Abstract
Using the modern hydroacoustic methods and the computerized software and hardware complex “AsCor”, the features of the distribution of fish of the Acipenseridae family in the lower reaches of the large transboundary river the Irtysh (Western Siberia) have been investigated: in the water area of the riverbed depression (turbulent flow) and control sections (laminar flow). The identification of sturgeon was carried out by the echometric method according to the shape of the swim bladder. It is shown that in the water area of the riverbed depression, increased density of fish is formed, the share of sturgeons being 4.9–5.8%. Among other fish species, the group of cyprinids always dominates. The significant excess of the average fish density in the riverbed depression, in contrast to the control, was 6–30 times. In the water area of the riverbed depression, the average fish density was 4,524, in the control sections 245–2,091 individuals/ha. The size structure of the group of sturgeon in the control sections was represented by individuals with body sizes less than 25–30 cm, and in the riverbed depression – by individuals of different sizes and ages with a body length to 35 cm. The water area of the riverbed depression is located in the meandering section of the river and is characterized by intense vertical vortex structures (whirlpools) and the presence of malfunctioning currents. Features of the hydrological characteristics of the riverbed depression are factors in the formation of aggregations of fish, since fish can use the energy of discrete vortices, low-velocity areas, and as a result, show preference for certain turbulence regimes.
Highlights
IntroductionA quantitative assessment of the movements of animals, including aquatic organisms, can reveal the spatial and temporal patterns of habitat use as a result of the influence of various factors, which in turn contributes to a greater understanding of their foraging strategies (Altenritter et al, 2013; Marenkov, 2018), the finding of optimal conditions for somatic growth (Nakayama et al, 2018) and shelter from predators (Muška et al, 2013), etc.The study of the influence of environmental characteristics and their dynamics makes it possible to determine the sections of aggregations for aquatic organisms, facilitating their registration and monitoring, including rare and endangered fish species (Bogdanov & Mel'nichenko, 2011, Thayer et al, 2017; Andrews et al, 2020;)
The water area of the riverbed depression and control river sections are located in coordinates: 58.857600° N.L., 68.742267° E.L. – riverbed depression, 58.853681° N.L., 68.716809° E.L. – control river section No1, 58.856008° N.L., 68.758043° E.L. – control river section No2, 58.863373°
As a result of hydroacoustic surveys and the creation of bathymetric maps of the formed riverbed depression, it was found that during the study period the maximum depth marks were more than 27 m, the deepest part was noted in the left-bank erosion zone in the meander section with mutually penetrating flows (Fig. 3)
Summary
A quantitative assessment of the movements of animals, including aquatic organisms, can reveal the spatial and temporal patterns of habitat use as a result of the influence of various factors, which in turn contributes to a greater understanding of their foraging strategies (Altenritter et al, 2013; Marenkov, 2018), the finding of optimal conditions for somatic growth (Nakayama et al, 2018) and shelter from predators (Muška et al, 2013), etc.The study of the influence of environmental characteristics and their dynamics makes it possible to determine the sections of aggregations for aquatic organisms, facilitating their registration and monitoring, including rare and endangered fish species (Bogdanov & Mel'nichenko, 2011, Thayer et al, 2017; Andrews et al, 2020;). The formation of aggregations of fish can be influenced by the features of the bottom morphology, hydrological characteristics (Pavlov et al, 2010; Bogdanov & Mel'nichenko, 2011; Westrelin et al, 2017; Thayer et al, 2017), availability of prey (Holubová et al 2019). In this regard, the purpose of the work is to determine the features of the distribution of sturgeon fish in the lower reaches of the Irtysh River, including the riverbed depression and control rectilinear sections.
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