Fish scarer
A fish scare system is used to keep the fish living within a body of water out of a certain area in which they are not wanted or in which they are at risk. Particularly in the case of transverse structures in watercourses, for example in hydropower plants or pumping stations , a fish scare system is often installed parallel to the flotsam rake to protect the fish .
Electric fish scare
An electric fish scare system uses electrodes immersed in the body of water to generate an electrical pulse field - the scare field - that is supposed to scare away fish. For this purpose, pulses in the millisecond range are generated with a randomly changing sequence and frequency (to prevent habituation effects) and a current density of at least 2.56 µA per square millimeter of water cross-section. The body of a fish that is in the Scheuchfeld is traversed by the current that acts on the fish. The current is applied in such a way that it flows as closely as possible to the direction of flow of the water. Since fish usually stand alongside the current, the current flows a longer distance through the fish's body and the effect is stronger. The systems are no longer effective at high flow speeds, which is why they are only permitted in Germany at flow speeds below 0.3 m / s. The systems (in Germany) use warning signs to warn of the risk of electric shock.
Such systems are z. B. used at the inflow to water turbines or the cooling water extraction point of power plants.
Optical scare away fish
A gentler way to scare away fish is to use optical stimuli. Many types of fish (e.g. allis shad , anchovy , perch ) can be successfully driven away by strobe-like flashes . Optical fish scare systems use flash tubes or high-power LEDs to generate flashes in the frequency range between 1 and 20 Hz. A sufficient number of luminous bodies must be installed in order to be sufficiently recognized in all water cloudiness.
Acoustic scare away fish
Acoustic scaring systems drive away fish through the use of infrasound underwater loudspeakers. Such a system is used in Tihange (Belgium) , for example . The low frequencies have a high deterrent effect on carp-like fish, e.g. B. roach , bream , bleak . The effect on eel and salmon has also been proven. High deterrence effects are also expected in other fish species, since all FFH-relevant fish species perceive infrasound.
Further acoustic scare systems were tested in the Schleusingen hydrolaboratory at the Bauhaus University Weimar, funded by the German Federal Environment Foundation .
Individual evidence
- ^ PH Patrick, AE Christie, D. Sager, C. Hocutt, J. Stauffer Jr .: Responses of fish to a strobe light / air-bubble barrier. In: Fisheries Research, 3, 157-172. 1985, accessed December 11, 2016 .
- ^ Jeffery K. Baker: The effects of strobe light and sound behavioral deterrent systems on impingement of aquatic organisms at Plant Barry, Alabama. December 19, 2008, accessed December 11, 2016 .
- ^ FFH compatibility study for the Brunsbüttel coal-fired power station. Retrieved December 11, 2016 .