One of the few remaining gray wolves of Isle Royale National Park has been found dead after escaping to the mainland across a Lake Superior ice bridge, a scientist said Tuesday.
The 5-year-old female's body was discovered earlier this month along the shoreline on the Grand Portage Indian Reservation in northeastern Minnesota, biologist Rolf Peterson of Michigan Technological University told The Associated Press. She apparently hadn't been shot and the cause of death could not be determined immediately, he said. She had been severely wounded last year in attacks by other wolves.
The dead wolf had been fitted with a radio collar and its serial numbers confirmed her identity, Peterson said. He and other scientists who study the island park's wolves and moose had nicknamed her "Isabelle."
Her loss was a blow to an already struggling wolf population at Isle Royale, which has fallen sharply in recent years. Only eight remained in 2013, down from 24 just five years earlier. The population last year was the smallest since scientists began observing the island's wolves in the 1950s.
Three pups are believed to have been born in the past year, boosting the population to 11, although Isabelle's death and the death of another adult on the island reduced it to nine.
The slump has touched off a debate over whether humans should bring more wolves to the island to replenish the severely inbred population. Peterson and Michigan Tech biologist John Vucetich, longtime leaders of the study, are among scientists who support the idea. Others oppose it, saying nature should take its course. The National Park Service is weighing its options.
This winter's prolonged deep freeze has caused most of Lake Superior's surface to freeze at times. Peterson and Vucetich had hoped that one or more wolves might use the opportunity to migrate from the mainland to the island, about 15 miles away, just as the park's first wolves are believed to have done in the late 1940s. None have done so this year.
But the scientists acknowledged there was also a chance that some of the Isle Royale wolves might head in the opposite direction.
"There's a tendency for people to think an ice bridge is a one-way street and will solve everything," Peterson said in a phone call from the island. "We've been telling people it's more likely that wolves will leave Isle Royale rather than come to Isle Royale."
Wolves are wanderers by nature and can cover many miles in a single day, he said. Despite their low numbers, their density on Isle Royale is actually high for their species.
"On the mainland their density is lower, they have a lot more directions they can disperse to," Peterson said. "Isle Royale wolves have a lot of reasons to leave ... and just one way to go."
Peterson and Vucetich spend seven weeks at the snowbound wilderness park every winter studying the wolves and the moose on which they feed. It's one of the world's longest continuous studies of a predator-prey relationship in a closed ecosystem and has generated numerous discoveries.
During their frequent observational flights in a small plane, they spotted Isabelle wandering shoreline areas late last month. She was last seen Jan. 21, heading toward the pack that had assaulted her last year, Peterson said. She may have veered across the ice that night.
At age 3, she had had left the pack into which she was born, which is normal behavior for a wolf, Peterson said.
"They disperse and look for vacant territory and an opportunity to mate," he said. "But she's been trapped on Isle Royale. She'd been traveling on her own for two years and never had pups."
Ice bridges in western Lake Superior were commonplace in the 1960s and 1970, and it's likely that other wolves crossed them to reach Isle Royale in those days, Peterson said. But they've become increasingly scarce as Great Lakes ice cover has shrunk in recent decades, contrary to the widespread cover this winter.
"That just isn't going to work very well" as a way to build Isle Royale's wolf numbers, he said. "Ice just is not forming the way it used to."