Application of an adapted index of biotic integrity to rivers of Lithuania

The species composition, community structure, trophic composition, abundance and biomass were investigated in 60 Lithuanian rivers. Leaning on the results of investigations, four main types of river fish communities (fish communities of the brooks, streams, middle-sized and large rivers) differing in species number and composition, trophic composition, density and biomass were singled out. Referring to the characteristic features of fish communities, the Index of Biotic Integrity (Karr et al., 1986) was modified and adapted to the conditions of Lithuania. In order to test biointegrity, nine metrics in three categories (species composition, abundance and biomass; trophic composition and fish condition) were selected. The metrics of this biotest assess attributes that are assumed to be correlated with biotic integrity. These metrics, by the sum of their ratings, characterize the underlying biotic integrity of the sampling site. Six integrity classes (excellent, good, fair, poor, very poor and no fish) of river fish communities were distinguished. Individual tests were adapted to brooks (up to 10 km in length), streams (up to 50 km and riverhead of bigger rivers), middle-sized rivers (up to 200 km and the middle reaches of the large rivers) and large rivers (over 200 km and the lower reaches of the middle-sized rivers). While brooks and streams mainly show intact conditions (class 1 and 2), middle-sized and large rivers are significantrly more impacted (class 2 to 3).