Researchers blame moose decline on wolves
The first messages from dead moose to Minnesota researchers have been coming in, and early results show wolves are taking their toll on the state’s beleaguered moose herd despite an easy winter.
Minnesota wildlife researchers trapped 111 moose in January and February and placed GPS trackers and transmitters on the big animals. It’s the most elaborate effort yet to find out what’s causing the rapid decline of the state’s moose population.
The goal is to get crews to dead moose quickly to retrieve key organs and tissue to find out what really killed the animals. Until now, by the time researchers found the dead moose, they were often too badly decomposed to be of much use, or had been munched on by wolves.
Already, six of the 111 moose in the study have died.
Of those, four are listed as having perished from capture-related mortality, meaning the stress of being tranquilized and collared somehow led to other problems and their death. That rate of about 3.6 percent is average for capture/collaring projects and is lower than recent Minnesota moose studies, said Erika Butler, Minnesota Department of Natural Resources veterinarian in charge of the moose mortality project.
“Any moose that dies within two weeks of capture is automatically counted as a capture-related mortality. … It may have been something else, but we count it as that,” Butler said. “Some animals are weak going into it and just can’t get back up. We don’t like it, but it happens.”
Lower body fat
Of the two animals that died from other causes, both appear to be victims of wolf attacks. One had been mostly eaten, and the other had injuries from a wolf attack but had not been eaten. From a post-mortem investigation at the scene, it appears wolves got the big cow’s calf and then left the area before the cow died, Butler said.
“She died from secondary issues after being wounded by wolves. … It was pretty cool how (the crews) went in there and figured out what happened,” Butler said.
While wolves were the ultimate cause of death for those moose, Butler said both of them, and even some of the moose that died from capture-related stress, had lower-than-usual body fat in what has been a fairly normal, if not mild, winter in moose country.
“When we are capturing them in January, that’s early enough in winter that they should still have some good body fat, and three of these didn’t. That’s not normal,” Butler said.
A reduction in nutrition, possibly from warm weather in the summer when moose are too hot to eat, or from habitat issues, is one theory why moose are having problems making it through winter.
Seth Moore, director of biology and environment for the Grand Portage Band of Minnesota Chippewa, said the winter in far northern Minnesota has seen below-average snowfall and about normal temperatures. Moose, which are perfectly adapted for deep snow and low temperatures, should have come through winter without major problems.
“This winter should not have had an impact on moose or even deer,” Moore said. “They should be in good shape.”
Moore is studying 19 moose captured in and around the Grand Portage Reservation and fitted with the same kind of collars the DNR is using.
So far, one of his moose has died, and investigators found a surprising cause.
“It was clear that wolves killed it. The site was just decimated from the struggle ... blood everywhere, trees knocked down. But when we got to looking in the lungs, they were just full of bright-green pneumonia,’ Moore said. “This was a health-compromised animal that wolves got to.”
Getting in fast
It’s possible that some of the dead moose, even those eaten by wolves, might have had other health issues, and scientists have sent samples of body parts to labs to find out.
It’s the quick-response team’s job to get to the newly dead moose within about 24 hours, especially to retrieve the brain, eyes, liver, heart, kidneys and spleen. Moose are so big and retain heat so well that their organs begin to decompose after just 24 hours.
“The brain decomposes faster than most of the tissues in the body. The brain is so important to us because we know some of our moose are experiencing neurological issues,” Butler said. “Getting to the brain, or any organ, with 24-ish hours ensures their histological architecture is still intact so that we can evaluate the organ microscopically for any lesions.”
Those could include brainworm, a viral infection or a bacterial infection.
“If there is a bacterial infection, the faster you get to the organ, the more likely you are to be able to culture the organism out of the tissue,” she said. “Once a carcass starts to decompose, the bacteria normally present in the guts begin to translocate into other organs, which can make culture results difficult to interpret.”
The expensive high-tech collar systems are sending satellite messages when a moose stops moving for six hours, about twice as long as the usual moose nap. Once located by ground crews, the 700-pound animals can be hauled into a lab or, if they are too remote, much of the work can be done in the field, with samples taken for complex lab analysis later.
The $1.2 million study, funded mostly from the state’s Legacy pot of sales tax money, has targeted moose in Lake and Cook counties.
Of the 111 collared moose, 27 also carry a censor in their stomachs that sends an instant text message when the moose’s heart stops beating, giving researchers an even faster jump to get at the body to test blood, tissues and especially organs like the heart, liver and brain.
The DNR has made saving the moose among its top wildlife management issues, and last year added moose to its list of troubled species as a “species of concern.” Just last month the state’s limited fall moose hunt, scaled back in recent years, was canceled altogether for 2013 and probably will never be held again — unless the moose stages an unexpected comeback.
According to aerial surveys, the Northeastern Minnesota moose population dropped a jaw-dropping 35 percent from last winter to this winter — from an estimated 4,230 in 2012 to 2,760 this January. That one-year decline was more than double the average drop in recent years of 15 percent. The population was as high as 8,800 in 2006.
The moose decline is a two-pronged problem. Not only are adult moose dying at an unusually high rate at the time in their life they should be the fattest and happiest and healthiest, Butler said, but nearly three-quarters of the calves born each spring also are dying before they reach a year, a death rate too high to sustain the population.
“If the calf mortality was as low as it was in the ’90s, we wouldn’t be here today,” said Ron Moen, a moose researcher at the University of Minnesota Duluth’s Natural Resources Research Institute. “The population wouldn’t have crashed nearly as much. But they have two things going against them now.”
Decline a mystery
The rapid demise of moose in Northeastern Minnesota comes just a few years after northwestern Minnesota’s moose population virtually disappeared, crashing from 4,000 to just a few dozen in just 25 years. The phenomenon is creeping north into Ontario as well.
Research papers identify higher summertime temperatures in recent decades as an underlying issue. But that’s not what’s actually killing the animals. Scientists believe it’s a combination of higher temperatures, parasites such as brain worm and ticks, disease and increased deer numbers as well as changes in where moose forage for food as temperatures warm up.
One Ontario researcher has found that calves are especially susceptible to brainworm, which are carried by the increasing number of deer in the region.
But a higher density of wolves — more wolves in the moose range — also might be killing more young moose than 20 years ago. And a reduction in logging spurred by lower demand and shuttered mills has caused the forest to age in the past decade beyond the young aspen stands that moose thrive on.
Article written by John Myers of the Duluth News Tribune