Rolf Peterson spotted the tracks from a fixed-wing airplane flying low over a swath of the Northwoods last winter: two sets of paw prints in the snow. The wildlife ecologist was on the lookout for a lone wolf but was surprised to discover that two still roamed Michigan’s Isle Royale, a 143,000-acre national park located in Lake Superior just off Minnesota’s north shore. This pair, though, wasn’t breeding. Being father and daughter as well as half-siblings, the wolves are too inbred to produce pups. They are also the last of a group of around 50 gray wolves that once prowled the island.
The surviving duo are descendants of wolves that came to Isle Royale in the 1940s via a 25-mile ice bridge. About 50 years earlier, moose had arrived on the island (scientists think they swam). The wolves would come and go, preying on the island’s older, weaker moose and young calves. But as winters got warmer, ice bridges formed much less frequently, and when they did, they were often too weak to withstand the strong winds blowing over Lake Superior. Without new arrivals to help diversify the gene pool, and with other elements like disease affecting the packs, Isle Royale’s wolves became inbred and eventually produced fewer pups.
Peterson co-leads a Michigan Technological University study on the predators and their prey. Every year he and another biologist, John Vucetich, survey the animals on Royale to see how their populations wax and wane. Now in its 60th year, the project―the longest running of its kind―documents the often unexpected events that transform the island’s ecosystem.
Over the past six decades, scientists have learned that human-introduced disease and one hard winter can decimate a wolf pack, and that immigration events (a single wolf coming to the island, for example) can alter it. Also, when there are too few wolves to keep moose numbers in check, the moose population soars.
Like most predator-prey relationships, what happens between wolves and moose—especially on an island—is complicated. Even conservationists debate the island’s “natural state.” Populations boom and then bust for various reasons. Thirty wolves in three separate packs appeared to be thriving on the island until 2006, when moose became increasingly scarce. By 2011, only nine wolves remained. And without wolves to hunt them, moose numbers have surged over the past seven years, doubling from roughly 800 to 1,600.
As wolf numbers fell, Peterson and Vucetich began pushing the National Park Service to intervene, and they published a paper in 2012 outlining why. This past March, six years later, the agency announced controversial plans to relocate 20 to 30 wolves to Isle Royale over the next three to five years in order to restore the predator-prey dynamic and the island ecosystem as a whole. The effort will be one of the first times the Park Service has intervened to mitigate the possible effects of climate change.
A number of factors including climate change led the Park Service to its final decision, says Mark Romanski, a biologist for the agency. This outcome doesn’t necessarily represent a shift in Park Service policy because a similar situation could have arisen even without climate change affecting the ice bridge, he says. In the 60 years of the predator-prey study, wolves crossed the ice bridge only a handful of times.
But at the moment, “that moose population has the momentum of a freight train,” says Vucetich, who has been with the program for nearly two decades. Moose are among the fastest-breeding ungulates, and on an island, lots of hungry herbivores can eat until there’s nothing left. The runaway moose population began browsing on younger and younger balsam fir trees, which kept the trees from growing tall enough to produce seed. The forest needs its howling hunters.
At first, the agency hoped the wolves would rebound without interference, but it’s now ironing out the logistics of how many wolves to bring in and from where (probably from other areas in the Midwest where the animals already hunt moose). Moving quickly, says Vucetich, is critical. Without wolves on the island, no balsam firs will make it to maturity.
In 1988 researchers tagged mature balsam trees on the island’s western side, counting more than 500. Of those, only 25 still stand. Balsam firs live for about a century, and very few smaller trees are growing up to replace their ancestors. Only when moose numbers stayed low did balsam firs get the chance to grow tall, and the moose have been booming for about seven years now. Due to the lag time between the new wolves’ anticipated arrival and their eventual effect on the moose population, the firs could still be in real trouble. “We’re really on a knife’s edge,” says Vucetich.
The project, however, isn’t popular with everyone. Some wilderness advocates say the Park Service should let nature take its course on the island—for good or for bad. As climate change alters habitat, many species may need human help to move to more suitable areas, a term biologists and botanists call assisted migration or translocation. But at what point should the interventions stop?
We don’t fully understand Isle Royale’s complexities, says Park Superintendent Phyllis Green, who feels any action taken must be thoroughly evaluated. “What parts we should be keeping is part of the ongoing dialog that we need to have,” she says.
Without ice bridges or other natural ways for wolves to come to the island, the Park Service effort may have to continue as time goes on—otherwise the wolf population could face the same genetic dead end. For Vucetich it’s worth it because here exists a group of predators, their prey, and a forest free of human hunting and harvesting. “Isle Royale may be the last forest where we had that, and I’m using the past tense because it’s not there right now,” he says.
Doug Smith, head of Yellowstone’s wolf reintroduction project, agrees. “Normally I don’t take issue with hands-off preservationists,” says Smith. But Isle Royale is a good example of where a small tweak—in this case, a little money and a few wolves—goes a long way. The alternative, he says, is “major ecosystem degradation.”
The Park Service will transfer new wolves to Isle Royale as soon as this year. No matter what happens, says Smith, the decision will set the park on a new path. As it was with Yellowstone’s wolf reintroduction, the ecosystem will become some version of its fully functioning past, but it won’t be the same. “The ideas of pristine nature are over,” says Smith. “We need to save as much as we can.”
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