Exotic rodents on Australian islands: issues paper

John Parkes and Penny Fisher Landcare Research P.O. Box 40 Lincoln 7640 New Zealand Email : Parkes j @landcareresearch.co .nz

James Russell University of Auckland Auckland New Zealand

Keith Morris Department of Enviromnent and Conservation Western Australia

Prepared for: Department of Environment and Water Resources Canberra Australia

Date: June 2007

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Contents

Summary of key questions for the workshop

1. Introduction 2. The scale of the problem 3. The culprits

3.1 Ship rats 3.2 Norway rats 3.3 Polynesian rats 3.4 House mice

4. Planning rodent management 4.1 Justification - impacts of rodents on biodiversity 4.2 Feasibility plans

4.2.1 Strategies to fix the problem (a) Preventing invasions (b) Eradication and preventing reinvasions (c) Quasi-eradication (d) Sustained control (e) Do nothing

4.2.2 Tactics and costs to fix the problem 4.3 Operational plans 4.4 Audit of benefits and consequences 4.5 Predicting and managing adverse effects

4.5.1 Adverse effects of the control - non-target impacts 4.5.2 Adverse effects of rodent removal

4.4 Planning to include other pests 5. Prioritising islands 6. Legal issues 7. Education 8. Capacity building 9. Case studies

8.1 Lord Howe Island 8.2 Barrow Island

10. Key references

11. Appendices 11.1 Australian islands known to have exotic rodents 11.2 Australian islands from which exotic rodents have been eradicated 11.3 Notes on biosecurity options for different island types

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Summary of key questions for workshop

Base information 1. Should the databases on Australian islands with exotic rodents be completed? 2. Are there key gaps in information - e.g., invasion risk factors , presence of non­

targets, inhabited or not? Accountabilities

3. Which agency and who makes the decisions to plan and act against rodents in each jurisdiction?

4. Who should ' deliver' the rodent control - building agency capacity or contract out to experts?

5. What are the legal obligations and constraints in each jurisdiction? 6. What are the current laws and practice to ensure ships are free of rodents?

Rodent biology 7. Are there predictable seasonal or yearly changes in food supply and breeding of

rodents on different types of islands so we can apply control at the best time? 8. Are there critical knowledge gaps for the rodents' biology?

Management planning 9. Which islands are candidates for eradication and which for sustained control? 10. How should the Commonwealth and States/Territories decide which insular

exotic rodents to remove first? 11 . Should jurisdictions select some islands where obvious benefits to iconic species

are expected as pait of wider plans to build public support for other islands? Management

12. Should island managers set up contingency response systems to counter rodent incursions and/or prophylactic control buffers around likely places of ingress?

13. What capacity is needed in agencies and among island users to enhance biosecurity?

14. What baits and toxins and which means of delivery are registered for use against rodents in Australia?

15. If sustained control is required (rather than eradication) what sequence of baits and toxins is best practice on islands?

16. What proportion or how many non-target species at risk to the baits and toxins proposed should be removed for the duration of any rodent eradication campaign?

17. Are reptiles at risk from anticoagulants? 18. When should any predicted and unmanageable adverse consequences of removing

rodents cmtail the rodent eradication? 19. How should managers plan and react towards any unpredicted adverse

consequences revealed once rodents are eradicated or controlled? 20. When should we include in plans the other pests that may be killed as by-catch or

that are trophically linked with rodents? 21 . How can State agencies with little capacity learn from operations in other

jurisdictions?

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1. Introduction

Exotic rats on islands were nominated in 2004 by World Wildlife Fund, Australia as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) . The Department of Environment and Water Resources (DEWR) has begun to consider this nomination with the eventual aim of producing a Threat Abatement Plan (TAP). This process includes consideration of and consultation around the various issues that will affect how exotic rodents (rats and mice) and their impacts on islands are managed by Commonwealth and State/Territory agencies, by owners of islands, and by wider stakeholders with an interest in sustainable ecosystems and biodiversity on islands.

The four species of exotic rodents found on Australian islands are ship or black rats (Rctttus rattus) , Norway or brown rats (Rctttus norvegicus), Polynesian or Pacific rats (Rctttus exulans), and mice (Mus musculus!Mus domesticus).

This first document summarises the background information that will eventually be expanded in a formal Background Rep011 appended to the TAP. It lists the key issues and (cmTent) gaps in information (as reminders to ourselves) to act as a resource document to strncture a workshop of key stakeholders planned for 25-26 June 2007. Only a few key references are noted in this rep011.

Ship rat taking fantail egg (photo David Mudge) .

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2. The scale of the problem

Australia has over 8300 islands (Table 1) of which at least 122 now have one or more species of exotic rodents (Appendix 1). To date 39 populations of rodents (on 38 islands) have been eradicated (Appendix 2).

On mainland Australia two invasive rodent species (ship rats and mice) are widespread - mice being almost ubiquitous while ship rats are largely absent from semi­arid areas and the wet-dry tropics (Caughley et al. 1998). Norway rats are largely restricted to urban areas while Polynesian rats are thought to be absent from the mainland. These distributions are reflected on islands with ship rats and mice being the most common species, often occurring together (Table 2).

Table 1. Status of exotic rodents on Australian islands by State/Tenitory. 1 Includes the 26 islands in the Southern Cocos/Keeling group.

State/Territory No. of No. islands No. where References and data islands <100 000 ha rodents sources

known to now have been have exotic eradicated rodents

Commonwealth 37 28 1 2 Burbidge (2004) Northern Territory 398 2 0 Rankmore (2005) Western Australia 3678 22 33 Burbidge (2004) South Australia 396 11 0 Burbidge (2004) Victoria 246 10 0 Burbidge (2004) New South Wales 439 8 1 O'Neill (2006) Tasmania 300+ 26 1 Terauds (2005) Queensland 1854 15 1 Burbidge (2004) Total 7344 122 38 New Zealand 710 145+ 92 Howald et al. (2007) Galapagos 50 38 4 B. Milstead (unpubl. data)

The 128 islands known to have exotic rodents range in size from < 1 ha up to 6 million ha for Tasmania (Table 2; Fig. 1). Of those less than 100 000 ha (the cut-off size for this TAP) rodents remain on at least 122 with a total area of 308 000ha. At a cost of say $200/ha to eradicate rodents it would cost $61 million to clear all islands less than 100,000 ha.

X% of islands with rodents are under some sort of conservation tenure, y% are owned by Aboriginal people, while the rest are either Crown-lease or private tenures (Fig. 2). Overall planning for Crown-owned island management is further complicated in most jurisdictions by the fact that several agencies operating under different legal instruments have responsibility in most States.

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Elsewhere in the world rodents have been eradicated from about 350 islands (Howald et al. in press and this repo11) (Table 3). Sympatric ship rats and mice have been eradicated from only five islands worldwide: Barrow in Western Australia where they were present in separate and small parts of island, Flat (253-ha in Mauritius), Rasa (60-ha in Mexico), Motutapere (46-ha in New Zealand), and Surprise (24-ha in New Caledonia). Attempts against both species on Denis and Bird Islands in the Seychelles failed to remove one or the other.

Table 2. Rodent species and combinations on Australian islands of < 1000,000 ha. 1 Assuming ship rats are present on all the South Keeling Islands.

Species combinations No. islands Largest island eradicated in Australia

Mice only 43 Varanus (83 ha) Ship rat onl/ 58 Hermite (1022 ha) Polynesian rat only 1 Norway rat only 1 Ship rat and mice 16 Barrow but only in separate parts

of island (around the camps for mice and over c. 270 ha for the rats)

Norway rat and mice I Ship rat and Polynesian rat I Ship rat, Norway rat and mice I

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"' 30

"0 25 = ~ 20 -~ 0 15 z

10 5 0

10000+ 1000- 100 - 1000 10 -100 10000

<10

Island size class (ha)

Figure 1. Size class distribution of Australian islands less than I 00 000 ha with rodents

Figure 2. Propo11ions of Australian islands under different tenures

Pie diagram figure to come when data available from all jurisdictions.

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Table 3. Rodent eradications worldwide. All these largest successes were achieved using brodifacoum baits sown from the air.

Species No. successful No failed Largest island with Eradications eradications successful eradication

Ship rat 160 15 Hermite (Australia) l 022 ha Norway rat 104 5 Campbell (NZ) 11 300 ha Polynesian rat 55 6 Hauturu (NZ) 3083 ha Mice 30 7 Enderby (NZ) 710 ha

Conclusions: • Mice and ship rats are the most common species on Australian islands. • The two occur together on at least 16 islands (see control implications). • Eradication has been attempted on only a few large islands. • Most attempts have been in Western Australia. • Most eradication operations have used ground baiting methods rather than

aerial methods. • Almost all have been against ship rats. • Scaling-up to large islands and aerial baiting will require either outside

contracting or capacity building by State agencies. • Government agencies are directly responsible for x¾ of islands with

rodents.

Knowledge gaps:

Issues:

• Many islands have not been adequately surveyed for the presence or absence of exotic rodents

• The species present on some islands is unclear. Mice, for example, may be cryptic and difficult to detect on islands with rats.

• The presence of ship rats may make it harder to eradicate mice, but the mechanism and solution remains unclear (see Witmer 2007).

• Risk factors for each island, e.g., those within swimming distance for rodents of mainlands and the presence of actively-used wharfs needs to be collated.

• The data on who ' owns' or has management responsibility under what legislative accountabilities needs to be collated for each jurisdiction.

• Should key islands where the status of rodents is unclear be surveyed? • Should States that have not completed their databases do so? • Should one agency or a cross-agency group take the lead in promoting the

Rodents on Islands TAP in each jurisdiction?

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• Non-target surveys and risk analyses are required for many islands.

3. The culprits

The four exotic rodent species present in Australia are recognised among the worst invasive mammal pests and together they have invaded over 80% of the world's oceanic island groups.

Body weights and lengths overlap for the four species when juveniles are considered, but they can be distinguished using some morphological characters (Table 4). Additionally they can be distinguished from skull characteristics or genetic profiling. Of course native rodents in the genera Melomys, Zyzomys , Pseudomys, Leggadina and Rctttus may also be present on some islands.

Table 4. Australian invasive rodent morphological measurements

Rctttus rattus R. n.orvef!icus R. exulans Mus musculus Body weight 95-340 200-400 30-100 10-25 (g) Ears Large and Do not cover Smaller than Smaller than

cover eyes eyes when for R. rattus but for the rats when pulled pulled forward also cover eyes forward when pulled

forward Belly fur White-tipped ( characteristic with grey for R. exulans) underneath Tail Much longer Clearly shorter About the same About the same

than Head/body than HBL; as HBL; thin as HBL; length (HBL); thick with pale and uniformly uniformly grey-uniformly dark underside dark brown

Tail length 185 - 245 150-215 125 -135 75-95 (mm) No. of nipples 10-12 (usually 12 8 10

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3.1 Ship rat (Rattus rattus)

The ship or black rat is common around most of the Australian coast, reaching highest numbers near human habitation, though also found in uninhabited areas. It has not penetrated into the central region of Australia probably due to a combination of lack of water and competition from native rodents, despite earlier fears that native rodents may be displaced. However, it does live on arid and semi-arid islands in the north of Australia.

Ship rats have an unresolved taxonomy consisting of a complex containing R. rattus, R. tanezumi and R. mansorius and possibly other 'species'. The European form is

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most widely distributed around the world (including Australia), though the Asian fonn has been found in Brisbane.

In Australia female ship rats can have up to 6 litters of 5-10 young per litter each year, with a 21-22 day gestation time and juveniles weaned by 20 days of age, and reproductively mature by 3-4 months. This can lead to rapid population expansion in suitable environments, although ship rats rarely live longer than one year in the wild.

Ship rats are adept swimmers and will cross channels hundreds of metres in width. In New Zealand ship rats have colonised islands over 500m offshore. They are also the most arboreal of the rodents.

3.2 Norway rat (Rattus norvegicus)

The Norway rat or brown rat is only found in coastal areas of Australia with major human habitation. No1way rats are colonial, generally ground-dwelling, and prefer wetter habitats (e.g. riparian zones). Like ship rats they are widely omnivorous, though they also utilise marine inter-tidal habitats.

In Australia female Norway rats can have up to 18 young in a litter, but usually only 7-10, with a 21-23 day gestation time. Juveniles are weaned by 20 days, and are reproductively active by 3-4 months. In colder habitats (e.g. subantarctic) Norway rats rarely live for more than a year, though in temperate zones they can live for 2-3 years.

Norway rats are very capable swimmers and will easily colonise islands over a kilometre from mainlands. Water is not seen as a barrier to routine movements of individuals within their home-range. In New Zealand Norway rats have colonised islands over 2 km offshore. Laboratory studies suggest that swimming ability is a learnt behaviour, and that water temperature variability across Australia would have little effect on swimming ability.

3.3 Polynesian rat (Rctttus exulans)

The Polynesian rat is only found on a few islands in northern Australia, although it has been a successful invader in the Pacific region, having colonised with early Polynesians. It is usually dominated by the two other introduced rat species.

Polynesian rats have limited swimming ability, and are not expected to be capable of crossing channels more than 200 m.

3.4 House mouse (Mus musculus)

The house mouse is a complex of four subspecies, at least two of which M. m. musculus and M. m. domesticus (and perhaps a third M. m. castaneus) reached Australia with European settlers. Morphologically, Australian mice (like those in New Zealand) are mostly of the domesticus form, but their genetic complexity argues for placing them as M. musculus (Singleton and Redhead 1990).

Mice are a major agricultural pest distributed across all of Australia, reaching plague proportions in some years in eastern and southern rangelands. In Australia mice breed opportunistically and usually have litter sizes of 4-8, with a 19 day gestation time and reproductive maturity by 8 weeks . During plague years mice probably impact other

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small native rodents tlu·ough compet1t10n. Outside plague-years mice often become undetectable in the landscape. This cryptic behaviour has implications for detecting re­invaders and eradication survivors.

Mice may attempt to cross waterways, particularly when they are at high densities, however they are not generally considered proficient swimmers. Most studies of mouse swimming ability have found poor orientation and movement.

Knowledge gaps:

Issues:

• Seasonality of breeding on subantarctic, temperate, arid, wet/dry and wet tropical islands (i .e., eradication is best attempted when there is no breeding) . Check what is known!!

• Swimming ability versus sea temperatures and conditions.

• Potential for range expansion (particularly Polynesian rat) • Low-density behaviour (pai1icularly mice) • Neophobia where rodent control has been conducted (Lord Howe) . • It is not always simple to morphologically distinguish house mice from

some native rodents.

4. Planning rodent management

Planning for rodent management has four components, each with a different purpose and aimed at different audiences:

• Justification • Feasibility plans • Operational plans • Planning to monitor outcomes

4.1 Justification - impacts of rodents on biodiversity

Those managing the islands and/or being asked to fund rodent management obviously need to be convinced by whoever is proposing actions that there is some need to act against the rodents and that some direct benefit will accrne, either directly or by opening opportunities for restoration. All four invasive rodents are omnivorous, eating most plant parts, insects., molluscs, snails, reptiles and other animals, sometimes much larger than themselves (e.g., Wanless et al. 2007). They may also compete with native species such as the native rodents and marsupials that are in the same niche on many Australian islands. So there is a priori evidence that they may affect native biodiversity.

Stronger evidence of impacts comes from the coincidence between the arrival of rats on islands and the extinction of native animals. On Lord Howe Island at least 6 species became extinct after ship rats arrived in 1918 (Table 5). On this island and elsewhere the arrival of rodents also caused the extirpation (loss from that island) of many species, and the reduction in abundance of very many species including some listed as threatened (Table 6). On continental islands in Western Australia ship rats have been

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implicated in the declines and extirpations of native mammals (e.g., burrowing bettongs (Bettongia leseur) on Boodie Island, golden bandicoots (Jsoodon auratus) on Middle Island, and bush rats (Rattus fuscipes), and a Pseudomys sp. on Woody Island) and seabirds (e.g., common noddy (Anous stolidis) and sooty terns (Sterna fi1scata) on Rat Island (Morris 2002; Burbidge & Manly 2002)

Rodents also cause more complex indirect effects when these have involved changes in species that 'engineer' the ecosystem - such as seabirds (Fukami et al. 2007).

The effect of mice has been more subtle ( at least to the human eye) as they have not had such catastrophic effects on avian species - although recent evidence from Gough Island shows that under some circumstances mice can kill large naive prey such as albatross chicks. Mice are efficient predators of invertebrates (particularly spiders) and seeds but their impacts on these prey species at population levels remains unknown.

Table 5. Lord Howe Island endemic taxa whose extinction followed the introduction of rodents (mice since c. 1860 and ship rats since 1918)

Species Nearest relative and location (after Hutton et al. (2007)

Vinous-tinted tlu·ush (Turdus T p. xanthopus from New Caledonia poliocephalus vinitinctus) Robust white eye (Zosterops Z. lateralis from Norfolk strenuous) Grey fantail (Rhipidura fit!iginosa R.f pelzilni from Norfolk cervina) Gerygone ( Gerygone insularis) G. modesta from Norfolk Tasman starling (Aplonis fi1sca A. tabuenisis from Samoa hulliana) Epiglypta howinsulae

Table 6. Tlu·eatened species listed under Commonwealth or State legislation for which rodent predation is thought to be a key threatening process

Species Island Status Listing Woodhen (Gallirallus sylvestris) Lord Howe Endangered EPBC Act Gecko ( Christinus guentheri) Lord Howe Vulnerable EPBC Act Skink (Oligosoma lichinigera) Lord Howe Vulnerable EPBC Act Green parrot ( Cyanoramphus novaezelandiae Norfolk Endangered EPBC Act coolcii) Golden whistler (Pachycephala pectoralis Norfolk Vulnerable xanthoprocta) Scarlet robin (Petroica m. multicolor) Norfolk Vulnerable Buff-banded rail ( Gallirallus philippensis North Keeling Endangered andrewsi) Placostylus bivaricosus Lord Howe Endangered NSW Panesthia lata Lord Howe Endangered NSW Etc To be completed for Report

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Exotic rodents may also impact native biodiversity by acting as the primary prey for other exotic predators such as feral cats or foxes. That is, the abundance of rodents drives the abundance of predators whose impact on secondary prey (the native animals) can drive these to extinction ( e.g., Pech et al. 1995).

Ship rats (and mice) have also been implicated in the decline of the native Christmas Island rat (Rattus macleari) by introducing diseases and by hybridisation (Pickering & Norris 1996).

Removal of the rodents may allow extant species to recover in situ or recolonise naturally, and offers opportunities to more-actively restore biodiversity by reintroducing extirpated species or closely related ones (Hutton et al. 2006).

4.2 Feasibility plans

Funding agencies usually want some evidence from people proposing rodent management that they have thought through all the risks and constraints likely to be present in any case, and so far as possible described how they might be reduced or removed. A feasibility plan is pai1icularly important for large-scale or novel proposals where eradication is the aim, in part to increase the chance of success, but also so that funding agencies know the risks and so are less likely to te1111inate other oppo11unities just because one fails. Note: internationally c. 9% of all attempted rodent eradications have failed (Howald et al. in press) .

A feasibility plan may include components of the justification (as above) but should address the risks and constraints present and indicate how these may be overcome and how that affects the choice of strategic option (as below). Feasibility plans usually include estimates of operational costs but do not usually include the fine detail of operational planning. They may also indicate what baseline data should be collected and how the eventual operation will be monitored.

4.2.1 Strategies to .fix the problem

There are five strategic options to manage pest rodents on islands - preventing establishment, eradication, quasi-eradication, sustained control, and do nothing. Here we briefly discus each.

(a) Preventing invasions Preventing invasions of exotic rodents to rodent-free islands needs to be seen as part of a wider biosecurity plan for each island. Most Australian islands do not have exotic rodents, but many will eventually be invaded either naturally or with human assistance via ship wrecks or in cargo. Similarly, the risk of reinvasion of islands cleared of pest rodents has to be managed (see the section on surveillance and detection).

Invasive rodents have been transported by humans to islands, both intentionally and accidentally, since humans first started travelling (e.g. Lapita people, Romans). The rate of ship and Norway rat and mouse invasion to rodent-free islands shows no pattern of change over the past century.

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The risk factors for rodent invasion include the obvious (within swimming distance of mainlands), the presence of a wharf and thus cargo volume, and the likelihood of ships wrecking on the island.

Overall, the risk of rodent invasion might be reduced by actions at the point of Departure of ships to reduce the probability that rodents will get aboard, by rodent control on ships to reduce the risk that they will disembark on the island, by proactive or prophylactic control around likely points of entry on the islands, or by surveillance and reactive management should a rodent be seen on the island. It is not clear which of these actions would give best results given limited resources - although the answer is likely to depend on the pathway of invasion, its likely frequency, and the practicality of conducting effective surveillance and responses (see NZ Department of Conservation's standard procedures in Appendix 11.3).

Control at points of departure: Best practice at ports and airpo1ts might include:

• Maintenance of an environment which minimises rodent densities and thus presumably the likelihood of invasive rodents being transpo1ted off-site by human-assisted means.

• Active control of rodents. • Active management of access routes onto vessels. Note: this includes

physical inspection of all cargo and luggage being transpo1ted to high­priority rodent-free islands in some countries.

Control on ships and planes: There are little data on the distribution of invasive rodents on vessels. Some data from large ships in Alaska suggests it is uncommon to find breeding populations on board, and that rats which embark on a vessel are likely to disembark not long thereafter. Data from smaller scientific/management vessels in New Zealand suggests that rats will commonly move on and off such vessels, especially during periods of high population pressure (i.e. high density).

International Health Regulations require ships to cany ce1tificates that they are rat-free, and Australia appears to rely on this system with its re-validation rules for rodent quarantine. Derat certification appears to be voluntary for vessels visiting some Australian islands when they originate from Australian ports but a re-validation of the certificate is required for all vessels ( over 25 m in length) originating in foreign ports. CHECK AND UPDATE.

Note: rodents on ships is a major issue for the oil and gas industry in Western Australia. Considerable effo1t is being expended on quarantine measures and on education of the workers and other island users.

Control on the island: Quarantine measures on the island might be proactive (inspection of cargo, buffers of control devices around likely invasion points) or reactive (surveillance and prompt action when a rodent is detected), or both.

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(i) Proactive actions: On particularly high conservation value islands that are also remote and uninhabited, best practice might include a final inspection of all cargo (generally from scientific or conservation expeditions) in ' debriefing rooms' on ship or ashore where all transpo1ted cargo which is to be landed is unpacked and inspection. In New Zealand both mice and rats have been intercepted at this point. It is unclear how practical this process would be for populated islands.

Some countries maintain a zone of rodent control around likely invasion points on rodent-free islands. The Pribilof Islands in Alaska have been kept free of exotic rodents despite hosting hundreds of ships each year by a buffer of traps and bait stations around the port (ref) . Increasing the bait-life and efficiency of such strategies is the subject of current research in New Zealand.

(ii) Reactive actions: Prompt reaction to shipwrecks on islands is used by some countries. Project Rat-Spill (a spin-off from the Exxon Valdez oil spill in Alaska) ensures that the crews of salvage ships and island residents (as the probable first on scene of a ship wreck) have equipment and training to react to any shipwreck with on-site rodent control.

The final line of defence is planned surveillance or monitoring on rodent-free islands and prompt action against incursions. This might be feasible on populated islands but is likely to be impractical on uninhabited islands (see section 4.2.4). The rate of rat population expansion across an island suggests most medium sized islands (< l000ha) can be fully invaded by rats in under two years. Thus, any surveillance planned needs to be done (assuming perfect detection) at frequent intervals if any invasion is to be intercepted (assuming perfect interception). Otherwise, proactive management to reduce risk is indicated.

(b) Eradication Eradication is the pennanent removal of the population from the whole island. It requires that all the rodents must be at risk and killed faster than they can replace their losses, that reinvasion risks are zero ( or near to it), and there should be no net adverse consequences (Hone et al. in press) .

Modern control tactics (aerial or ground baiting in one operation) 'over-engineer' the application of baits, apply the baits outside the breeding season which is usually when natural foods are least abundant to meet the first rnles. The zero immigration rnle can never logically be met - the rodents got to the island once so theoretically could so do again - but commonsense and ongoing experience should allow us to judge this risk. Eradication should be considered simultaneously with reinvasion prevention (i.e. surveillance and quarantine). Mitigation of invasive rodent impacts by complete removal is both eradication and ongoing reinvasion prevention. We discuss the net benefits/costs rnle later.

(c) Quasi-eradication On islands where reinvasion is certain (i.e., those within easy swimming distance of populations on mainlands) eradication itself is never achievable and ongoing control will always be required. Quasi-eradication is where the resident population is removed and the potential immigrants are all killed on buffers on the mainland or the actual

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immigrants are killed as they arrive. The effect on the island's biodiversity is the same as if eradication was achieved but at an ongoing cost to managers.

(d) Sustained Control On large islands where eradication is not considered feasible or cost-effective, and there are species urgently requiring protection from invasive rodents, targeted control can provide an on-going means of species conservation. Targeted control is often used for species with restricted distributions such as remnant populations or colonial nesting birds ( e.g. , Providence petrels on Mt Gower on Lord Howe Island, protection of green parrots on Norfolk Island).

The trick with sustained control is to know how to intervene, i.e. , optimising the scale, frequency and intensity of control sufficient to achieve the protection goals. Knowledge of both the rodent's biology and that of the species/ecosystems being protected is usually desirable if such control is to be efficient - and therefore sustainable.

Sustained control is also an imp01tant strategy for managing source populations such as around points of depaiture for both human-assisted and naturally dispersing rodent invasion.

(e) Do nothing In many cases managers may do nothing, at least against the rodents. However, this is only justifiable, now that we have the ability to act, where there is no obvious reason to act, i.e., where there is no impact to be mitigated. Nevertheless, even ' ruined ' islands may have some value as restoration sites.

Where nothing can be done against the rodents that are having unacceptable impacts on biodiversity, managers still might consider managing the resource species, e.g., by removing the threatened populations.

Conclusions: • It is best to stop rodents arriving by effective quarantine systems (see case

studies), and then by eradicating populations.

Knowledge gaps:

Issues:

• What are the cmTent laws and practices on derat certification on ships? • Prevalence of rodents on ships with regular schedules to key islands • Detection probabilities of survivors or immigrants using different devices

are unknown. • Check the quarantine systems used in the oils and gas industry in WA.

• Should States set up 'rat-spill' capacity • Should island managers set up prophylactic control systems around ports

and wharfs? • Should 'island managers' be appointed to oversee quarantine issues on

high-priority islands with a high risk of rodent invasion? • Education and provision of infonnation to island visitors .

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4.2.2 Tactics and costs to fix the problem The issue in this section is that while there are many ways to kill rodents all come with various benefits and constraints that have to be considered in each circumstance.

The strategic choice is the first of these circumstances that will determine the best combination of tactics. Only a few control methods are capable of consistently killing 100% of rodents. Third generation anticoagulants such as brodifacoum in cereal baits are the cunent best practice for eradication - sown from the air on large islands but with the option to dispense from bait stations on smaller islands or where non-target constraints are significant. Conversely, the ongoing use of anticoagulants is not the best method when sustained control is required because of the risk of inducing toxin resistance ( especially to first generation anticoagulants) and because some (such as brodifacoum) accumulate in the food chain if used too often at the one place.

The second-generation anticoagulant toxicant brodifacoum has an established track record in successful eradication of introduced rodents from islands (Howald et al. in press). Brodifacoum presents a high ' hazard' to target rodents through its acute toxicity and corresponding potential to deliver an effective lethal dose to rodents in a single feed of bait containing an appropriate concentration (usually 25 ppm but in some cases 50 ppm). 'Exposure' of 100% of target rodents to bait in many successful island eradications has been through blanket aerial distribution of baits, at rates which ensure rodents will encounter bait quickly. Baits have generally been cereal-based pellet formulations with high palatability to rodents to ensure ingestion of a lethal amount upon encounter, and weathering/degradation characteristics that ensure their availability and toxicity to rodents over a suitable period.

Costs to manage rodents vary widely depending on the remoteness of the island and its scale, but also on the difficulty of managing people or non-target species. A ball­park figure of $200/ha for eradication has been used as a first cut of costs .

Tools which successfully eliminate rats at high density may not work successfully for low density populations. Differences between devices may interact with the behaviour of invading rats, above and beyond a simple lower probability of encounter and hence detection (Russell et al. 2005). At high density rats are almost exclusively controlled through exploiting their lack of food resources, by generally baiting traps or using toxic baits. At low density, and especially on a pristine island with abundant food, rats will no longer be limited by food supply (Dilks & Towns 2002) . Instead they may be limited by such requirements as social interaction, evoking hitherto unknown behaviours in the invader (Russell et al. 2005). It will be necessary to exploit these requirements at low density in order to successfully control invading rats.

Current experience suggests that artificial type bait stations (e.g., plastic) deter rats, and high-density contingency response grids (e.g., 25 111) generate neophobia. Contingency responses in general are more likely to evoke neophobia by placing novel devices in an environment a rat has only recently become familiar with. A rat invading a novel environment should find surveillance devices less intimidating. Even if surveillance devices ( covers, e.g. wooden boxes) are 'inactive' , their presence means they can be activated with devices when a response is required. Additionally, invading rats usually roam more widely, and so a sparse grid of surveillance devices is appropriate. The key to eliminating an invading rodent is for one device to work well, rather than to saturate an area with devices . This may initially seem counter-intuitive. This additionally

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means less devices are needed, though over a wider area which overall makes for easier fieldwork.

Recent research has also shown that tunnel-type covers are more appealing to rats that prefer to see an entrance and exit. Poison baits, although becoming mouldy, retain much of their toxicity over a one year period. Continued use of poison as a surveillance tool is not recommended, particularly due to toxic build-up in the environment in resilient species such as insects. As a contingency response tool the hand-spreading of poison around a suitable target area is probably the most effective. This removes the neophobia­generating aspects of bait stations, though it increases the risk to non-targets . This trade­off is still worthwhile if it prevents a rodent invasion. There may be legal issues which prevent the rapid response of hand-spreading bait to a suspected rodent incursion.

Issues: • When should managers consider alternatives to brodifacoum for

eradication? • What sequence of baits and toxins are best in sustained control operations?

4.3 Operational planning

Examples of operational plans will be attached to the background document

4.4 Planning audit of benefits and consequences

4.4.1 Measuring biodiversity bene.fi.ts Demonstrating to the funding agencies and the wider public that management of exotic rodents was money well-spent requires robust monitoring. Usually, we are dealing with a single island so that the niceties of experimental replication ( c.f. , Fukami et al. 2007) cannot be achieved. However, it is important that baseline or pre-control measures are taken of the abundance or condition of species or processes expected to benefit or change following rodent control - a condition not universally costed in to eradication plans.

4.4.2 Measuring eradication success

This section focuses on the question of detennining whether rodents remain after any eradication attempt.

When bait stations are used to achieve the eradication they can 'mutate' into detection devices by monitoring the take of non-toxic bait, i.e., they can both detect (with unknown efficiency) and locate any survivors which can then be the focus of secondary control of some sort. However, when aerial baiting is used this array of detection devices is not in situ and is generally too expensive or impossible to establish - the choice of aerial control is generally dictated by the size and/or topography of the island. This is a major issue with aerial control - what does the discovery of a survivor mean? Is it just one rodent or indicative of a scattering of survivors at unknown locations? The New Zealand Department of Conservation solution is largely to wait and see if failure is revealed by a resurgent rodent population.

18

4.5 Predicting and managing adverse effects

Managing rodents may cause adverse effects on biodiversity either as a consequence of the control tools used or as a response to the removal of the rodents. While it is unlikely that these adverse effects will outweigh the benefits of controlling rodents in most cases, a wise manager needs to consider them and either avoid or mitigate them.

4.5.J Adverse effects of the control- non-target impacts The risk to target rodents, non-target pests, and non-target native animals can be estimated using a basic fonnula:

Risk ( of mortality) = Hazard (toxicity, concentration in bait) x Exposure (ingestion of bait)

Inevitably, the application of toxic bait over islands will also present a hazard to non­target wildlife. The fonnula above can also be applied to a priori assessment of non­target risk, which should be undertaken for individual islands, according to the species anay and conditions. Data that can inform 'hazard' (e.g., LD50 figures for similar species, reports of poisoning cases) and 'exposure' (e.g., dietary information, foraging habits, home range) estimates for each non-target species should be collated to provide a ranking of the theoretical risk of primary poisoning i.e. from ingesting bait. This exercise will identify significant gaps in knowledge which can be addressed by pre-eradication trials to scope toxicity and/or bait acceptance, particularly for non-target species of high value. There may also be instances on islands where common non-target species which are less susceptible to the toxicant but find the bait palatable e.g. land crabs, could significantly reduce the availability of bait to target rodents.

There is also a need for a priori assessments of the secondary risks to non-target wildlife (see the case studies). Brodifacoum is residual especially in the livers of mammals and birds, with poisoned target rodents in particular representing an 'environmental reservoir' of brodifacoum to which non-target wildlife (potentially including species unlikely to ingest bait) may be exposed;

a) non-target predators that take live rodents within the period between rodents ingesting a lethal dose and dying (usually several days)

b) Scavengers of the carcasses of poisoned rodents -this hazard will remain until rodent carcasses degrade.

Previous monitoring of non-target impacts during island rodent eradications has focused most on predatory and scavenging birds, which will be influenced by the extent on which they rely on rodents in their diet or exploit available rodent carcasses, as cumulative sublethal exposure will increase the risk of mortality. However, mammals, reptiles and invertebrate species will also require consideration of secondary risk (using the approach described above) on an island-by-island basis. Ground-dwelling invertebrates or reptiles that feed on baits also represent an 'environmental reservoir' so that secondary risks to species that feed on them need to be considered. Again, pre-eradication trials to scope

19

toxicity or likelihood of exposure for particularly significant non-target species may be appropriate to consolidate a risk estimate.

Where an unacceptable theoretical risk to a non-target population is identified, mitigation planning will be required. It should be recognised that individual non-target mortality should be expected for at-risk species and must be weighted within a population approach to overall impact and benefits of the eradication. A number of approaches to mitigation can be used, each with logistical and cost constraints to be considered within the eradication planning. It is critical that non-target mitigation measures do not compromise the target efficacy of the bait application - any manipulations of bait formulation or application method intended to reduce non-target risk must be considered in this context.

Mitigation of the 'hazard' component to non-target wildlife could be achieved by using an alternative toxicant with a known lower toxicity to non-target species and/or selective toxicity to the target rodents, or by reducing the concentration of brodifacoum in baits. Relative to 'hazard' of brodifacoum to non-target wildlife, the availability of an effective treatment for brodifacoum poisoning (Vitamin K1) offers the possibility of recovery in captivity, and eventual release of individual non-targets found to be affected. Mitigation of non-target 'exposure' might comprise restricting their access to bait e.g. bait stations; bait additives to reduce attractiveness or palatability of bait to non-targets e.g. dyes, deterrents; or supplemental feeding of non-target species during and after the eradication to reduce exposure to baits or residual brodifacoum e.g. goat carcass stations for hawks. For high-value non-target species e.g. endemic to island, temporary removal of a suitable portion of the population to a captive-breeding situation for repatriation once eradication success is confirmed, would ensure that risk is absolutely minimised.

Issues: • The effect of brodifacoum on reptiles remains unclear. • What propo11ion or number of non-target species at risk in any rodent

eradication operation should be removed for the duration of the operation? • How long should such removals be maintained?

4.5.2 Adverse effects of rodent removal Once invasive rodents become established on an island they integrate themselves into and subsequently alter the ecosystem. The control or eradication of invasive rodents may generate unexpected outcomes in the ecosystem. These unexpected outcomes can be both positive (the recovery or rediscovery of other native species) or negative (the release of another pest species, either animal or plant). Where unexpected outcomes are possible, or suspected, it if often advisable to undertake pilot research such as local control and outcome monitoring, in order to be fully prepared to react to such unexpected interactions.

In particular, invasive rats usually maintain invasive mice at low density on islands, often at undetectable levels. The eradication of invasive rats may release invasive mice, possibly undetected until that time. Given the difficulties with controlling and eradicating mice, it is impo11ant to consider a multi-species integrated approach to invasive rodent management.

Once invasive rodents are eradicated, an ecosystem may become more susceptible to reinvasion, both because there is no longer an incumbent rodent species preventing any

_.J

20

other species establishing (particularly mice) and because the restoration of the island will make it more resource rich for new invaders, which will interact with surveillance methods.

Issues:

• When should predicted but umnanageable adverse consequences of rodent removal curtail the rodent removal?

4.4 Planning to include other pests

Many of the islands with rodents also have other introduced pests such as rabbits, feral cats and foxes. These pests may be killed during any rodent control although experience suggests that typical rodent eradication methods will not kill 100%. However, it would be sensible to consider in operational plans whether eradication using secondary follow-up methods is justified.

One justification for this is that pests such as cats and foxes may be using the rodents as primary prey. Removal of the rodents may lead to prey switching, at least in the short-term, to native species.

5. Prioritising islands

The rationale for prioritisation is: • It costs c. $100-200/ha to attempt eradication so it is clearly not possible to

do all candidate islands in the short-term. • It is easier and cheaper to do smaller islands than very large islands, and

the feasibility of success might decrease with increasing scale. • Not all islands are equally valuable for their biodiversity • Not all rodent populations are equally threatening to biodiversity • Some islands might be selected as representatives, i.e., volcanic,

continental, atolls, sand cays, or tropical versus temperate habitats. • The status of rodents and biodiversity values present is uncertain for some

islands • Equally valued islands might differ in the constraints (non-target issues,

social issues) that make eradication more or less difficult • The ability to stop rodents reinvading will differ between islands

according to such factors as distance offshore, presence of human settlements and wharfs.

• Some islands have a higher public profile than others and might act as demonstration sites.

How have other countries gone about prioritising rodent management on islands? Examples are available from New Zealand, the Falkland Islands, British Overseas Territories and the Galapagos Islands.

Knowledge gaps: • Have any States prioritised islands for biodiversity or pest control?

21

Issues: • Should Australia have a single system to prioritise islands? • Is a mixed-motives system better?

6. Legal issues

• State and Commonwealth obligations to manage rodents on islands • Ability to manage rodents on islands in private tenures • Legal use of toxins • Issues around protection of non-target species

7. Capacity building

In Australia, only the Western Australians have substantial experience in eradicating rodents on islands, but other countries have ongoing eradication campaigns. Agencies contemplating rodent eradication should consider seconding staff to suitable operations to build their operational capacity.

There is also a need to build capacity within key island user groups. For example, training for biosecurity within the oil and gas industry using WA islands, and ensuring that emergency response systems (such as salvage ships) have rodent control capacity and training to act when dealing with shipwrecks.

8. Education

8.1 People living on or visiting islands

People live on some key Australian islands where rodents affect high priority biodiversity values (e.g., Lord Howe, Norfolk, Christmas, Cocos/Keeling islands). Island residents exposed to toxic baits may be concerned about long-term contamination of soil, water, or food sources? Brodifacoum has low solubility in water so contamination of waterways is not expected. Plants also have a low ability to take up brodifacoum. Nevertheless, 'controlled' . exposure via bait station delivery may be favoured over 'involuntary' exposure via aerial baiting over residential areas.

Visitors to islands are already regulated in many cases, i.e., they may need permits and can only conduct ce11ain activities. Successful eradication of rodents from such islands may lead to increased regulations on island visits for which the active cooperation of visitors will be required.

8.2 Gaining wider public support

People are used to controlling rodents and often do so themselves using the same toxins (anticoagulants) used in eradication campaigns. Thus there is usually less objection to killing rodents than is seen when more attractive animals are killed as pests.

22

Most proposed rodent eradications are likely to be funded by taxpayers and so they (and thus ultimately the decision-makers) have to consider it money well spent.

8.3 Dealing with opposition

A number of rodent eradication campaigns overseas have been met with fierce opposition from animal liberation groups, e.g., on Anacapa Island in California. Early public infonnation on the benefits of rodent eradication, while not necessarily dissuading people whose opposition is based on liberation ethics, will at least minimise their ability to sway wider public opinion against the operation using arguments about benefits.

Opposition based on perceived lack of humaneness of poisoning, or on risks to non-target species (at least at a population level) has to be addressed within the feasibility and operational planning process. If reasonable objections cannot be met there may be good reasons not to proceed until they are.

Conclusions

Issues:

• High profile successes in eradicating rodents, especially with obvious benefits to iconic species, to engender public enthusiasm for further actions.

• Good biosecurity education programmes are required, especially for key island user and resident groups.

• What motivates island visitors to take precautions about introducing rodents?

9. Case studies

9.1 Islands with people - the plans for Lord Howe Island

Lord Howe Island (1455 ha) is a remote island with a high degree of endemism and relatively intact native ecosystems, albeit without a few elements as a consequence of human settlement and the introduction of pests . It was one of the very last places discovered by humans in 1778 and only settled in 1834. Part of the island suppo11s a population of about 320 people who rely on tourism and a palm nursery business to make a living. The islanders have eradicated several exotic pests (feral pigs, cats and perhaps feral goats) but both mice and ship rats remain. Eradication of these species has been justified (Saunders & Brown 2001), deemed feasible with some management of non­target issues (Parkes et al. 2002), and an operational plan is being developed (ref).

What makes Lord Howe interesting for rodent eradication is: • The original biota is quite well described and the losses to mice and rats

are better known than for many other islands.

• J

23

• The islanders do not like rats because they affect their livelihoods both economically by eating palm seeds and potentially by affecting biodiversity values of interest t many tourists.

• Many of the lost species could be replaced by con-specifics, at least at the subspecies level, from other Pacific islands.

• The solution is testing with both rats and mice present and because two techniques - aerial baiting in the mountains and bait stations in the settled areas - will be required.

• The solution is also testing because iconic native species will be at primary risk from the baits (woodhens) and secondary risk from eating poisoned rodents (cmrnwongs).

• But the problem is tractable and affordable.

9.2 Islands without people - Barrow and surrounding islands

Many of the islands along the no11h-west coast of WA are nature reserves with significant conservation values. These include being refuges for threatened mammals and secure breeding sites for marine turtles and seabirds. Barrow Island in particular is of national significance for threatened mammal conservation and marine tmile nesting. Ship rats were accidentally introduced to several of these islands during the 19th century by the pearling industry which used the islands as camp sites and for careening their vessels . Ship rats were first recorded on islands around BaITow Island in 1918 and on Banow Island in 1990 (although they have most likely occurred there previously but had been undetected) .

Eradication Program

The rat eradication program on the 6 islands around Barrow Island commenced in 1983 and successfully used pindone bait stations at 25 m intervals to eradicate rats. One of these islands, Boodie Island, was the first attempt in WA to eradicate rats without impacting a native mammal, the boodie (Bettongia lesueur). While the rat eradication was successful, boodies were also eradicated but have since been reintroduced. Most of the other islands in this program did not have any non-target mammals. However, one of the larger islands in this group, Middle Island (350ha), did have a population of golden bandicoots (Isoodon auratus), and after the failed attempt to exclude boodies from pindone baits, the plans to eradicate rats from this island were suspended.

However in 1990, ship rats were discovered at the south end of Barrow Island (23 590 ha). Because of the significant threat this posed to the biota of this A Class nature reserve, an immediate program was developed to eradicate rats from the south end and nearby Middle Island. Fortunately the rats were found to be restricted to only about 170ha at the southern end of Barrow Island. However in this area, seven species of mammal (5 of these were listed as threatened species at the time) were at potential risk from eating pindone baits. This required the development of a bait station that allowed access by rats but restricted access to the native species.

A bait station comprising a 20 litre plastic bucket with lid and access holes, and climbing planks was developed. The pindone bait was laid on sand inside the bucket.

24

This prevented access to the pindone bait by the euro (Macropus robustus isabellinus), spectacled hare-wallaby (Lagorchestes conspicillatus conspicillatus ), brnshtail possum (Trichosurus vulpecula arnhemensis) and boodie (Bettongia lesueur) through physical exclusion from the bait, and golden bandicoot (Jsoodon auratus barrowensis) through their inability to climb the ramps. Rats gained access to the bait by climbing the ramps and entering the bucket through the 38mm access holes. Two native rodents, the common rock-rat (Zyzomys argurus) and Banow Island mouse (Pseudomys nanus ferculinus), could not be excluded. Their numbers declined during the eradication on Barrow Island, however they had recolonised the baited area within 12 months.

The eradication program on Barrow and surrounding islands was successful with ongoing monitoring failing to find any signs of ship rats. There is some evidence that both the reintroduced boodies on Boodie Island and the golden bandicoot on Middle Island have increased in abundance since the removal of the rats. At the time, Middle Island was the largest island in Australia to have had ship rats eradicated. The eradication program on Barrow and surrounding islands occurred over nine years and is estimated to have cost approximately $500, 000, plus a significant amount of in-kind support from W APET (later Chevron).

10. References

Burbidge, A.A (2004). Introduced mammals on Western Australian islands. CALM Report to DEH.

Burbidge, A.A.; Manly, B.F.J . (2002). Mammal extinctions on Australian islands: causes and conservation implications. Journal ofBiogeography 29: 465-473.

Caughley, J.; Bamford, M.; Parker, B.; Sinclair, R.; Griffiths, J.; Kelly, D. (1998). Managing vertebrate pests: Rodents. Bureau of Resource Sciences, Canberra.

Dilks, P.; Towns, D. (2002). Developing tools to detect and respond to rodent invasions of islands: workshop report and recommendations. DOC Science Internal Series 59. Department of Conservation, Wellington, NZ.

Fukami, T.; Wardle, D.A.; Bellingham, P.J.; Mulder, C.P.H.; Towns, D.R.; Yeates, G.W.; Bom1er, K.I.; Durett, M.S.; Grant-Hoffman, M.N.; Williamson, W.M. (2006). Above- and below-ground impacts of introduced predators in seabird-dominated island ecosystems. Ecology Letters 9: 1299-1307.

Hone, J.; Bamford, M.; Parkes, J. (in press). An evaluation of criteria suggested for eradication ofve1iebrate pests . Benyman Bulletin I:

Howald, G.; Donlan, C.J.; Galvan, J.P.; Russell, J.; Parkes, J.; Samaniego, A.; Wang, Y.; Veitch, D.; Genovesi, P.; Pascal, M.; Saunders, A.; Tershy, B. (2007). Invasive rodent eradications on islands. Conservation Biology.

Hutton, I.; Parkes, J.P.; Sinclair, A.R.E. (2007). Reassembling island ecosystems: the case of Lord Howe Island. Animal Conservation I 0: 22-29.

Morris, K.D (2002). The eradication of the Black Rat (Rattus rattus) on Barrow and adjacent islands off the north-west coast of Western Australia. Page 219-225 in Veitch, C.R. and Clout, M.N (eds). Turning the tide: the eradication of invasive species. Occasional Paper of the IUCN Species Survival Commission Number 27.

O'Neill, L. (2006). Introduced animals on New South Wales Islands. Depaiiment of Environment and Conservation NSW Report to DEH.

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Parkes, J.; Ruscoe, W.; Fisher, P.; Thomas, B. (2004). Benefits, constraints, risks and costs of rodent control options on Lord Howe Island. Landcare Research Contract Report LC0304/64 (unpublished).

Pech, R.P.; Sinclair, A.R.E.; Newsome, A.E. (1995). Predation models for primary and secondary prey species. Wildlife Research 22: 55-64.

Pickering, J.; Norris, C.A. (1996). New evidence concerning the extinction of the endemic murid Rattus macleari Thomas, 1887 from Christmas Island, Indian Ocean. Australian Mammalogy 19: 29-26.

Rank.more, B. (2005) . Introduced animals on Northern Territory islands: improving Australia's ability to protect its island habitats from feral animals. DNRE&A report to DEH.

Russell, J.C .; Towns, D.R.; Anderson, S.H.; Clout, M.N. (2005). Intercepting the first rat ashore. Nature 437: 1107.

Saunders, A.; Brown D. (2001). An assessment of the feasibility of eradicating rodents from Lord Howe Island group: a repo11 to the Lord Howe Island Board. Endangered Species Recovery Council Repo11 (unpublished), 78 pp.

Singleton, G.R.; Redhead, T.D. (1990). Structure and biology of house mouse populations that plague irregularly: an evolutionary perspective. Biological Journal of the Linnean Society 41: 285-300.

Terauds, A. (2005). Introduced animals on Tasmanian islands. DPIWE Repo11 to DEH. Wanless, R.M.; Angel, AQ.; Cuthbe11, R.J.; Hilton, G.M.; Ryan, P.G. (2007). Can

predation by invasive mice drive seabird extinctions? Biology Letters: www. J ournals.royalsoc. ac. uk.

Witmer, G.W.; Boyd, F.; Hillis-Starr, Z. (2007). The successful eradication of introduced roof rats (Rattus rattus) from Buck islands using diphacinone, followed by an irruption of house mice (Mus musculus) . Wildlife Research 34: 108-115.

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11. Appendices

Appendix 11.1. Australian islands known to have one or more species of exotic rodents. A = Aboriginal trust or freehold, B = national park, C = other conservation reserves, D =

non-reserved Crown lands, E = Crown-leased, F = private. Islands linked to the mainland (e.g., by causeways, tombolos or at low tide) have been excluded.

Island Area (ha) State Species present Management agency Tasmania 6 200 000 Tas Ship rat, Norway rat,

Mice Melville 573 000 NT Ship rat Kangaroo 450 000 SA Ship rat, Mice Groote Eylandt 228 522 NT Ship rat, ? Mice Bathurst 164 520 NT Ship rat Flinders 134720 Tas Ship rat, Mice King 110 000 Tas Ship rat, Mice Dirk Hartog 58 640 WA Mice Crown lease Cape Barren 46 220 Tas Ship rat, Mice Elcho 28 243 NT Ship rat Arnhem Land Aboriginal

Trust N. Stradbroke 26 344 Qld Ship rat, Mice Bribie 17 500 Qld Mice French 17 470 Vic Mice, Ship rat? Parks Victoria 70%; Private

30% Moreton 17 021 Qld Mice Christmas 13 470 Com Ship rat, Norway rat

(?), Mice Macquarie 12 785 Tas Ship rat, Mice Maria 10 401 Tas Ship rat, Mice Three Hummock 6 966 Tas Mice Faure 5 148 WA Mice Crown lease to Australian

Wildlife Conservancy Snake 4 623 Vic Mice St Peter 3 731 SA Mice Flinders 3 642 SA Ship rat, Mice Norfolk 3 450 Com Ship rat St Margaret 1 934 Vic Mice Wardang 1 756 SA Mice Rottnest 1 705 WA Ship rat(?), Mice Rottnest Island Authority Deal 1 576 Tas Ship rat National Park Long 1 480 WA Ship rat(?) Unallocated Crown land Lord Howe 1 455 NSW Ship rat, Mice Lord Howe Island Board Sunday 1 330 WA Ship rat, Polynesian rat Aboriginal Reserve 26 S. Cocos I. 1 310 Com Ship rat, Mice Prime Seal 1 220 Tas Mice Unallocated Crown land;

lease land Badger 1 243 Tas Mice Aboriginal Land Council Depuch 1 121 WA Ship rat WA Museum Sunday 1 034 Vic Mice

Status

E

A

B,F

C B B,E C

C B D C, F A

D, E

A C

l L

Long Gidley Lindeman Thevenard

Outer Sister Dixon Quail Howick Babel Maer S. Molle Great Dog Reevesby Hummock Truant

Mt. Chappell Waterhouse N . Twin Peak Passage Figure of Eight Swan Hogan Adele Woody North Tin Kettle Forsyth E. Kangaroo Clonmel Dog Trefoil Broughton

Great Glennie Big Green New Year Little Green Little Dog Allthorpe Carey Newry Rocky Montague

Boullanger Broughton

987 845 610 589

545 500 480 446 440 390 380 377 373 313 305

297 287 272 253 248 239 232 217 195 176 176 167 157 140 140 140 138

119 119 98 86 83 81 78 51 38 36

34 32

27

Qld Ship rat WA Ship rat Conservation Commission C Qld Ship rat WA Mice Conservation Commission; C,E

Crown lease Tas Mice C,E WA Mice Unallocated Crown land D Vic Mice Qld Ship rat Tas Mice Aboriginal Land Council A Qld Qld Ship rat Tas Ship rat (?), Mice A SA Mice Vic Mice NT Ship rat Arnhem land Aboriginal

Trust Tas Ship rat, Mice A Tas Mice D,E WA ? Ship rat (?) Conservation Commission C Tas Ship rat (?), Mice D,E WA Mice Conservation Commission C Tas Mice D,F Tas Ship rat D WA Polynesian rat Conservation Commission C WA Ship rat Conservation Commission C WA Mice Minister for Fisheries C Tas Ship rat(?) D Tas Ship rat (?), Mice C Tas Mice Nature Reserve C Vic Mice Vic Ship rat, Mice Tas Mice F NSW Ship rat(?) Dept. Environment & B

Conservation Vic Ship rat Tas Ship rat Nature Reserve C Tas ? Mice Game Reserve C Tas Mice CA, private C,F Tas ? Ship rat (?), Mice (?) Game Reserve, private C, F SA Ship rat,.Mice WA Mice Conservation Commission C Qld Ship rat Qld Ship rat NSW Mice Dept. Environment & C

Conservation WA Mice Conservation Commission C NSW Ship rat Dept. Environment & B

Conservation

28

Little Broughton 32 NSW Ship rat Dept. Environment & C Conservation

Fairfax 21 Qld Ship rat(?) Camac 19 WA Mice Conservation Commission C Baird 18 SA Mice Venus Bay I. 17 SA Mice Actaeon 16 Tas ? Ship rat Game Reserve C Boydong 16 Qld Ship rat Green 15 Qld Ship rat Browse 12 WA Mice Conservation Commission C Penguin 12 WA Mice Conservation Commission C Mistaken 10 WA Ship rat Conservation Commission C Lion 8 NSW ? Ship rat(?), Mice Dept. Environment & C

Conservation Muttonbird 8 NSW Norway rat, Mice Dept. Environment & C

Conservation Southport 7 Tas Mice Whitlock 7 WA Mice Conservation Commission C N . Bickers 6 SA Mice Goose 6 SA Mice Wreck 4 Qld Ship rat(?) Little Boydong 3 Qld ? Mungary 3 SA Mice Doughboy 2 Vic Ship rat George Rocks 2 Tas Ship rat Nature Reserve C Little Goose 2 SA Mice Snapper 1 NSW Norway rat Sugar Loaf Rock 1 WA Mice Conservation Commission C

Appendix 11.2. Australian islands from which rodents have been eradicated

Island Area (ha) State Species Management agency Statu s

Barrow Part of 22 483 WA Ship rat, Mice Conservation Commission C Hennite 1 022 WA Ship rat Conservation Commission C Trimouille 522 WA Ship rat Conservation Commission C Middle 350 WA Ship rat Conservation Commission C,E Boodie 170 WA Ship rat Conservation Commission C,E North West 135 WA Ship rat Conservation Commission C Alpha 118 WA Ship rat Conservation Commission C Varanus 83 WA Mice Conservation Commission C,E West 82 WA Ship rat Conservation Commission C Bluebell 65 WA Ship rat Conservation Commission C Middle 60 WA Ship rat Conservation Commission C Renewal 58 WA Ship rat Conservation Commission C Rat 56 WA Ship rat Minister for Fisheries C

.1.

29

Campbell 47 WA Ship rat Conservation Commission Crocus 41 WA Ship rat Conservation Commission Primrose 41 WA Ship rat Conservation Commission Delta 38 WA Ship rat Conservation Commission Brush 36 NSW Ship rat Dept. Environment &

Conservation Bedout 30 WA Ship rat Conservation Commission Bridled 27 WA Mice Conservation Commission S. Double 23 WA Ship rat Conservation Commission Ah Chong 22 WA Ship rat Conservation Commission Brooke 15 WA Ship rat Conservation Commission Heron 13 Qld ? Ship rat W. Coringa Cay 13 Com Ship rat South east 13 WA Ship rat Conservation Commission N. Double 12 WA Ship rat Conservation Commission Shelter 8 WA Ship rat Conservation Commission Sandy 6 WA Ship rat Conservation Commission Boomerang 5 WA Ship rat Conservation Commission West Ashmore 5 Com Ship rat(?) Ivy 4 WA Ship rat Conservation Commission Prince 4 WA Ship rat Conservation Commission Blood wood 3 WA Ship rat Conservation Commission Pigeon 3 WA Ship rat Minister for Fisheries Pasco 2 WA Ship rat Fisher 1 Tas Ship rat Beacon 1 WA Mice

Appendix 11.3. Notes on biosecurity responses suggested for different island types in New Zealand

The ability to maintain an adequate surveillance regime will depend considerably on the nature of the island under management ( e.g. frequency of visits, size of island) . The New Zealand Department of Conservation considers five general categories of islands:

1) Regular visits on large islands

Multi-purpose attractive (preferably wooden) rodent stations/motels which can incorporate bait and traps should be maintained on the island. Island should be regularly checked by rodent dog.

2) Regular visits on small islands

As above at about 1-2/ha with additional tracking tunnels (ink cards) and gnaw devices (e.g. waxtags). If this can not be serviced regularly (3-4 times annually) then revert to above.

3) Remote and seldom visited islands

C C C C C

C C C C C

C C C C C

C C C C C

' '

I.

30

Baiting in high-risk areas ( e.g. in buildings, around points of landing), and empty covers (preferably wooden) GPSed and ready for activation with more traps and poison. Surveillance should be unde11aken whenever groups (e.g. management or research) visit the island, for a period of at least one week.

4) History of many invasions

A combination of (1) and (3) with empty wooden covers on a more intense grid (e.g., 50 m) .

5) One rodent species already exists

Do not use poison. Operate traps only when visiting the island. Use suitable devices which exclude non-target rodent species ( e.g. traps triggered by weight, elevated bait stations). For mice incumbent rodent species may need trapping out before mice become detected.