Abstract
Abstract During the last century a large portion of small and medium-sized rivers in Latvia were channelized, hydroelectric power stations were also built, which led to changes in the hydrodynamic conditions, geomorphological structure, as well as a change in the fish fauna. Fish are an integral part of any community in natural or man-made bodies of water. They actively participate in maintaining the system, balancing/equilibrium, energy, substance transformation and biomass production. They are able to influence other organisms in the ecosystem in which they live. The aim of the paper “Pike distribution and feeding comparisons in natural and historically channelized river sections” is to find out what pike feed on in different environments in Latvian rivers, such as natural and straightened river sections, as well as what main factors determine the composition of their food. Several points were assessed during the course of the study: the impact of environmental conditions on the feeding habits and the distribution of pike; the general feeding habits of predators in Latvian rivers; the feeding differences of predators in natural and straightened river sections; and lastly, rhithral and pothamal habitats were compared. The study was based on data from 2014 and 2015 on fish fauna monitoring. During the study, 347 pike were collected from 136 plots using electrofishing method.
Highlights
Water is one of the most important natural resources, but human activity is directly threatening freshwater resources, and due to climate change, this exacerbating the problem
The oxygen concentration analysis showed that the straightened parts of the river show some evidence of low oxygen concentration (7.2 mg/l ± 2.7 mg/l), compared to parts of the river that have not been channelized (8 mg/l ± 1.7 mg/l)
It is emphasized in literature, that the main factors influencing the spread of pike is the temperature, speed of the current, and vegetation density – the optimum temperature for metabolic processes is between 4 °C to 23 °C, and current velocity over 1.5 m/s limits the pike migration, a medium dense macrophyte vegetation provides shelter and food habitats [13], [30], [31]
Summary
Water is one of the most important natural resources, but human activity is directly threatening freshwater resources, and due to climate change, this exacerbating the problem. Freshwater resources are effect by changes in land usage, industrialization, urbanization, irrigation, and the formation of reservoirs and channels [1]. Such activities homogenize the hydraulic and geomorphological characteristics of streams. This results in a decrease in the amount of species, their incidence and prevalence in certain areas, which negatively affects the function of the ecosystem [2], [3]. In which in last century from year 1939 to 1974 were built three hydro power plants, which adversely affected the river flow, completely destroyed riffle structure, completely end migration of diadromous species, altered the distribution of species in Daugava River basin [4]
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