Are the Wolves of Isle Royale Going Extinct?

April 04, 2014

By Paul Burton

 

Ecological challenges occurring on Isle Royale in Lake Superior have made international news. On February of this year, the prestigious international science journal Nature ran a story with the headline: “Iconic island study on its last legs.” The headline referred to ongoing studies begun in 1958 that followed the ecological interdependence between moose, wolves and even balsam fir trees on the isolated island.

Claimed by Michigan, the wilderness island is 45 miles long and about 9 miles wide. Its area of 893 square miles is large enough to sustain its own populations of moose, wolves, foxes, rabbits and other mammals. Vegetation is typical of a boreal forest, with balsam fir a dominant species, along with spruce, cedar, aspen and other tree species. For years wolves, moose, and the plants eaten by moose, have been in a relatively predictable balance.

In 2008 there were 700 moose and 23 wolves on Isle Royale. In 2013 there were 975 moose and only eight wolves. In five years the island had lost 63 percent of its wolves and those that remained had not been breeding, even though a number of females were available.

Also, during the last few years dead wolves showed signs of skeletal deformities, leading researchers to suspect that inbreeding was limiting diversity in the wolves’ gene pool. This would increase the possibility that “broken” genes would show up in offspring and affect a characteristic necessary for survival. A skeletal deformity, for example, might limit the ability of a wolf to successfully run down and help capture a prey, which is usually an arthritic moose or a young one separated from its mother.

Genetic diversity for wolves on Isle Royale arrived by chance in 1997 when an old but virile male, given the scientific name “Old Gray Guy,” wandered over frozen Lake Superior and sired 34 new wolves to add to the island’s population. This was a rather rare event, for in recent years the lake has not frozen over enough to establish a bridge from the mainland.

The winter of 2014 may be an especially important one if other adults migrate over the frozen lake to the island. Scientists are not counting on this, however, and a few feel it may be too late.

Although Old Gray Guy’s genes did not provide the “genetic rescue” hoped for by the scientists, after his offspring began hunting, the moose population did diminish. This is the way a predator-prey relationship should work. As the predator population increases, the prey population drops to point where predators have difficulty feeding themselves, and when their population decreases the prey population has a chance to recover. Until about 2000, this cycle repeated itself on Isle Royale.

Without wolves, the moose population may increase and begin stripping away key vegetation on the island in their search for food. Even today, with 975 moose roaming Isle Royale, it is hard to believe they are not approaching the carrying capacity of the island. The life span of a moose is 12 to 25 years (compared to six to eight years for a wolf) and in time they may begin to show deleterious genetic changes due to inbreeding. Such changes may make them less fit to survive, especially in the absence of wolves to help weed out weaker moose.

So what is to be done? The National Park Service has three options: 1) Immediately introduce new wolves to the island to provide genetic diversity, an approach known as genetic rescue; 2) Take no action and allow nature to take its course, and if the existing wolves go extinct, release new wolves on the island; 3) Do nothing, and let the wolves disappear if it is nature’s way.

The National Park Service is interested in input on the pending decision regarding the future management of wolves on Isle Royale. If you have thoughts to share on the three options, send your input to: ISRO_Wildlife@nps.gov. While expressing your view, consider providing as much detail on the reasons for your preference, as the Park Service believes the reasons for your view are as important as your view.

 

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