Fishing weir

More generally serve fish weirs to catch migratory fish. Previously mainly to acquire food and for commercial fishing operations, they are now used mainly for the study of fish migration.

For fish weirs in rivers, a flow profile is locked with Leitzäunen in the form of computing in general. Migratory fish of a certain size can not pass the rake and are either fished at Weir directed ( for example, networks ) or in a fish trap from which they can be easily removed.

• 2.1 Inventories
• 2.2 catching spawning fish

• 3.1 Monitoring of fish migrations
• 3.2 autecological studies

Dynamic Fischwehr

The Dynamic Fischwehr is a further development of conventional techniques developed from the desire for a fish weir that is easy to maintain, portable, and inexpensive, and - what is particularly important in rivers - is not destroyed by flood. It was developed at the Institute of Hydrobiology and Aquatic Ecology (IHG ) at the University of Agricultural Sciences Vienna ( Mühlbauer et al, 2003). As an example of the so-called "resistance board weir" ( Tobin, 1994) was used which is used in North America for the detection of the migration of salmon. In spring 2004, only one year after publication of the Dynamic fish weir, this method is already on four rivers in Austria and Germany in use.

Construction, installation, maintenance

The dynamic fish weir consists of grid-like panels that are composed of plastic pipes. One end is anchored to the sole of the other with a float on water held. Due to the computational structure of the fish weir only coarse flotsam on the construction remains hanging in the rule making maintenance work is extremely reduced.

Flood safety

The most important feature of the Dynamic fish weir is its flood safety. To achieve this, the Reuse box should be made of solid steel or equivalent. In contrast, the Dynamic Fischwehr must be as flexible as possible to give to the water masses in the event of a flood. With increasing discharge the burden on the defense is getting bigger, until finally no longer sufficient buoyancy of the float and the fish weir is pressed and flows downward. Increases the outflow continued, the fish weir flows over successively. Concurrently, more and larger floating debris on the can endanger the system. As a rule, Reuse box and Fischwehr are already low enough to not be damaged under water. In order to use the hydraulic load on the stream bottom to withstand the fish weir must be carefully processed and adequately anchored. In March 2002, the Dynamic fish weir at the Pielach was flowing 4 to 5 feet tall with an outflow of 150 cubic meters per second. Through the 10 - year flood event, however, no damage to the fish weir was built.

Dynamic weirs can be used especially in the following scientific questions.

Fishery issues

Inventories

Of stockings to individual appointments usually represent only snapshots dar. through weirs can also use the moving fish populations are detected.

In large rivers, the quantitative intake of fish stocks is usually not possible. In situations where large population segments move into tributaries, about to spawn there, they can be detected and labeled by a fishing weir. After return migration to the main river may be determined by relatively few recaptures the total stock of a fish species. Thus, the existence of a species for an entire section of the Danube was through the use of a fish weir and the marking of the fish for the first time determined - as happened in the LIFE - Danube salmon project for migrating from the section of the Danube Wachau noses that were marked at the fish weir at the Pielachmündung ( Zitek et al., 2004 in preparation).

Fishing for spawning fish

For the rearing autochthonous fill material spawning fish can be caught in a gentle way by means of a fishing weir. Another advantage is that the spawning fish are caught only when actually migrate to the spawning ground.

Ecological issues

Monitoring of fish migrations

An increased environmental awareness means that Rivers is trying to deal with today in terms of sustainability and to take on their ecological function into consideration. The EU has this thought in the EU Water Framework Directive. The impairment of passability for aquatic organisms is one of the strongest interference in the ecology of our rivers. It is caused by power plants and river regulation. In waters networking projects ( fishways, reconnecting tributaries, ...) is trying to compensate for the negative effects of fragmentation waters. Through both weirs already realized waterway integration can be checked whether they are actually eaten by the fish and can be used to determine the priority of measures the potential on workers wishing fish are collected.

Autecological studies

With a fish weir, it is possible to capture fish migrations in quantitative scope and their natural occurrence in time. In combination with other methods for monitoring fish migration ( marking experiment, telemetry, ... ) the result is a complete picture of the migratory behavior of individual species.

Constructional water applications

With fish weirs abgefischte fish may already be permanently kept away from the area of river sites.