Migrations and movements of fish in the system "riverbed depression - river"

The researchers have been carried out in the basin of the Lower Irtysh at the mouth of the River Konda, where there is one of the large wintering riverbed depression; the patterns of distribution of fish in different parts of the river during the period of intensive spring migrations - fish moving downstream and upstream in the "riverbed depression - river" system - have been studied; the direction and intensity of the movements of fish, its size range as in the midstream and in the coastal waters of the watercourse have been established. Migratory fish has been recorded round the clock as they passed through controlled sections of the river by hydroacoustic method using the complexes NetCor. The hydroacoustic survey has been performed simultaneously on different sections of the river in the transverse direction - as the midstream, and in coastal waters. It has been determined that the movements of fish in different areas and in different directions have high values of the correlative connection, indicating a high activity of fish in spring. Numerically, fish predominate migrating upstream. The numerical predominance of fish moving in the coastal zone in comparison with the river site located on the midstream than 2.5 times has been noted. In the coastal area among the up streaming and down streaming migrants, small and medium-sized fish (20 cm) prevailed, and on the midstream - larger individuals dominated (35 cm). Cluster analysis confirms the difference between the coastal and midstream zones based on the size structure of migrants. The revealed regularities reflect the mechanism for reducing energy loss and optimal distribution of fish in the river flow during the migration period.