Dynamics of Water Levels in the Gorky Reservoir (Russian Federation) During the Spawning Period and Its Influence on the Area of Spawning Grounds and Natural Reproduction of Limnophilic Fish Species

On the base of geographic information systems (GIS) the relationship between the areas of spawning areas of the Gorky reservoir and water levels were analyses, as well as assess the influence of the dynamics of spawning areas on the efficiency of natural reproduction of limnophilic fish species. The boundaries of 54 spawning areas of the Gorky reservoir have been digitized and georeferenced using Landsat satellite images. For the first time for the Gorky reservoir, the areas of spawning grounds were calculated at different water levels and formulas were obtained for the dependence of the areas of spawning grounds on the water level. It is calculated that the area of spawning grounds for the lower river, lakes, and dam sections of reservoir at different water levels can change by 1.2 times, the area of the Kostroma spill—by 1.7 times. The dynamics graph of the water levels of the Gorky reservoir in the flood in years of different water content, as well as the interannual dynamics of spawning areas and the number of fingerlings are presented. It is shown that the course of the water level in the Gorky reservoir during the spawning period is usually favorable for the processes of natural reproduction of fish due to the stability of the levels during the spawning period. No correlation was found between the degree of flooding of the spawning grounds and the number of fingerlings, which can be explained by the relative constancy of water levels during spawning in the interannual dynamics, or by the insufficient volume of materials from the fry surveys.