Great ecological benefit will be gained if effective barriers can be constructed to control the movement of invasive common carp. Carp feeding habits lead to an over-enrichment of nutrients in lakes that dramatically reduces water quality and ecosystem health. Bajer et al.  demonstrated that in Minnesota lakes, juvenile carp are recruited from nursery lakes to larger water bodies through small connecting channels. Reducing juvenile carp recruitment through the use of a barrier at the entrances to the interconnecting channels could prove useful in an integrated carp management plan for the entire watershed. Current barrier technologies are not well suited for these sites due to the shallow water and rapidly changing water level. This research focuses on the use of bubble curtain barriers, which has been relatively ignored in previous barrier studies, as a barrier technology that shows promise for this application. Bubble curtains generate distinct acoustic and hydrodynamic fields, and through proper manipulation could be used to deter juvenile carp migration.
The initial stage of the barrier design was to quantify and measure the physical fields generated by a bubble curtain. An understanding of the physical fields helps to design full barrier systems by exploiting certain features of the bubble curtains. Experimental data revealed that a coarse-bubble curtain created a weaker flow field, but a stronger acoustic field than a fine-bubble diffuser. The subsequent stage of research included barrier tests with live carp using a PIT tag tracking system, which allowed quantification of carp passage over a barrier sans video recording. Three incrementally stronger bubble barriers were designed. A single diffuser design exhibited a mildly retarding effect of carp passage time (passages were delayed 10-15 sec) but not on the actual number passage attempts. Two separate multi-diffuser barriers (varying in configuration and air-supply) exhibited approximately a 75% decrease in carp passages, in upstream and downstream directions. The reduction of passes for each barrier was calculated by taking the ratio of the number of passages during a barrier-on trial to the number of passages during a control (barrier-off) trial. Carp mobility remained constant between tests, indicating that the two larger barriers did not limit total carp activity, but limited carp passage over the barrier.
This research represents the first stage of characterization of bubble curtain features with respect to carp sensory systems and rigorous testing of bubble barriers under controlled laboratory settings. The experimental results suggest that bubble barriers create a flexible barrier that appears to deter juvenile carp movement in shallow channels, and may prove to be an effective tool in an integrated carp management plan.