Bayesian modelling reveals differences in long-term trends in the harvest of native and introduced species by recreational hunters in Australia

Context. Little is known about wildlife harvesting by licensed recreational hunters in Australia, where both native and introduced species are hunted. It is important to understand harvest trends to assess sustainability for native species and implications for population control of introduced species. Aim. The aim of this study was to analyse trends in hunter participation, activity and efficiency, and wildlife harvest, including effects of climate, in Victoria, Australia, for three game species groups: introduced deer, native waterfowl (ducks) and one native grassland species, stubble quail (Coturnix pectoralis). Methods. Telephone surveys of a random sample of licenced Victorian hunters were performed annually from 2009 to 2019. Hunters were asked to quantify their hunting effort and the number of animals harvested. The respondents' answers were analysed to estimate measures of hunter success, activity and efficiency. Bayesian modelling was applied to these data, accounting for changes over time, differences between survey periods for all licence types, and random effects for over-dispersion. The effect of climate on game bird hunter activity and harvest was estimated, as measured by the El Nino-Southern Oscillation (ENSO). Results. Over 11 years, annual deer harvest (all species) increased exponentially, at a mean annual rate of 17% (95% credible interval: 14-21%), and the number of deer hunters increased at 8% (5-11%). In contrast, for ducks and stubble quail, hunter numbers remained relatively unchanged, with no evidence of consistent change to total harvests over time, unrelated to changes in environmental conditions or regulations. The annual duck harvest was influenced by ENSO and hunting regulations. The annual stubble quail harvest exhibited 'boom-and-bust' dynamics, with an exceptionally large harvest immediately after a La Nina season. Conclusions. Long-term monitoring of harvest trends in south-eastern Australia revealed stark differences between introduced deer and native birds: harvest of deer increased rapidly whereas equivalent rates for game birds were either stable or declining. Seasonal effects had a strong influence on game bird harvest. Environmental and regulatory conditions were influential for harvest outcomes for ducks and stubble quail. Implications. This study filled a key knowledge gap around managing harvesting of game species, but increased scrutiny is warranted in this field.