MOOSE POPULATION DYNAMICS DURING 20 YEARS OF DECLINING HARVEST IN BRITISH COLUMBIA

Abstract

Licenced harvest of moose (Alces alces) in British Columbia, Canada declined by approximately half over the 20-year period from 1996–2015. To better understand changes in moose populations coinciding with this period of declining harvest, we modelled population dynamics within 31 Game Management Zones (GMZs). We used aerial survey data (180 density and 159 composition surveys) combined with licensed harvest to develop 4 competing statistical models to assess population dynamics based on constant parameters and temporal trends in calf:cow ratios at 6 months, juvenile survival from 6–18 months, or cow survival. The models indicated that moose populations declined (λ < 1) in 7 GMZs (23%) from 1996–2005 and in 22 GMZs (71%) from 2006–2015. Over the 20-year period, the best model was fit with declining trends in calf:cow ratios in 8 GMZs, declining juvenile survival in 6 GMZs, and declining cow survival in 8 GMZs. Population growth rate was slightly reduced in those GMZs where licenced antlerless (cow and calf) hunting occurred but was not considered the primary factor causing population decline. Total licenced bull harvest influenced bull:cow ratios that were significantly lower in 2006–2015 (mean = 37:100) than 1995–2005 (mean = 48:100); significant predictive relationships existed between harvest rates and bull:cow ratios. Provincial moose numbers and harvest were highly correlated (r = 0.81) suggesting that declining harvest was a reaction to declining population trends. We found that the provincial moose population increased 6% from 1996–2005, subsequently declined 32% from 2006–2015, and declined 29% overall during the 20-year study period.

Keywords

• Alces alces
• bull:cow ratio
• calf survival
• cow survival
• harvest
• juvenile recruitment