Abstract

Topic: Moose management and monitoring

Long-term decline in Norwegian moose calf weights

Alina L Evans¹, Alexandra Thiel², Boris Fuchs², Signe Helene Lund³, Ole Mattis Lien³, Barbara Zimmermann², Karen Marie Mathisen², Ane Eriksen², Ada Bredalen³, Marius Hassve², Anne Randi Græsli²

Inland Norway University of Applied Sciences, Evenstad, Norway
Department of Forestry and Wildlife Management, University of Inland Norway, Evenstad, Norway
Norwegian Hunting and Fishing Association, Norway

The weight of a moose calf before its first winter is crucial for its survival and future reproduction. Several studies have reported decreasing trends in slaughter weights of moose calves in Norway, influenced by factors such as high summer temperatures and winter snow conditions. Moose hunting has been used to decrease moose density and browsing pressure, but a concerning reduction in slaughter weights is still observed. We analyzed 338,525 moose slaughter weights over a period of 38 years (1985-2023) from seven counties in Norway. We examined the relationships between calf weights, yearling moose weights, cow weights, calf-per-cow ratios, moose density, climate, tick prevalence, latitude, and the proportion of mountain birch forests. The analysis used a Bayesian generalized additive model framework to investigate slaughter weights, and principal component analysis (PCA) was used to identify dominant patterns and correlations among the variables. Moose slaughter weights have been decreasing in all counties and all age categories, but the reductions were more extreme in more southern counties, and for calves. The total number of small calves (≤ 55 kg) shot and recorded moose observations increased over the period. We found a clear north-south gradient in moose slaughter weights; the heaviest moose were shot in the northernmost counties. These north-south patterns appear linked to geographical differences including access to mountain forest, tick prevalence, spring and summer temperatures, and the start of the growing season. The negative trend in moose slaughter weights has persisted over a long period and across a large geographical area. Many potential driving factors correlate, and we could not identify the definitive cause of the declining carcass weights. In the context of previous research, our results suggest climatic changes as the likely cause. In conclusion, we must consider changing the Scandinavian moose management paradigm entirely, transitioning to a conservation-based approach.