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Wolves and Moose on Isle Royale

In the northwest sector of the big lake they call Gitchigoomie ( Superior ) lies an island 44-45 miles in length and roughly  8-9 miles in width, named by French explorers, looking as though it broke off from Canada, but legally a part of Michigan.  Following a commitment made in 1931, the United States acquired all of the island by 1940 and dedicated it as a national park in 1946. Although there are no roads for the public, there are 165 miles of trails and an expensive lodge. Most of the 17,000 visitors per year are backpackers.

Thus, the island was relatively isolated from deleterious human impacts.

    Isle Royale is rich botanically, having 60 plants recognized as rare, and fir and spruce forests as well as several types of deciduous forests.  An estimated 50 to 75% of the Park's land-based acres, 66,900 to 100,336 acres, are old growth.  The number of mammal species is relatively small, but there are significant populations of moose and wolves.  Moose arrived, probably swimming from Canada, around 1900. By 1930, they multiplied to a herd of several thousand, an unsustainable number which denuded large parts of the forests, precipitating starvation and a population collapse to around 300. They rebounded after fire stimulated new forest growth, to the point where another crisis loomed in 1949. That year, fortunately, a pair of mated eastern timber wolves arrived and produced enough of their species to control the moose population. Thereafter, numbers of the two species, prey and predator, alternated in natural cycles, until recently.

     In 1958, Durward Allen, a professor of wildlife ecology at  Purdue University, inaugurated the “world’s longest running study of a top predator and its primary prey.” He was assisted by graduate students from Purdue, and their work has served as a baseline for similar studies in Scandinavia and in Yellowstone National Park .

     Rolf Peterson, a professor of wildlife ecology from Michigan Technological University, and his wife, also a scientist, took over the project in 1975. Assisted by personnel from the Earthwatch Institute, they carry on a variety of activities, including the collection and analysis of moose bones, thus discovering much not only about the misfortunes and health of individuals but also about effects of atmospheric pollutants, such as carbon dioxide on the herd.

     A record high number of wolves (50) in 1980 resulted in a decrease in the number of moose to 750. But two years later, there were only 14 wolves, because in 1981, a fisherman illegally brought to the island a dog that spread canine parvovirus, decimating the wolf packs. So the moose herd shot up to 2400 by 1995. The ensuing winter was harsh, the moose were infested with debilitating ticks, and their number fell to 500 by 1997. In 2005, there were 1100 moose and 30 wolves, and in 2007, the moose number was down to only 385, and there were 21 wolves.

    According to John Vucetich, a population biologist at Michigan Tech, global warming has interfered with the natural cycles. His reasoning is that in hot summers, the moose rest more, eat less, and put on less of the fat that should get them through the winters. Furthermore, warm falls and springs produce infestations of ticks, which weaken the moose by sucking their blood and by causing loss of much of the hair that should insulate them in winter.

    Thus, the cycles of predator and prey populations, already subject to several influences, have been further complicated. So it appears that the nefarious impact of man has reached Isle Royale, by neither land nor water, but by air.    

 (A summary by Robert M. Davis of Les Line, "The Long View," Audubon, March-April 2008, pp.93-99, with supplemental information from Old Growth in the East: A Survey. Online edition. Available on this web site.)

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