At the Test Case Freudenau the cues and stimuli for orientation of fish during upstream migration are being investigated.  

The Test Case Freudenau is located on the Danube in Vienna, Austria. When the HPP Freudenau was built in 1992-98 by VERBUND, ecological measures, such as the creation of new biotopes, reconstruction of shoreline with backwaters, coves and gravel banks as well as an ecologically designed bypass stream as a fishway, were undertaken. This nature-like bypass stream has its entrance situated approximately 500 m downstream of the power plant’s weir system. Two estuaries with permanent flow ensure attracting currents through which fish can find the entrance of the fish pass.

Orientation of migrating fish is predominately based on hydraulic cues, which influences the positioning of the fishway entrance and the minimal flow requirements there. However, different  species might also use additional cues, such as sound and chemical signals, for orientation.  Therefore the fish swimming behaviour in connection to other stimuli that could be of importance for orientation is being studied at the hydropower plant Freudenau.

Orientation, stimuli and fish swimming behaviour

In order to explore potential alternative stimuli for orientation of potamodromous fish, the fish swimming path in front of and at the fishway entrance are being investigated with an acoustic telemetry study. For the 2D telemetry study the hydrophones had to be mounted downstream of the power station under the high flow conditions of the free flowing Danube (picture at the top). Due to these difficult conditions, a feasibility study was carried out this year as a first step, testing two hydrophone arrays at different abiotic conditions Following this, fish will be tagged at the beginning of next year to record their swimming path during migration.

At the same time, a terrain model of the fish pass and downstream reach at Freudenau has been set up by TUM, to be used as a basis for a numerical model. Using Flow3D, the numerical model coupling hydro-thermo-chemical-mechanical cues has been created.


In the next step, these simulations will be combined with the fish swimming paths to be able to get information about the cues and stimuli influencing the fish swimming behaviour.

Text: Lea Berg
Picture rights: BOKU Wien, TUM




Leave a Reply