Abstract
On the basis of recent hydroacoustic method with using “PanCor” computerized program-technological complex, research was conducted on the distribution of fish of different taxonomic groups in the water area of Irtysh, a large trans-border river on the bend (meander) with a vortex zone. A hydroacoustic complex allows one to conduct remote size-taxonomic identification of fish. It is demonstrated that on the examined area of the river, fish of different taxonomic groups and sizes concentrate in the zones of increased turbidity and intense whirlpools (vortices) which form as a result of opposite currents at the river meander. The largest concentrations of fish form in the deepest zone of the examined water area and in front of it – vortex zone. It was determined that in the zone of recorded vortices, the number of fish of different taxonomic groups (Cyprinidae, Percidae, Coregonus, Esocidae, Sturgeon, burbot) is on average 2.14–2.61 times reliably higher compared to the observations at the studied part of the river with no vortices at comparable parameters of depth. The size structure of the fish was dominated by small individuals (<10 cm) in the vortices, and large fish out of these zones, which can be an additional element of the survival strategy. The peculiarities of the studied area of the river with vortices, on one hand, are the factors of formation of fish concentrations, and on the other hand – factors of differentiation by taxonomical and size parameter, related to inability of certain groups of organisms to resist the hydrodynamic force of the vortex structure.
Highlights
Many hydrobionts, including fish, chose a certain intensity and orientation of different ecological factors as optimum conditions for somatic growth (Altenritter et al, 2013), feeding (Nakayama et al, 2018), and shelter from predators (Muška et al, 2013)
This study mostly focused on whirlpools which were recorded visually and by hydroacoustic sounding, in the zone of which there was found excess in the number of fish of all taxonomic groups, recorded using the hydoacoustic method, more than two times the number detected in the open water area of the pocket
The dominant fish were those with body sizes of less than 10 cm, in the rest of the water area, larger fish dominated
Summary
Many hydrobionts, including fish, chose a certain intensity and orientation of different ecological factors as optimum conditions for somatic growth (Altenritter et al, 2013), feeding (Nakayama et al, 2018), and shelter from predators (Muška et al, 2013). Rapid fluctuations of currents of water masses and transition of particles into the water column form a hydrodynamic and optimum non-uniformity of the environment preferred by many hydrobionts which use this effect as a “window of anti-predation” (Hansen & Beauchamp, 2015). Sharp bends in the stream beds of rivers, cause a complex of phenomena in the deep parts of rivers – whirlpools (vortices) (Velikanov, 1958; Baryshnikov, 2007) formed due to turbulent circulations of water masses (Ovsyanik, 2016; Verin, 2017) and clouds of increased turbidity (clouds of effervescence), the formation of which is the result of large scale vortex structures. The objective of this study was to determine the size-taxonomic peculiarities of distribution of fish in the water areas of the Kondiskaya riverbed depression within and outside vortexes
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