TRAVERSE CITY, Mich. (AP) — Two gray wolves have been relocated from the Minnesota mainland to Isle Royale National Park, kicking off a multiyear effort to restore the species on the Lake Superior island chain, officials said Thursday.

The National Park Service said a 4-year-old female and a 5-year-old male were flown to the park Wednesday from the Grand Portage Indian Reservation. They were released separately in locations well away from the territory of two aging wolves already there.

The female quickly left her crate and began exploring her new surroundings, while the male did likewise after dark.

“Releasing these two wolves on the island is the first step to restoring the ecological dynamic in the park,” Superintendent Phyllis Green said.

Plans call for moving four additional wolves to the park this fall and building the population to 20 to 30 over the next few years, restoring numbers that would enable the wily predators to keep the island’s abundant moose herd in check as they did for decades after arriving in the late 1940s.

Scientists believe the wolves crossed ice bridges from northeastern Minnesota or the Canadian province of Ontario to the park, an archipelago nearly 15 miles (24 kilometers) off the mainland.

Their numbers rose as high as 50 but generally ranged in the low- to mid-20s before crashing in recent years.

Some fell victim to accidents or diseases. But researchers with Michigan Technological University say the biggest problem was abnormalities resulting from inbreeding, as a warming lake surface has frozen over less often in winter, giving mainland wolves fewer opportunities to cross over, mate and freshen the gene pool.

Meanwhile, the moose population has reached about 1,500. Park managers say if the surge continues, they could overeat trees and shrubs, potentially damaging the ecosystem. Officials decided to intervene when the wolves failed to bounce back on their own, despite the usual policy of letting nature take its course in federally designated wilderness areas.

The two newcomers, each weighing about 75 pounds (34 kilograms), were caught by trappers Tuesday and held overnight for a veterinary exam, vaccinations and fitting with tracking collars.

The transfer went smoothly despite gusty winds and heavy cloud cover that raised questions about whether the floatplane could make the trip, park spokeswoman Liz Valencia said.

“Finally we got a window of good weather and had to hurry up and get the wolves ready to go,” Valencia said. “Fortunately, we didn’t run out of daylight.”

Managers hope the other wolves to be taken to the island this fall will come from Michigan’s Upper Peninsula as well as Minnesota to enhance genetic diversity, she said.

The park service said it will evaluate the project’s success by monitoring moose kill rates, genetics, wolf-to-moose ratios and vegetation conditions, among other factors.