The first phase of the Isle Royale wolf relocation project has ended earlier than anticipated thanks to bad weather, the National Park Service announced Friday.

But four wolves — three female and one male — were successfully transferred from the Grand Portage Band of Chippewa reservation on Minnesota’s North Shore to the wilderness island.

They are part of an unusual experiment to revive the predator population on Isle Royale to help control the growing number of moose.

Park Service officials had hoped to bring six or eight wolves from Minnesota and Michigan this year, the first of 30 that would eventually be captured and moved.

“Animal welfare is the primary concern,” said Isle Royale National Park Superintendent Phyllis Green. “The continued cold weather, which created safety issues for trapping, and high winds and waves in the marine forecast … led to the decision to end this phase of the project a little early.”

The park and its partners in the project are already looking at the next phases of the translocation process, which may include relocating wolves from Canada this winter, she said.

The addition of the four wolves brings the number on the island to six because there are two remaining that descended from the animals that crossed ice bridges decades ago. At one time the number of wolves peaked at about 50, but their numbers have declined because of inbreeding, disease and accidents. The four new ones are all wearing GPS collars, which allow scientists to track their movements as they hunt moose and form packs.

“All of the wolves are moving about and exploring the island,” said Mark Romanski, the park’s chief of natural resources.

In all, sixteen different wolves were captured on the Grand Portage reservation during the two weeks of trapping. Wolves deemed too young for transferring to the island were ear-tagged and released to help the Grand Portage band wildlife officials with their research. Three were collared with GPS devices and released on the mainland.