SEMI-AQUATIC MAMMALS OF THE IRTYSH RIVER FLOODPLAIN AS BIOINDICATOR SPECIES AND THEIR ECOSYSTEM SERVICES

The Irtysh River floodplain in Kazakhstan is home to diverse semi-aquatic mammals that serve as key bioindicators of ecosystem health. This study investigates six species: the muskrat (Ondatra zibethicus), Eurasian beaver (Castor fiber), water vole (Arvicola amphibius), American mink (Neogale vison), Eurasian otter (Lutra lutra), and Eurasian water shrew (Neomys fodiens). These species play critical roles in ecosystem services, contributing to water purification, extreme events mitigation, pest control, retention of greenhouse gases, ecosystem engineering, increase in riverside’s recreational potential, prey base, seed dispersal. However, invasive species such as the American mink and muskrat pose threats through competition with native fauna and alteration of local biodiversity. Field surveys conducted in 2023 along the Black Irtysh and Pavlodar Irtysh recorded 168 activity traces from four key species. Population densities of Eurasian otter and American mink in the Black Irtysh and the Eurasian beaver and American mink in the Pavlodar Irtysh were assessed. The studied section of the Black Irtysh River hosts 6-8 otters, with approximately 10 individuals found from the China border to Lake Zaysan, at a density of 1-1.2 otters/10 km. In the Kalzhyr River near Boran, the otter density is at least 2 animals/10 km. The mink inhabits the Black Irtysh (river and tributaries) area at 0.3-0.5 individuals/km, and the Kalzhyr River at up to 1 individual/km. In the Pavlodar Irtysh, the mink density is lower, at 0.2-0.3 individuals/km. In suitable habitats along the Irtysh River, beaver settlements occur every 3-4 km, and if there are three beavers per settlement, the total population in the Pavlodar Irtysh region is estimated at 300–400 individuals. Overall, our studies reveal a high species density in areas with preserved habitats, while human disturbances negatively impacted their presence in certain regions. More data are necessary to better understand ecosystem services provided by semiaquatic mammals. Keywords: Irtysh River floodplain, river ecosystem, semi-aquatic mammals, bioindicators, ecosystem services, population densities