Abstract
The article discusses the features of the dynamic process of migration of ichthyofauna from wintering sites to the wetlands of a large boreal river for feeding and spawning. The influence of factors of temperature and water level on various groups of fish is estimated, and the role of water bodies of various types during fish migration in a flooded floodplain is also established. The research was performed during the spring flood in the floodplain-channel complex of the Irtysh River (Western Siberia, Russian Federation) in the water area of the conjugate water bodies: the lotic and lentic parts of the riverbed depression and the mouth of the tributary – transit section of the migration pathway of fish to the flooded floodplain. The research work was performed by “AsCor” – computerized hydroacoustic complex, hydroacoustic survey data were processed in the laboratory. The “AsCor” complex remotely performs taxonomic identification of abundant species of fish at the family level by groups (Cyprinidae, Percidae, Coregonidae–Esocidae, Acipenseridae–Lotidae). It was found that after the breakup of ice cover, maximum densities of fish were observed in the wintering sections – the initial location of the spring migration. During the 30-days observation period in the wintering sections and conjugate water bodies, the density of fish decreased from 4 to 13 times due to their migration to the floodplain. The response to a decrease in the overall density of fish in the year-round functioning lotic part of the riverbed depression to the influence of factors of water level and temperature regimes was >0.300 in general for ichthyofauna and for all groups of fish registered by hydroacoustic method (Cyprinidae, Percidae, Coregonidae–Esocidae, Acipenseridae–Lotidae). We constructed regression models of changes in the density of fish in the wintering sections of the river depending on the considered factors. Use of ANOVA analysis of variance confirmed the adequacy of the choice and the acceptability of the constructed models. We established a high statistically significant inverse correlation between the density of the fish, the water level and temperature regime for the mouth of the Konda River and the lentic part of the riverbed depression, which are transit sections of the migration pathway of fish in the floodplain. The lentic part of the riverbed depression may perform the function of a temporary station of fish during migration to the floodplain, which is beneficial from the point of view of bioenergetics resources. During the observation period, in the river flows there was a decrease in the proportion of larger fish and an increase in smaller individuals; in the lentic part of the riverbed depression, on the contrary, there was a reduced proportion of small fish and increase in the proportion of larger individuals.This pattern is explained by the reduced risk of predation by small fish in more turbulent conditions, as well as by an initial entry into the flooded floodplain of larger individuals of fish for spawning, followed by the smaller ones for feeding.
Highlights
Seasonal changes in hydrological (Dutterer et al, 2013; Walton et al, 2017; Jin et al, 2019) and temperature conditions (Dutterer et al, 2013; Espínola et al, 2016) are significant factors in the dynamics of fish populations in floodplain-channel systems of large rivers and their tributaries
Inside the complex of a wintering riverbed depression consisting of lotic (L1) and lentic (L2) sections located in the Irtysh River and the mouth of the Konda River associated with them (K), during the observation period we noted differences in taxonomic and size structure of fish communities, as well as in the dynamics of fish density
Zander and perch dominated among the percids in the riverbed depression, ruff to a lesser extent, perch and zander prevailed at the mouth of the Konda River, and ruff was represented slightly
Summary
Seasonal changes in hydrological (Dutterer et al, 2013; Walton et al, 2017; Jin et al, 2019) and temperature conditions (Dutterer et al, 2013; Espínola et al, 2016) are significant factors in the dynamics of fish populations in floodplain-channel systems of large rivers and their tributaries. Researchers have studied the duration and direction of migration in the floodplain-channel complexes of the Amazon (Goulding et al, 2019), Yangtsi (Jin et al, 2019; Wang et al, 2019) and Parana Rivers (Baumgartner et al, 2018), and investigated the abundance and structure of the fish population, its dimensional taxonomic features in the areas of flooded floodplains, that is, either in the middle or at the end of the migration pathway, even on the territory of the Russian Federation, for example, in the Volga-Akhtuba river system (Van de Wolfshaar et al, 2011).
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