ISLE ROYALE - At least three rare wolves drowned in an abandoned mine shaft on Isle Royale, explaining a drop in their population on the island, a expert said.
Michigan Tech University experts in Houghton wondered why the annual winter count only found only nine wolves and one confirmed female.
It was the lowest since scientists began observing the predator-prey relationship between the remote national park's wolves and moose more than 50 years ago.
"We found there had been a real catastrophe in early winter, before we arrived on the island in January," said population biologist John Vucetich of MTU.
At the time of the count, Vucetich and wildlife ecologist Rolf Peterson said that it might be a sign that the wolves were becoming extinct in the remote national park, where they live in balance with the moose population.
In late May, a National Park Service biologist reported animal carcasses floating in water at the bottom of a deep, 19th-century mineshaft. An examination found at least three wolves drowned, and one was a young female that would have helped maintain the wolf population.
"There were three dead wolves from the Chippewa Harbor Pack in the shaft: a collared male that we had been unable to locate this winter, an older male - maybe the alpha male - and a female born in 2011," Vucetich said. "We believe the incident occurred between mid-October and mid-January.
"There is no way to know how the three wolves ended up falling into the pit, but very likely, accumulating snow and ice played a role in the accident."
According to Michigan Tech spokeswoman Jennifer Donovan, the drowned female pup and the older male "showed noticeable fat in their internal body organs, suggesting they were not suffering from a food shortage before they died."
Peterson and Vucetich are cleaning the bones of the dead wolves and examining their spines to collect data. The two scientists also plan to do a DNA analysis to determine the animals' age and prior history.
Moose are believed to have first reached the island - probably by swimming - in the early 1900s. Their population rose rapidly but crashed twice before wolves migrated across an ice bridge from the mainland around 1950 and established packs.