The Asian carp species bighead carp (Hypophthalmichthys nobilis) and silver carp (Hypophthalmichthys molitrix) are invasive species have become a major problem to the native fish populations the North American waterways. In the last three decades they have successfully spread throughout the Mississippi River and are in the Illinois River, which is connected to the Great Lakes via the Chicago Sanitation and Ship Canal. Asian carp pose a significant threat to the Great Lakes ecosystem. An electrical barrier designed to repel fish was placed in the waterway but is not 100% effective as evidence of the invasive species was found upstream of the barrier. This however is presently the only defence in place. Bighead and silver carp are known to be within 22 miles of the electric barrier which is about 25 miles from Lake Michigan. The main limitation of electrical barriers in this type of application is that the electric field may not be effective on very small fish and may be disrupted by large steel-hulled barges and other vessels passing through.
Both Asian carp species are exceptionally sensitive to underwater noise and respond well to acoustic deterrents tuned to appropriate sound frequencies. FGS acoustic and HIL barriers have been trialled over a number of years by the Illinois Natural History Survey (INHS). To ensure that the barriers would specifically target invasive species, audiograms of the Asian carp species were measured using the auditory brainstem response (ABR) technique, allowing deterrent signals to be tuned to the most sensitive frequencies. This same method was then applied to the indigenous lake sturgeon (Acipenser fulvescens) and the paddlefish (Polyodon spathul). The data were used to create a highly effective deterrent against the Asian carp but which had no effect on either the lake sturgeon or the paddlefish, allowing them free passage past the barrier. (Ref Taylor et al., 2005; J Nedwell, J M Lovell and M. Pegg 2005).
Initial trials undertaken by INHS tested a SPA-driven BAFF in a hatchery raceway and after some fine-tuning achieved >90% protection efficiency. Larger-scale long-term trials carried out at Quiver Creek on the Illinois River (see illustration below) using a combined achieved high success over two trial seasons and were 99.9% effective against bighead carp and 100% against silver carp. Barrier effectiveness for a wider range of species was increased by adding High Intensity Light strobes and was found to be 97% effective against passage of all fishes present (Ref: Ruebush et al., 2012).