Isle Royale wolves inbred but likely to survive, study says

Researchers found Isle Royale wolves brought to the island in 2018 are likely to survive but are inbred and increasingly isolated.

In 2016, the island had only a pair of inbred wolves not having babies. So, between 2018 and 2019, Isle Royale National Park officials, with the help of researchers, brought 19 wolves onto the island in hopes of reestablishing the population.

A team of international researchers, including park officials, studied the transported wolves the first five years after their relocation to estimate their likelihood of survival and recently published the results in the journal Conservation Science and Practice.

They found the wolf population has a greater than 80% chance of lasting 20 years but will face complications from inbreeding and an island increasingly cut off from the mainland because of global warming.

Since the study period ended in 2023, the wolf population on the island has increased. A separate study on the island’s wolf and moose population led by Michigan Technological University researchers estimated that, as of last winter, 37 wolves lived there.

“The number of wolves that are currently on the island suggest that the population is doing OK,” said Sarah Hoy, one of the researchers who worked on the Michigan Tech study. “But I would say that issues with inbreeding and inbreeding depression are still an important concern for the population.”

To transport wolves in 2018 and 2019, researchers captured them in Minnesota, the Upper Peninsula of Michigan and two Ontario locations — on the mainland and on Michipicoten Island, another island in Lake Superior.

They went out of their way to select nice-looking wolves — not too skinny, with both eyes, no lice or mange.

But a problem started early on that they didn’t expect: Two siblings became a couple. They were brought over from Michipicoten Island with their parents and four other siblings. That left 11 nonrelative wolves for them to potentially mate with.

“Given the availability of unrelated wolves, it is notable and unanticipated that these animals bonded shortly after translocation,” the study published in Conservation Science and Practice reads.

But perhaps it was the presence of the wolves they weren’t related to that brought the siblings closer together, researchers said: “For social animals, establishing new social bonds is stressful and familiarity likely reduces stress when acclimating to a new environment.”

The brother and sister couple went on to found one of three packs on the island and had at least 12 babies. At the conclusion of the study, researchers estimated the island had 27 wolves and believed all pups born during the experiment were related to the brother and sister couple, their siblings or their parents.

“We found that releasing socially bonded wolves facilitated pack formation; however, the numerical and social dominance of a family group may complicate the long-term genetic health of the population.”

Inbreeding is troubling, researchers said, because it likely contributed to the decline of the wolves on the island before new ones were introduced.

Wolves were thought to have arrived on Isle Royale in the 1940s by crossing an ice bridge from Canada. For decades, Isle Royale’s wolf population was relatively stable. Between 1960 and 2000, the island averaged 22 wolves at any given time.

Scientists think the ice bridge that would sometimes form in the colder months might have helped maintain some gene pool diversity on the 205-square-mile island — about 1.5 times the size of Detroit — as wolves could occasionally come over from the mainland and vice versa.

But throughout the 1900s, as the climate warmed, the likelihood that an ice bridge would form each year decreased. Eventually, so did the number of wolves on the island, down to the last pair in 2016.

It’s not entirely clear what happened to the wolf population prior to 2016. Disease was a known factor and the researchers think malnutrition and the adverse effects of long-term inbreeding, known as “inbreeding depression,” were also at play. Inbreeding — especially over time — can lead to smaller body size, weaker immune function, physical abnormalities and reduced fertility.

Since the reintroduction of the wolves on the island, the moose population has sharply declined, from around 2,000 in 2019 down to 524 this past winter, a reduction of about 75%, according to the Michigan Tech study. Plus, no moose calves were counted in the winter of 2026.

“While it’s great to see the wolf population doing well, it’s hard — although not unexpected — to see both the moose population and the forest struggling,” said Hoy, the Michigan Tech researcher, on the university’s website.

Hoy said the moose population is down as a result of the reintroduction of the wolves but also because moose were starving. When moose numbers were higher, between 2018 and 2021, they ate a lot of balsam fir tree saplings, a key food source for them in the winter. The balsam fir population has yet to bounce back.

While the moose population, a key food source for wolves, is going down, “visitor behavior has emerged as another important management concern,” said a statement from Mark Romanski, an Isle Royale National Park biologist who also worked on the wolf relocation study.

A press release sent from Isle Royale National Park in July said “a wolf has been spotted in the campground, sniffing and pawing at tents, dragging backpacks away from tents, and entering a tent.”

As a result, some campsites were temporarily closed on the island so that park staff could attempt to discourage the wolf from entering the area by “loudly shouting, stomping, clapping, sounding airhorns, and discharging paintball guns.”

In the summer of 2025, the park killed a wolf after it was causing similar issues.

Romanski told Bridge “park managers have strengthened food storage and waste-management requirements, installed 68 food storage lockers, closed campsites or areas when necessary, and used deterrents to reduce these interactions to protect both visitors and wildlife.”

___

This story was originally published by Bridge Michigan and distributed through a partnership with The Associated Press.