TRAVERSE CITY, Mich. — 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 who studies the predators said Tuesday.
The 5-year-old female's body was discovered 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. She had been severely wounded last year by other wolves.
The carcass was found Feb. 8, Isle Royale Superintendent Phyllis Green said, adding that a park service veterinarian and Peterson's team will perform an autopsy.
The dead wolf had been fitted with a radio collar and its serial numbers confirmed her identity, Peterson said. He and other scientists who follow 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. Their numbers last year were the lowest 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 favoring the idea. Others oppose it, saying nature should take its course.
The National Park Service is weighing its options. Green said most experts she has consulted believe the wolves will hang on for at least five years.
"So we don't need to rush to a decision, but we need to proceed," she said.
The park service hosted several public meetings on the issue last year and has received more than 1,000 comments, illustrating the widespread interest in the wolves' fate, Green said.
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 appear to have done so this year, although Green said that wouldn't be certain until scientists conduct genetic analyses of recently collected feces samples, which would reveal if any newcomers have slipped onto the island undetected.
But the scientists had 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 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."
Scientists long believed it was extremely rare for wolves to cross from the mainland to the park, but evidence is mounting that it has happened more than they realized — which would explain how the population has maintained some genetic diversity despite its inbreeding, Vucetich said.
Ice bridges in western Lake Superior were more common in the 1960s and 1970, and it's likely that wolves made the crossing back then, 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."
Green said it was too early to give up on ice bridges as a pathway, with some scientists predicting climate change will bring more extreme weather swings.
"Nature may yet provide course corrections," she said.
Follow John Flesher on Twitter at http://twitter.com/JohnFlesher .