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MACQUARIE ISLAND: FROM RABBITS AND RODENTS TO RECOVERY AND RENEWAL A majestic landscape Roughly half way between Tasmania and Antarctica lies Macquarie Island. At approximately 34 kilometres long and 5.5 kilometres wide at its broadest point, this subantarctic island is renowned for the spectacular beauty of its remote and windswept landscape. Its steep escarpments, lakes, and dramatic changes in vegetation provide an outstanding spectacle of wild, natural beauty complemented by vast congregations of wildlife including penguins and seals. It also provides a unique opportunity to study geological features and processes of oceanic crust formation and plate boundary dynamics. It is the only place in the world where rocks from the earth’s mantle are being actively exposed above sea level. Macquarie Island’s inscription on the World Heritage List in 1997 was in recognition of its outstanding natural values. Its birdlife in particular has always been extraordinary. The breeding populations of penguins (including the endemic royal penguin), albatrosses, petrels and prions are recognised as one of the greatest concentrations of seabirds in the world. Royal penguins. (Photo: Greg Stone) environment.gov.au Images (L–R): Shield ferns. (Photo: Stephen Horn), Petrels nesting at Gadget Gully. (Photo: Chris Howard). HER89.0613 Macquarie Island on a misty day. (Photo: Richard Dakin) Rabbit and rodent invasion Eradicating the invaders European rabbits were introduced to Macquarie Island in the 1870s, while black rats and house mice were first recorded on the island in the 1890s. Following the eradication of feral cats in 2000, rabbits and rodents became the dominant pest species on the island. A dramatic increase in their populations caused devastating damage to the island’s vulnerable vegetation and wildlife. The Macquarie Island Pest Eradication Project was developed to eradicate all three invasive species at the same time. In June 2007, the Australian and Tasmanian governments agreed to $24.6 million of joint funding to implement the Plan for the Eradication of Rabbits and Rodents on Macquarie Island. The plan was based on New Zealand’s experience in successfully eradicating rabbits and rodents from similar subantarctic islands. Rabbits consumed the large leafy megaherbs and grasses, which lacked the ability to adapt to grazing. Extensive damage was occurring to the tall tussock grassland, resulting in a loss of breeding habitat for nesting seabirds and the destabilisation of slopes. Rats had been preying on seabird chicks and eggs, and were a threat to at least nine bird species breeding on Macquarie Island. The presence of rats and mice was also inhibiting plant regeneration. This important project required several years of detailed planning, with management by the Tasmania Parks and Wildlife Service. The project is overseen by a steering committee which includes representatives from the Tasmanian Government, Australian Government and the New Zealand Department of Conservation. The Australian Government is committed to continuing the success of the program. Poison baits were dropped by helicopter in the winter of 2010. The bait drop was carried out in winter for three main reasons: to reduce the impact on native wildlife, much of which leaves the island during the winter; to target rabbits and rodents when they were at their lowest numbers; and to increase the likelihood of bait uptake by the target species as there is less alternative food available. Around eight per cent of the bait was distributed before bad weather forced the postponement of the bait drop to the winter of 2011. Rabbit and rodent activity decreased markedly in areas that had been baited. Effects of the rabbit population. (Photo: Image courtesy of Tasmania Parks and Wildlife Service) However, the number of seabird deaths following the limited baiting was higher than estimated, primarily due to poisoned rabbit carcasses being eaten by scavenging seabirds. A review of the program found that no entire population of seabird was expected environment.gov.au Images (L–R): Galium Shield ferns. antarcticum. (Photo: (Photo: StephenNick Horn), Fitzgerald), Petrels nesting Track protecting at Gadgetsensitive Gully. (Photo: vegetation. Chris Howard). (Photo: Chris Howard) Aerial baiting was completed in the winter of 2011 and was supplemented with a limited amount of hand baiting. Ground hunting teams made up of skilled hunters and specially trained detector dogs worked to eliminate surviving rabbits. The dogs were trained to locate rabbits but not to harm native animals. In addition, three specially trained rodent detector dogs were sent to the island in March 2013. Ground hunting teams have now covered over 65 000 km on foot since August 2011 looking for signs of rabbits and rodents. Revegetation and renewal King penguins and detector dogs. (Photo: Dana Boyte) to be lost as a result of the continuation of the project. It also found that if the eradication program was not continued catastrophic damage to the ecosystem would continue and some seabird populations could become extinct on the island. The eradication program was subsequently modified to lessen the impact on native wildlife. Calicivirus was introduced early in 2011 with the aim of reducing the rabbit population and the number of poisoned rabbit carcasses following baiting. More people were employed to search the island and remove poisoned carcasses before they could be consumed by scavenging seabirds. Although the program has not yet been completed, great progress has been made with both the eradication of pests and the recovery of vegetation species. Vegetation is re-establishing itself on the island with regrowth of tussock grasses and Macquarie Island cabbage particularly noticeable in places. Many seedlings have sprouted and some of the smaller plant species are more numerous than prior to the aerial baiting. There have been no confirmed sightings of rats and mice since the last bait drop in July 2011. Out of an estimated pre-eradication population of over 100 000, only 13 live rabbits have been found during the ground hunting phase, with no confirmed signs of rabbits since December 2011. A two year monitoring period includes intensive searching for any surviving rabbits. There may not be signs of rabbits or rodents on the island, but there is ever growing evidence of ecosystem recovery. environment.gov.au Images (L–R): Macquarie Shield ferns. Island (Photo: on a Stephen misty day. Horn), (Photo: Petrels Richard nesting Dakin), at Gadget RoyalGully. penguins. (Photo: (Photo: ChrisGreg Howard). Stone). In March 2013 long term vegetation monitoring plots were revisited for the first time. Rapid recovery was noted in some of the most palatable and visible species, such as the megaherbs Stilbocarpa (Macquarie cabbage), Pleurophyllum hookeri (silver-leaf daisy) and Poa foliosa (tussock grass). The shield fern, Polystichum vestitum, is showing good recovery in the exclosures built six years ago to conserve a ‘seed’ population. Small populations of the shield fern are also starting to appear in scattered locations across the island. The introduced species Poa annua (meadow grass) forms thick lawns in places. Epilobium brunnescens (a low-growing, mat-forming herb) also appears to be more common than previously recorded. Moss cover is higher at all sites in 2013 than in previous years. The most unexpected and exciting find on the island was the rediscovery of the small herb Galium antarcticum (subantarctic bedstraw) on the northern shore of Skua Lake. The species was only known on Macquarie Island from a single collection at Skua Lake in 1983. Searches by botanists over following years had failed to relocate the species. The species has recently been listed as critically endangered under Australia’s national environmental law, reflecting its extreme rarity in Australia. Galium antarcticum. (Photo: Nick Fitzgerald) Shield ferns. (Photo: Stephen Horn) It is not only the vegetation that is recovering. Blue petrels are now breeding in more widespread nests on the island, whereas in the past rat incursions restricted their breeding to offshore stacks. Terns have been seen breeding on cobblestone beaches and grey petrels have had their most successful breeding season since recording of their populations commenced in 2000. The intervention and action to eliminate rabbits, rats and mice on Macquarie Island is leading to a resurgence of this unique landscape’s spectacular natural beauty and recovery of its outstanding World Heritage values. Petrels nesting at Gadget Gully. (Photo: Chris Howard) environment.gov.au Images (L–R): Macquarie Shield ferns. Island (Photo: on a Stephen misty day. Horn), (Photo: Petrels Richard nesting Dakin), at Gadget RoyalGully. penguins. (Photo: (Photo: ChrisGreg Howard). Stone).