The battle between predator and prey on Lake Superior's largest island is turning out to be a lose-lose situation this winter as wolf and moose numbers continue a downward spiral.
Isle Royale moose numbers crashed another 15 percent from last year's record low level of 450, at just 385 animals. Wolf numbers declined nearly one-third, from 30 to 21.
Moose on the island are dying for a variety of reasons, including hot summers, infestations of ticks and relentless hunting pressure from remaining wolves, said John Vucetich, an assistant professor at Michigan Technological University who helped conduct this winter's survey.
With fewer moose to eat, wolves are battling and killing each other over the right to the remaining moose.
In recent years, warm summers have been a two-pronged problem for the island's moose. First, the big animals are stressed by heat and feed less on warm days, making them less likely to add weight for winter. The changing climate also seems to favor ticks, thousands of which can infest a moose, sucking pints of blood over the winter.
The combined loss of blood, loss of hair from scratching and time lost from feeding has proven deadly for many moose, Vucetich said.
This is the 49th year in which the relationship on the island between moose and wolves has been studied, led now by Michigan Tech researcher Rolf Peterson. Moose peaked at 2,445 in 1995 and were as high as 1,000 just five years ago, Vucetich noted in the annual report.
Wolves are relatively new to the island, crossing the ice in 1949. Their numbers have ranged from just 11 in 1993 to a high of 50 in 1980.
Wolves have been so hungry that their pack hierarchy has been thrown into chaos. Last year, researchers witnessed the island's east pack attack and kill the alpha male of the Chippewa pack. This year, they killed his mate, the alpha female.
"All we found were [her] skull and a radio collar,'' Peterson said.
Wolves are so hungry that they are eating nearly every scrap of the moose carcass, an unusual sign of tough times. That also leaves less for scavengers such as foxes, which also are now declining on the island.
Peterson said he expects moose numbers to level off and begin a slow increase by 2010. Wolf numbers will follow, but not for many years. Until then, any new disease that might hit wolves could threaten their population.
"It could be a decade, likely longer, before wolves begin to come back very much,'' Peterson said. "They are killing all the calves and there won't be any old moose to speak of in a few years.''
If there is a good side to the moose decline, Peterson noted, it is that the island's vegetation is starting to rebound after being over-eaten by moose in the 1990s. Some species, such as balsam fir, have been nearly wiped out by on parts of the island.
"The vegetation is getting a break from the moose now,'' he said.
Experts say that a perfect balance would mean about 1,000 moose and 25 wolves, but note that balance is almost never met -- that one species or both is usually out of whack.
The annual study is paid for by the National Park Service, the National Science Foundation and Earthwatch. It is the world's longest running predator-prey study.