Abundance, spatial distribution, and diet of endangered Hovsgol grayling (Thymallus nigrescens)

The Hovsgol grayling, endemic to Lake Hovsgol, Mongolia, is considered endangered, but published descriptions of the species abundance, distribution, or behavior do not exist. We used hydroacoustics, vertical and horizontal gillnetting, zooplankton sampling, and stomach content analysis to characterize abundance, distribution, prey availability, and diet of Hovsgol grayling. Pelagic Hovsgol grayling densities averaged 34.2 ± 6.8 individuals·ha ^-1 (biomass of 4.4 ± 0.9 kg·ha ^-1) and were concentrated along the western and northern areas of the lake. Gillnet catch rates were 7.5 times higher for littoral sets than pelagic sets. Pelagic vertical distributions of zooplankton and Hovsgol grayling were concentrated above 50 m, with grayling exhibiting diel vertical migrations from 15 m at night to 30 m during the day. Smaller Hovsgol grayling fed primarily on zooplankton while larger individuals fed more heavily on benthic prey in littoral and pelagic areas. The results from this study may be used to guide conservation management and monitoring strategies for Hovsgol grayling, and provide a conservation reference point as human population growth and environmental change continues in the Lake Hovsgol catchment.