DEMOGRAPHY AND SUSTAINABLE HARVEST RATES OF LOW-DENSITY MOOSE IN NORTHERN BRITISH COLUMBIA

Abstract

Numerous moose (Alces alces) populations throughout Alaska, Yukon, and the Northwest Territories occur at low-density, a condition that often persists for decades and is referred to as a low-density equilibrium (LDE). The demographic conditions for these populations include low-density (≤ 0.4 moose/km²), low annual recruitment of calves (~ 0.25 calves/cow), and static population growth (λ ~ 1.00). I used data from aerial surveys and hunter harvest surveys to assess if these conditions applied to 4 moose populations in northern British Columbia, Canada over a 20-year period from 1996/97–2015/16. All populations exhibited low-density, low recruitment, and static growth suggesting that moose in this part of the province exist within a LDE state. Harvest and moose densities were positively related. Harvest rates from survey data ranged from 2.4–3.2% of the total population and 6.1–10.5% of the bull population. A stochastic model was used to estimate sustainable harvest rates defined as rates where the harvest risk was ≤ 10% probability that the post-hunt bull:cow ratio dropped below a given adult sex ratio threshold after 50 years of harvest. Sustainable harvest rates averaged ≤ 2.4% of the total population or ≤ 8.4% of the bull population with 0.50 bulls/cow as the threshold, ≤ 3.2% of the population or ≤ 13.0% of bulls with 0.40 bulls/cow as the threshold, and ≤ 4.1% of the population or ≤ 20.4% of bulls with 0.30 bulls/cow as the threshold. Modelling indicated that even small changes in harvest rates could greatly affect the probability of bull:cow ratios dropping below adult sex ratio thresholds. Research focussed on specific factors contributing to low moose density and increased population survey effort should improve estimates of sustainable harvest rates and management of moose in northern British Columbia.