Kangaroo ecology
Eastern grey kangaroo populations can realistically increase by 10% annually, red kangaroos by 13.5%, and wallaroo by 12%. These are observed growth rates that take into account the high juvenile mortality and actual biological processes. Consequently, shooting quotas of 15-20 % of population estimates exceed actual kangaroo population growth rates.
Estimating the number of the various commercially killed species of kangaroo and wallabies is challenging, given the vast size of the commercial kill zones into which each harvesting state is divided. Four main species of kangaroo – the Eastern Grey (Macropus giganteus), Western Grey (M. fuliginosus), Red Kangaroo (Osphranter rufus) and Wallaroo (O. robustus) – are killed for commercial purposes in the states of New South Wales, Queensland, South Australia, Western Australia and Victoria. The state of Tasmania has recently begun to harvest Forester kangaroos, and Bennetts wallabies.
While recognising that the vast size of the commercial kill zones makes the task of obtaining accurate population estimates challenging, the IKPA raises serious concerns about how the kangaroo population estimates and subsequent quotas are determined.
The commercial killing of kangaroos and wallabies is based on a quota system. This quota is based upon the estimated population size of the species in that region in the previous year. The annual quota for a particular species is the maximum number of that species that the government allocated to the commercial industry during the following year. If the estimates are inaccurate, in the case of overestimating the population of a species this can have potentially devastating effects for kangaroos.
IKPA have serious concerns over the methodologies used to estimate kangaroo populations. Key areas of concern include:
- Design of the aerial surveys,
- The methodology (i.e correction factors) and modelling used extrapolate estimates across large Kangaroo Management Zones.
- The deliberate changing of survey methodologies (e. g bin strips, adding areas, changing transects over time.
IKPA is concerned by the large year-by-year biologically impossible increases in these government population estimates because they do not correspond with their low reproductive capacity. IKPA question the validity of population estimates and are concerned by regional population depletions, particularly in times of drought.