St. Paul — A pair of studies aimed at shedding more light on what’s killing moose in northeastern Minnesota is wrapping up, as researchers and wildlife officials begin the process of turning research discoveries into management actions.
DNR researchers since 2013 have employed high-tech means, including sophisticated GPS collars that give off mortality signals and allow researchers to retrieve fresh carcasses, to determine why moose in that part of the state are dying at an alarming rate. The study has pinpointed sources of mortality for both adult and young moose, and been a lightning rod for controversy, with Gov. Mark Dayton two years ago putting an end to new moose-collaring operations out of concern for their effects on the animals.
While the two researchers leading the studies – Michelle Carstensen, the DNR wildlife health program supervisor who’s leading the adult study, and Glenn DelGiudice, the agency’s moose and deer project leader, who’s leading the calf study – had to adapt as a result of Dayton’s orders, they say they’re pleased with what they’ve learned.
“To me, these studies have been and are real big successes,” DelGiudice said. “But now, what can we do with the data (we’ve collected) so far, and how are we going to proceed?”
The path isn’t necessarily clear.
“There is no simple answer to what’s driving down the moose population,” Carstensen said.
In the first three years of the study (2013-2015), researchers captured and collared 173 moose. Twenty-eight of those animals still have functioning collars, from which the DNR will continue to collect data this year, and 57 have died. A large portion of the other moose – 53 as of last week – had collars that failed; researchers don’t know the status of those animals.
In an email update about the project, Carstensen wrote that, “Collar failures (e.g. dead batteries or other technology malfunctions) have really depleted our sample size and have been very disappointing for us, given the enormity of this project.”
Of the collared adult moose that have died, wolf predation (18), parasites (17), and bacterial infection (12) have been the main causes. The survival rate for moose in the study so far this year is 91 percent. The survival rate was 85 percent in 2016, 86 percent in 2015, 88 percent in 2014, and 81 percent in 2013. Mortality rates, as a result, are on the high end of what would be expected in populations that are stable or growing, Carstensen said.
While wolves have been a key source of adult moose mortality, Carstensen doesn’t believe they’ve been a big driver in bringing down the population.
“Wolves are doing what they should do in a predator-prey system,” she said, noting the Minnesota DNR doesn’t currently have authority to manage wolves in the state. “Our parasite problem is the worst piece of this.”
Wolves also have been culpable in about two-thirds of the deaths of moose calves included in the study. Bears accounted for about 16 percent of the calf deaths, with other causes – natural abandonment and drowning among them – accounting for the remainder.
“What the study’s collective findings addressing reproductive success (production and survival) have shown is that fertility (pregnancy) of the adult female moose in this population is quite ‘normal,’ a reflection of reasonably adequate nutrition leading up to and during the fall rut,” DelGiudice wrote in a study update. “However, as mortality of adult (reproductive) females remains relatively high, it will continue to negatively impact annual calf production. That, and low survival of calves to one year of age, primarily due to wolf predation during their first 30 to 50 days of life, will make it very difficult for the population’s performance (growth rate) to support increasing numbers of moose into the future.”
Along with the mortality studies, there have been a number of other “spin-off” studies undertaken in recent years.
DelGiudice, for example, has been assessing moose nutritional status during the winter. According to initial results of that investigation, “Winter undernutrition is playing a key role in the poor population performance influencing the decline of moose in northeastern Minnesota since 2006,” DelGiudice wrote. “The source(s) of the varying incidence of severe nutritional restriction and exactly how severe nutritional restriction relates to the health-related causes of mortality and predation of moose are the subject of ongoing analyses, but also require additional study.”
The moose population in northeastern Minnesota dropped precipitously from 2009 to 2013, but has been relatively stable since 2014. DelGiudice says that stability is a good thing, though it doesn’t forecast what will happen in the future.