Should biologists step in to save Isle Royale’s wolves or let nature take its course?
By Laurie McClellan
A pack of wolves races through a field of unbroken snow, followed by scientists in a small plane buzzing overhead. For more than 60 years, this wild scene has come to life every winter on Michigan’s Isle Royale, the island in Lake Superior that forms the bulk of Isle Royale National Park. But all that may be about to change. After years of inbreeding, Isle Royale’s wolf population, which once approached 50, is down to eight adults and two or three pups, and the Park Service must decide what, if anything, should be done about it.
The roots of today’s dilemma go back to the late 1940s, when three gray wolves from Canada set off across the ice of Lake Superior and walked 15 miles to Isle Royale. The animals arrived to find dinner waiting for them: a population of moose descended from animals believed to have swum to the island a few decades earlier. The natural laboratories of islands have long interested biologists (think of Darwin studying finches in the Galapagos), and the elegant two-step of one prey species interacting with one predator soon caught the notice of researchers. Started in 1958, Isle Royale’s Wolf-Moose Project is now the longest-running study of predator and prey anywhere in the world.
Scientists have worried about wolf inbreeding for years. Yet until recent decades, the waters of Lake Superior between the mainland and the island froze over during most winters, allowing new wolves to find Isle Royale. Starting in the 1970s, steadily rising temperatures began to chip away at lake ice; ice bridges now form roughly once a decade. The chance of new wolves showing up to supplement the gene pool is now very slim. The result is “the most extreme case of inbreeding ever documented in wolves,” according to Rolf Peterson, who began leading the Wolf-Moose Project in the early 1970s. This inbreeding shows up in the animals’ very bones—every wolf skeleton found since 1994 has contained abnormalities. Most crucially, the wolves aren’t reproducing fast enough. No pups were born in 2012, and only two or three were born in 2013.
To date, humans have attempted genetic rescue of only a handful of species. The best known of these is the Florida panther. In 1995, the cat’s numbers hovered between 20 and 30. Fearing it would go extinct, biologists captured eight female cougars in Texas and released them in Florida. By 2010, the number of Florida panthers had roughly tripled. Geneticist Phil Hedrick, who worked on the project, has also measured the level of genetic variation in the Isle Royale wolves. In 1998, he was surprised to find it nearly four times higher than expected, given the number of ancestors the scientists know about. (Those ancestors may include a male and a female from the 1952 introduction of captive-raised wolves from the Detroit Zoo). “It appears that… some wolves crossed to the island undetected and added to the gene pool,” says Hedrick.
How does a wolf sneak onto Isle Royale? Pretty easily. They’re counted only in January and February, when researchers take to the air in small planes about every other day, look for tracks in the snow, and follow those tracks to the wolves. Dozens of gray wolves can be hard to tell apart. Rolf Peterson knows that two radio-collared wolves left the island on the last ice bridge, which formed in 2008. He can also identify two arrivals: a black wolf that showed up in a pack in 1967 and eventually became an alpha male, and an unusually light-colored male, nicknamed Old Gray Guy, that crossed to the island in 1997. Old Gray Guy performed a sort of one-wolf genetic rescue, and today, all eight wolves on the island are his descendants. In a sense, he was almost too successful at mixing up the gene pool. While his fresh infusion of DNA decreased inbreeding at first, now that every wolf on the island carries some of his genes, inbreeding is on the rise again.
Although Peterson hasn’t proposed any specific plans, in a forum held by the National Parks Conservation Association in June, he stated that importing two wolves of the same sex might be sufficient. Still, the question isn’t so much whether genetic rescue will work; it’s whether it should be attempted at all. Peterson believes the main reason to keep the wolf population going is to preserve the island’s ecosystem. To him, that boils down to trees, specifically the balsam fir that moose love to browse on. Peterson believes that a moose population unchecked by wolves could quickly get big enough to mow down every growing balsam fir tree on the island, leading to the trees’ eventual extinction—a change that would cascade down island food webs. He holds out the last two years as evidence for concern. In an average year on Isle Royale, about 10 percent of the moose were killed by wolves. In the last two years that figure dropped to 2 percent, and the moose population has quickly increased.
Although the Wolf-Moose Project has captured the public’s imagination, many experts point out that there’s a bigger picture. Back up and look at the entire last century, they say, and wolves appear as just one species in a revolving carousel of animals that have come and gone. In 1900, the largest animals on Isle Royale were caribou and lynx. These species eventually disappeared, along with smaller residents like coyotes and spruce grouse. In recent years, tricolored bats and a new type of tree frog have shown up. It turns out that compared with other species, wolves and moose have a relatively short history on the island.
The bigger picture also means seeing Isle Royale not just as a national park but also as a federally designated stretch of wilderness. Nearly the entire island is protected under the 1964 Wilderness Act. In the past, environmentalists’ approach to these wildest parts of our country has been a two-word mantra: don’t meddle. At the NPCA forum in June, Kevin Proescholdt, conservation director of the nonprofit Wilderness Watch, described his opposition to genetic rescue: “We should be aware of the slippery slope of manipulation,” he said. “If we intervene now… will we want to continue with additional manipulations?”
The stakes of the Park Service decision go far beyond the fate of eight wolves. When wolves were reintroduced to Yellowstone National Park, officials were correcting a problem created by humans—wolves were native to the park but had been hunted to extinction. Because wolves aren’t native to Isle Royale, performing a genetic rescue would break new ground. “Park Service policies don’t point to a clear course of action on this particular issue, and the best available science is sometimes conflicting,” says Christine Goepfert, program manager in NPCA’s Upper Midwest field office. “It’s a lot to sort through—many people are watching this decision because it could have implications for wildlife management in other national parks.”
The stakes are so high, in fact, that Park Superintendent Phyllis Green says the decision could go all the way to Washington. “It’s my responsibility to determine the right course of action at the park level,” she says. “If those actions alter… policy, then that’s where Park Service Director Jon Jarvis weighs in.” Green says that before making any decision, the park will interview more experts, including scientists who have worked with small populations of red wolves and Mexican wolves. A report on climate change released by the park in November has just added a new element to the complex swirl of data and policy. It forecasts that neither wolves nor moose may be capable of surviving the next century amid warmer temperatures.
In the parlance of biologists, the natural process of change on an island causes a rotating cast of species to “wink in” and later “wink out.” For now, it’s not clear whether the park’s wolves will remain on the glorious stage of Isle Royale for years to come, or whether they will wink out, just like the shooting stars that streak across the park’s inky night sky.