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generally fish weirs serve for the catch of moving fish. In former times particularly to the food procurement and to commercial fishing, they are predominantly used today for the study of the fish migration.

With fish weirs in running waters a river profile with guidance fences is usually locked off in the form of rakes. Moving fish starting from a certain size cannot pass and become the rakes either to resistance abgefischt (e.g. with nets) or into a staggered array led out of that it to be simply taken to be able.

Dynamic fish resistance

Dynamic fish resistance is an advancement of conventional techniques, developed from the desire for fish resistance that uncomplicated to maintain, transportably, and is economical and - which is not destroyed in rivers particularly substantially actual by floods. It was developed at Institut for Hydrobiologie and waters ecology (IHG) at the university for soil culture Vienna et al., 2003). When model served the "resistance board in such a way specified weir" (Tobin, 1994) in North America for the collection the migration of the salmon is used. In the spring 2004, only one year after publication of the dynamic fish weir is this method already at four rivers in Austria and Germany in use.

Methodology

Construction, assembly, maintenance

dynamic fish resistance consists of gridlike panels from plastic tubes is compound. An end held at the sole embodies the other one with a float over water. Due to the computing structure of the fish weir usually only rough driving property remains hanging on the construction, whereby the maintenance work is extremely reduced.

Flood security

The most important characteristic of the dynamic fish weir is its flood security. In order to reach these, the staggered array box from substantial steel or comparable should be manufactured. However dynamic fish resistance must be able as flexibly as possible to be around the Wassermassen in the case of flood giving way. With rising discharge continues to increase the load for weir, until finally the lift strength of the floats is not sufficient any longer and is pressed downward and overflowed fish resistance. If the discharge continues to rise, that is rushed over gradually fish resistance. Equal time steps ever more and larger driving property on that the plant to endanger can. Usually staggered array box and fish resistance are not already sufficiently deeply under water over to be then damaged. Over the hydraulic load at the waters reason conditions to hold to be able that must be fish resistance carefully finished and sufficiently embodied. In March 2002 dynamic fish resistance was highly rushed over to the Pielach with a discharge of approx. 150 cubic meters per second 4 to 5 meters. From the approx. 10-year old flood event resulted however no damage to fish resistance.

Dynamic fish weirs can be used particularly with the following scientific questions.

Fischereiliche questions

Stocktakings:

Befischungen to individual dates represent usually only snapshots. Also the moving fish populations can be seized by fish weirs.

In large running waters the quantitative admission of fish existence is usually not possible. In situations where large population parts pull in about over there to abzulaichen, can do these by means of fish resistance seized and is marked. According to back migration in main waters total stocks of a fish type can be determined by relatively few recatches. Thus by the employment of a fish weir and marking the fish the existence of a fish type was determined for the first time for a whole section of the Danube - so happened in the LIFE Huchen project for the noses immigrating from the Danube section Wachau to fish resistance to the were marked (Zitek et al., 2004 in preparation).

Catch of Laichfi:

For the raising trimming material can by means of fish resistance Laichfi autochthonen in careful way become imprisoned. A further advantage is the fact that Laichfi becomes only imprisoned even if actually to the Laichplatz moves itself.

Ecological questions

Monitoring of fish migrations:

An increased ecological consciousness leads to the fact that one tries rivers today in the sense of the lastingness to treat and on their ecological function consideration take. The European Union considers to this thought in the European Union water framework guideline. The impairment of the wandering through barness for aquatic organisms ranks our rivers among the strongest interferences into the ecology. It is caused by power stations and channel regulation. In waters cross-linking projects (fish moving assistance, rebinding of to compensate tries the negative effects by waters fragmenting. Both waters cross-linkings already carried out can be examined by fish weirs whether it by the fish are also actually accepted and/or knows the potential at migration-willing fish for determining the priority from measures is raised.

studies:

With fish resistance it is to be seized possible fish migrations to quantitative extent and their natural temporal occurrence. In combination with other methods to the monitoring of fish migrations (marking attempt, telemetry,") such a complete picture of the moving behavior of individual kinds develops.