TRAVERSE CITY, Michigan — The gray wolves of Isle Royale National Park, which scientists have studied closely for more than half a century along with the moose on which they feed, are on the verge of disappearing as the most recent census showed that only three remain, scientists said Friday.
Inbreeding and illness appear to have caused a sharp drop-off in wolf numbers on the Lake Superior island wilderness, where visitors thrill at hearing their quavering howls. The count stood at 24 in 2009 but has fallen every year since, according to Michigan Technological University researchers who lead what they describe as the world's longest-running study of a predator-prey relationship in a closed ecosystem.
They have urged the National Park Service to bring more wolves to the island to reinvigorate the gene pool. But it may be too late to rescue the current population, which likely consists of one mating pair and a pup — all heavily inbred, biologist John Vucetich said.
"These are the last dying gasps," he said.
Scientists have held out hope that the wolves, whose numbers stood at nine a year ago, would rebound. But federal officials probably will have to choose between starting over with a new group or leaving the park without a top predator, Vucetich said. In that case, the moose population — already 1,250 and climbing — could get so high that trees will suffer as that much more foliage gets eaten, he said.
"One thing we know with great certainty is that wherever there are large herbivores like moose, elk or deer you have to have a top predator to maintain ecosystem health," Vucetich said.
Moose made their way to Isle Royale around the turn of the 20th century, possibly by swimming from mainland Canada or Minnesota, roughly 15 miles away. The first wolves crossed an ice bridge in the late 1940s.
As wolf numbers grew, moose provided a steady diet. Wolves kept their prey species from overpopulating.
The wolf population has averaged a couple dozen. Scientists say newcomers arrived at least twice during icy winters, breeding with existing wolves.
But ice bridges have become less common, although they formed during the past two winters. A pair of wolves wandered over from Canada in February but didn't stay.
Meanwhile, six island wolves disappeared in the past year. One, fitted with a radio collar, is known to have died, biologist Rolf Peterson said. The others either died or migrated to the mainland.
So few wolves remain that they no longer even limit the moose population, Peterson said. During their annual winter study on the island, he and Vucetich observed just one moose kill. They usually spot 20 to 30.
Park Superintendent Phyllis Green announced last year that officials would not intervene as long as a breeding wolf population remains. She said Friday the park service soon will invite public participation in a study of options for wolf, moose and vegetation management.
The agency prefers letting nature take its course but acknowledges that humans have left a big footprint on the island environment, Green said. Wolves have fallen down mine shafts and died from parvovirus spread by pet dogs. Climate change also could make future ice bridges rare.
"We're going to do the best job we can to manage for the kinds of changes we expect to happen," Green said.
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