Figure: Central Asian fish species as target of HP impact mitigation within Hydro4U (© Jennifer Clausen, www.jacdraws.com)
First findings on fish ecology of snow trout
Snow trout (Schizothorax sp.) belong to the most important fish species in Central Asia. They are adapted to fast-flowing, high-sloped mountain rivers. These fish, which reach up to 60 cm in length and 4 kg in weight, have a diet comprising algae, detritus, macroinvertebrates, and smaller fish. Their life cycle includes reaching sexual maturity at 3-4 years and a notable spawning period from April to September.
A habitat preference study of Schizothorax eurystomus in the Shakhimardan basin performed by Hydro4U researchers using point electrofishing revealed that juvenile snow trout prefer shallow waters around 20-40 cm of depth, while sub-adults and adults favor deeper areas of >30 cm and >50 cm, respectively. All size classes showed a high plasticity for diverse flow velocities and inhabit various substrates, with juveniles showing a preference for mid-sized substrates. This research is significant as it expanded the known distribution range of S. eurystomus and provided baseline data for environmental flow assessments.
Fish use various habitats to complete their life cycle such as spawning habitat, wintering sites and foraging areas. These habitats can be located at different parts of a river system and used by fish at different, seasonal-specific moments in time. Knowledge on the movement and habitat use of snow trout species Schizothorax eurystomus in the rivers of the Shakhimardan enclave is currently lacking. Hence, the effect of the planned hydropower plant in the River Koksu on the habitat use of snow trouts is unknown.
We used radiotelemetry to tag and track (position) 29 snow trouts in October 2022 to reveal their habitat use over the course of one year so we could learn when they reside and Koksu and why.
As the dataset is almost complete, we learned that the snow trouts seasonally visit the Koksu River, in particular during autumn months, which reasons for are to be clarified. However, these data suggest that the construction of the hydropower plant needs to take into account the life cycle of snow trout. In the next months the tracking data will be analyzed deeper to learn when and under which environmental conditions snow trout visits specific habitats. This information is not only crucial for the Shakhimardan enclave but can help future planning of river regulating structures in fish-ecologically, similar places in Central Asia.
Migration facilities and EFlow
The information for target species Schizothorax eurystomus has been used in Shakimardan for simulations with the habitat model CASiMiR to find a seasonally adapted E-Flow providing fish habitats in adequate quality and availability when the HPP is diverting part of the natural flow. The existing weir will integrate a state-of-the-art fish way and a bypass installation that enable up- and downstream migration for snow trout. Another artificial migration barrier within the river will be made passable as well. In Atbashy the modernized irrigation weir, equipped with a shaft turbine, will also integrate upstream- and downstream migration facilities. The attraction flow leading fish into the bypass channels and preventing them from entering the turbine inlet is investigated using a newly developed module of CASiMiR to possibly optimize the inflow conditions. The findings from these studies together with the results from the monitoring of the HPPs that both go into operation during the project period will deliver information for the adaptive management as part of the EIA.
Authors: Matthias Schneider (SJE), Tobias Siegfried (HSOL), Daniel Hayes (BOKU), Pieterjan Verhelst (EVINBO), Bakhtiyor Karimov (TIIAME-NRU), Erkin Karimov (TIIAME-NRU), Otabek Omonov (TIIAME-NRU).
Further contributors: Iana Kopecki (SJE), Tobias Haegele (SJE), Beatrice Marti (HSOL), Bernhard Zeiringer (BOKU), Johan Coeck (EVINBO), Ine Pauwels (EVINBO)