ISLE ROYALE, MI - And then there were four.

After years of debate over Isle Royale's wolf pack that had dwindled to just two, this week a new pair of wolves was caught and airlifted to the remote island in Lake Superior, kicking off an effort by the National Park Service to replenish the predators.

More wolves mean a better chance of keeping the island's growing moose population in check before Isle Royale's wilderness can be overbrowsed.

Late Wednesday, two gray wolves were taken from the Grand Portage Indian Reservation in Minnesota and taken aboard a U.S. Fish and Wildlife Service plane to the island.

The wolves, a 4-year-old female and a 5-year-old male, were taken to separate release sites, and well away from the island's two remaining wolves.

"It did not take long for the female to leave the crate and begin exploring her new home on the island. The male left his crate after dark," the NPS said in a release.

"Other wolves will join the two in the coming weeks."

Up to 30 wolves are expected to be caught in Minnesota, Michigan's U.P. and even Ontario, Canada as part of this relocation effort.

Isle Royale's moose population was last estimated at 1,600 and accelerating.

Accidents, disease and inbreeding all have contributed to a sharp decline in the island's wolves in recent years. The two wolves left on the island are deeply related and unlikely to produce any viable offspring, according to scientists who have been studying the island's wolf-moose scenario for decades.

The wolves released Wednesday come from different packs on the tribal reservation in northest Minnesota, the NPS said.

Both animals were examined by veterinarians before they were airlifted. They were deemed to be healthy, about 75 pounds each.

GPS collars to help researchers track them were put on the wolves before they were released. They were also vaccinated.

Isle Royale sits in the northwest portion of Lake Superior. It's about 15 miles from the Canadian border, and 56 miles from Michigan's Upper Peninsula mainland.

Wolves crossed over to the island on ice bridges in the 1940s, researches said. But any wolves that may have come over when ice bridges have formed in recent years have not stayed.