Habitat loss and fragmentation are leading contributors to the endangered status of species. In 2006, the Nakai Plateau contained the largest known Asian elephant (Elephas maximus) population in the Lao People’s Democratic Republic (Lao PDR), and the population was among those with the highest genetic diversity reported for Asian elephants. In 2008, completion of the Nam Theun 2 hydroelectric dam inundated much of the Plateau, resulting in the loss of 40% of elephant habitat. We studied elephant presence, movements, and the incidence of human–elephant conflict (HEC) on the Nakai Plateau and surrounding areas from 2004-2020, before and for 12 years after dam completion. To examine contemporary population dynamics in the Nakai elephants, we used genetic sampling to compare minimum population numbers, demography, and levels of genetic diversity from the wet and dry seasons in 2018/2019, 10 years after dam completion, with those reported in a pre-dam-completion genetic survey. After dam completion, we found a major increase in HEC locally and the creation of new, serious, and persistent HEC problems as far as 100 km away. While we were unable to compare estimated population sizes before and after dam completion, our data revealed a decrease in genetic diversity, a male-biased sex ratio, and evidence of dispersal from the Plateau by breeding-age females. Our results raise concerns about the long-term viability of this important population as well as that of other species in this region. Given that hydropower projects are of economic importance throughout Laos and elsewhere in southeast Asia, this study has important implications for understanding and mitigating their impact.

From 2004 to 2020, teams from The Wildlife Conservation Society, The District Agriculture and Forestry Offices (DAFO) of affected districts in Lao PDR and the Nam Theun 2 Power Company (NTPC) conducted studies of the dynamics of elephant populations and the incidence of HEC on the Nakai Plateau and surrounding areas. They recorded the GPS location of each HEC incident, any available details about the elephants involved such as sex, age and group size, and the types of damage incurred. We analyzed the number and distribution of incidences of HEC in the periods before (2004-early 2009) and after dam completion. To characterize the elephant population on the Nakai Plateau 10 years after dam completion, we collected fresh dung samples on the Nakai Plateau from 01 March 2018 – 01 May 2018 (dry season), and from 01 October 2019 – 01 November 2019 (wet season). We genotyped those samples at 18 microsatellite loci and one sexing marker. We regenotyped 10 samples from our Nakai 2006 study (DOI: 10.1007/s10592-010-0148-y) and 9 samples from our Sepon 2011 study (Eggert and Ruiz-Lopez 2012) at the 9 loci that all studies had in common. We compared levels of genetic diversity, sex ratio and age structure across the three studies. Literature cited: Eggert LS, Ruiz-Lopez M. 2012. Analysis of fecal DNA samples to estimate the sex ratio and size of the Sepon Asian elephant population in the Lao PDR using capture-recapture methods. Report to the Wildlife Conservation Society.

None, these genotypes are provided in a Microsoft Excel file using GenePop 6 digit (2 alleles, 3 digits each) format.