Shakimardan was a busy place between the 24th of March and the 4th of April. Project partners from various research groups stayed in the exclave to conduct impact assessment studies of the vertical slot fish pass and downstream bypass. In addition, various stretches of the rivers Koksu, Aksu and Shakimardan were electro fished to get a better understanding of the fish density and population structure in the river basin, which will be compared when the hydropower is operational, resulting in a residual flow between the hydropower intake and the power house. The five research groups visiting the site were SJE (Germany), BOKU (Austria), TU-Dresden (Germany), TIIAME (Uzbekistan), IGF Jena (Germany) and EVINBO (Belgium).
During the stay, EVINBO focused on the impact assessment of the passability of the hydropower weirs. To do so, they installed antennas to detect fish tagged with passive integrated transponders (PIT), which is a kind of microchip. They installed three antennas in the vertical slot fish pass (one at the entrance, one in the middle and one at the outlet) and one antenna downstream of the weirs. This allows to quantify how many fish reach the weirs and what proportion effectively finds the fish pass and uses it. Finally, a fifth antenna on the downstream bypass next to the trash rack was installed to study the downstream passage. In parallel, a part of the EVINBO team was fishing together with scientists from BOKU and TIIAME to catch and tag as many fish as possible with PIT tags. As we already assumed, there were not that many fish in the River Koksu in March and also not in the River Shakimardan. Instead, the largest catches were done in the River Aksu, likely as fish were either coming from, or still going to, the upstream spawning grounds. Even more, during electrofishing, we found rearing habitat of juvenile snowtrout with fish ranging from less than half a centimetre to a few centimetres, suggesting that spawning likely started a few weeks or even months ago in winter for at least a part of the population. Consequently, the pieces of the puzzle about the snowtrout’s life cycle are coming together. In total, 206 fish were tagged: 160 snowtrouts and 46 loaches.
SJE’s involvement in the OptiPass research project with the partners TUD Dresden University of Technology and IGF Jena Institute of Freshwater Ecology and Fisheries Biology resulted in a collaboration between Hydro4U and the OptiPass consortium, which was searching for a field site to study fish responses to high spatial velocity gradients (SVG) in bypasses for downstream migration of fish. Due to the conditions, the Shakimardan site is ideally suited for the OptiPass field study. To exploit synergies between the two projects, the OptiPass team traveled together with the Hydro4U group and started the site works with the set up and commission of an infrared-camera system at the bypass adjacent to the plant-intake. Snowtrouts caught and tagged by EVINBO, BOKU and TIIAME were carefully placed near the bypass entrance to study if they pass downstream without strong delay and avoidance behavior. The resulting one-week video footage from the first study campaign will allow an analysis of the effects of hydraulic conditions on the downstream migration behaviour of snow trout. The results will be compared with the results from ethohydraulic experiments carried out earlier in the TUD laboratory to gain an understanding of general behavior patterns in bypass-typical flow conditions.
The preliminary assessment of fish behavior indicates that the initial design of the bypass was implemented with construction deficiencies preventing a fish passage without delays. A minor but obvious optimization is needed. These will be realized before the end of the Hydro4U project.