Imported Animals Outfox Native Ones Down Under : Nature: Australia and New Zealand are beset by ecological problems caused by rabbits, opossums and other species introduced from around the globe.

Australia and New Zealand are cursing the introduction of rabbits, foxes, opossums and other foreign animals that breed virtually unchecked because their natural predators were not brought along.

“New Zealand could be said to be facing a creeping ecological disaster with the impact of introduced species on our environment,” said Philip Woollaston, the country’s conservation minister.

“We have a long and inglorious history of introducing new and alien elements into our environment. Homesick settlers brought familiar plants and animals to a country that looked foreign to them.

“It has taken a long time for us to shake off the settler mentality of wanting to create a Southern Hemisphere European country.”

Some introduced species are assets. Sheep, cattle and various crops have become economic mainstays of both countries, but the lists of foreign pests are long.

New Zealand’s problems include goats, chamois, opossums, wasps and deer. Predators or parasites sometimes have been brought in as controls, but they often created new problems.

“Foxes were once thought to be the answer to the rabbit menace,” Woollaston said. “Fortunately, they did not take hold in New Zealand as they have in Australia, where they have done terrible damage to indigenous fauna.

“Unfortunately, stoats and weasels, which also were introduced for rabbit control, have found New Zealand a very suitable habitat.”

The opossum, introduced from Australia in the 19th Century for its fur, now is the main threat in New Zealand. The government has declared war on the animal, which outnumbers the 3.1 million New Zealanders about 23 to 1.

Opossums devastate foliage in many forests and carry a form of tuberculosis that has infected other species, particularly cattle.

There has been little public resistance to poison pellets intended to kill opossums, even though other animals also die.

Agriculture Minister Jim Sutton said New Zealand needs a major research project to find biological methods of wiping out the opossum through disease or sterility without harming other species.

“We have to do the research ourselves, because this is a uniquely New Zealand problem,” he said.

Sutton said opossums could withstand a death rate of 5 million a year without a permanent reduction of their numbers.

Margaret Evans, mayor of the North Island city of Hamilton, has suggested an opossum-hunting program to give jobs to the unemployed.

Foxes and rabbits were brought to Australia by Europeans to be bred for hunting. They now are blamed for contributing to the extinction of 18 marsupial species and threatening 30 others.

The fox preys on birds, reptiles and farm animals; the rabbit destroys vegetation.

Victoria state alone has about 25 million rabbits. Officials estimate that the animals cost the national wool and cattle industries $100 million a year, which does not include environmental damage.

Steve Crabb, the state’s environment minister, suggests marketing fox pelts as an “environmentally friendly” alternative to other furs.

“The fox did not co-evolve with our native wildlife, so these small animals have no defense mechanisms against it,” said Clive Marks of the Keith Turnbull Research Institute. “We’ve never had a predator like the fox. It’s a very efficient killing machine.”

Australia has strict quarantine laws to keep out rabies and other animal diseases, and officials fear the fox as a carrier.

“Should we get rabies, our fox population would be the prime spreader of the disease,” Marks said.

Introduction of fleas carrying a rabbit-specific myxoma virus reduced the number of rabbits for a time until they developed immunities. As with the opossum in New Zealand, the best hope for controlling Australia’s rabbits and foxes lies in research.

Efforts are under way to genetically alter existing viruses so they will make the animals sterile.