Fish guidance and deterrence technology is evolving at a rapid pace.
Better understanding of behaviours and the differences between species, combined with the development of innovative solutions, is helping achieve the objectives of complex marine projects all over the world.
And while the electric vs acoustic debate has raged among guitarists for decades, when it comes to fish deterrence, there is now a clear winner.
Electric barriers were once considered a leading option for deterrence, proving to be effective at managing invasive species in some environments. But they have significant drawbacks and are not suitable for many applications, so acoustic fish deterrents (AFDs) are coming to the fore as the most practical option.
An electrical deterrent uses a current to generate an electric field in the water. The voltage typically gets progressively stronger, initially deterring large fish which feel the effects first, before preventing the passage of smaller fish with a higher current.
The technique has been successfully deployed in the Chicago Area Waterway System, where there is a serious risk of invasive species entering the Great Lakes.
However, a feasibility study prepared on behalf of the Minnesota Department of Natural Resources highlighted the potential drawbacks of such systems. The study, which assessed the suitability of various deterrents in efforts to limit upstream movement of invasive carp in the Upper Mississippi River System, identified several significant challenges, including:
- Extremely high initial construction costs
- High monthly operating costs
- Safety concerns
Safety concerns may include risks for swimmers, as well as the potential for sparks to fly between the electrodes and barges carrying flammable material.
Sound-based solutions, however, have been developed with the protection of fish in mind.
Many systems have been designed specifically to guide migrating populations away from harmful routes, while others divert fish away from dangerous power plant intakes.
An acoustic barrier is a safe, humane approach informed by the science of a target species’ hearing characteristics. And they are now being used to deter invasive species, notably in the case of the BAFF (BioAcoustic Fish Fence) installed by Fish Guidance Systems at Kentucky’s Barkley Lock.
This system generates a ‘wall of sound’ by generating deterrent signals and injecting them into a curtain of air bubbles. The sound signals are customised to provide control over a target species and the BAFF requires less maintenance than an electrical barrier or physical screen.
The best of both worlds
As battles against invasive species intensify, a combination of deterrents may be the inevitable result. Research by the Invasive Species Unit of the University of Minnesota has shown the BAFF system is the most effective acoustic deterrent against invasive carp available.
This is in part because it combines multiple stimuli, with High Intensity Light Bars and complex sound signals helping to prevent fish from adapting to the deterrent. And as the evolution and optimisation of AFDs continues, guidance and deterrence of target species will only improve.