Experimental Assessment of Risk for Breach of Electric Barriers on the Chicago Sanitary and Ship Canal by Invasive Asian Carp

Bighead carp Hypophthalmichthys nobilis and silver carp H. molitrix are nuisance invaders of the Mississippi River System and potential invaders of the Great Lakes.  Electric barriers have been deployed in the CSSC as barriers to the dispersal of aquatic nuisance species through the waterway. The risk for breach of barrier fields by juvenile and young-of-year (YOY) Asian carp was evaluated in a series of experiments; the influence of electric field characteristics [field strength, E, V/cm; pulse-frequency (Hz); pulse-duration (ms); referred to as operational protocol for brevity] water conductivity, volitional challenge of electric fields, and water velocity on risk for breach of barrier fields were evaluated in a controlled environment. In the experiments on effects of operational protocol, water conductivity, and water velocity, fish were subjected to electrical exposures in a fashion that mimicked exposure received by fish penetrating the electric field of Barrier IIA on the CSSC (simulations of encroachment). The immobilization of encroaching fish (i.e., fish rendered incapable of swimming motions), first-response to electrical stimulation, and flight behaviors were the primary outcomes of interest. The simulations were based on a hypothesized worst-case scenario for preventing passage of the targeted fish through the barrier field: (1) encroaching fish were small, (2) encroaching fish were swimming at the surface of the Canal, (3) fish penetrating the electric barrier continued upstream despite receiving electrical stimulus, (4) fish traversed the barrier at maximum swimming speeds, and (5) water velocity was zero or minimal. In the experiment on effects of water conductivity, the simulations were conducted at various levels of water conductivity (100 μS/cm to 4,000 μS/cm). In the experiment on water velocity, condition 5 was changed, as the simulations were conducted at three levels of water flow. Experiment outcomes showed that : (1) risk for breach of the barrier by encroaching fish was strongly dependent upon the operational protocol applied, (2) risk for breach of the barrier field was inversely related to fish size, (3) fish effective conductivity for YOY bighead carp was 90 μS/cm, (4) risk for breach of the barrier ranged from 0.00 to 0.20 in water of 100 – 4,000 μS/cm, (5) YOY fish demonstrated positive rheotaxis to water current flow and avoidance of barrier fields was unlikely, and (6) that risk for breach of the barrier was inversely related to water current velocity.