The aim of the research is to substantiate the opportunity for creating favorable conditions for natural reproduction of anadrom and semi-anadromous fishes at the spawning in the basins of small and medium rivers. Before Tsimlyanskoe Reservoir began regulating runoff and series of pools and reservoirs in the basins of small and medium rivers were built, hydrological regime of these rivers enabled to create favorable conditions for effective natural reproduction of valuable anadrom and semi-anadromous fishes at separated sites in lower and medium reaches. Firstly, favorable conditions were characterized by such parameters as discharge, stream velocity, spawning depth, and water temperature. After the filling of Tsimlyanskoe Reservoir and bringing into service pools and reservoirs at small and medium rivers their hydrological regime have changed severely. So, the duration of flood at small and medium rivers decreased in 1.2–1.4 times, the value of maximal discharges – in 2.0–2.5 times. As a result, natural reproduction in small and medium rivers of the basin fell down to catastrophic level, what had reflection on fish capacity of the Don River and all Azov-Don basin. However, most of the small and medium rivers of the Don basin preserved potential for restoration fish capacity providing favorable hydrological regime for spawning. To achieve this it is required to restore rivers’ runoff to natural one by realizing ameliorative activities at watershed, stream-regulating at hydrographic net, or by organizing fishery discharge from existing pools and reservoirs.
Keywords: Don Basin, basin of small and medium rivers, natural fish reproduction, spawning ground, hydrological regime, fishery discharge.
