Mr. Ugyen Dorji is a freshwater ecologist with extensive expertise in the conservation of freshwater fauna and flora. Currently serving as the Dean of Student Affaris at the College of Natural Resources, Royal University of Bhutan, he is an Editor for the Bhutan Journal of Natural Resources and Development and he was also the Programme Leader for the MSc in Natural Resources Management (HDR). His research interests include freshwater biodiversity, aquatic ecosystems, and the impacts of anthropogenic activities on freshwater habitats. Over the years, he has successfully led numerous research projects, including molecular analysis of aquatic species, climate change impacts on water sources, and macroinvertebrate diversity studies. He is also a co-founder of Water Research Bhutan and has served as a National Consultant for various hydropower and ecological impact assessments. With proficiency in GIS software, R, SPSS, and statistical modeling tools, Mr. Ugyen Dorji is a skilled educator and mentor, having facilitated over 60 capacity-building programs for both national and international participants. His contributions extend to policy-making as a member of the National Technical Working Group on water resource management in Bhutan. Mr. Ugyen Dorji is an accomplished researcher with numerous peer-reviewed publications on freshwater ecology, biodiversity, and climate change impacts. His current projects focus on addressing river pollution and enhancing ecosystem services in the Hindu Kush region.
Ecohydrological factors regulating Brown Trout in Himalayan River Systems in Thimphu, Bhutan
The introduction of brown trout (Salmo trutta) to Himalayan river systems, including Thimphu, Bhutan, has raised ecological concerns due to competition with native fish, especially the snow trout. This study explores the ecohydrological factors influencing brown trout distribution and habitat selection across seasonal variations within these river systems. Fieldwork was conducted in the Thimphu Chhu River, spanning elevations from 2,485 to 5,620 m, across three seasons (pre-monsoon, monsoon, and post-monsoon) in 2023-2024. Systematic sampling across 30 stretches involved electrofishing and habitat assessments of water depth, velocity, substrate type, cover, and water quality. Results show significant seasonal shifts in habitat use: during the monsoon, brown trout predominantly occupied pool habitats for refuge, while runs were favored during pre- and post-monsoon seasons for foraging. Substrate composition also influenced habitat choice, with a preference for cobble substrates during high flows in the monsoon, shifting to organic substrates like dead wood in calmer pre-monsoon conditions. Larger individuals (>30 cm) were found in deeper, faster sections, especially during monsoon flows, whereas smaller trout (<15 cm) occupied shallower areas with slower currents. Spatial analysis indicated the highest trout densities in mid-altitude zones, with a decline at higher altitudes, likely due to colder temperatures and steeper gradients. This research underscores the adaptability of brown trout in diverse ecohydrological conditions, highlighting their competitive edge over native species. Findings contribute to understanding brown troutβs invasive success in Himalayan rivers, emphasizing the need for habitat management and conservation efforts to mitigate impacts on native biodiversity.