The BioAcoustic Fish Fence (BAFF) is one of the most effective ways to guide or block fish, whether for their own protection or to prevent them causing damage to an ecosystem.

The technology was born out of naval research into ways to communicate with submarines without detection. A founder of FGS realised the principles could be applied to fish guidance and the team developed a system that would help aid species in their migration.

It is now also used to deter fish from hydro-electric power stations, as well as to control the spread of invasive species.

The BAFF system combines repellent sound signals with an air bubble curtain. Sound Projectors are mounted on a chassis in sections, along with bubble pipes, and these sections are lowered to the river bed.

Once connected, they form a barrier of sound and air that can be used to guide the fish, and yet still allow vessels to freely pass by.

What does it look like?

The BAFF system is visible above the surface only as bubbles on the water. Below, hearing-sensitive fish are deterred from the ‘wall of sound’, which decays rapidly upstream and downstream, allowing for precise guidance of the fish.

While FGS has installed BAFF systems up to 600 feet long, the modular nature of the design means they can be as short or as long as necessary. At Kentucky’s Barkley Lock, for example, the system is 200 feet long and made up of five concrete sections. 

This particular system goes further than the typical guidance application as it also offers the potential of an area for capturing fish, made possible in part by the layout of the chosen site. This is particularly useful because the system has been installed to help mitigate the spread of invasive carp.

The continuing evolution of BAFF

Elsewhere, BAFF systems have been used to great effect to deflect salmonid smolt during spring migration. At California’s Georgiana Slough, an initial trial installation achieved a deflection rate over 90% and this led to the recent confirmation that a permanent system will be installed until 2030.

BAFF technology continues to evolve and although laboratory tests of some of the latest systems recorded a 98% success rate in deflecting invasive carp, real-world applications are providing insight into ways to refine them even further.

It is known, for example, that species such as bighead, silver black and grass carp learn to stay away from the air bubble curtain once they encounter it, but at projects such as Barkley Lock there are plans to experiment with ways to maximise deflection. When vessels pass through the bubble curtain the sound output could be increased, as could the volume of air in the bubble curtain.

This flexibility has been designed into the BAFF system, helping to ensure it can meet a wide variety of environmental and regulatory needs.

Evaluating the ability of sound, an air curtain, and high-intensity light, both alone and together, to deter bighead and common carps