Abstract
An ecological assessment method for lakes based on fish communities similar to the IBI‐system was developed and further tested on two Austrian prealpine lakes. Important quality criteria used were species composition, reproductive success, size structure and total fish biomass. The reference status of each lake was established by the reconstruction of the native fish community and the native total fish biomass.
In Hallstättersee only minor deviations from the reference status could be observed. Additionally to the 12 native (reconstructed) fish species two exotic species were found inhabiting this lake. There was no change in the number of intolerant fish species and for 10 native fish species reproduction success was confirmed.
The fish community of Irrsee differed to a higher extent from the reference status. Three native fish species were missing. Seven exotic species were confirmed by catches and four of these are reproducing in Irrsee. No reproductive success could be verified for five native species. The sum of scores in our proposed scoring system revealed a value of 92 points for Hallstättersee, which corresponds to a “high ecological status” and of 60 points for Irrsee, which corresponds to a “moderate ecological status” of the fish community.