TRAVERSE CITY, Mich. — With the wolves of Isle Royale National Park on the verge of dying out, federal officials Thursday announced a plan to relocate 20-30 of the elusive predators from the mainland to the Lake Superior archipelago over the next several years, starting as early as this fall.

The National Park Service formally committed to rebuilding the island's gray wolf population after three years of study and debate, acknowledging the move was contrary to the usual hands-off approach toward designated wilderness areas.

Superintendent Phyllis Green described the move as a necessary trade-off to prevent the park's moose from becoming so abundant they overeat its trees and shrubs, damaging the environment and eventually threatening their own food supply.

"This decision is an important step forward in attempting to obtain a proper predator-prey dynamic within the Isle Royale National Park ecosystem," said Cam Sholly, the park service's Midwest regional director.

Wolves are believed to have made their way to the park in the late 1940s by crossing an ice bridge from the Canada or Minnesota mainland, about 15 miles (25 kilometers) away. Their numbers grew as they feasted on moose, eventually forming several packs that battled each other for territory.

Their numbers peaked at 50 in the early 1980s but averaged in the 20s before falling sharply in recent years, a decline that scientists attribute to inbreeding, disease and accidental deaths. Only two remain — a closely-related male and female that are unlikely to breed.

As climate change shrinks Lake Superior's winter ice cover, it's considered increasingly unlikely that more wolves will reach the park on their own and refresh the gene pool, as happened previously.

With wolf predation down, the moose population — normally around 1,100 — has reached nearly 1,500 and is likely to keep rising, according to Michigan Technological University researchers.

The park service considered several alternatives, including letting nature take its course or restoring the wolves over 20 years, before settling on a plan to transport several dozen wolves to the park over the next five years.

Details are being worked out, but Isle Royale natural resources chief Mark Romanski said the park service expects to seek suitable wolves from elsewhere in the Great Lakes region, including Michigan, Minnesota and Wisconsin as well as tribal lands and Ontario. Both individual wolves and packs will be targeted, with roughly equal numbers of males and females.

The operation is expected to begin this fall, with perhaps six to 10 wolves being relocated in the first year.

"We hope to capture from as many wide-ranging geographical areas as possible to maximize genetic variability," Romanski said.

A Minnesota-based group called Howling for Wolves urged the park to use captive wolves, including those in rescue centers. Green said captives would be less likely to survive in the wild, being too familiar with humans and unaccustomed to hunting.

The replacement wolves could be trapped with leg holds or darted from helicopters, Romanski said. They'll be sedated, vaccinated and taken to the island by aircraft or boat. Some will be fitted with radio collars to help biologists track their progress.

An environmental impact study estimates the relocation cost at $660,000. Monitoring and other measures are expected to bring the restoration effort's price to about $2 million over 20 years.

The National Parks Conservation Association, an advocacy group, said the federal agency based its decision on extensive scientific research and gave the public ample opportunity to weigh in.

"We encourage the National Park Service to act soon and bring more wolves to Isle Royale National Park so we might once again hear their unmistakable howls," said Lynn McClure, the group's senior regional director.