The gray wolves in Isle Royale National Park in northern Michigan are increasingly threatened, scientists said Monday, with no pups spotted during the past year and concern growing that the animals may have stopped reproducing.
The wolves have long been a symbol of the wilderness character of the island chain, one of the least-visited national parks because of its remote location in western Lake Superior.
Only eight remain, down from 24 just five years ago, according to a summary of a Michigan Technological University study obtained Monday by The Associated Press before the full report's public release. There were nine wolves last year, and scientists said the entire population could die out soon if the animals don't reproduce. Wolves usually live only four to five years.
The report comes as the gray wolf population elsewhere in the Great Lakes region has recovered enough for the animals to be taken off the federal endangered list and hunting allowed. Hunters and trappers in Minnesota and Wisconsin killed 530 wolves combined last winter, and Michigan could allow a hunt this fall.
The wolves on Isle Royale, however, have been struggling for years with inbreeding and may now be unwilling or unable to mate, said John Vucetich, who leads what the university and the National Park Service say is the world's longest study of predators and prey in a single ecosystem. University scientists who visited the island found no evidence that pups were born during the past year — the first time the wolves have failed to produce offspring since biologists began monitoring their reproduction in 1971.
"Next year will be very telling," Vucetich said in a telephone interview. "If they don't reproduce two years in a row ... it would seem the end is imminent."
Inbreeding has been the wolves' biggest problem, causing spinal malformation, among other physical abnormalities, said Rolf Peterson, another researcher. It also could be making the wolves increasingly reluctant to mate.
"Most species have a strong taboo against inbreeding," Peterson said.
But disease and a lack of food also could be contributing to the wolves' decline, Vucetich and Peterson said. The wolves prey mostly on moose, whose population in the park fell to about 400 in 2007. Since then, they've rebounded — partly because so few wolves have been around to attack them — and now total about 975.
As the threat of wolf extinction grows, park officials are grappling with whether to intervene or let nature take its course. Managers could bring wolves from the mainland to breed with those struggling on the island. Another possibility would be waiting to see if the existing wolves recover on their own. If they don't, the park could start over with a new group of transplants or simply let the island go without wolves, although that could allow moose to balloon and potentially strip the forests on the 45-mile-long archipelago.
"We've made no decisions at this point," said Phyllis Green, the park superintendent. "We need to approach this very thoughtfully before we start tinkering. ... We have to sort through what we can do and what we can learn through either taking action or taking no action."
Peterson said scientists observed what appeared to be "courtship behavior" within one of the packs this winter, raising hopes for another litter of pups next month. But without a fresh infusion of genes, the wolves' long-term prospects remain precarious.
Two panels of experts are studying the situation, one focusing on the wolves' genetic issues and the other on how climate change may affect wolves, moose and the broader environment. The park service expects to release a report with options for public comment this fall, Green said.
Scientists believe Isle Royale's first moose swam to the island from the Canadian mainland, about 15 miles away, in the early 20th century. They endured boom-and-bust cycles until a few wolves arrived around 1950, probably by wandering across an ice bridge. As the wolves' numbers grew, they formed packs and helped keep the moose in check.
The island is an ideal field laboratory to study interactions between a predator and prey. Because it's a federal wilderness area, human activities that would affect either species — especially hunting and trapping — are prohibited. There are no deer or other major prey animals that would complicate the food chain.
Peterson, Vucetich and other biologists collect bones and fit wolves with radio transmission collars in summer. For seven weeks each winter, they conduct aerial surveys.
The wolf population reached 50 in the early 1980s before a parvovirus outbreak reduced it to 12. But the hardy canines fought back, aided by the arrival around 1997 of a male from the mainland that reinvigorated the gene pool. Their numbers had averaged a couple dozen until the recent slump.
There are now just two small packs, each with three wolves, and two wandering loners.