Immigrants of all stripes occupy New World, crowding out native species. Success stories are few. : Arctic Foxes Prey on Geese in Alaska, but Sanctuary Helps

Cold weather and remote geography usually work against invasive species gaining a foothold in Alaska. But those elements were just what 18th century Russian fur traders wanted when they introduced arctic foxes to the Aleutian Islands.

The rocky, treeless islands kept the free-ranging foxes from escaping. Winters were cold enough that the animals’ fur grew thick and valuable, but the snowfall was light enough that trappers could get around easily.

Best of all, resident seabirds presented a plentiful food supply for the hungry foxes. Among the easiest pickings was the Aleutian Canada goose, a migratory species that nests on the ground.

Foxes spread and multiplied after the United States bought Alaska from Russia in 1867 and expanded the fur-farming industry to nearly 200 islands in the birds’ nesting range. Fur farming faded after the 1930s, but the foxes remained and continued eating the goose population.

“The only islands where the goose was maintained was where foxes were not introduced,” said Dan Boone, deputy refuge manager for the Alaska Maritime National Wildlife Refuge. “Those were the islands too difficult to access for the fur trappers.”

The Aleutian goose had a change of fortune in the early 1960s. Biologists discovered 200 to 300 of the birds on Buldir Island in the far western Aleutians.

Wildlife officials shot, trapped or poisoned all of the foxes on a handful of islands, then borrowed young birds from Buldir to reestablish goose colonies. The reseeding worked so well that the goose count now is up to about 32,000 birds.

“This phenomenon is now back,” Interior Secretary Bruce Babbitt said in July, announcing the government’s proposal to remove the goose from the federal list of threatened species. “It’s a wonderful story.”

Fox eradication continues on other islands where the government wants to reestablish goose populations. More than 500 were killed last year on Kanaga Island, but Boone said typically 200 or so foxes are removed each year from any one island, either dead or alive for relocation.

Conservationists who might protest the slaughter of foxes under other circumstances are backing the government because the arctic foxes are not native to the Aleutians.

“It is a very responsible action,” said John Schoen, Alaska director for the National Audubon Society. “It’s incumbent on wildlife managers to prevent introduction of exotic species.”

The rat is another interloper that officials are watching. Introduced to a few Aleutian islands during World War II, rats have ravaged colonies of auklets, storm petrels and other seabirds.

If a cargo ship or fishing vessel were to spread rats to an uninfested island, the result could be disastrous, Boone said.

“A rat spill on an island would be much worse than an oil spill,” he said. “An oil spill would eventually go away, but a rat spill . . . we haven’t figured out how to get rid of them.”