Wolf Predation Decline on Isle Royale due to Inbreeding

During their annual Winter Study at Isle Royale National Park, scientists from Michigan Technological University counted nine wolves organized into one breeding pack and a second small group that is a remnant of a formerly breeding pack.

In the Isle Royale Wolf-Moose Study’s annual report released today, the researchers say that over the past three years, they have tallied the lowest numbers of wolves ever: nine in 2011–12, eight in 2012–13 and nine in 2013–14. During the same period, predation rates—the proportion of the moose population killed by wolves—also dropped to the lowest ever recorded, while the number of moose doubled, to approximately 1,050 moose.

Wolves are the only predators of moose on the remote island national park in northwestern Lake Superior. The moose population has been increasing because wolf predation has been so low.

"The poor condition of wolf predation on Isle Royale appears to be caused by inbreeding," said John Vucetich, director of Michigan Tech's study of the wolves and moose of Isle Royale. In its 56th year, the research project is the longest continuous predator-prey study in the world.

In the annual report, Vucetich and Rolf Peterson, research professor in Michigan Tech's School of Forest Resources and Environmental Science and a codirector of the wolf-moose study, document analysis of the DNA of more than 1,000 fecal samples collected from wolves over the past 15 years. Doing so allowed them to construct a family tree from 1999 to 2013.

That pedigree enabled them to monitor the rate of inbreeding among the wolves. They found that an immigrant wolf, who eventually came to be known as the Old Gray Guy, came to the island across an ice bridge from Canada in 1997. He brought a fresh infusion of genes that so dominated the Isle Royale wolves' weakened gene pool that, by 2008, most of the wolves on the island were descended from the Old Gray Guy.

"This represents a very high standard of evidence that Isle Royale wolves had been suffering from inbreeding prior to the immigrant's arrival," says Vucetich.

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