It seemed like a good idea at the time: Remove all the feral cats from a famous Australian island to save the native seabirds.
But the decision to eradicate the felines from Macquarie island allowed the rabbit population to explode and, in turn, destroy much of its fragile vegetation that birds depend on for cover, researchers said.
Removing the cats from Macquarie "caused environmental devastation" that will cost authorities $16.2 million to remedy, Dana Bergstrom of the Australian Antarctic Division and her colleagues wrote in the British Ecological Society's Journal of Applied Ecology.
"Our study shows that between 2000 and 2007, there has been widespread ecosystem devastation and decades of conservation effort compromised," Bergstrom said in a statement.
The unintended consequences of the cat-removal project show the dangers of meddling with an ecosystem — even with the best of intentions, the study said.
"The lessons for conservation agencies globally is that interventions should be comprehensive, and include risk assessments to explicitly consider and plan for indirect effects, or face substantial subsequent costs," Bergstrom said.
Located about halfway between Australia and Antarctica, Macquarie was designated a World Heritage site in 1997 as the world's only island composed entirely of oceanic crust. It is known for its wind-swept landscape, and about 3.5 million seabirds and 80,000 elephant seals migrate there each year to breed.
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Authorities have struggled for decades to remove the cats, rabbits, rats and mice that are all nonnative species to Macquarie, likely introduced in the past 100 years by passing ships.
The invader predators menaced the native seabirds, some of them threatened species. So in 1995, the Parks and Wildlife Service of Tasmania that manages Macquarie tried to undo the damage by removing most of the cats.
Several conservation groups, including the International Union for Conservation of Nature and Birds Australia, said the eradication effort did not go far enough and that the project should have taken aim at all the invasive mammals on the island at once.
"It would have been ideal if the cats and rabbits were eradicated at the same time, or the rabbits first and the cats subsequently," said University of Auckland Prof. Mick Clout.