Quantifying deer control efficiency using non-invasive genetic sampling and spatial capture–recapture

Context Sambar deer (Rusa unicolor) are the most numerous of the six species of introduced deer in Australia. They cause significant environmental damage and pose a considerable biosecurity threat to livestock. Because of their negative impacts, effort is often made by state organisations to eradicate or control sambar deer populations through aerial or ground shooting. These programs can be time-consuming and expensive and, therefore, it is imperative that their effectiveness is evaluated to ensure that program objectives are met. Aims In this study, we aim to quantify deer control efficiency at three different sites across Victoria, Australia; The Bogong High Plains in the Alpine National Park, Lake Tyers State Park and Snowy River National Park. Methods We use non-invasive genetic sampling and spatially explicit capture–recapture population modelling to estimate deer density before and after control operations. Key results Our results showed a reduction in deer density after control at Lake Tyers. Conversely, we were unable to definitively detect a change in deer density in the Bogong High Plains and at Snowy River National Park. Conclusions We hypothesise that the differing results between Lake Tyers and the other two sites may be due to the size of the control and survey areas, timing of our surveys relative to control operations, insufficient control effort, seasonal deer movement and/or re-incursion into our survey areas from the wider parks. Importantly, our results suggest that re-incursion may have a significant impact on deer control in Victoria, particularly in large parks. Implications To minimise re-incursion risks, control operations should be implemented in the summer months at high-altitude sites, and small, isolated populations should be targeted for eradication. At large parks, increased control frequency and intensity over time may be required if continuing reductions in deer density are desired. Our research emphasises the value of genetic sampling and capture–recapture modelling as effective techniques for wildlife monitoring.