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Wolf count down at Isle Royale, moose steady

April 21, 2010 at 10:28 PM

TRAVERSE CITY, Mich. (AP) - The number of gray wolf packs at Isle Royale National Park fell by half within the past year, which could mean the predators are entering a tough period but aren’t necessarily in danger of dying out, scientists said Wednesday.

Two of the park’s four packs have disappeared since the winter of 2009, while the overall population declined from 24 to 19, Michigan Tech University biologists Rolf Peterson and John Vucetich said in their annual report tracking wolves and moose on the Lake Superior island chain.

A 50 percent dropoff in the number of packs is known to have happened just once before - in the 1980s, when a parvovirus outbreak threatened the wolves with extinction, Vucetich said in a telephone interview.

It’s significant because each pack has just one breeding pair - the alpha male and female. “So the overall reproductive potential has been cut in half,” he said.

Vucetich and Peterson have predicted a sl ide in wolf numbers for several years because moose, their primary food source, declined during most of the past decade and their population is languishing at roughly half its long-term average.

During their recently completed winter study at the park, the scientists estimated the moose total at 510, down slightly from 530 the previous year.

Biologists have been observing interactions between moose and wolves at the park since 1958, making it one of the world’s oldest continuous predator-prey studies in a closed environment.

Isle Royale is far enough from the Canadian mainland to prevent other species such as deer and coyotes from migrating there and disrupting the wolf-moose relationship. But it’s just close enough - about 15 miles from the Ontario shore - for moose to have swum to the island around 1900. The first wolves are believed to have crossed an ice bridge to the park around 1950.

Moose give wolves a steady food source. Wolves help prevent mo ose from starving themselves by over-browsing vegetation at the park, which consists of one 45-mile-long island and 450 smaller ones.

During observation flights, Peterson and Vucetich discovered that wolf groups they had dubbed East Pack and Paduka Pack had disappeared.

“East Pack’s extinction is the end of a dynasty,” Peterson said. “There has been a territorial wolf pack centered on the east end of the island since 1972.”

In addition to scarcity of moose, attacks by rival wolves and the effects of inbreeding may have helped doom the East and Paduka packs, he said.

Still thriving were the Chippewa Harbor Pack, with nine wolves, and the seven-member Middle Pack. Three other wolves wandered alone. At least one may have been a survivor of an otherwise extinct pack.

It’s too early to say whether long-term climate change is affecting either species, Vucetich said. But hot summers and infestations of blood-sucking ticks - which favor heat - have take n their toll on the moose.

The low numbers of moose may be enabling vegetation such as balsam fir, aspen and yellow birch to recover, which in turn might give the moose an eventual boost, he said.

One conclusion the scientists were able to draw: air pollution laws are paying off.

They reported that lead and mercury levels in moose teeth - which they’ve collected and studied for decades - have declined sharply since Clean Air Act regulations and removal of lead from gasoline took effect in the 1970s.

Isle Royale is a good place to measure such changes because its isolation from industrial sites means trends detected there reflect large-scale conditions instead of influence by a single polluter, the report said.

“These declines clearly indicate the value of our current anti-pollution regulations,” it said.

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