Influence of the Level Regime and Temperature Factor of the Lower Reaches of the Oka River during the Spawning Period for the Natural Reproduction of Phytophilic Fish Species

For the first time for the lower reaches of the Oka River within the Nizhny Novgorod region, the combined influence of level and temperature regimes on the efficiency of natural reproduction of the phytophilic group of fish was assessed. Changes in the areas of spawning areas of the Oka River at various water levels was studied for the first time using satellite images. The boundaries of 45 spawning areas are tied to a geographic coordinate network using Landsat satellite images, and 20 options for the area of spawning areas at different water levels have been identified. It has been determined that the area of spawning grounds can change 12 times depending on the water level. A formula has been obtained for the dependence of the area of spawning grounds on the water level (applicable in the level range of 67.00–74.52 m). Data are provided on the timing of fish spawning in the Oka River. It has been established that the long-term median relative abundance of underyearlings of phytophilic fish species in the Oka River (in the water area of the Nizhny Novgorod region) – 4.9 thousand individuals/ha, which is 2.9 times more than in the Gorky reservoir and 1.6 times more than in the Cheboksary reservoir. Partial coefficients of multiple correlation of indicators of the level regime during the spawning period and the number of fingerlings of various fish species are given.