There Are Now Just Three Wolves Left On Isle Royale

Rolf Peterson
Janet Fang 23 Apr 2015, 22:50

For 57 years, researchers have been observing wolves and moose on Michigan’s Isle Royale National Park. And while the moose population has been booming, as of February, only three resident wolves remain—two adults and a nine-month-old pup—according to a report [pdf] released last week. The world’s longest running predator-prey study may be running out of predators soon.

The remote island sits 24 kilometers (15 miles) from the northwest shoreline of Lake Superior. Moose arrived in the early 1900s, and the first wolves likely showed up 65 years ago, walking over ice connecting the island to land near the Minnesota-Ontario border. They typically number between 18 and 27, organized into about three moose-hunting packs. There may have been as many as 50 at one time, but with the dwindling frequency of winter ice bridges, inbreeding has seriously impacted the wolves during the past few decades. The last influx of DNA came from a lone male in 1997. Their numbers began declining in 2009, plummeting 88 percent.

Finding wolves is a challenge. A team led by Michigan Tech’s John Vucetich and Rolf Peterson spent hours staring out the window of a small plane looking for tracks and other signs, and it paid off this winter. “I could see these two wolves, they were on top of a ridge, curled up in tight little balls,” Vucetich says in a news release. “Wolves can sleep for quite some time.” Based on their colors and a serendipitous radio collar, these were visitors from the U.S.-Canadian mainland. Within a week, they trotted across an ice bridge and left, perhaps in search of easier prey. “That’s how [wolves] get information,” Peterson tells Science. “They walk.” Maybe some others escaped as well, but if they hadn’t, that means the mortality rate was 70 percent.

Just one winter ago, when there were nine wolves, park officials believed there was hope despite the low genetic diversity that nature might replenish the gene pool. “Many people are waiting for us to bring new wolves to Isle Royale or to announce that we’re leaving their future gene pool up to wolves that may migrate from the north shore of Lake Superior when winters are cold enough for an ice bridge to the island,” park superintendent Phyllis Green said in an announcement last April. “This issue is bigger than only wolf genetics.” 

In addition to the three resident wolves and two visitors, there are about 1,250 moose on the island. The gap between predator and prey has been growing, with a 22 percent increase of moose each year since 2011—which may spell trouble for forest vegetation. “It’s not the presence of wolves that matters so much, it’s whether wolves are performing their ecological function,” Vucetich says

In any case, with only three wolves, “there is now a good chance that it is too late to conduct genetic rescue,” he adds. And the pup doesn’t look healthy: constricted waistline, hunched posture, and a short, deformed tail. Even if it lives, and if the adults are a mating pair, a natural recovery is unlikely without new genetic material. The team suspect that the adults are an alpha pair from West Pack, and they’re waiting on genetic tests from two dozen scat samples to confirm the wolves’ identities. If they are a pair, they probably won’t be interested in introduced mates. 

Funding for the study has been renewed for another five years. “They can kick me out if they want,” Peterson tells Nature, “but I won’t walk away.”

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