Hydroakustisches Monitoring der Fischwanderung an der unstrukturierten Blockrampe (UBR) am Wehr Brunau

The goal of this work was to create a comprehensive concept for fish monitoring of an unstructured block ramp, which can subsequently serve as a basis for other fish monitoring campaigns in running waters. The unstructured block ramp Brunau is located at the lower course of Ötztaler Ache in the district Imst (Tyrol). By using a hydroacoustic method, it was demonstrated that the structure has restored the longitudinal connectivity and enables fish migration. Another aim was, that the machine learning algorithms used could significantly reduce the effort required for visual observations of the hydroacoustic videos. But the low-resolution of hydroacoustic videos turned out to be problematic for the existing models. However, the manual analyses of hydroacoustic videos documented the passage of fish, which is also supported by electrofishing surveys. During one of these surveys a grayling was caught upstream the ramp. This species was not present upstream of the weir, before the construction of the unstructured block ramp.