Meander reshaping – the formation process of a wintering riverbed depression of fish

A A Chemagin

doi:10.15421/012148

Abstract

The study of the spatiotemporal distribution of fish is an important and poorly studied aspect of the ecology of aquatic organisms. The research work was performed using the modern hydroacoustic method and geographic information systems. A section in the lower reaches of the Irtysh, a large transboundary Siberian river (in Western Siberia, Russian Federation), was studied. It has a strong development of meandering. The merging (i.e., reshaping of closely spaced meanders and erosion-accumulating channel processes) results in development of wintering riverbed depression, which is a critical “temporal bottleneck” during the winter period of the fish life cycle. The average density of fish in the study area in summer and autumn was 8,031 and 9,194 individuals per ha, respectively. Analysis of the distribution of fish showed that the distribution in the horizontal aspect had a more aggregated character in the autumn. In the vertical aspect, it had a more surface (pelagic) character. The ichthyofauna in the water area of the riverbed depression is mainly represented by cyprinids. The loop-shaped evolution of the channel formed a section of the river with multidirectional, circulating, and counter-current flows. It also created zones with depths exceeding 20 m and aggregations of fish. These features characterize the studied water area as a wintering riverbed depression of the fish of the Lower Irtysh. This section of the river should be included in the list of protected wintering biotopes of fish in the West Siberian fishery basin, which will ensure the conservation of fish at the critical stage of the life cycle.

Highlights

The Irtysh River is an important component of the Ob-Irtysh Basin and the largest tributary of the Ob River (Ecology of fish of the Ob-Irtysh Basin, 2006)
In the lower reaches of the Irtysh River, there are wintering riverbed depressions with significant depths (> 35 m), which form on the meanders of the watercourse (Borisenko et al, 2013; Mochek et al, 2019)
Wintering is one of the critically important stages of their life cycle (Thayer et al, 2017; Wang et al, 2019; Studd et al, 2021; Sutton et al, 2021); in winter, juvenile fish have increased mortality compared to fish of older age groups (Deslauriers et al, 2018; Fernandes & McMeans, 2019; Takegaki & Takeshita, 2020)

Summary

Introduction

The Irtysh River is an important component of the Ob-Irtysh Basin and the largest tributary of the Ob River (Ecology of fish of the Ob-Irtysh Basin, 2006). Wintering is one of the critically important stages of their life cycle (Thayer et al, 2017; Wang et al, 2019; Studd et al, 2021; Sutton et al, 2021); in winter, juvenile fish have increased mortality compared to fish of older age groups (Deslauriers et al, 2018; Fernandes & McMeans, 2019; Takegaki & Takeshita, 2020) During this season, many species of fish (including sturgeons) prefer “temporal bottleneck” – wintering riverbed depressions (Thayer et al, 2017; Andrews et al, 2020). Aggregation in the “hydrodynamic shadow” of the riverbed depression is part of the fish survival strategy, because it allows them to reduce the waste of accumulated lipids (Thayer et al, 2017; Takegaki & Takeshita, 2020), since it has been shown (Secor & Carey, 2016; Thayer et al, 2017; Takegaki & Takeshita, 2020) that the body’s ability to survive during prolonged fasting is based on behavioural patterns and mechanisms that reduce metabolism

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