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Where is Macquarie Island?
Macquarie Island is an Australian sub-Antarctic island with an area of 12, 875 ha. It is 34 kilometres long and up to 5 kilometres wide, and is located 1500 kilometres southeast of Hobart, Tasmania.
The island is a Nature Reserve managed by the Tasmanian Government through the Parks and Wildlife Service (PWS). The PWS also manages the island as a World Heritage Area on behalf of the Australian Government.
The Australian Government has a facility on the island with the Australian Government Antarctic Division maintaining a research station, and the Bureau of Meteorology collecting weather data, including upper air soundings.
Why is it so special?
Macquarie Island was declared a Wildlife Sanctuary in 1933, a State Nature Reserve in 1972, and a UNESCO Biosphere Reserve in 1977. It was listed in the Register of Critical Habitat in 2002. The various designations reflect the importance of the reserve and the natural and cultural values it embodies.
Macquarie Island was inscribed on the World Heritage List in 1997 to recognise its geological significance and outstanding natural beauty. It is the only island in the world composed entirely of oceanic crust and rocks from the Earth’s mantle and is notable for its remote and windswept landscape and vast congregations of wildlife.
The Nature Reserve designation recognises the importance of the subantarctic flora and fauna, including several endemic species.
Macquarie Island is one of only a very few islands in the Pacific sector of the Southern Ocean where fauna in the region breed. Around 3.5 million seabirds and 80,000 elephant seals arrive on Macquarie Island each year to breed and moult. Fur seals are beginning to re-establish populations on the island after nearly being exterminated in the early 19th century.
What problems are caused by introduced species?
In recent years rabbit damage to vegetation on Macquarie Island has increased significantly. This is resulting in serious vegetation changes and is impacting on burrowing seabirds that require vegetation cover around their breeding habitat.
In 2006 landslides - at least partially caused by rabbit grazing - were responsible for the deaths of penguins and damage to visitor boardwalks on the island.
Rodents are also having a significant impact on the island, with ship rats in particular eating the eggs and chicks of burrow-nesting petrels. With no vegetation on the island higher than tussock grass, all species must breed on or in the ground. Mice and rats are also predators of invertebrate species.
What does the eradication project involve?
The eradication of rabbits, rats and mice on Macquarie Island should be seen as three specific eradications being conducted concurrently, in order to maximise the efficient use of resources. The techniques to be used are based on successful eradications on other islands worldwide and on the characteristics of each of the three target species.
Firstly, helicopters will spread pellet baits containing brodifacoum targeting rodents, although rabbits will also consume the bait. GPS units in the helicopters will ensure accurate coverage of bait spreading. This should eradicate all of the rodents and a high proportion of rabbits. This method has been used on many islands around the world to successfully eradicate rodents.
Secondly, field teams will follow up on the ground eliminating surviving rabbits by shooting, fumigating and trapping them. Dogs will be used to indicate areas where rabbits are surviving, and are considered critical in locating rabbits in the rugged terrain of Macquarie Island.
Work has started on several aspects of the eradication project:
- An automatic weather station was established on the southern plateau in 2007 to assist in determining weather patterns – an important factor for planning helicopter flights for spreading poison baits.
- Trials testing the effectiveness of bait pods and over-flight of penguin rookeries have been conducted in 2007 and 2008. Non-toxic baits have also been trialled to assess weathering characteristics and palatability of the bait, and whether non-target species are likely to be at risk from the bait.
- 21 plots around the island have been fenced to protect plant species that may not recover from severe rabbit grazing.
- Planning has commenced on some of the approvals required to implement the plan.
- Contractors have been engaged to train dogs to detect rabbits. The dogs will be trained to ignore other animals on Macquarie Island.
Won’t poisoning the animals be cruel?
The use of poisons is an accepted practice in dealing with pest species. No other technique has proven successful in eradicating rodents on sub-Antarctic islands Various toxins were considered and brodifacoum identified as being the most suitable. All three target species (rabbits, rats and mice) are known to consume the baits, although only rodents are expected to be eradicated by this method. The toxin used is the same as that in rat poison which is widely available for domestic use.
Is it likely that native animals would be affected by poisoning?
The need to keep non-target species impacts to a minimum has been an important consideration in all planning for the eradication. An Environmental Impact Statement is being prepared to assess the likely impact of the project on the environment. The baiting will be done in winter when most of the native animals are absent from the island, thus minimising or avoiding any effects on their populations. Trials have been conducted on the island with non-toxic baits to determine the response of native birds to the baits. These indicated that most native bird species are not interested in the baits, although some gulls may consume them.. Recovery of the vegetation on the island following rabbit eradication, and removing rats as a predator, will vastly improve conditions for all native species, and at least 28 native bird species are expected to increase in population following a successful pest eradication..
What about using myxomatosis and/or RHVD?
Myxomatosis has been used to control rabbits on the island for over 25 years. Further supplies are now unavailable and the virus appears to be losing effectiveness on the island. RHVD (calicivirus) is not an eradication tool and the efficacy in the cool moist climate is unknown. It is ineffective against rodents so baiting would need to be done to eradicate them anyway.
When will the aerial baiting occur?
Aerial baiting operations will be undertaken between May and August of 2010. The winter months have been identified as the best time to conduct aerial baiting for the following reasons:
- There is less natural food around for the rabbits and rodents thus a greater chance they’ll eat the baits;
- There are lower numbers of rabbits and rodents during winter (less breeding and higher mortality) so there are fewer animals to target, meaning that fewer need to be killed;
- Baiting during this period avoids the breeding season for native animals, so fewer of them are on the island; and
- It avoids the summer tourist season so tourism operators will not be affected.
How long will the eradication project take?
One of the most important aspects of planning such a challenging operation is the time required to complete the complex logistical planning required, and to obtain the relevant approvals. Eradication operations are typically a “one chance only” scenario and it is critical that the planning is thorough and comprehensive.
It will take until 2010 to complete all the planning required prior to the aerial bait drop, including acquiring and training the dogs to the high standards required.
After aerial baiting, three years has been allowed for eradication of surviving rabbits Once the last known rabbit has been removed, a monitoring period of two years will commence to check thoroughly for any indications of rodents or rabbits surviving.
Isn’t it too late anyway – haven’t the values of Macquarie been lost?
The natural ability of the island ecosystem to restore itself is demonstrated by the revegetation apparent in fenced exclosure plots, and the return of grey petrels to breed on the island in 2000 following eradication of feral cats. Removal of the animals causing the decline in the island’s values will, in time, enable the island to recover.
Will the island need to be revegetated once rabbits are removed?
Exclosure plots constructed on the island since the 1960s have demonstrated that the rate of vegetation recovery can be high in favourable sites. Because of that recovery, no revegetation activity is planned (see a series of photos of an exclosure plot constructed in 2006 - PDF 786Kb).
Macquarie Island has harsh growing conditions for plants and recovery of some vegetation communities may take decades.
What if this doesn’t work – what are the other options?
Should the project prove unsuccessful in eradicating any or all of the three target species, future management may involve control of rabbits to low numbers and possibly future eradication attempts for rodents. Before this could be considered, the lessons learnt from this project would need to be carefully assessed along with the ongoing development of eradication techniques.
Eradicating rabbits and rodents is the best way to protect Macquarie Island’s native flora and fauna and World Heritage values. There have been successful pest eradications on other islands, and this project has benefited from that experience. While the project is very ambitious, the conservation gains to the island from a successful eradication are immense.