The sterlet (Acipenser ruthenus) is the smallest of the six Danube sturgeons. It reaches a maximum length of around one meter and spends its whole life cycle in freshwater without the need to migrate to the Black Sea. While the other sturgeon species have become extinct in the Upper Danube, the sterlet still occurs in small isolated populations. Currently the estimated stock of self-reproducing sterlets consists of a few hundred specimens. Due to the small population size and the highly restricted habitat (fragmentation through damming), even small negative impacts threaten this population with extinction.
Very large and old animals, as well as fish coming from unregulated stocking, are caught by anglers on occasion. Due to the extremely low densities and the lack of imprinting of the stocked fish to the Danube, no reproduction has been observed in the last decades. The sterlet inhabits the Danube and its tributaries like the Morava, the Drava, the Mura, the Sava, the Tisa and other large tributaries. Additionally it appears in other streams of the Caspian-, the Black- and the White Sea. In the past, its range reached from the Danube Delta upstream to Ulm in Bavaria. Its spawning migration took them up to 300 km upstream. The main reason for its decline in the Upper and Middle Danube results from loss and fragmentation of habitat as well as overfishing.
In this project the sterlet represents all sturgeon species of the Danube and should draw attention to this highly threatened fish family. In the year 2014, the sterlet was chosen the fish of the year in Austria. As flagship or umbrella species, it needs a variety of different and special habitats, which are also necessary for other FFH- species like the streber (Zingel streber) or the yellow pope (Gymnocephalus schraetser).