A retrospective evaluation of the effects of parelaphostrongylosis on moose populations

Abstract

Long-term historical data were examined for associations between moose (Alces alces) population declines, white-tailed deer (Odocoileus virginianus) densities, and reports of parelaphostrongylosis as a test of the hypothesis that Parelaphostrongylus tenuis causes moose declines. Moose declines over the past 80 years were associated with deer densities greater than 5/km2. This observation may be useful to managers but did not allow any effects of P. tenuis to be separated from other possible causes of moose declines. Whether moose numbers were stable, increasing, or decreasing was independent of the occurrence of reports of sick moose. The best test of causality that could be constructed, namely an increase in the reporting rate of observed sick animals concurrent with moose population declines, did not support the hypothesis. Although we doubt that reporting rates are representative, a reasonable test of the hypothesis has been possible, and the suggestion that P. tenuis has caused declines in moose populations is not supported by the historical information available. However, this question, and the ways and extent to which the disease may instead limit moose populations cohabiting with infected deer, remain in need of research.