The single predator-single prey relationship between wolves and moose on Isle Royale in Lake Superior is unique, and has been the subject of detailed study since 1958. Isle Royale, the principal island of Isle Royale National Park in Michigan in the United States, is an isolated island with little migration of animals into and out of the island, and as a national park, human interaction and impact on the two species is also limited. Both the wolves and the moose first became established populations on Isle Royale in the 1900s. The populations of both moose and wolves have shown repeated spikes and declines and have not settled to a balanced relationship. The moose populations have ranged from 500 to 2500 while the number of wolves has ranged from almost 50 to down to two. From 2018 to 2019, 19 wolves were released at Isle Royale in hopes of bringing stability to the ecosystem, and as of 2020, there are estimated to be 14 wolves remaining on the island.
The relationship between wolves and moose on Isle Royale has been the subject of the longest predator-prey research study, begun in 1958. The wolves have been subject to inbreeding and carry a spinal deformity. As of the 2014 count, there were only 9 wolves on the island, with the 2015–2017 counts showing only 2. A review completed in 2014 determined that new wolves would not be introduced into the park to attempt a genetic rescue, but as of December 2016, the National Park Service had instead decided to introduce 20 to 30 wolves to the island. In 2018, three females and one male wolf from Minnesota were transferred to the island system.
