Re-opening the Danube tributaries for
the rare Danube salmon
The Danube salmon – Hucho hucho – is a central European salmonid that lives exclusively in freshwater. It can reach two metres in length and weigh up to 100 kg. Once widespread in Austria and southern Germany, its range shrank dramatically following the construction of a series of large hydroelectric power plants, which effectively blocked access to many of its natural spawning streams.
Nowadays, the Austrian population is restricted to four separate tributaries of the Austrian Danube, but even here populations are all threatened with extinction. One of these last strongholds is the Pielach-Melk river system in Lower Austria. Here the spawning grounds are still relatively intact, but their access is restricted by a whole series of obstacles, such as weirs and small hydroelectric mills.
Re-opening migration corridors
The Huchen LIFE project was the first project in Austria, which sought to eliminate all such migration obstacles along this river section. A number of later LIFE projects have taken over this strategy (Donau-Ybbs, Wachau, Lafnitz II, Obere Mur, Lech) expanding the river continuum further up- and downstream of the Huchen zone.
By linking the Pielach and Melk/Mank tributaries with the still free flowing stretch of the Danube in the Wachau region, the Huchen LIFE project improved migration opportunities over a total of 78 km. It did this by removing or altering 11 weirs and other obstacles across the tributary rivers, so that fish are able to come in from the Danube to spawn and juveniles can head back out again. This was no easy task however. Approval had to be given by the private owners of water use rights; which in turn required agreement about one-off compensations, especially if water had to be redirected through fish ladders instead of being used for power generation.
Technical solutions had to be worked out for every single weir to ensure that they offered an optimal upstream migration for a range of different fish species at all times of the year despite the variation in seasonal discharge,. Finally, arrangements had to be made with the water boards for the control and maintenance of the fish bypasses, and an agreement reached on who is responsible for the repair work if a major flood event destroys a fish pass.
All weirs have been rendered passable not only for large and mobile fish like Hucho hucho, Chondrostoma nasus and Barbus barbus, but also for the smaller bottom-dwelling Annex II fish species such as Zingel zingel, Gymnocephalus schraetzer, Cobitis taenia and others. That Danube fish are again able to enter both Pielach and Melk/Mank during their spawning migrations, was confirmed by the monitoring carried out as part of the project. Because the hitherto mutually isolated sub-populations are now able to mix again, their genetic pool will increase.
Snowball effect of LIFE-Nature
The Huchen LIFE project has had a real incentive effect, setting new standards for fish management within the regional administration. A number of smaller projects are now underway, copying the techniques of the LIFE project.
In the Danube itself, the Donau-Ybbs LIFE-Nature project is following up this project’s work by constructing a fish migration channel at Melk power station, thereby opening up an extra 90 km of Danube river continuum. All key players are involved; main project partner is the electricity company Austrian Hydro Power, contributing about 35% of the total cost. Other projects are tackling the Danube’s tributaries. The Obere Mur project is removing obstacles from the river Mur and its tributaries and a fish bypass will be built near Murau, allowing free fish migration over another long stretch of river (80km).
In another tributary, the Lafnitz, a LIFE project will construct 9 fish bypasses and modify 6 weirs to allow migration, and will reconstruct the river bed over a 300m length to bypass a weir 3.5m high. This will re-open a free-flowing continuum for migration over the whole river course (120 km). Currently isolated populations will be brought together again, thereby lowering the risk of local extinctions, and new habitats will be created as spawning grounds for fish, breeding habitats for amphibians and foraging places for birds.
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