AUTHORS: Glenn D. DelGiudice, Forest Wildlife Populations and Research Group, Minnesota Department of Natural Resources and Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota; William J. Severud, Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota; Tyler R. Obermoller, Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota
ABSTRACT: Since pre-European settlement northern Minnesota’s moose (Alces alces) population has been steadily declining and their primary range shrinking with increasing human settlement and harvests, habitat disturbance, northward expansion of white-tailed deer (Odocoileus virginianus), and wolf (Canis lupus) predation. But since the mid-1980s, the northwestern population decreased precipitously from about 4,000 to less than 100 moose by 2007, attributable to low adult survival rates associated with parasites, malnutrition, and infectious disease [1]. Predation appeared to play only a minor role, but malnutrition also contributed to low fertility and reproductive output. More recently, in the northeast, the state’s remaining viable moose population has declined an estimated 66% from 8,840 (6,790−11,910, 90% CI) in 2006 to 3,030 (2,320−4,140) in 2018 [2]. A VHF study (2002−2008) of adult survival estimated average annual rates for males and females of 0.84 (SE = 0.05) and 0.78 (SE = 0.04) and a long-term stochastic growth rate of only 0.85 [3,4]. A follow-up study (2013−2017) of GPS-collared adults, that included aggressive cause-specific mortality investigations, documented a mean annual survival rate of 85.3%, with two-thirds of the mortality assigned to health-related issues (e.g., parasites, bacterial infections, and unknown health issues) and one-third to confirmed and suspected wolf predation [5]. Parasites had the greatest impact, including meningeal worm (Parelaphostrongylus tenuis), winter ticks (Dermacentor albipictus), and giant liver flukes (Fascioloides magna). While fertility in this population proved to be robust (mean 84% pregnancy rate), calf production was declining due to loss of adult females, and mean annual recruitment was low (0.35); wolf predation accounted for a mean 67% of the calf mortality and black bear (Ursus americanus) predation for 16% [6]. Most of this mortality occurred before the calves were 50 days of age [6]. Furthermore, evidence gathered in the northwest and the northeast has indicated that performance of both moose populations is being negatively impacted by climate change, although additional study is required to test for cause-and-effect [1,3].
Research and survey findings have afforded the Minnesota Department of Natural Resources (MNDNR), other management agencies, and research biologists within the state a much better understanding of the primary factors contributing to the moose decline, and have helped crystalize the complex management challenge of recovery and long-term persistence. But this improved understanding does not provide all of the answers. Presently, close scrutiny of the major health-related issues affecting adult moose, associated demographics, and spatial and temporal considerations indicates that potential management options for effectively addressing their adverse impacts on survival at the population level are very limited [7].
However, one option that could play a key role in the success of moose recovery is wolf management. Wolf predation is having a biologically significant impact on both drivers of the moose population’s performance, adult survival and reproductive success, particularly the latter. Reducing densities of predators, especially wolves, can have a positive effect on the performance of ungulate populations through increased calf, yearling, and adult survival [8].
Conceivably, perhaps the most serious obstacle to wolf control at the population level and landscape scale as one viable moose management option is that in December 2014, they were federally re-listed as a “threatened species.” This was despite Minnesota’s wolf population (estimated 2,423 in 2014) being twice the Recovery Plan goal of 1,251 wolves [9]. Since initial removal of Great Lakes wolves from the Endangered Species List in 2007, they have been re-listed 3 times (2008, 2009, 2014) and delisted twice (2009, 2012), even though Minnesota’s wolves have remained above 2,211 since 1998. When wolves are federally listed, the MNDNR loses management jurisdiction. The agency successfully conducted closely monitored state harvests of wolves in 2012, 2013, and 2014 while under state regulatory authority. Population modeling has indicated that managing annual adult/calf survival at 89%/25% or 82%/57% would allow the MNDNR to manage a stable moose population of 4,000 to at least 2025, whereas increasing annual adult/calf survival to 89%/57% would support an intrinsic growth rate of 1.07 through at least 2025 (R. A. Moen, unpubl. data). White-tailed deer are the primary prey of wolves in most of northern Minnesota and have increased 22% in wolf range from spring 2015 to spring 2016, supporting an estimated 25% increase in wolves during the same period [9]. Delisting wolves and regaining management jurisdiction would allow the MNDNR to formulate more coordinated and balanced management strategies for wolves, deer, and moose that may be critical to successfully stabilizing or growing the northeastern moose population.
