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.