REVISITING THE RECRUITMENT-MORTALITY EQUATION TO ASSESS MOOSE GROWTH RATES

Abstract

Hatter and Bergerud (1991) developed a recruitment-mortality (R-M) equation to estimate the annual finite rate of change (λ) in a moose (Alces alces) population from a single estimate of calf recruitment and adult mortality. I present and assess an alternative formulation of the R-M equation and compare it with the original. A modification to the R-M equations is provided to accommodate early to mid-winter composition surveys where recruitment is measured when calves are less than 1 year-of-age. An example with the modified R-M equation illustrates estimation of λ for the female component of two moose populations under recent study in British Columbia, Canada. Due to potential biases with estimating recruitment and mortality rates, the calculation of λ with the R-M equation should be verified with periodic density surveys whenever possible. The R-M equation is most useful for estimating λ when moose density surveys are not feasible or an estimate of the adult survival rate is available.