Moose arrived on Isle Royale, a remote island in northwest Lake Superior, in the early 1900s, thriving in the absence of natural predators. The island remained a sort of hooved paradise until the forties, when a group of wolves crossed an ice bridge from mainland Ontario and started a battle that has been raging ever since. Now, researchers are taking sides. Some say the island's inbred wolf packs need an infusion of fresh genes – one they may not get thanks to global warming's effect on the ice pack – while others advocate a wait-and-see approach.

For decades, Isle Royale harbored between 18 and 27 wolves organized into three packs, and between 700 and 1,200 moose, according to an ongoing study at Michigan Technological University (begun in 1958, it's the longest continuous research on a predator-prey system in the world). In the past three years, though, wolf numbers have hit lows; only nine were counted this year. At the same time, the moose population has doubled, reaching roughly 1,050. Without wolves to keep them in check, moose could over-browse island vegetation, dooming themselves.

Park managers have discussed the wolves' recent decline with experts around the continent and will start work this fall on a management plan to address it. But wolves and moose aren't the only moving parts, says park superintendent Phyllis Green. "There are a lot of dynamics at play on the island. Everyone wants to reduce it to the wolves, but the real question is when do you tinker with the dynamics of an island? When you choose to manipulate wildlife populations, that is a significant step. We're studying it from multiple angles."

The Michigan scientists note that ice bridges between Isle Royale and the mainland formed seven out of 10 winters in the 1960s, but only two have occurred in the past 17 years. Resulting inbreeding has reduced the reproductive success of the wolves and, in a recently published paper, MTU scientist John Vucetich and colleagues recommend human assistance. But one of the effects of climate change has been that local weather conditions have become more extreme in terms of both heat and cold (think about the Polar Vortex), which is why U.S. Geological Survey scientist L. David Mech counters that climate change could actually increase the chances of future ice bridges and fresh wolf genes. The presence of more wolves on the mainland now improves those chances. Mech also notes that not intervening on Isle Royale offers greater scientific value – continuation of those decades of study in a natural laboratory. Further, intervention can’t be undone while the decision can always be made to intervene.

"As long as there are sufficient moose, you can add wolves at a later point in time," Green says. "At several points in the past 15 years researchers have said, "Add more wolves," and that would have negated the research that has been done. We have to ask what is most important here, to fully understand inbreeding and how it affects pack interaction, or to understand how genetic rescue works."

"We are concerned," she adds. "We realize that wolves pull a lot of emotional weight and have a significant role in predator-prey relationships. But right now, we continue to have a breeding pack. Taking time to consider some of the trade-offs is the best course of action."  The park will continue to collaborate with Michigan Tech and has initiated a project with the USGS to model moose impacts on vegetation.

About 14,000 people a year visit the 132,018-acre national park, open from mid-April to November 1, to fish, hike, backpack, camp, canoe, kayak, and scuba dive. Only a handful of them ever see a wolf, and even then it's usually just a glimpse. Moose, on the other hand, can be seen wandering around campgrounds and feeding in the island's inland lakes and wetlands at dawn or dusk. Depending on how the wolves fare in the coming years, moose could get even easier to spot.

More information: The ferry to Isle Royal leaves from Copper Harbor, Michigan, a small town about five hour's drive away from Green Bay through Ottawa National Forest.