January 12, 2009

Cat Removal Devastates Island

A new Australian study finds that the removal of cats in 2000 caused "catastrophic" damage to Macquarie Island, a World Heritage Site that lies roughly halfway between Australia and Antarctica.

The cats, which had served as a check on rabbits, were eradicated because they were also eating seabirds.  Since then, rabbit numbers have risen sharply, and the animals have devastated the flora to the extent that the changes can even be seen from space.

The Australian government now plans to eradicate rats, rabbits and mice from the island next year by dropping poisoned bait throughout the area.

The researchers are calling on conservation agencies to "learn lessons" from the events.

"Our study shows that between 2000 and 2007 there has been widespread ecosystem devastation and decades of conservation effort compromised," Dana Bergstrom from the Australian Antarctic Division told BBC News.

"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."

For the current case, one component of the cost is the $17 million that the government must now spend to eradicate rabbits, rats and mice that eat seabird chicks.

Seal hunters first introduced rabbits to Macquarie Island in 1878 to provide food. Initial attempts to control their number during the 1960s involved introducing myxomatosis, which brought the number down to about 10,000.  

However, there are now 100,000 rabbits on the island since the removal of cats in 2000.

Macquarie Island is thought to be the most important breeding site for the royal penguin and many other penguin species.  Removal of plant cover is believed to make penguins more susceptible to predation.
The study was published in the Journal of Applied Ecology.


Image Caption: View over Macquarie Island bluffs (with a small view of King penguins on the beach below). Courtesy Wikipedia


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