Martin Schletterer

Hydrology and temperature are known as key drivers for fish migration in floodplain-channel systems of large rivers. The Lower Irtysh contains valuable species of whitefish and sturgeon. Thus, along the Konda River, a complex study was carried out in order to investigate fish migration in spring, with a focus on daily and monthly dynamics. To estimate the number of fish passing up- and downstream, a hydroacoustic system with a scanning beam frequency of 455 kHz was deployed in May 2017. The survey revealed the presence of three peaks in migration activity, as well as differences between a location close to the shore and another in the main channel. Regression analysis revealed a high degree of reliability of the influence of water temperature on the number of migrating fish (p < 0.001). The dataset also showed a daily rhythm of fish migration. An analysis of the daily variation in the illumination index and the intensity of fish migration revealed the presence of noticeable and high correlations for upstream (RS = 0.55; p < 0.05) and downstream migration (RS = 0.71; p < 0.001), respectively. Our data underline the importance of temperature as a trigger for fish migration and reveal diurnal patterns related to illumination.