Moose Mortality in Eastern Interior Alaska

Abstract

We investigated causes of mortality and the physical condition of moose (Alces alces gigas) in a multiple-predator system in eastern interior Alaska, USA, from 1998 to 2000. We identified the sources of mortality of calf and cow moose and collected fecundity and fitness data to obtain information on range quality and carrying capacity. Radiocollars were placed on 30 cow moose in 1998 and on 62 moose calves in 1998 (n = 29) and 1999 (n = 33). Estimates of fecundity and fitness parameters indicated that reproductive potential for moose was high, with a twinning rate of 63%, a pregnancy rate of 89%, and above-average body sizes of female and neonate moose. We inferred that range quality may not be a significant limiting factor for this population. We documented low neonate survival through the first 14 weeks of life (28%). Predation was responsible for 92% of known calf mortality; black bears (Ursus americanus; 45%) and grizzly bears (Ursus arctos; 39%) were the major causes of mortality. Despite low population densities in this region, grizzly bears were an important predator on neonates as well as adult female moose. Mean annual calf and adult female moose survival (20% and 88%, respectively) were similar to rates reported in other low-density moose populations in North America. We also estimated from 7 to 12% of the population was harvested annually by humans, and of that, illegal cow harvest constituted at least 33%. Our data suggest that low calf survival, adult mortality from wolf (Canis lupus) and grizzly bear predation, illegal cow harvest, and low predator harvest, all act in concert to maintain this moose population at a low density.