Optimal harvest of age-structured populations of moose Alces alces in a fluctuating environment

We analysed sex- and age-specific harvesting strategies of moose using an a ge-structured population model that includes density dependence as well as environmental stochasticity. In order to find the strategy that maximises t he mean annual yield we simulated the process over a large number of years. The mean annual yield is a function of the three parameters (number of har vested individuals of calves, adult (greater than or equal to1 1/2 years ol d) bulls and adult females) that are involved in the definitions of the str ategies. We compare, by numerical maximisation of a function in several var iables, two harvest strategies: proportional harvesting, i.e. removal of a certain proportion of individuals in a given age and sex-class, and thresho ld harvesting, i.e. all individuals of a given sex- and age-class are harve sted when the size of this subpopulation exceeds a certain threshold. In ge neral, proportional harvest gives a smaller mean annual yield than threshol d harvesting. The variance in the annual yield is, however, larger for thre shold than for proportional harvesting. These differences between the two h arvest strategies increase when the annual survival of calves is low, when there is high environmental stochasticity and when there is strong density regulation operating on survival. For both harvest strategies, the optimal harvest strategy involves high harvest of calves and adult buns, whereas ad ult females should hardly be harvested.