The method chosen for the LHI REP is to eradicate rats and mice by distribution of the toxin Brodifacoum at a concentration of 20 ppm in the cereal based product Pestoff 20R. Justification for this methodology, toxin and bait is provided.
The bait will be distributed at a nominal dose rate of 20 kg (12kg first application + 8kg second application of bait (or 0.4 g of toxin) per hectare on average over the island. Bait will be distributed by a combination of aerial and hand broadcast and through the use of bait stations/trays.
Less than 1.2kg of the active ingredient (toxin) Brodifacoum will be used in total, over 2 baiting applications.
Each pellet has a Brodificoum concentration of 20 parts per million, 2 ½ times lower than the bait that can be bought in shops.
Area to be Baited
Rats and mice occur throughout LHI, including the settlement. LHI is the only island in the LHIG that is known to contain rodents. However, ship rats are able to swim over 500 m and both rats and mice are difficult to detect at low densities. It is therefore possible that either species may occur on offshore islands and islets close to the main island or may invade those islands prior to the implementation of the operation. To minimise the risks of operational failure, the main island and all nearby islands and islets, other than Balls Pyramid and its associated islets, will be baited. The 23 km distance between Balls Pyramid and the main island renders the chances of invasion by rodents very low.
Number of Bait Drops
The proposal is for aerial and hand baiting to be carried out twice only, the applications separated by about 14-21 days (depending on the weather) although the number of applications in and around dwellings may be more as it is dependent on the rate of removal by rodents of distributed baits. This will maximise the exposure of rodents to the bait. The proposed application rate for the first bait drop is 12 kg of bait per hectare, and 8 kg per hectare for the second drop. These application rates relate to the actual surface area of the islands. Most rodents will be killed by bait from the first bait drop. However, it is beneficial to carry out a second bait drop to eliminate the likelihood of any gaps in the distribution of baits, ensure bait is available long enough to ensure that all individuals receive a lethal dose and to target:
- individuals that may have been denied access to bait distributed in the first application (by more dominant individuals that will now be dead), and
- any surviving young that have recently emerged from the nest.
The operation is programmed to take place in winter 2019 (June-August), when the availability of natural food for rodents is low, rodent breeding is greatly reduced or absent and the rodent populations are likely to be at their seasonal lowest. This is also a period when most non-target seabirds are absent from the LHIG. Bait drops will be timed to avoid periods of predicted heavy rainfall (as this may prematurely dissolve the bait) and cannot take place in high winds or in the presence of low cloud. Therefore weather will influence the actual timing of the two bait drops. Weather forecasts of rainfall and wind speeds will be obtained from the Bureau of Meteorology station on LHI from June onwards. A forecast of less than 15 knots and four fine days (three fine nights) without significant rainfall (less than 6 mm daily) is preferred for each drop but the decision to apply bait will be taken by the operations manager at the time when all relevant factors are known.
Given the possibly limited operational window, approval is sought for at least a three year period to account for unforeseen delays beyond winter 2019, however the operation would only occur once during that period.
Aerial baiting will be conducted throughout the LHI PPP and other areas of the main island excluding the settlement area and identified buffer zones. In all areas baited aerially, 10 mm baits (approximately 2 g each) will be broadcast at a density of 12 kg/ha (one bait every two square metres) for the first drop and 8kg/ha for the second drop on average over the island.
The bait will be dispersed using a purpose built spreader bucket (see Figure 15) slung below a helicopter. A rotating disc typically throws the bait 360o to 35 m (note outlier pellets may be thrown to 45 m); enabling a swathe of up to 70 m to be baited in a single pass.
Overlapping (50%) each swathe will ensure that there are no gaps in the distribution of baits (see Figure 16). Application rates out of the bucket are calculated to account for the 50% overlap (i.e. for the first drop 6 kg/ha on each swathe with 50% overlap will be applied to achieve a 12kg/ha application rate on the ground). Each bait drop will take approximately two days to complete dependant on weather.
Figure 15 Custom built spreader bucket being prepared and in use on LHI during 2007 trials.
Figure 16 Aerial Application Method
In order to achieve the required baiting density on the cliffs and steep slopes (particularly around Mt Gower and Mt Lidgbird) several horizontal flight lines will be flown at approximately 50 m vertical spacing along these areas to ensure adequate bait coverage. Baiting around the coast line will occur above the mean high water mark to minimise bait entry into the marine environment. A deflector arm can be attached to the spreader bucket to restrict the arc of the swathe to 180o and will be used particularly when baiting the edge of buffer zones and to minimise bait entry into the marine environment when baiting coastal areas including cliffs. The sowing rate, bait direction and swathe width can all be controlled within set limits and will be adjusted as required for specific requirements for different types of flight lines (inland, coastal or buffer zone). Other aerial dispersal options include the idling or turning off of the spinning motor on the spreader bucket which will result in bait trickling vertically below the helicopter for narrow areas if required. The combination of techniques will enable all terrains on the LHIG to be effectively baited. The exact methodology of distributing bait aerially on LHI will be finalised in consultation with the helicopter contractors.
Buffer zones for aerial application to individual properties will be agreed with the relevant occupiers and in accordance with relevant regulations and considering outliers from the bait swath. The LHIB has committed that this would be no closer than 30 m to dwellings, by agreement or if agreement to the contrary is not reached, then the buffer zone will be 150 m. In these buffer zones bait will be applied by hand, or in bait stations. This will be covered in a Property Management Plan for each property. 30 m buffer zones will also be established around containment areas for the dairy herd.
GPS will be used to guide the helicopter along a set of pre-determined flight lines designed to ensure that all areas are adequately baited. Computer-generated plots of the actual path flown will be inspected at predetermined times during and at the completion of the flight to confirm that this has been done. Any identified gaps will be treated. Flight-path height will be set at an altitude that ensures effective and safe baiting. It will be determined in discussion with the baiting operator, and take into account topography, weather conditions, aircraft safety and the need to avoid significant disturbance to roosting birds.
This baiting methodology is similar to (and is based on) established techniques for other island pest eradications undertaken worldwide. In Australia this technique has been used on islands such as Montague (2007) and Broughton (2009) islands in New South Wales and Hermite Island (1996) in Western Australia. It was also used on World Heritage listed Macquarie Island in Tasmania over autumn and winter 2011.
The aerial baiting technique has been trialled on LHI with non-toxic bait and a custom built spreader bucket (DECCa, 2007). The trials have shown aerial baiting to be an effective technique that could be utilised in an operation on Lord Howe Island. The trial report is included in Appendix D – LHI Trials Package. The trial provided an opportunity to establish the correct flight configuration: air speed and settings to produce the required flow rate to achieve the on ground density of bait during operations. Methodologies for loading procedures, and determination of bait usage on flight runs were developed for use in future baiting operations.
Further detailed calibration of the equipment with non-toxic baits (i.e. helicopter, spreader bucket, GPS equipment etc.) will be undertaken immediately prior to the operation as part of an operational readiness check overseen by an international eradication expert most likely from the New Zealand Department of Conservation’s Island Eradication Advisory Group.
Hand Broadcasting of Bait
Hand broadcasting of bait will be conducted concurrently with aerial baiting. It will be undertaken throughout the settlement area where agreed by residents under individual Property Management Plans and in buffer and exclusion zones (i.e. the lagoon foreshore and Ned’s Beach). In the settlement area, either 10mm (2 g each) or 5.5 mm Pestoff baits (0.6 g each) will be hand-broadcast at a density of 12 kg/ha (one bait every two square metres for the 10mm pellet or one bait every half square metre for the 5.5 mm pellet on average) for the first application of bait and at 8 kg/ha for the second application.
Provisional areas to be hand-baited are subject to completion of individual Property Management Plans and collation into a revised operational plan.
Trained personnel will move through such areas and apply bait at the designated rate. All personnel will carry a GPS unit capable of continuously tracking their path. Computer-generated plots of their paths will be used to check baiting coverage. The aim will be to distribute baits in garden beds and other areas of vegetation around dwellings, rather than broadcast on lawns. These details will be contained in the individual property management plans which will be established between property occupiers and the LHIB.
It is essential that all hand-broadcast bait be out in the open so it is subject to degradation by weathering. No bait will be hand-broadcast directly in or under buildings where it will not be subject to weathering.
Commercially available or specifically designed bait stations (see Figure 17) will be used where aerial or hand broadcasting cannot be undertaken. Bait stations will also be placed within all areas containing livestock (i.e. dairy herd, horses and goats). The bait stations used in livestock areas will be designed specifically to be able to withstand interference and trampling by stock. Where practicable, and with the agreement of householders, small amounts of bait in open containers (‘bait trays’) similar to commercial products currently available, will be placed within buildings including kitchens, pantries, pet food storage areas etc. Where possible, bait trays will also be put in accessible roof spaces and under-floor cavities.
Note: there is a potential for currently registered Brodifacoum products to be used in accordance with label conditions by residents in some dwellings. This will be considered on a case by case basis assessing higher palatability of pellets vs. higher dosage, quality control and resident acceptability.
All bait trays and bait stations will be monitored regularly and bait replenished as necessary for approximately 100 days after the second baiting (this could be longer if surviving rats or mice are detected). Bait uptake will provide an indication of rodent activity, along with other detection techniques such as detector dogs, chew blocks and tracking tunnels. Bait in these locations will not be exposed to weathering, and so any remaining bait will be removed once project staff are confident all rodents have been eradicated from the island.
When using bait stations or trays it is important that they are set close enough together that individual rats and mice encounter at least one station during their nightly movements. Rats are wide-ranging and can be eradicated using a grid spacing of 25 m -50 m. Mice, however, are not as wide-ranging, and require a grid spacing as close as 10 m.
It is expected that the combination of hand broadcasting and setting and arming of bait stations will take approximately 5 days each application (coinciding with the aerial application) dependant on results of the property management plan process and actual staff numbers.
Indicative areas to be treated using the three methods above are shown in Figure 18 and Figure 19.
Property Management Plans
The LHIB has been consulting with all property owners and residents on the island to develop individual Property Management Plans (PMPs) as part of the REP. The PMPs include the agreed baiting methods for each lease on the Island, including the settlement area. This can include the desired combination of hand broadcast and bait stations on individual properties and if properties are on the edge of the settlement area, the appropriate buffer distances for aerial distribution.
The PMPs are confidentially discussed and negotiated with the leaseholders / residents individually and consider mitigation of specific risks and areas of concern on individual properties and in accordance with any regulatory approvals or conditions received. The PMPs will only need to be signed once all government approvals have been received and the final decision to proceed with the eradication project has been made by the LHIB. The PMPs will not impact on the tenure of the leases.
At the manufacturing plant in New Zealand, the bait will be packaged into 25 kg bags and loaded in approximately 1 tonne weatherproof bait pods for transport by ship to mainland Australia. After customs and quarantine clearance in Australia, the bait will be barged to LHI. On arrival on LHI, bait will continue to be stored in the weatherproof bait pods in a secured premise most likely at the LHI Airport.
A limited amount of contingency bait will be purchased with the order in case of physical damage including weathering or bait loss so it is anticipated that there will be bait remaining at the end of the operation.
Unused Pestoff 20R is likely to be retained in case it is needed for follow up or incursion response. It may also be transported back to the mainland for sale to other similar projects or for disposal at an appropriately licensed facility. Unusable spillage will be collected and transported to the mainland for disposal. Emptied Pestoff bags may be disposed of in a similar manner as discarded bait pellets or they may be incinerated on LHI in accordance with all legal requirements.
Rodent and non-target carcasses will be collected wherever possible by ground staff during and immediately after the operation, particularly in the settlement area, however due to the large size of the island and rugged and inaccessible terrain this will not be possible across most of the island. It is proposed that carcasses collected will be buried, incinerated on island or transported back to the mainland for disposal at an appropriately licensed facility.
In the event of a spill, the area will be isolated and all practicable steps taken to manage any harmful effects of the spillage including preventing baits from, as far as practical, entering streams or waterways. Spilled baits will be collected and put into secure containers. Fine material will be swept up and placed into bags for disposal as above.