and cats from Stewart Island / Rakiura has met with unequivocal support. The main thrust of this funding is to develop a road map for getting to eradication. Key steps in this are identifying the barriers (e.g. lack of knowledge), developing further community buy-in, and putting costs and timeframes on each of these steps, Page 7 of 55

8 including the eradication itself. This will be a key initial document in identifying the feasibility of eradication and in inviting investment. This is far from a new idea. In 1983, Andy Roberts (DOC Southland) investigated the potential to fence and remove rats from the southern half of the island to protect kakapo. The idea of eradicating rats off the whole of Stewart Island / Rakiura has been talked about for at least the last eight years. It is about time that we had a serious look at the feasibility of this eradication suggestion. That said, this feasibility study has no set timeframe for eradication; it would only occur when the community wants it to, be that five or fifty years. 1.2 Potential Benefits Social, Ecological and Financial the triplet Single largest conservation gain in NZ Simple, tangible benefits identified e.g. rats not eating stored food, possums not eating garden plants. Eradicating rats, possums and cats from Stewart Island / Rakiura will have immense benefits on a number of fronts. Supporting Families and Social Services The fishing industry no longer provides the backbone of the Stewart Island / Rakiura economy. Until another major industry is developed, the community and some key social services will continue struggling to survive. For example, the school roll has dropped from approximately 70 to 14 within one generation. These problems are exacerbated by the small rating base of Stewart Island / Rakiura, making it unrealistic for the community to fund these services themselves. Eco-tourism is still in the early stages of development and that growth is dependant on the quality of products and hindered by perceptions of weather and access across Foveux Strait. Having the largest predator free island in New Zealand will cause a positive growth in eco-tourism that should result in a self sustaining industry, with financial flow-on to the community. The increase in job opportunities will encourage families to stay on the island and secure the school. It is the belief of many that a healthy community requires a healthy working economy. While the potential growth in tourism is hard to quantify, it is not hard to imagine the potential draw card of being able to see kiwi foraging on the front lawn of your accommodation or a saddleback sitting on your balcony. Of the visitors who go to Stewart Island / Rakiura each year, approx visit Ulva Island. This figure alone demonstrates the draw of pure nature. Encouraging Enterprise and Employment. With a better than world class environment available, Stewart Island / Rakiura s potential as a key eco-tourism destination will be realised. This will lead to a natural growth in the tourism sector (e.g. travel, accommodation, guides, meals, facilities, Page 8 of 55

9 etc). At the 2006 New Zealand Tourism Conference, Geoff Burns (chair of the tourism association), described Stewart Island / Rakiura as one of the undiscovered jewels of the world The opportunities created by the proposed eradication, will increase community employment and enterprise, innovation and entrepreneurship. Caring for our Environment and Preserving Biodiversity An eradication of rats, possums and cats from Stewart Island / Rakiura would be the biggest, single conservation gain that NZ could make. A ha predator free area would be a major step in stopping the decline of New Zealand s biodiversity. It would set-up large back-up populations of almost all of New Zealand s unique vertebrates, preventing their extinction. This would free-up conservation money that is currently used intensively managing these species, to be spent on other high priorities. For example, yellow-head / mohua are struggling to survive on the mainland of New Zealand. Rat plagues in beech mast years are decimating populations. In 2000, a rat plague extirpated the whole population at Mt Stokes and reduced the Eglington Valley population from over 200 birds, to less than ten. Stewart Island / Rakiura could support a safe and secure mohua population numbering in the tens of thousands. Other species that could benefit over time include: the kakapo, takahe, Stewart Island fernbird, South Island saddleback, Stewart Island robins, harlequin gecko, southern skink, kokako, southern NZ dotterel, both bat species and Stewart Island weka. This list does not even mention the many other species of birds, reptiles, invertebrates and plants that would increase substantially in number, reversing current trends of decline. NZ Biodiversity Strategy outcomes The New Zealand biodiversity strategy has made a bold stand for where it wants to see New Zealand s biodiversity health in For example, the desired outcome for biodiversity on land is: A net gain has been made in the extent and condition of natural habitats and ecosystems important for indigenous biodiversity. Scarce and fragmented habitats (such as lowland forests and grasslands, wetlands and dunelands) have increased in area and are in better ecological health due to improved connections and the sustainable management of surrounding areas. Some modified habitats are restored No further extinctions have occurred. Populations of all indigenous species and subspecies are sustained in natural or semi-natural habitats and their genetic diversity is maintained. Fewer threatened species require active recovery programmes and ex situ management. It is unlikely that all of our efforts combined will be able to achieve the goals we have set ourselves as a nation unless we start taking bold action. Removing predators from Stewart Island / Rakiura is an action that will allow us to achieve these goals. Page 9 of 55

10 The risk of failing to achieve eradication pales into insignificance when one considers the outcome of succeeding. 1.3 Why is Stewart Island / Rakiura important? endemism, etc how many?? Is there a list? Number of threatened species and lack of pests Stewart Island/Rakiura is the most accessible remnant of wild, pre-human New Zealand. It still retains a natural landscape, with many areas of exceptional natural beauty. The intact sequence of the island s indigenous vegetation is the outstanding ecological feature on land, an unbroken green mantle from subalpine shrublands down to thick coastal forest. The Mason Bay duneland, 12 km long in one magnificent sweep, is of national conservation importance because of its range of threatened plants. These include the sand tussock Austrofestuca littoralis, a rare creeping herb Gunnera hamiltonii, and the shore spurge Euphorbia glauca. Many of the northern beaches (Smokey, Hellfire, and Ruggedy beaches) are outstanding examples of natural dune systems free of major weed species and human development. Stewart Island/Rakiura is also notable for the southern tokoeka, a distinct variety of kiwi, as well as its high level of endemism (plants and animals that are only found on the island), including two skink species, two geckoes, weka, fernbird and the only breeding site of the Southern NZ Dotterel. The island is fortunately still free of many alien animal pests (stoats, ferrets, weasels, mice, goats, pigs, wallabies and rabbits), which have caused so much ecological damage elsewhere in the country. The freshwater ecosystems of Stewart Island/Rakiura are significant habitats for indigenous freshwater communities because of the absence of human-induced modifications and alien species. Indeed, of all the groups of indigenous species on Stewart Island/Rakiura, the freshwater communities are arguably the most intact. The Freshwater and Rakeahua Rivers, the main rivers feeding into Paterson Inlet/ Whaka a Te Wera, are of outstanding scientific value as two of the last remaining large, floodplain river systems in New Zealand that have remained essentially free of human induced impacts throughout their catchments. They also contain abundant populations of giant kokopu, a nationally threatened fish species. In their entirety, the island s freshwater communities are of great importance as the largest, most diverse examples of intact freshwater ecosystems that are probably representative of those which occurred in mainland New Zealand prior to the impact of European settlement. As far as forest cover goes, Stewart Island / Rakiura is as close to pristine as it is possible to get on mainland New Zealand. Unfortunately, this is not enough for many of the individual species that live on the island. The removal of rats, cats and possums is a necessary step if we want to keep many of these species. Page 10 of 55

11 1.4 Why is getting rid of rats, cats and possums important? Rodent impacts on indigenous biodiversity Reports from the community members of Stewart Island reflect community observations on the noticeable significant negative impact rats have had on bird diversity and population density, as well as... Result monitoring SIRCET? Possum impact on hall s totara, tree fushia, etc Rats, cats and possums are, without doubt, having a detrimental impact on our native flora and fauna, driving many to extinction. 1.5 Getting to know the enemy 2 Part of the reason that Stewart Island / Rakiura still holds high ecological value is the absence of a number of alien animals that are wrecking havoc throughout the rest of New Zealand. Nevertheless, the island s systems cannot sustain the long term onslaught of the existing alien species: rats (Norway, Ship and Kiore), possums, cats and deer (white tailed and red). This plan is focussed on the potential eradication of all three rat species, cats and possums. Norway rats (Rattus norvegicus) This is the largest rat in New Zealand. Most weigh in the range of g, with few weighed over 400g. The combined length of body and tail averages about 335mm. They have a stout body, heavy tail and relatively short ears. They swim readily and well, hence water rat is a common alternative name. This skill enables them to reach new islands unaided - depending on water temperature and sea conditions, up to 600m of water can be crossed. Norwary rats can climb with agility when necessary, but do so more rarely than ship rats. Where they co-exist, Norway rats usually remain on the ground, whilst ship rats occupy the trees. Norway rats still get aboard ships now and then, and this remains a potential source of new island invasions. The extensive world distribution of the Norway rat is almost entirely the result of accidental dispersal by man. The species is thought to have originated in northeastern China. It is now found across Europe, Asia Minor and southern Siberia to the Pacific coast, in China, Korea, Japan, temperate North and coastal South America, and locally in Africa and southern Australia. It has also become established on many oceanic islands from the tropics to polar regions. Norway rats were the first of the European rodents to become established in New Zealand. Almost certainly they got ashore in the late 18 th century from visiting European or North American sailing ships, especially the many sealers and whalers which began calling from 1792 onward. Today, Norway rats have a wide but patchy distribution in New Zealand. The most extensive populations are commensal with man in virtually all towns and cities, around farms and on cropland. Away from 2 Description taken from handbook of NZ mammals. Page 11 of 55

12 habitation, they are much less common, normally living only in isolated populations in wetlands and along watercourses and coastal areas. The Norway rat is omnivorous and has an opportunistic attitude to potential food. Dietry studies of wild rats in New Zealand have identified mainly seeds, fruits, leaves, fern rhizomes, insects, molluscs, crustaceans and annelids. Populations on islands rely to a considerable extent on shoreline foods collected at low tide or by diving. Vertebrate items such as eggs, birds and lizards are sometimes taken. Carcasses of dead animals are readily scavenged, including other rats caught in traps. Food may be hoarded in burrows and sheltered places. The terrestrial habits of Norway rats make native animals which live, roost or nest on the ground particularly vulnerable (e.g. seabirds). The rats take eggs and nestlings, and are also large enough to kill adults of most bird species. Many invertebrates, usually the larger ground-dwelling species, have suffered from the introduction of these rats. The impact of Norway rats on native reptiles and plants has been given little attention, but is likely to be high. The understorey and seedling vegetation on Ulva Island has changed dramatically since Norway rats were removed. Ship rats (Rattus rattus) Anything from James Russels work?? Ship rats are found throughout the world, from Sweden at 63 o N to Macquarie Island at 45 o S. Ship rats have been spread with human trading activities throughout the world from its evolutionary homeland in India (Oceanian form). Ship rats arrived in New Zealand later than Norway rats, probably in the early 19 th century, but did not spread until after They are now, by far the most uniformly distributed of the three rat species on the mainland. Ship rats are among the most widespread mammals on the New Zealand mainland, yet are seldom seen and little known, largely because they are nocturnal, often aboreal and shy. Ship rats are skilful climbers in forest and can scale rough vertical surfaces, traverse fine wires and run through lattices of fine branches. Ship rats are unwilling swimmers, but nevertheless are capable of swimming 300m. Ship rats are smaller than Norway rats at about 130g and about 340mm long. They are omnivorous generalists, yet can be very selective feeders. They eat both plant and animal foods all year round. The main animal food are arthropods, especially wetas, but also beetles, spiders, moths, and stick insects. Important fruits include rimu, miro and supplejack. They also eat birds and lizards. Ship rats are known predators of birds eggs and young, especially of forest passerines. On Big South Cape Island / Taukehepa in 1964, ship rats at high density browsed punui (Stilbocarpa lyalli) to ground level and defoliated five-finger (Pseudopanax arboreus); they also quickly eliminated five endemic bird species, one bat species and a large flightless weevil. Page 12 of 55

13 Kiore (Rattus exulans) The kiore is the smallest of the three species of rats in New Zealand at about 260mm in total length and about 70g in weight. They can swim, but not willingly or well (130m max). Kiore range through the tropical zone from continental and insular south-east Asia eastward across numerous islands in the western and central Pacific as far as Easter Island; north to Burma and to Kure Atoll of the Hawaiian group; and south to Stewart Island / Rakiura. Kiore were brought to New Zealand by the Polynesians and had become widespread throughout New Zealand between 800 and 1000AD. They were used for food by maori and the care taken in trapping and preparing Kiore suggests that they were much esteemed as food, even though they did not contribute a major part of the diet. It appears that mice and kiore have similar niches to each other and distinct from those of the two larger rats. This may explain why mice have not been able to yet establish on Stewart Island / Rakiura. Kiore disappeared from most of the North Island by about and from the northern part of the South Island by the 1890s. This may have been due to the invasion of the other two European rat species. They are now restricted to a number of offshore islands around the top of the North Island, islands in Cook Strait and on the mainland in Fiordland, South Westland and on Stewart Island / Rakiura. They eat a wide range of animal food sincluding lepidopteran larvae, wetas, centipedes, spiders, earthworms, ants, beetles, weevils, snails and less often, lizards and birds; and also the flowers, fruit, stem, leaf and roots of many forest plants. Their impact on New Zealand biota is demonstrated by some lizards, snipe, bush wren and a number of insects being restricted to kiore free islands. Feral Cats (Felis catus) The house cat was domesticated in the eastern Mediterranean at least 3000 years ago, from the North African wild cat. House cats have been taken to many parts of the world as pets and for rodent control. They are now present in most human settlements from the equator to high latitudes. From these settlements, feral populations have frequently become established. Cats were brought to New Zealand in the ships of the early European explorers, from 1769 onward. All ships of the period were infested with rats and carried a large number of cats to control them. Feral cats had probably become established in New Zealand by the 1830s to 1850s. They were introduced to many offshore and outlying islands by sealers and whalers, settlers, farmers, muttonbirders and lighthouse keepers. Feral cats are now widely distributed throughout all three main islands. On Stewart Island / Rakiura, feral cats feed mainly on rats (over 80% of diet); but birds, lizards and insects also make up parts of the diet. They will also eat carrion and often forage in coastal areas along high tide lines. Seabirds, if present, can make up a Page 13 of 55

14 large proportion of a cats diet. Cats have been implicated in the decline of kakapo and NZ dotterel on Stewart Island / Rakiura and a cat was killed at Mason bay with over 20 skinks in its stomach. Species have disappeared from many islands after cats were introduced (Stephens Island wren, saddleback, petrel species). Cats introduced onto Herekopare Island in about 1925 eradicated at least six species of land birds yellow-crowned kakariki, robin, fernbird, brown creeper, snipe and banded rail as well as large breeding populations of diving petrels and broad-billed prions. Both short-tailed and long-tailed bats are killed by cats, and cats may be a significant cause of mortality, especially at more accessible roosts. There have been reports of cats killing kiwi on Stewart Island / Rakiura. There is a strong body of evidence that cats have, and continue to have, a major effect on native fauna. Possums (Trichosurus vulpecula) The brushtail possum is endemic to mainland Australia, Tasmania and some offshore islands. It has the widest distribution of any marsupial in Australia. Possums were introduced to establish a fur trade similar to that which had flourished in Australia since the early 1800s. The first successful liberation was made in the forest behind Riverton in Most importations were made by the regional acclimatization societies. The total imports numbered only about , with over half of these coming from Tasmania. The consequent spread of possums was accelerated by additional liberations of New Zealand bred progeny of the original introductions. Legal liberations continued until the 1920s and possums were protected, off and on, to some degree until Possums are now found throughout all three of the main islands of New Zealand, as well as about 13 offshore islands. Possums are best described as opportunistic herbivores, feeding mainly on leaves. They also take buds, flowers, fruits, ferns, bark, fungi, invertebrates, birds and eggs. Selective browsing of preferred plant species intensifies the impact of possums on New Zealand forests. The effects are unquestionable; extensive canopy defoliation and mortality attributable to possums has been described in many areas. Selective browsing on particular species and individual trees eliminates some species and favours others less palatable to possums, resulting in a gradual change in forest composition. Nowhere in New Zealand have possums yet attained an equilibrium with native vegetation. Secondary effects of possum browsing may be less obvious. Canopies weakened by browsing may be more susceptible to windthrow, salt damage, pathogens, insects or climatic extremes. Possums may compete with native birds for resources. Possum browsing of leaves may reduce the production of flowers and fruit, with consequent effects on native animals. Possums may compete for nest sites with hole nesting birds (e.g. kiwi) and kill native birds and disturb their incubation. Page 14 of 55

15 1.6 Why eradication instead of control? Expand this section Also discuss the sensitivity of some native species and opportunities this provides higher reward Eradication is proposed as the best long-term solution for Stewart Island / Rakiura. This is mainly because eradication provides opportunities that control does not (higher reward). Many of our native species exhibit extreme sensitivity to depredation by even low levels of these alien species, making control an unsuitable option. Differences between control and eradication CONTROL Potentially feasible at any defined site, but generally limited in size, especially for rats. Targeted population is managed at prescribed levels. Population can be targeted in specific areas only, and these can vary according to need On-going management with associated monitoring. On-going quarantine and contingency measures (for targeted species) not necessary. Generally low-medium, on-going investment. Variable benefits dependent on effectiveness of control regimes. Multiple long term toxin availability. ERADICATION Essentially only feasible on islands where the risks of re-invasion by terrestrial pests is relatively low or can be managed. Every individual of the targeted population is removed. The total island area must be comprehensively treated A one-off operation with on-going surveillance. On-going quarantine and contingency measures required to prevent recolonisation. High initial investment, followed by relatively low on-going inputs. Significant potential benefits which improve over time. Short term pulse of toxin over only a few months. Page 15 of 55

16 2. Can it be done? Five principles have been identified which must be met in every case, for all target species to achieve eradication (Parkes, 1990, Bomford & O Brian, 1995): 1. All individuals can be put at risk by the eradication technique(s); 2. They can be killed at a rate exceeding their rate of increase at all densities; 3. The probability of the pest re-establishing is manageable to near zero; 4. The project is socially acceptable to the community involved; 5. Benefits of the project outweigh the costs. These principles are addressed individually in this chapter. 2.1 All individuals can be put at risk by the eradication technique(s). Can we cover the ground? Offshore islands map and discuss Section showing map of land area to be eradicated Timing of operation important especially when best by-kill cats Allocate issues identified in spreadsheet to titles WHAT HAS WORKED BEFORE? Update table from Russel et al World wide and especially within New Zealand, rat eradications have moved from experimental to standard practice for small to medium sized eradication areas. From 1960 to the mid 1980 s most eradications were of rats and were done by ground based techniques. From 1986, aerial spreading of bait by helicopters eventually led to the removal of rodents from Campbell Island (11,300 ha) in The most significant technical advance recently was not in the baits or the means of spreading them, but the availability of satellite navigational guidance systems (GPS). The capacity to precisely identify helicopter flight paths has enabled the elimination of refuge (unbaited) areas in which a few target animals could survive, as well as allowing coordinated approaches to the rapid spreading of baits over very large areas (Towns & Broome 2003). Further refinements, such as the use of differential GPS (DGPS) and the ability to download flying path lines on the day of the drops, has further increased the confidence in the success of this methodology. By the end of 2004, there had been 218 successful eradications of 17 different alien mammal species from New Zealand islands (Norway rats from 44 islands up to 11,300 ha and ship rats from 12 islands up to 88 hectares). The following table summarises eradication attempts for our target species. Page 16 of 55

17 Table 2.1.1: Summary of known completed eradications. Successful operations Failures Largest Successful Area (NZ) Norway rat 33 1 Campbell (11000 ha) Largest Successful area (World) Campbell (11000 ha) Ship rat 8 0 Pearl Island (500 ha) St Paul (700 ha) Pacific rat 27 1 Kapiti (1970 ha) Kapiti (1970 ha) Possum 16 0 Rangitoto (2321 ha) Feral Cat 9 0 Maungatautari (3500 ha) Rangitoto (2321 ha) Maungatautari (3500 ha) Multi-species eradications In New Zealand, eradications have historically been the domain of the Department of Conservation and limited to offshore islands. However, the 1990 s saw rapid growth in the uptake of the mainland island concept by community groups as well as the development of predator proof fencing technology. Suddenly a whole new era of eradications on mainland sites was born, with the fence creating the island. Naturally this led to an increase in multi-species eradications, primarily on the mainland. These Mainland Island eradications have ranged from 16ha to 3500ha. All have targeted multiple pest species usually successfully (see Table 2.1.2). In this table a species was not considered eradicated if that target species re-established from survivors or from re-invasion. Table 2:1.2: Mainland multi species eradication programmes Location Size Pest species targeted Eradication techniques and success rate Warrenheip 16ha Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Rabbits Ground based baiting, shooting and trapping programme. All species eradicated. Success for rats, cats and possums? Yes Page 17 of 55

18 Pigs Goats Deer Macraes Flat 19ha Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Rabbits Hares Pigs Maungatautari Ecological Island Enclosures 35ha northern enclosure & 65ha southern enclosure Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Rabbits Bushy Park 98ha Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Rabbits Hares Pigs Goats Deer Ecological Preserve Stewart Island / Rakiura Karori Wildlife Sanctuary 160ha 225ha Ship rats Norway rats Kiore Cats Possums White-tailed deer Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Ground based bait station, shooting and trapping programme. Most species appear to have been eradicated. Last mouse seen August Rabbit eradication ongoing. Aerial baiting using Pestoff 20R at 15kg/ha and then 8kg/ha with ground based follow up. Eradication successful all species in northern enclosure. Mice still in small numbers in southern enclosure as of June Aerial baiting using Pestoff 20R at 10kg/ha and then 10kg/ha. Eradication successful for all species except mice. Ground based techniques bait stations (100 x 50m), feratox and dogs for possums, dogs and live traps for deer. Operation still underway December Aerial drops using Pestoff 20R for rodents & rabbits 8kg/ha and then 7kg/ha. Ground based follow-up with hand broadcasting, trapping and bait stations. All species eradicated, but Yes Yes Yes Possums and cats only. Yes Page 18 of 55

19 Tawharanui Open Sanctuary Maungatautari Ecological Island 550ha 3500ha Rabbits Hares Pigs Goats Deer Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Rabbits Pigs Goats Deer Ship rats Norway rats Mice Mustelids Cats Possums Hedgehogs Rabbits Pigs Goats Deer mice now present. Aerial drop using Pestoff 20R for rodents at 8kg/ha and then 7kg/ha. Ground based follow-up with hand broadcasting, trapping and bait stations. Rats, possums, feral cats, hedgehogs eradicated. Mice and rabbits still present. Three aerial bait applications at 15kg/ha, then 8kg/ha, and 8kg/ha. Hunters used for pigs, deer and goats. Eradication successful for all species except mice. Two cats trapped (feeding on non-poisoned rabbits). Yes Yes ERADICATION SUCCESS BY SPECIES Rats Using aerial techniques, rats seem relatively easily eradicated. With the successful completion of Campbell Island, size seems to be less of a limiting factor. While most eradications have been successful, a small number have failed or partly failed to achieve their objectives. In most, if not all of these operations, failure was both predictable and avoidable. In one instance the island was found to be within the natural swimming range of the rats and was subsequently re-colonised. In another, Norway rats may have dominated bait stations and prevented access to some by mice which subsequently survived the operation (this could also be an issue for Kiore). Inexperienced operators and/or a failure to make toxic baits available to every individual rodent were the likely causes of failure in at least two other operations. The Department of Conservation has established peer review systems and a national Island Eradications Advisory Group. Their purpose is to review operational plans and project activities to minimize the risks of any further avoidable failures. Page 19 of 55

20 Eradication attempts where more than one rodent species have been targeted have been proportionately less successful in achieving total eradication than have singlespecies eradications. This is particularly so when the combination has involved a rat species as well as mice. Several projects which were successful in removing rats have failed to achieve mouse eradication as part of the same operation. Thankfully, mice are absent from Stewart Island / Rakiura. Successful eradication of all three species of rats was achieved on Pearl Island but Norway rats subsequently recolonised. [get this paragraph clarified by Jo Ritchie or Pim did rats turn up in tracking some time later or were these immediately after?] At Maungatautari, subsequent to the aerial baiting, rats were found alive in both small enclosures. Most were subsequently trapped six in the southern enclosure and four in the northern. Seven out of the ten had brodifacoum in their livers. No rats have been detected in either enclosure since March Some of the reasons that a small number of rats could have survived are (EPRO, 2006): Some young rats of almost weaning age may have still been in natal dens when the second drop occurred and survived long enough that when they emerged baits had degraded to where they were no longer palatable. Some individuals may simply be overly cautious making them less vulnerable to baits and/or detection methods. However this is unlikely as ship rats caught during the ground mop up were found to readily eat baits. Reinvasion may also have been a contributing factor. With careful planning and prior research (e.g. when are rats breeding?), these possibilities could all be avoided. Two bait drops were undertaken for the main mountain eradication at Maungatautari in late As a result of the difficulties of eradicating rodents from the enclosures, the potential for some rats to be totally arboreal and the large size of the main mountain, provision was made for a third drop. However no rats had been detected since these first two drops. Rats are the species we have the most eradication knowledge about. Eradication seems feasible but further research is likely to be required on the interactions of all three species with each other and with possums around baits. Possums Both aerial baiting and use of bait stations appear to be effective at eradicating possums but occasionally a small number do survive. At Tawharanui, two possums (a female and a juvenile) were caught in traps in the same location seven months after the second drop. It is likely they were a mother and baby that may have been in a den during the aerial baiting. No possums have been detected at Tawharanui since. Small numbers of possums (1-4) also survived baiting operations on Stewart Island / Rakiura and at Karori. In all cases, these individuals were finished off by ground based follow-up. [Maungatautari follow-up] This suggests that while some bait operations are successful at killing all possums, others miss a small number of individuals. Unless the reasons why there were some Page 20 of 55

21 survivors can be identified and resolved, then follow-up work should be planned for possum eradication on Stewart Island / Rakiura. Feral cats Was there pre-op diet studies done on Raoul or Maungatautiri?? Did rats make up 80% of diet as they do on Stewart Island? Given that theres not much else for them to live on, may increase chances of killing them? Cats appear to have been eradicated from all sites by secondary poisoning after aerial baiting. However, cats can avoid secondary poisoning if too few rodents (or rabbits) are poisoned, or if the cats are not hungry enough to eat the liver, stomach and intestines of prey containing lethal concentrations of brodifacoum. This was the case on Motuihe and Raoul islands (Gillies & Fitzgerald in King, 2005). Two cats were detected on the main mountain at Maungatautari in January 2007, post bait drops. Both animals were easily live trapped and were found to be male. It seems that these animals survived as they were feeding on rabbits that had not been exposed to bait. While we may proceed with the expectation that cats are likely to be eradicated as a by product of the rat and possum eradication operation, planning for some ground based follow-up work would be sensible. BAIT DISTRIBUTION OPTIONS Bait spreading is a critical aspect of any rodent eradication. It is imperative that sufficient bait for a toxic dose is available to every target animal on the island. Failure to achieve this will lead to failure of the operation. Helicopter broadcast poison bait Iriquois 3000ha per day work this out and write in. West Coast model Woody, how long, how many machines, etc. Arawhata operation as example? Aerial broadcasting is the most common technique used for applying bait on larger eradication areas. It involves the use of helicopters with purpose-built underslung bait buckets. A power-operated spinner at the base of the bucket assists to evenly spread the bait, typically to a distance of 40m from the bucket, generating an 80 metre wide swath as the helicopter flies along set lines at set speeds. More recent operations have employed differential global positioning (DGPS) navigational systems, which enable more precise positioning and for the true flight path of the helicopter to be accurately recorded. Analysis of this flight information during the operation assists in ensuring complete coverage of the treatment area. Aerial baiting, possibly in combination with other methods, will be the key way that baits could be delivered to every rodent and possum on Stewart Island / Rakiura. There is no way that baits could be spread on the cliffs or other steep areas by people on foot or in some vegetation types. Aerial baiting is also much faster than groundbased approaches, with consequently lower risks of rodents not encountering toxic Page 21 of 55

22 baits, and lower costs per hectare. With modern navigational equipment aerial baiting is also more accurate than ground-based operations, with consequently less risk of failure due to bait gaps. A recently-developed aerial application technique uses overlapping swaths whereby each swath of baits overlaps with the previous one by 50%. This means, in theory at least, all areas are covered twice. In practice this approach substantially reduces the risks of significant bait gaps - especially over steep terrain. While such an approach takes more time and is more expensive, the benefits from reduced risks of gaps outweigh these costs. Provided suitably eradication experienced operators were employed, with tried and proven equipment, there is a very high probability that baits could be delivered to every rodent on Stewart Island / Rakiura using this method. Fixed Wing broadcast operation Diagram/map example of fixed wing broadcast squared off area Fixed wing aircraft have been used for many years for fertiliser distribution and like helicopters have access to Differential GPS technology. They have only been discarded from island eradications due to their lack of precision in small areas. Nevertheless, fixed wing use tends to be considerably cheaper than helicopter and they have potential for a large load capacity. It has been suggested that large squared off areas of Stewart Island / Rakiura could be effectively and cheaply treated by fixed wing application. Helicopters could then be used to fill in all of the coastal or non-linear areas. For this to be used with confidence, further work would be required, including field trials, on refining distribution techniques from fixed wing, to ensure even bait coverage. Hand broadcast poison bait Hand-spreading simulates the effect of aerial distribution. It involves people carrying bait and dispersing a pre-determined quantity per set distance traveled at set bait intervals. It is useful for treatment of small areas where bait stations cannot be safely established, such as steep cliffs or to supplement bait station work (i.e. work on a small Stewart Island / Rakiura area has demonstrated that hand spreading was required on top of a 100m x 50m bait station grid to eradicate all three species of rat). This technique is limited to small areas and is not appropriate for the whole of Stewart Island / Rakiura due to the time required as well as the potential for gaps to occur. Consideration should be given to hand-spreading bait in buffer areas between the boundaries of aerial and ground-based operational zones, as well as in areas with bait stations (e.g. the township) where this is acceptable. Hand-spreading on Bob s Point, Stewart Island / Rakiura in conjunction with bait stations resulted in the eradication of possums, rats and cats. Page 22 of 55

23 Poison baiting using bait stations. Research on what bait station is best Bait station operations involve the establishment of a grid system of stations across the entire area to be treated. Often bait stations are left in position but unbaited to allow rodents to become accustomed to them, thereby reducing any initial neophobia before bait is made available. Bait stations are normally loaded simultaneously (ie on the same day) with toxic baits, and replenished daily, always ensuring that bait will be available every night at each station. Some rats and possums may occupy areas around particular bait stations, thus preventing subordinate rats and possums reaching bait. As a result, bait take may persist for some time after the poisoning operation. However, once the dominant animals have died, the baits become more accessible to others. Bait take may occur over several weeks, and even months, before all individuals succumb. The duration of a bait station campaign depends on various factors, including the density of rodent populations (basically, the more bait stations there are the quicker the operation will be). The correct spacing of bait stations is critical for rats in New Zealand it appears a grid system varying between 50 x 50m, 100 x 50m and 100 x 100m are appropriate. Bait stations require intense effort, not only in establishing a track network and putting the bait stations in place, but then regular filling for extended periods. Due to the size of Stewart Island / Rakiura, it is not practicable to use bait station over the whole island (XX req), but this technique could be employed in the township area. THE TOWNSHIP where is Lord Howe at?? Alan Saunders The eradication of alien pests from permanently inhabited islands is a relatively new step in the progression of eradication technology. It may be assumed that eradicating these pests from inhabited islands involves additional operational challenges compared to uninhabited ones. Already however, Midway Island (300 inhabitants) in the northern Pacific has been successfully treated, as well as some islands in the inner Seychelles group. While eradication was achieved at these islands, it is probably too soon to determine how successful they have been in preventing re-invasion. Treating the settlement area on Stewart Island / Rakiura does present particular and unique challenges and risks, but these are not of a magnitude that suggests eradication should not be attempted. Because of risks to pets, as well as public health and safety reasons (not to mention the strong negative social implications), the township and immediate surrounds should not be considered for aerial baiting. In these areas the same bait being used in the aerial operation could be applied in bait stations, perhaps in association with some hand- spreading. For an eradication to succeed, bait stations and other control methods must be employed in every house and every other structure (offices, sheds, shops, guest Page 23 of 55

24 rooms, public buildings, restaurants, etc) on the island. Baits would need to be placed in all ceiling cavities and attics, and all other likely locations where rodents might possibly occur. Ensuring such coverage is achieved would probably constitute the greatest challenge and present significant risks to the operation overall should eradication proceed. This will require virtually universal community support (or, at least, compliance) for the project. The key to achieving total bait coverage in the settled area on Stewart Island / Rakiura will be gaining the support of all local house owners for bait and traps to be laid in houses and other buildings. Fence Using ground based eradication techniques around the town, poses logistical issues in regard to aerial treatment of the rest of the island. These could be overcome by separating the two treatment areas with a predator-proof fence, effectively making them two independent operations. A predator-proof fence could be built from Paterson Inlet through to Lee Bay a distance of about 5km. This fence should be double hooded to create a barrier to movement both into and out of the township area. Careful placement of gates would ensure that people have relatively unimpeded access across the fence line (the fence line could also be utilised as a new walking track). As well as creating two independent operational zones, the fence may contribute a sense of security to local residents in regard to the aerial baiting a physical barrier that the aerial baiting will not cross. On top of this, the fence would have the added advantage of creating a containment area, should an alien species re-invade Stewart Island / Rakiura (i.e. if a rat managed to get to the wharf, we could be reasonably confident that it would be contained around the township). Conclusion Is success likely? Will follow-up monitoring/ control be required? Summarise above All individuals can be put at risk by eradication techniques. With rigorous eradication planning, the use of second generation anticoagulant baits (e.g. Pestoff ) and improved methods of aerial bait distribution, it is now possible to remove rats from large islands over 10,000 ha in area (Clout & Russell in press). The considerable experience of carrying out rat eradications in New Zealand should not be underestimated as a contributing factor to making this eradication feasible. Eradicating rats and cats from Stewart Island / Rakiura presents a considerable challenge. If an eradication attempt is undertaken it will be the largest island ever Page 24 of 55