Ecological Quality Assessment of Salmonid Rivers in Bulgaria Using Ichthyologic Parameters

The salmonid rivers in Bulgaria are characterized with naturally poor species composition of the ichthyo-cenoses what makes the existing fish indices based on the species richness as an indicator inapplicable for ecological quality assessment. An algorithm is proposed for assessment the ecological status of all trout rivers within the both Eco-region 12 and Eco-region 7 according WFD. Ten ichthyologic parameters were used: total number and biomass of ichthyofauna, total number, biomass and number of size-age groups of the trouts of genus Salmo, percentage in number and number of the size-age groups of Bullhead (for Danube tributaries), percentage in number of cyprinid species, percentage in number of the introduced species, health status of fish community. The values of the used parameters were organized in four ranges with respective rates 0, 1, 3, and 5. The integrated Trout River Index (TRI) was calculated as the score of the rates. The ecological quality assessment was made through comparison of the values obtained with the referent values of TI taking in account the river type. The proposed algorithm was tested for ecological quality assessment of salmonid river stretches within the watersheds of both the Danube River and Aegean Sea.