ST. PAUL - Minnesota Gov. Mark Dayton on Tuesday ordered the state Department of Natural Resources to stop radio-collaring moose "immediately, and indefinitely."

DNR researchers had been placing radio collars on moose as part of efforts to learn why northern Minnesota's moose population has been dropping significantly in recent years. But Dayton said he was alarmed by reports of collared moose calves being abandoned by their mothers, or dying -- as well as reports that some adult moose had died soon after being collared, too.

"I respect that DNR researchers are trying to understand why our moose population is declining," Dayton said in a news release. "However, their methods of collaring are causing too many of the moose deaths they seek to prevent. Thus, I will not authorize those collaring practices to continue in Minnesota."

Last May and June, researchers put GPS collars on 25 moose calves just hours after they were born. But 19 of the 25 calves either were abandoned by their mothers and had to be rescued, or their collars fell off or stopped working, leaving only six calves to be studied.

By August, all six had been eaten by predators, mostly wolves.

The disappointing 2014 calf study was even less successful than 2013, when 49 calves were collared and 15 either lost their collars or were abandoned by their mothers.

Many of 2013's abandoned calves perished. Some of last year's abandoned calves were rescued and given to the Minnesota Zoo. Both years saw public complaints that the research wasn't worth the loss of calves.

Minnesota DNR Commissioner Tom Landwehr said Tuesday that he agreed with the governor's decision.

"I understand and empathize with those who were concerned by the unintended loss of moose in this study," Landwehr said in statement. "We support the decision to end this phase of the research. Suspending new radio collaring on moose -- both calf and adults -- will eliminate the risk of unintended losses of individual moose."

Ron Moen, moose researcher with the University of Minnesota Duluth's Natural Resources Research Institute, said wildlife researchers will continue to seek answers for why northeastern Minnesota's moose population has crashed in the past decade.

"We still have 99 collars on the air; 99 moose we can watch. So we will have some new data coming in," Moen said. "And we still have data to analyze from past years that will give us some clues."

Moen said the complete loss of the third season of calf moose research will impact the effort to find out why calf numbers are declining. But he said the first two years provide limited but obvious data that followed most hunches: Wolves are killing a lot of calves.

"As a scientist, a biologist, you would have liked to have more. A third year, especially one with a normal (warmer) spring, would have been nice. But the data we have really lines up what we would have said if we hadn't done it at all. It's wolves that are bringing calf numbers down," Moen said.

Wolves don't fully explain why the adult moose population is declining, Moen noted.

"There's also a big health-compromised factor that we don't fully understand yet," Moen said, noting winter ticks, brainworm and other factors appear to be combining to bring adult moose numbers down. Moen also is studying whether habitat and nutrition are a problem for moose in the region.

"We aren't the only ones who are having problems," Moen noted, adding that New Hampshire and southern Maine are seeing a significant decline in moose numbers even though they have no wolves.

Until it was blocked by Tuesday's executive order, this year's collaring effort would have started as calves are born in the next few weeks. Glenn DelGiudice, lead moose researcher for the Minnesota DNR, had told the Duluth News Tribune earlier this year that he planned to collar 50 calves each in 2015 and 2016 to get a larger sample size to determine what is naturally killing the young moose.

Northeastern Minnesota's troubled moose herd continues to dwindle, according annual winter aerial surveys headed by the DNR.

This year's survey produced a region-wide estimate of about 3,450 moose. That's down from 4,350 in 2014 but up from an estimated 2,760 in 2013. Numbers can vary from year to year based on survey conditions, such as the amount of snow on the ground.

The recent estimates are less than half of the 8,840 moose estimated in 2006.