What This Winter's Ice Bridge to Isle Royale Means for the Island and Its Wolves

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Rolf Peterson

In this file photo, a pair of wolves walk on harbor ice during an Isle Royale winter. This year's ice bridge is just the second to form since 1997, when a lone wolf crossed from Ontario and reinvigorated the gene pool. In 2008, researchers believe two wolves used the ice bridge to leave the island.

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NASA/MODIS

Lake Superior Ice Cover: Feb. 16, 2014

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NASA/MODIS

Isle Royale Ice: Feb. 16, 2014

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Rolf Peterson

Most wolves that survive to adulthood live three to four years, while the alpha males and females live six to nine years. The current generation on Isle Royale is the 15th.

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Isle Royale's Wolves

The inbreeding coefficient measures how closely related a population is. After the "lone gray guy" arrived on the island in 1997, the coefficient plummeted. Today, though, all of Isle Royale's wolves are descendents of that single individual.

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A solid ice bridge over Lake Superior has formed between Isle Royale and the mainland, an increasingly rare link that could bring new life – quite literally – to an isolated and inbred Isle Royale National Park wolf population facing extirpation.

But whether or not wolves cross the 20-some miles of ice this winter, park officials say many of the island’s species face an uncertain future as the climate continues to warm. How the U.S. National Park Service should manage those changes has divided public opinion.

Crossable ice bridges were never commonplace, says Paul Brown, Isle Royale’s chief of natural resources, but for some island species past and present – like wolves and the now-extirpated caribou and lynx – ice is an important dispersal method, a means for new genes to enter an otherwise closed ecosystem. With warming winter temperatures in recent decades, “we have seen a lessening of the number of times ice bridges form,” Paul says.

According to buoy data analyzed by the University of Minnesota Duluth’s Large Lakes Observatory, Lake Superior’s summer surface temperature increased by 4.5° F from 1979 to 2006, to 68° F, with a corresponding loss in winter ice cover.

Rolf Peterson, a Michigan Technological University researcher who has studied Isle Royale’s wolves and moose for more than 40 years, says this year’s bridge is just the second to form in 17 years. On average, the Lake's ice is decreasing by 0.5 percent each year. By 2040, he expects that Lake Superior won’t have any significant ice cover in the winter.

Isle Royale’s 133,782 acres of land can’t support many wolves, a highly territorial species. (The most common cause of wolf deaths on the island has been other wolves, Paul says.) They numbered just eight last year, down from 24 in 2009. The small population and its genetic isolation mean the wolves have become highly inbred since arriving by ice bridge in the late 1940s, about 15 wolf generations ago. For wolves, the problem is exacerbated because only the alpha male and female in a pack mate, further limiting the gene pool.

“The fewer animals that are in a population, the more genetic anomalies and fitness consequences there are,” says Paul. Many of Isle Royale’s wolves are born with spinal malformations. “That’s why it’s so important to have an ice bridge or any method for an animal to disperse to and from the island. The influx of new animals reinvigorates the gene pool … and allows it to naturally fix some of the consequences of inbreeding over time.”

In 1997, when the population was significantly more inbred, a lone wolf, dubbed “the old gray guy,” arrived on the island via an ice bridge. His reproductive successes and outside genes buoyed the population for a time, but today all of Isle Royale’s wolves are descended from that one individual, a gene pool that could be too small to be sustainable. According to the park’s climate models, “the likelihood of extirpation could be high” without ice bridges.

The last time an ice bridge formed, in 2008, researchers lost track of two radio-collared wolves. Rolf believes they used the bridge to leave the island.

“If something happens this winter,” says Isle Royale Superintendent Phyllis Green, “it’ll probably take another year to really decipher what all is occurring as a result of it. … They’re not exactly embraced with open arms once they get to the island, necessarily. Maybe if it’s a female in heat, it might be, but wolves are pretty territorial overall.”

The packs defend their turf from outsiders “with a high degree of violence,” Phyllis adds.

Inbreeding hasn’t done the wolves in yet, though. Rolf, currently on Isle Royale conducting winter research for the island’s long-running predator-prey study of wolves and moose, has confirmed that two pups were born last year and survived to face their first winter. No pups were born in 2012, sparking fears that the wolves could no longer reproduce. The births have given park officials more time to decide whether or not to intervene.

The Options

Last November, Phyllis and Paul hosted a series of public meetings about the options: non-intervention, even if it means extirpation; genetic rescue of the existing population by introducing additional wolves; and reintroduction, if the existing wolves die out.

Ninety-nine percent of the park’s land is federally protected under the Wilderness Act, which generally mandates a hands-off approach. Says Phyllis, “Your fallback in wilderness is always do no harm and don’t escalate human-caused changes within the park boundaries. But there’s still room in our policies to figure out what’s best given the circumstances at the time.”

Rolf and other researchers who run the wolf-moose study on Isle Royale have publicly advocated for genetic rescue. The study is in its 56^th year, making it the longest continuous predator-prey study in the world. “Basically, it’s all about maintaining ecosystem health,” Rolf says in an email. Without a top predator on the island, an unchecked moose population would devastate the forest, he says.

Others say that the wolves could yet surprise us – and that heavy-handed intervention in our wild places robs us of the chance to be surprised.

Kevin Proescholdt, conservation director at the Wilderness Watch organization, says, “At a forum last June, [longtime wolf researcher] Dr. David Mech at his presentation had photocopies from 25 years ago saying, ‘The Wolves Are Dying Out,’ ‘The Wolves Are Inbred,’ ‘The Wolves Have Lost Their Genetic Diversity,’ ‘We Have to Do Something Immediately.’ And obviously the wolves hung on for the last quarter-century without that human manipulation.”

The key, guiding word in the Wilderness Act, Kevin says, is “untrammeled.”

“And though it’s sort of an archaic word, it means unmanipulated or unconfined, so that we allow wilderness areas to do their own thing.”

Rolf contends that humans have already significantly impacted Isle Royale through climate change and other influences, so wilderness preservation today requires active human assistance, not merely drawing up park boundaries and stepping away. “The 20th century notion of ‘wilderness’ is not immutable.” He argues that intervention is essential to fulfilling the NPS mission of conservation.

Wilderness management, Phyllis says, has long focused on minimizing direct change. “When you get these really large effects that are more indirect, I mean, climate change is so huge, it’s not like a situation where people went in and trapped out a species. You have this very insidious effect that’s going to happen over time to multiple species. So trying to sort out our role in that is why this decision process is taking the time it is.”

Climate scientists, in addition to predicting increased volatility and the kinds of extremes we’re experiencing this winter, believe that Isle Royale will become generally hotter and drier in the coming decades, according to Paul, with “a shift in the species composition out on the island toward a more savannah-like structure in both plants and animals.”

That means boreal species like spruce and fir are likely to disappear, their places being taken by red maples, oaks and grasses. The higher temperatures and habitat change could also mean extirpation for cold-loving moose, the wolves’ primary food source.

“It is a slippery slope,” Kevin says of genetic rescue. Will wolves have to be imported regularly? If moose die out, will they be reintroduced, too? “Once we get on it, we may never be able to get off of it.”

Next Steps

Park officials are still in discussion about decision-making on the wolves and on climate change. Says Phyllis, “Right now the public opinion certainly covers the gamut of options.”

Beyond the trio of choices about the wolves, Paul says they are also examining climate-change mitigation options like facilitated transportation – the idea of helping the island ecosystem keep up by “bringing some of the species that naturally would have gotten there if this was a natural progression of change” – and a restoration ecology plan that would give the ecosystem the resiliency to cope.

“There’s an idea in ecology called island biogeography,” says Paul. “And that kind of general assumption about the ecosystem tells us that change is inevitable and that change is natural and not necessarily bad. So climate change is definitely something that is going to affect the island. … Hopefully the change will occur at a pace that the island can keep up with.”

Phyllis doesn’t have a timetable for policy decisions yet, on either front. “This is the first time the park service has had to wrestle with this in a significant way, so we’re taking our time on it.”

But until then, with plenty of cold still to come this winter and with the unpredictability of the wolves, “there’s still chances for them to continue to surprise us.”

UPDATE, 2/25/14: An Isle Royale wolf nicknamed Isabelle was found dead on the mainland after crossing the ice.