Causes of mortality among collared moose in Northeastern Minnesota from 2010-2015

The Minnesota moose population (Alces alces), like many along the southern extent of the North American moose range, has been experiencing a precipitous decline in recent years. Ongoing population surveys of moose on Grand... [ view full abstract ]

The Minnesota moose population (Alces alces), like many along the southern extent of the North American moose range, has been experiencing a precipitous decline in recent years. Ongoing population surveys of moose on Grand Portage Indian Reservation (GPIR), MN reveal high levels of adult mortality and low annual calf recruitment. To understand causes of mortality in the population of moose on GPIR, our team GPS-collared 112 moose since 2010, including 86 adults and 36 calves. Collars signaled mortality, triggering a prompt investigation of mortality. Cause of death was based on a) site examination (particularly in cases of predation), b) necropsy/histopathological examination or c) a combination thereof. Average annual mortality rates of adult collared moose was 22% (range: 14.3 -40.9%), and calves 76.6% (range: 71.4 - 85.7%). Of 27 adult mortalities, causes of death included parasitic infection (33.3%), predation (11.1%), capture-related mortality (7.4%, Note: of 104 total adult captures, which includes recaptures of individuals, only 2 captures [1.9%] resulted in mortality), mixed infection (3.7%) and undiagnosed (44.4%). Parelaphostrongylus tenuis infection was associated with mortality in 25.9% of the cases. Among three predation events, two were associated with illness based on abnormal antemortem behavior and necropsy findings, suggesting that underling health issues predisposed predation. Additionally, almost 15% of adults were considered to be in a state of cachexia at the time mortality. The majority of calf mortalities were due to predation or predator-inflicted wounds (61.5%); other confirmed causes of death included septicemia, orphaning, and capture-related mortality. Our study also documented the occurrence of two stillbirths, although underlying cause of fetal death was undetermined. Overall, adult moose mortality appears to be associated with compromised health, whereas predation is primarily associated with calf mortality. These findings suggest that different management strategies may be needed to support this declining population.