The number of wolves, however, is near an all-time low.
Wildlife researchers who spent the winter on an island in Lake Superior report that Isle Royale’s moose population is booming while wolf numbers remain near an all-time low.
Moose have roughly doubled in the past three years, Michigan Technological University biologists Rolf Peterson and John Vucetich said in a blog post.
The two spend seven weeks every winter on the 45-mile-long island monitoring wolves and moose — both by foot and by air — in one of world’s longest continuous studies of predator-prey relationships.
That relationship has tipped clearly in favor of moose, whose population the biologists said has been increasing at an annual rate of more than 20 percent in each of the past three years.
The latest population figures and a host of other data will be released probably next week, Peterson said. A year ago in their last report, Peterson and Vucetich counted 975 moose from their winter observations.
That means moose numbers in the latest count could increase to more than 1,100.
The picture, however, is far different for wolves. The population now stands at nine. The lowest number ever recorded since research began in the 1950s was the eight that were counted last winter.
The declining population has sparked a debate about human intervention: Should wolves be imported to the island to boost the genetic pool?
Elk have been reintroduced to northwestern Wisconsin, and turkeys and whooping cranes were brought back to the state.
Isle Royale is different because, as an island, it is virtually a closed ecosystem.
In Wisconsin, the results of reintroduction efforts have been mixed: Turkeys have flourished while elk and whooping cranes have struggled.
Peterson and Vucetich favor a genetic rescue, and the National Park Service, which manages the island, is studying the issue.
This winter was marked by prolonged cold — the average minimum temperature was below zero on 33 of 48 days, the scientists reported.
The cold and record ice cover in the Great Lakes raised the possibility wolves from the mainland would venture onto the island. That has happened in the past but has been less common in recent decades. An over-the-ice migration last occurred in 1997 when a male, known as Old Gray Guy, walked across and provided the island’s wolves with a genetic shot in the arm. Numbers rose, and so did the wolves’ efficiency in killing moose.
But instead of new arrivals this winter, a 5-year-old female, Isabelle, who had never found a mate, wandered over the pack ice and was found dead on Feb. 8 on the Grand Portage Indian Reservation in northeastern Minnesota.
A necropsy revealed the wolf had been killed by a pellet, fired from a low-power pellet gun, that hit her between two ribs and severed an artery. An investigation by the park service and the Minnesota Department of Natural Resources found no violation of wildlife laws.
Now with so few wolves, the biologists say those remaining suffer from a lack of genetic diversity and a growing inability to hunt. Only six moose were killed over a 47-day period this winter, the biologists reported.
“All told this amounted to an estimated predation rate of only about 2 percent …,” Peterson and Vucetich wrote. “This was the third year in a row that wolf predation has been so low, almost absent.”
While the biologists are at a loss to explain it, the declining genetic vigor has “reduced the ability of wolves on Isle Royale to effectively kill moose.”