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Wolf population on Isle Royale drops to 3, lowest ever observed in 57-year study

Apr 17, 2015

The ongoing study of wolves and moose on Isle Royale in Lake Superior has hit a critical juncture. Researchers in charge of the longest continuous study of a predator-prey system anywhere in the world released their annual report today. 

You can read the full report here.

They found an exploding moose population (currently at 1,250 animals), while wolf numbers have hit an all-time low of just three.

From their report:

These changes are part of a longer trend. Since 2009 the wolf population has dropped by nearly 90%. As a result of very low wolf abundance, each of the past four years has seen unprecedented low rates of predation. In response, the moose population has been growing at a mean rate of 22% per year for each of the past four years. If that growth rate persists, the moose population will double in size over the next three years.

This chart from their study shows the dramatic changes over the years:

Changes in the wolf and moose populations on Isle Royale National Park from 1959 to 2015.
Credit Rolf Peterson, John Vucetich / Isle Royale Wolf-Moose Study

Study leaders Rolf Peterson and John Vucetich have advocated for the National Park Service to bring more wolves to the island.

Last April, Park Superintendent Phyllis Green announced they wouldn't bring more wolves to the island, saying genetic rescue wasn't needed at the time. She also indicated the Park Service might take a hands-off approach.

From the Duluth News Tribune:

“There are bigger issues at hand than just wolf genetics,” she added. “We don’t want to bring new wolves in only to set them up to fail because the island is changing and won’t be able to support them.”

At issue, Green said, is how much humans should be “tinkering” with a natural system, especially an island system that for millennia has evolved differently than the mainland just 20 miles away.

Before they began their winter study, Vucetich told The Environment Report's Rebecca Williams that the study would likely end should the wolves disappear from the island. 

"We'll continue the study as long as there are wolves there," Vucetich said. "My interest is to study moose-wolf interactions and that's really not possible to do when there are no wolves. And we have a really a very, very good idea of what happens to an ecosystem when you have large herbivores in the absence of any top predators. We've seen that in many of our national parks in past decades. They do great damage to the ecosystem."

Two wolves that visited Isle Royale for six days in late February.
Credit Rolf Peterson and John Vucetich / Isle Royale Wolf-Moose Study

Their winter study found that two new wolves from the mainland visited the island by crossing an ice bridge, but they didn't stay. The researchers say if these animals had crossed paths with the other wolves on the island, they likely would not have mated:

If the visiting wolves had been aware of the presence of the Isle Royale wolves, it is far from certain that genetic rescue would have occurred. For example, if the two larger Isle Royale wolves are a mated pair, they would have had little interest to mate with any immigrating wolf.

Vucetich and Peterson conclude the summary in their report by saying they expect a continued boom in the moose population on the island with the absence of predators, and "there is now a very good chance that it is too late to conduct genetic rescue" of the remaining wolves on Isle Royale.