Migration of Mongolian Grayling (Thymallus brevirostris) in the Khovd River, Mongolia: Implications for Ongoing Hydropower Development

Mongolian grayling is a large piscivorous grayling endemic to the endorheic basin of the Khovd and Zavkhan River systems in western Mongolia. Ongoing large-scale hydropower development in the Khovd River has raised concerns about potential impacts on the Mongolian grayling populations in the area. Very little is known about the behavior and biology of Mongolian grayling, which makes it difficult to predict the impacts of damming and to plan for conservation and management mitigation actions. In this study, we used acoustic telemetry to track migration and survival of Mongolian grayling in the Khovd River system before the onset of hydropower construction. We found that the Mongolian grayling in the Khovd River conduct extensive seasonal migrations (> 170 km) to reach overwintering and spawning habitat and that migration routes pass through the Shijigtiin Canyon which is currently being developed for hydropower. We also found that Mongolian grayling in the downstream Khar Lake predominantly reside in the lake and only use lotic habitat during the spawning season, including the dammed Chono-Kharaikh River. Based on our results, we argue that the ongoing hydropower development of the Khovd River will have severe impacts on the grayling population by disrupting the annual migration cycle, prohibiting access to spawning and overwintering habitat, and altering flow regimes on downstream spawning grounds.