Isle Royale's moose, wolves both decline

“Both poor nutrition and wolf predation are thought to have contributed to the decline in moose numbers,’’ Rolf Peterson said.

A moose fitted with a transmitting collar stands on Isle Royale during last winter's annual survey of moose and wolves on the island. Moose declined from 2019 to 2020 and now stand at about 1,876 animals. Wolves also declined to 12. (Photo courtesy Sarah Hoy/Michigan Tech)

Isle Royale’s population of moose declined last year after nearly a decade of rapid growth, a sign that newly transplanted wolves released on the island are doing their jobs.

Results of the annual winter survey of the island’s wolf and moose population have been released after being delayed several months due to pandemic issues, showing 1,876 moose and an even dozen wolves were on the island as of February, when the survey was conducted.

It’s believed several pups likely have bolstered the overall number of wolves. Both trail camera and other data shows at least three pups have been born on the island over the past two springs, from new females brought to the island in recent years, but the pups won’t be officially counted until the next winter survey, if they survive until then.

The moose population dropped about 7% from 2019 to 2020, considered a modest decline after averaging 19% annual increases since 2012.

The number of wolves on the island had been as high as 17 as recently as mid-2019, including the last two remaining native wolves and 15 that had been relocated in recent years from Minnesota, Michigan and Ontario. Of those 17 wolves, the last remaining male native wolf, an 11-year-old, perished in 2019, as did four of the recently transplanted wolves.


That leaves only one female wolf remaining from the island’s native population, which had been hit hard by genetic defects from inbreeding due to a lack of new wolves coming to the island from the mainland. Facing the total elimination of wolves, National Park Service officials developed a plan in recent years to rebuild the island’s wolf population with fresh genes from mainland wolves from other nearby Lake Superior-region populations.

Isle Royale moose and wolves 2020.jpg

Researchers said most of the wolf deaths were due to battles between wolves as the big canines form groups, stake out territories and develop organized packs in their new island home. Researchers said it appeared more organized packs were forming, according to observations made during the winter survey.

This was the 62nd year of the survey, conducted by researchers from Michigan Technological University. It's the longest continually running predator-prey survey in the world.

Rolf Peterson, who has been involved in the last 51 of those surveys, said the island's moose population, which had been growing for a decade, was due for a collapse as the best forest food on the island was being over-browsed. Moreover, Peterson said many of the moose calves born in 2019 were eaten by the new wolves — exactly why they were brought to the island. (The new wolves also have been eating beaver and snowshoe hares at various times of year.)

“Both poor nutrition and wolf predation are thought to have contributed to the decline in moose numbers,’’ Peterson told the News Tribune. At one point of the winter, the wolves killed 25 moose in 48 days.

While only a small drop, the survey results signal an end to constantly increasing moose numbers which “had been impacting Isle Royale’s forest in a pretty intense way,’’ said John Vucetich, who now heads the research project for Michigan Tech. In 2019, Vucetich reported extensive damage to parts of the island's forest due to moose browsing, especially to balsam fir.


Research last year showed some 100 moose already had starved to death, unable to find quality food.

A gray female wolf courts black male with a “play bow” invitation to engage in an aerial photo taken last winter. Both wolves were transplanted to Isle Royale from an Ontario islad on Lake Superior. They appear to have formed a pair bond and may have produced pups this spring, although they face the challenge of not having a clear territory of their own. (Photo courtesy Rolf Peterson/Michigan Tech)

At 45 miles long, Isle Royale is the largest island on Lake Superior, sitting about 14 miles off Minnesota’s North Shore from Grand Portage. The island is a national park and mostly designated wilderness with few human visitors. There are no other major predators on the island, no human hunting is allowed and moose are the only large prey species, making it a unique wild laboratory for the ongoing study.

While the Park Service had authorized up to 30 wolves to be relocated to the island, it’s unclear if or when more wolves might be moved.

“The wolf situation on Isle Royale remains dynamic as these wolves continue to work out relationships with one another,” said Mark Romanski, the National Park Service biologist who has coordinated the wolf reintroduction effort on the island.

Romansky said the wolves should soon settle in to established packs and territories. But he added that wolves often surprise researchers trying to figure them out.

Moose came to the island around 1900, peaking at 2,445 in 1995 and hitting bottom at just 385 in 2007. Wolves are relatively new to the island, having crossed the ice from the North Shore in 1949. Their numbers reached a high of 50 in 1980, and 24 wolves roamed the island as recently as 2009.


Climate change, spurring far fewer years of ice bridges between the island and the mainland, has reduced the number of new wolves venturing to the island in recent decades and reduced the pack's genetic diversity. With no new wolves coming to the island, the animals simply inbred and developed genetic deformities that doomed their survival, spurring the dramatic reintroduction effort to maintain some natural limit on the island’s moose.

Another ongoing study looking at the island's moose, now with 25 animals wearing transmitting collars, aims to compare the Isle Royale population with moose on the Grand Portage Reservation on the mainland to measure impacts of human hunting, bears, climate change, disease, parasites and other factors facing moose in the region.

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at
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