Ichthyofauna of a mountain river upstream from a big dam reservoir (the upper San River, South-eastern Poland)

Abstract

Changes in the ichthyofauna in the San River drainage basin since establishing the dam reservoir were observed, and major environmental factors, influencing the distribution of 15 fish species were stated. A hierarchical cluster analysis was used to classify 37 sites into 4 groups of streams of different fish community composition. Habitat preferences of particular fish species were assessed using canonical correspondence analysis. Brown trout and Siberian sculpin occurred in the whole drainage area but preferred smaller streams with a large gradient. However, brown trout was less abundant in streams where anglers' catches and poaching were more frequent. Streams with wide beds were preferred by gudgeon, nase and roach. Minnow was abundant in the drainage basin, but correlation with any environmental variables was not found. Significant statistical changes in occurrence of a few species were observed. Their appearance or disappearance was directly related to the establishment of the dam reservoir. Perch and roach, abundant in the dam reservoir, settled in the rivulets upstream, while two species of barbel, present before the river impoundment, disappeared. Grayling, introduced by stocking, was quite abundant. The mean biomass of fish communities in the big stream and rivers was significantly higher than in small streams.