Across the last three years, researchers studying wolves in Michigan's Isle Royale National Park have counted the lowest numbers ever tallied there.

This year's winter report revealed nine wolves in the park In the past three study seasons, researchers from Michigan Technological University have only spotted eight or nine wolves, the lowest numbers ever in the history of the 56-year Winter Study at Isle Royale National Park, which is the longest continuous predator-prey survey in the world.

Low wolf population, the researchers report, is linked to a growing moose population. This winter's study reveled that the proportion of the moose population killed by wolves dropped to the lowest ever and that the moose population in the park has doubled to about 1,050 moose.

Researchers suggest that the low number of wolves now living in the isolated park is a function of inbreeding.

Wolves have not always inhabited the Isle Royale, and researchers suggest that prior to the 1997 arrival of a wolf known as the Old Gray Guy, the genetic diversity of wolves on the island was very low. The Old Gray Guy apparently crossed an ice bridge and got to the island, bringing with him much needed boost in genetic diversity. By 2008, most of the wolves on the island were a descendant of the Old Gray Guy.

"A large portion of the Old Gray Guy's descendants were the result of two consecutive generations of close inbreeding," the researchers said in a statement. "Of those wolves, all lived short lives, all were dead by 2011, and only one reproduced in this case, a single pup.

That these wolves lived short, unproductive lives suggest that the benefit of genetic diversity brought by the Old Gray Guy has run its course.

"Few documented instances of genetic rescue have been observed long enough or in sufficient detail to understand how long one can expect the beneficial effects of genetic rescue to persist," the researchers said in a statement.

With the dwindling wolf population, it is likely that the moose population will increase dramatically, the researchers report, noting that a huge increase in moose population would be harmful to the forests of Isle Royale.

In the future, the scientists said the most likely outcome will be that new wolves are introduced to the island by humans in an effort to restore the gene pool of the Isle Royale wolves.

"There is time to fully explore all the consequences of such an action," said Isle Royale National Park Superintendent Phyllis Green. "Bringing wolves to the island remains an option, however the final decision will be based on the best available sound science, accurate fidelity to the law and long-term public interest.

The annual Winter Study at Isle Royale National Park is available here.