Ascertaining whether an enhanced bubble curtain could deter Asian carp movement into small tributaries in a practical manner; immediate installation of sound deterrents in the Mississippi River
In 2009, the University of Minnesota developed an enhanced new bubble curtain design that reduces up- and down-stream movement of the invasive common carp by 70-80% (results under peer review). The primary advantage of this new technology is that it is very practical and inexpensive: a simple industrial blower connected to PVC pipes with holes drilled in a specific manner (that costs less than $2,000) can stop about 75% of all common carp. This technology also has the potential to be taxon-specific because it is based on sound and hydrodynamic fields generated by the bubbles and additionally will work safely and efficiently in shallow waters.
Because the silver and bighead carp are just as (and possibly more) sensitive to sound as the common carp, this technology could have great potential for stopping these new, highly invasive species in the hundreds of small tributaries to Minnesota's large rivers that are too expensive and difficult to protect with other methods, such as electrical or mechanical barriers.
In continuation of MAISRC efforts to use sound deterrents to control movement of bighead and silver carp in Minnesota's rivers, and response to the recent report of late-stage bighead carp embryos being found in Mississippi River Pool 9, MAISRC proposes to immediately purchase and install underwater transducers at Lock & Dam #8.
This activity installed the first sonic deterrent system in a lock system and clearly demonstrated that enhanced bubble curtains and sound alone can function as behavioral deterrents with potential to selectively control the movement of fish with high sensitivity to sound including the invasive carps. Due to their low cost, ease of installation, safety, and taxon-specific effects, we believe bubble curtains hold great promise for protecting the many low head tributaries connecting with the Mississippi River. In this particular study we investigated the effectiveness of a bubble curtain as a deflection screen which directed carp away from one channel into another and found this approach (vs. blocking) to be especially promising. Using a split passage experimental channel we determined that common carp, silver carp, and bighead carp passage could all be diverted away from a specific channel in the laboratory with a success rate of 82-90%. This rate was approximately 10-15% higher than we noted earlier with a design that simply blocked. It also used 1/10th of the air flow rate.
In addition to demonstrating the diversion functions more efficiently than blocking, we also demonstrated in a different experimental design for the first time in either a freshwater or invasive fish that carps detect and respond to sound in directional manners and thus sound could be used in directional and predictable manner to divert. It is very possible that sound alone produced by speakers could be highly effective in the natural world, especially if sound is engineered correctly. This is important because air curtain use is limited to shallower waters because of possible deflection by water currents, need to produce highly pressurized air, and limited sound pressures generated. Part of a separate grant continues this line of research by evaluating the response, or lack thereof, of native, non-hearing specialist species, lake sturgeon (Acipenser fulvescens) and brown trout (Salmo trutta), to an acoustic deterrent to quantify the species specific differences.