Analysis of rhino (Rhinoceros unicornis)population viability in Nepal: impact assessment of antipoaching and translocation strategies

Small populations with restricted geographic ranges such as rhinoceros (Rhinoceros unicornis) are prone to extinction due to anthropogenic factors. The identification of factors underpinning the survival of such species is of critical importance for population persistence. We used VORTEX population viability analysis (PVA) to assess rhino population viability in Nepal. We simulated deterministic single-population models under different scenarios to assess viability of two distinct rhino populations in Nepal: a source population in Chitwan National Park and an augmented population in Bardia National Park. The impacts of poaching on the populations and the potential for rhino translocation from one population to another were assessed under the PVA framework. Population and demographic data were obtained from censuses and from published literature. The model output suggested that the Chitwan population is stable and capable of supplying at least 10 rhinos every 3 years for translocation provided poaching is restricted (≤15 animals per 3 years). However, the Bardia population is more vulnerable and unable to persist without supplementation even at the lowest poaching rate (2 animals per year). Supplementation of at least 10 animals every 3 years for 30 years is crucial for establishing a viable population of rhinos in Bardia. This level of supplementation can withstand the poaching rate of ≤2 animals per year. Our study demonstrates that poaching is the major factor determining rhino population viability in Nepal. The supplementation of the Bardia rhino population with animals from the Chitwan population and increased effort to reduce poaching are expected to enhance the viability of rhino populations in Nepal.