Creation of fish passes and other fish migration aids

Creation of fish passes and other fish migration aids
Numerous versions of fish migration aids exist. In the picture: fish pass. © Umweltbundesamt

Involved sectors

Water management, Fishery, Nature protection, Other: Energy

Affected habitats

Waterbodies

Description

Obstructions such as river bottom steps, weirs, retention basins etc. can be found along many Alpine streams and rivers. These constitute insurmountable obstacles to the migration of fish and other organisms in flowing waters. Fish migration aids (also known as fish ladders or fish passes) are installed in flowing waters in order to give fish, in particular, the opportunity to overcome these artificial obstacles. There are numerous versions of these aids (river bottom slides, fish ramps, fish passes, bypass flume(s) …), which can be deployed to suit the target species, the obstacle to be overcome, and local conditions.

Impact

Impact in particular on Insects, Fish
Ecological impact  
Reduction of fragmentation or creation of new valuable habitats Weirs and other installations in streams constitute insurmountable obstacles to almost all organisms living in water, and divide streams into many small sections. Fish passes provide a connection between the sections.
Element of ecological network Should acidification or water pollution cause a species of fish to die out in one section, an isolated section cannot be repopulated. Fish ladders take over the role of corridors here.
Other The migration aids can lessen the impact of the changed ecological conditions (silt and sludge deposits, higher temperatures, lower oxygen concentrations) caused by the alternation between fast-flowing areas to practically stagnant stretches of water at weirs and similar installations.
Time of realisation for measure Immediate: The migration aids can be used by fish and other living organisms in flowing waters as soon as they have been installed.
Impact scope Local (municipality): The impact is primarily of importance in the flowing waters in question and, in this case, in the affected section in particular. However, in larger bodies of water or on major fish migration routes, the measure can gain regional importance.

Implementation

Implementation period Weeks: Many of the migration aids addressed are complex structures which, on top of the planning process, also take some time to build.
Frequency Non-recurring: Should be accompanied by monitoring of effectiveness.

Economic and legal aspects

Costs High (100'000-1 Mio EUR): Fish migration aids are very expensive installations. Depending on the structure, the costs can range from 100,000 to several millions of euros.
Socio-economic impacts Low: Increased fish stocks, improved water quality in the flowing waters.
Sources of financing Private sponsor, Other private sources, Public: local, Public: regional, Public: national, Public: European
Legal situation The need for fish migration aids is regulated by law throughout Europe by, inter alia, the EU Water Framework Directive.

Further information

Evaluation The technical know-how for the construction of fish migration aids has improved significantly and the new opportunities and variants enable suitable solutions to be proposed for every obstacle or situation. The ecological importance and impact of the migration aids have been shown in numerous scientific studies.
Information Other: e.g.: Salzburger Fischpass-Fibel: Erfahrungen zu Bau und Betrieb von Fischaufstiegshilfen (2002). Land Salzburg, Abt. Naturschutz, Referat Gewässerschutz. 152 S.

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