Eutrofizacja jezior a ichtiofauna

Prejs, Andrzej

doi:ISSN 0013-2969

Download

Title: Eutrofizacja jezior a ichtiofauna

Abstract:

Papers by different authors have been used to compare examples of reaction of fish communities which seem to be the result of eutrophication of oligotrophic lakes iin Northern America and in Europe (Table I). The mechanisms and causes of such reactions as, e.g., better growth of some Salmonidae, higher infestation of fish by parasites, lesser ability for effective reproduction of species considered as typical for waters of a very low trophy, are discussed. Thus, possibilities of changes due to the increase of trophy are taken into consideration, namely the stratification pattern of fish communities, intra- and inter-specific relations of fish communities, efficiency of the influence of predators.The described by Colby et al. (1972) general relation between the size of catches and the species composition of a fish community and the degree of trophy, is presented (Fig. 1). Evidence is given that the curve illustrating this relation does not reflect the static system, but illustrates the dynamic, succesional sequence which is of course limited by the character of lake bed and drainage basin, The position of Polish lakes, where meso- and eutrophic water bodies dominate in the successional sequence presented is discussed. These lakes are dominated by Cyprinidae—Percidae. This community, although frequently less abundant ir. species, develops well even in shallow, highly polytrophic lakes. This shows that eutrophication of lakes of an intensity which does not disturb their natural development, i.e., does not lead to saprotrophy, is not yet dangerous for the existence of the majority of that community. To the contrary, in some mesotrophic lakes higher lertility, and thus more intense development of macrophytes, may provide better conditions for reproduction and existence for the majority of these fishes. However, it seems that already now the majority of Polish mesotrophic lakes either approaches or has attained the eutrophication level, which when surpassed would mean that further increase in trophy would not result in an increase of the total biomass of fishes (Table III).The situation of Coregoninae in Polish lakes is discussed stressing that despite the introductions the lake area in which they occur increases, but the number of lakes with autochthonous populations of these fish is smaller. This is usually caused by the fact that reproduction conditions in lakes become worse as the trophy increases.