The number of moose in Minnesota plummeted by one third in the last year, a startling decline that prompted state wildlife officials to suspend indefinitely the annual hunt of the emblematic animal.

The sudden acceleration -- double the rate of recent years -- adds new urgency to an unprecedented research effort to understand, before it's too late, why moose are dying in such numbers.

"It reaffirms the conservation community's need to better understand why this species of the north is disappearing from our state," said Tom Landwehr, commissioner of the state Department of Natural Resources (DNR).

Results of the annual aerial survey, conducted in January and released Wednesday, indicated that 2,760 moose are left in Minnesota, down from 4,230 in 2012. In 2006, the population in the northeastern corner of the state peaked at 8,840, but by then moose had already largely disappeared from the northwest corner of Minnesota, where they had long been part of the landscape.

State wildlife officials say that, at the current rate of decline, moose could be gone from Minnesota in a matter of years.

"That's pretty grim," said Rolf Peterson, a wildlife researcher from Michigan Technical University who has studied moose on Isle Royale for decades and who advised the DNR.

Landwehr stressed Wednesday that, while the moose's decline remains a puzzle, the state's limited hunts are not to blame. Biologists say that even with the annual shooting harvest of about 50 bulls a year, the state still has plenty of males to ensure a healthy population. But, Landwehr said, suspending the hunt is "the only tool we have to control the mortality of moose."

Other moose researchers say that they often hear from members of the public who ask why a hunt is allowed. "If 50 moose die, then that's 50 less that are out there," said Ron Moen, moose researcher at the University of Minnesota Duluth.

The DNR has also begun discussions with three bands of Chippewa about suspending their hunts as well, but Landwehr said it isn't clear what decision they will make. Their hunts, which last year took 36 animals, are of great cultural importance to the tribes, Landwehr said.

Tracking moose

Just weeks ago, the DNR launched the largest and most high-tech moose research effort ever, one that is attracting attention from wildlife researchers around the globe.

Using planes and helicopters to find moose that are visible against the snow, they are fitting 100 of the animals with GPS collars to track their movements and collect a variety of data on each animal and its environment. When a moose stops moving, the collar will alert researchers at a central location, notifying them of its death. Within 24 hours, before it decays or is eaten by scavengers, a team of biologists will use ATVs and snowmobiles to drag the up to 1,000-pound carcass out of the woods and send it to a veterinary laboratory at the University of Minnesota for a necropsy.

In spring, the researchers will use the collars to find cows when they give birth, and then repeat the exercise to collar about 50 new calves. That will allow them to determine with great accuracy why the calves die and which predators -- wolves, bears or coyotes -- prey on them most frequently.

"It's the biggest moose research program ever in terms of its comprehensive nature," Peterson said.

The science is designed to ferret out the many interconnected factors that could be behind their decline -- everything from climate change to predators to infestations of winter ticks, researchers said. Muddying the picture is the fact that moose populations are healthier in other places, particularly on Isle Royale, which is just off the North Shore of Lake Superior.

Ticks and brain worm

In Minnesota, moose face several problems that they don't always encounter in other regions. For example, they are exposed to brain worm, a parasite carried by deer, which have expanded into moose territory. Unlike deer, moose can be devastated by brain worm, and many of the dead moose studied in Minnesota had tracks from the parasite in their brains. No deer are on Isle Royale, and far fewer of them are in such northeastern states as New Hampshire and Maine, researchers said.

But that is likely too simple an answer because many moose survive brain worm, said Glenn DelGiudice, a DNR biologist. "It can be more fatal to moose, but it's not always what kills them," he said.

Other studies have connected winter moose deaths to higher average temperatures. The huge animals are exquisitely sensitive to heat, and when it's hot in the summer, they tend to lie in cool damp places and pant instead of eating. Then they don't put on enough fat to carry them through the winter.

Moen said he expects his research on collared moose to reveal a lot about their choice of habitat, which could help with conservation efforts.

And then there are winter ticks. The insects attach themselves in late fall, then feast on the moose throughout the winter. Large infestations, which can reach as many as 50,000 bugs on a single animal, can kill a moose. Research on Isle Royale linked ticks to a 25 percent crash in moose numbers in the 1980s; they spent so much time scratching they didn't eat enough.

It could be six or seven years, however, before enough moose die to reveal clear patterns, researchers said.

"And it's not necessarily going to save the moose," Peterson said.

Josephine Marcotty • 612-673-7394