The next chapter in the long-running scientific story of Michigan’s Isle Royale wolves will not include a dramatic genetic rescue. After 2 years of consideration, the National Park Service (NPS) announced this week that it will not introduce mainland wolves to revive the genetically inbred and declining wolf population on the isolated island. “The decision is not to intervene as long as there is a breeding population,” Isle Royale National Park Superintendent Phyllis Green tells ScienceInsider.
Isle Royale, in Lake Superior, is a wilderness area where hands-off management has been the rule. But a recent record decline in wolf numbers—and ripple effects on the island’s moose and forest—convinced researchers studying the predator-prey system that genetic rescue of the wolves was an ecological necessity. The decision not to introduce wolves is disappointing to many scientists who have consulted with NPS about its plan.
Wildlife ecologist Rolf Peterson of Michigan Technological University (MTU) in Houghton, who has been studying the Isle Royale wolves since 1970, notes that the park service announcement makes no mention of ecosystem functioning or health. He and MTU collaborator John Vucetich are planning a response to the NPS decision, which they will release next week. It will accompany their annual report on this winter’s fieldwork, the 56th year of the study. “I’m sure the word disappointed will be in our statement,” Peterson says.
Evolutionary biologist Robert Wayne of the University of California, Los Angeles, one of several scientists involved in early consultations with the park service, takes a similar view. A fresh infusion of wolves also would have provided researchers with an unusual opportunity for experimental work, he says, adding that such studies could be useful in understanding other isolated and threatened wildlife populations worldwide. “Maybe it’s too much to ask the [park service] to do an experiment,” he says.
But U.S. Geological Survey wildlife biologist L. David Mech, who began his career studying Isle Royale wolves, thinks NPS made the right call by continuing what he calls “watchful waiting.”
NPS says it will reconsider a genetic rescue if, for example, all the male or female wolves die, or if moose overbrowse the island’s vegetation. It issued no analysis or report in support of its decision, which is part of a larger management planning and environmental impact statement exercise, but Green says details of the plan will be forthcoming this fall. The management plan for the island will include efforts to model how climate change will interact with the wolves, moose, and vegetation.
The birth last summer of three pups to Isle Royale wolves was a factor in the decision, Green says. The pups survived into the brutal winter, although two adults did not. That puts the official count of the island’s wolves at nine. The moose, meanwhile, have doubled in number over the past 3 years. “We’ve already lost the ecological value of wolves,” Peterson says, because the predators can no longer cull the moose herd to keep its numbers in check. A new analysis by Vucetich, Peterson, and others correlates a decline in the wolves’ predation of moose with an increase in wolf inbreeding.
The wolf population is clearly inbred and showing signs of skeletal deformities that may be a factor contributing to the reduced moose predation. But a separate DNA analysis to be published soon in Conservation Genetics, based on wolf blood and scat collected over the past decade, argues that the wolves have not been as isolated as typically thought. In 1997, an immigrant from the mainland joined the population and its genes became predominant in the island population, a well-documented and now widely known event. In addition, researchers now argue that other mainland wolves may have done the same in earlier winters, when ice formed more commonly between the island and Canada, but went undetected.
An ice bridge formed again this past winter, the first time since 2008, and lasted 16 days. Researchers did not observe any newcomers to the island, but for the first time did document wolf traffic in the reverse direction. One of the radio-collared adults lost from Isle Royale, a lone female nicknamed Isabelle, was found dead on 8 February on the northeastern Minnesota shore. Autopsy later revealed the cause of death: a pellet gunshot in the chest.