Increasing in numbers, Isle Royale moose devouring forest
ISLE ROYALE NATIONAL PARK - Moose on Isle Royale are so numerous that they are starting to damage the forest, with moose numbers approaching historic highs just as new wolves are calling the island home.
That's the report from wildlife biologists at Michigan Technological University as they release results Monday, April 29, from their 61st annual survey of moose and wolves on Lake Superior's largest island.
It's the longest continuous predator-prey survey in the world.
The annual winter survey counted about 2,000 moose, up from about 1,500 the past couple of years.
Scientists already knew they had 15 wolves on the island — two natives that have been hanging on, unable to successfully mate, as well as 13 newcomers from Minnesota and Ontario relocated to the island between October and March.
John Vucetich, a Michigan Tech biologist who now heads the study, said surveyors this winter saw heavily moose-munched balsam fir trees, the first serious over-browsing since about 1996. That's about the time moose numbers peaked at 2,445 before they ran out of food and began to starve, crashing to 700 a year later. The moose are thriving after years with few wolves around and a string of mild or, like this year, average winters.
"We're seeing the first really obvious damage to the balsam fir that we've seen since that 1996 time period," Vucetich said. Balsam fir is a key winter food for the moose.
Vucetich said he expects moose numbers to level off and begin to drop, if not by next winter's survey then shortly thereafter, as food becomes a limiting factor in herd size and as the new wolves get better at hunting in packs.
"We don't know yet whether moose can sustain this (population) level for some time or if it will start to drop slowly or drop rapidly. ... But I tend to think this is about the peak for carrying capacity," he said. It's the second-highest moose count in the 61-year history of the survey.
The 45-mile-long, 143,000-acre island is located about 15 miles off Minnesota's North Shore. It's managed by the National Park Service, mostly as federal wilderness.
Moose came to the island around 1900, peaking at 2,445 in 1995 and hitting bottom at just 385 in 2007. Wolves are relatively new to the island, having crossed the ice from the North Shore in 1949. Their numbers reached a high of 50 in 1980, and 24 wolves roamed the island as recently as 2009.
Climate change, spurring fewer years of ice bridges between the island and the mainland, has reduced the number of new wolves venturing to the island in recent decades and reduced the pack's genetic diversity. With no new wolves coming to the island, the animals simply inbred and developed genetic deformities that doomed their survival. The final two wolves left on the island last year were a father-daughter pair, unable to successfully breed.
Vucetich said it was personally gratifying for him to see new wolves thriving on the island this winter. So far the new wolves — all fitted with GPS transmitting collars — are still feeling each other out and haven't developed specific social groups or packs as yet, he said.
They have however been able to kill enough moose to survive "so they are learning," Vucetich said. "It's going to take at least 12 months, maybe 24 months, of us watching to see how they form into their social groups and adapt to one another. Remember that most all of the new wolves were strangers to each other, and that will require some time to sort out."
Vucetich said the decision to bring new wolves to Isle Royale from elsewhere marks the first of likely many natural resource questions raised by human-caused climate change — namely how often humans should intervene to solve a climate change-caused problem.
"For me, what's important is how wolves were represented in how we answered this questions on climate change," Vucetich said. "We had to answer the question that if climate change caused this problem for wolves on Isle Royale, what, if anything, should we do about it? I believe it was the right decision to bring wolves back. But it's a tough question, and it's going to get raised more and more often in many areas of the world."
The Park Service decided one year ago to bring up to 30 wolves to the island over three years. Phyllis Green, Isle Royale superintendent, said that after looking west to Minnesota and north to Ontario for new wolves, the focus will shift south later this year.
"We are looking at translocation of wolves from Michigan in the fall," Green said Monday.