Distribution of endangered freshwater mussel species Unio crassus Philipsson, 1788 in Serbia

Abstract

The Thick Shelled River Mussel, Unio crassus Philipsson, 1788 is one of Europe’s most endangered freshwater mussel taxa – according to the IUCN criteria assessed as endangered (EN) The aim of this study is to present the current distribution of this species in Serbia, based on the research performed between 2001 and 2013. Previous studies in Serbia indicated only sporadic findings of the species in a restricted area over the last several decades (BAES database). Our study covered the entire territory of Serbia. Out of 500 sites covered by the study, the mussels were recorded at 23 sites. U. crassus has been recorded at the Velika and Zapadna Morava rivers, the Kolubara River Basin and the Danube, the Tisa and Sava rivers. The species has been sporadically found in Serbia, with low frequency of occurrence and low abundance along the Danube and Tisa rivers (up to 1.75% of the total mussel community), while it was found almost along entire stretches of the Velika Morava and Sava Rivers, with higher relative abundance compared to the Danube and Tisa rivers (up to 15.49% of the total mussel community). Based on our study, a positive population trend, reflected in extension of the known distribution range and increasing of population density has been recorded in Serbia.