Killing cats to restore island backfires as rabbits take over

Two attempts to reverse a man-made environmental catastrophe on a tiny sub-Antarctic island have backfired, necessitating the implementation of a $16-million rescue plan and providing a warning for scientists attempting to remove invasive species in other regions of the world.

The site of the disaster is tiny Macquarie Island, a 50-square-mile dot in the Southern Ocean about halfway between Australia and Antarctica. It was named a World Heritage Site in 1997 because it is the only place on Earth where rocks from the Earth’s mantle are being actively exposed above sea level.

Soon after the island was discovered in 1810, seafarers began visiting it to slaughter fur seals, elephant seals and penguins for their fur and blubber. When the sailors docked, rats and mice abandoned the ships and took up residence, attacking food stores on land. To counter them, the sailors started bringing cats to the island about 1818.

Following a common tradition, sailors also introduced rabbits to the island about 60 years later to provide a food source for stranded seamen. Cats and rabbits both proliferated, with the population of rabbits reaching about 130,000 in the 1970s. The cats fed on both the rabbits and native birds; two species, a flightless rail and a parakeet, were exterminated. The rabbits were stripping the island’s vegetation bare.

In 1968, in an effort to control the situation, scientists introduced the Myxomatosis virus, which is lethal to rabbits, and the European rabbit flea, which spreads it. By the early 1980s, the rabbit population had fallen to about 20,000. But the cats were hungry, and they began feeding on burrowing sea birds, threatening their existence. Again, researchers intervened and began shooting the cats. By 2000, there were none left.

But to the researchers’ great surprise, biologist Dana Bergstrom of the Australian Antarctic Division and her colleagues report in the current Journal of Applied Ecology, the rabbits began proliferating again despite the presence of the virus. The animals have now stripped as much as 40% of the island bare of vegetation. They were even blamed for a 2006 landslide that wiped out part of a penguin colony.

The next stage, Bergstrom said, could be an “ecosystem meltdown,” in which the entire island’s ecology is disrupted.

Scientists’ only course now is to eradicate all the rabbits, mice and rats on the island, which could cost at least $16 million and take years. Bergstrom hopes this works better than previous interventions.

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thomas.maugh@latimes.com