Managing the movement of fish can be integral to infrastructure projects, whether that be construction, power generation or agriculture. High frequency systems are one of a number of tools used by Fish Guidance Systems to manage the movement of fish and this article provides an introduction to how high frequency systems work, what species of fish are sensitive to them and how Fish Guidance Systems can use them.
High frequency sound can be any frequency between the large bandwidth of 20-180kHz however, high frequency fish deterrent systems tend to concentrate on the more specific frequencies between 120kHz and 130kHz.
Which Species of Fish are Sensitive to High Frequency Systems?
The response of fish to high frequency deterrents is restricted to members of the clupeid species in the subfamily Alosinae and this includes blueback herring (a member of the shad family, not herring family) twaite shad, gizzard shad, alewife and gulf menhaden.
Clupeid fish can typically hear sound up to 4Khz, however certain species within the Alosinae sub family can detect sound up to 180Khz. Previous experiments conducted with blueback herring[1] demonstrate that high frequency sounds (122-128 kHz[2]) elicited significant avoidance responses.
On the other hand, behavioural studies of American shad, and their response to ultrasound, demonstrate a range of responses [3]. Most notably, they are more responsive to the sound level, but less-so to the frequency.
When higher sound levels are employed, fish appear to be diverting away from the source with a more exaggerated change of direction.
How Fish Guidance Systems use High Frequency Systems
Fish Guidance Systems has been innovative market leaders for Acoustic Fish Deterrents (AFDs) for over 25 years. This has resulted in FGS equipment and systems being deployed and installed across the globe.
Transducers are a vital component of a high frequency system, as it is the transducers that convert electrical energy into high frequency ultrasonic sound waves.
Fish Guidance Systems produces both low frequency Sound Projectors and high frequency transducers. The difference between the two is in the shape and size of the output sound beam pattern. Low frequency Sound Projectors are capable of projecting an approximately equal level of sound in all directions,creating an omni-directional sound field. When a projector is mounted close to a wall, the backwards-travelling sound reflects off the surface and travels forwards, reinforcing the sound experienced by the fish.
In a high frequency system, typical transducers produce tight beams of sound, similar to a torch beam, and generally extend to a shorter range as the higher-frequency sound is absorbed with increasing distance. Fish Guidance Systems produces bespoke high frequency transducers that can be deployed to focus the signal in a very precise area, but FGS has also developed a high power transducer providing a near hemispherical sound field that can be used to screen larger areas in front of intakes.
Due to the diverse nature of the marine environment, specific variables have to be considered when deciding which transducer will provide the most effective fish deterrent results, and Fish Guidance Systems works with every client to determine the most suitable system and design of transducer for every application.
References
- [1] Popper, A.N., Plachta, D.T., Mann, D.A. and Higgs, D., 2004. Response of clupeid fish to ultrasound: a review. ICES Journal of Marine Science, 61(7), pp.1057-1061.
- [2 ] Gurshin, C., Balge, M., Taylor, M. and Lenz, B., 2014. Importance of Ultrasonic Field Direction for Guiding Juvenile Blueback Herring Past Hydroelectric Turbines. North American Journal of Fisheries Management, 34(6), pp.1242-1258.
- [3] Nestler, J.M., Ploskey, G.R., Pickens, J., Menezes, J. and Schilt, C., 1992. Responses of blueback herring to high‐frequency sound and implications for reducing entrainment at hydropower dams. North American Journal of Fisheries Management, 12(4), pp.667-683.
