Evaluating the Effectiveness of an Electric Dispersal Barrier
John M. Dettmers, Richard E. Sparks, and Traci Barkley
The most recent invasive species threatening Illinois’ aquatic ecosystems are the bighead and silver carps, two of four species commonly called Asian carps. These fish grow extremely quickly to sizes over 50 lbs. by consuming 30-50 percent of their body weight each day of small algae and other tiny organisms, reproduce very quickly, and migrate long distances to spawn. Currently in the Mississippi and Illinois rivers, these Asian carp are moving quickly upriver toward the Chicago Sanitary and Ship Canal (CSSC) where they could enter Lake Michigan and affect the entire Great Lakes basin. Because of the immediate danger of Asian carps crossing into the Great Lakes basin through the CSSC and the more general and persistent threat of invasive fishes passing this artificial connection between the Great Lakes and Mississippi River drainages, an electric barrier to fish movement was constructed in the CSSC near Romeoville, approximately 28 miles downstream from Chicago Harbor. Currently, Asian carp have been found about 22 miles downstream of the dispersal barrier location in Romeoville.
This barrier creates a graded electric field that should repel fish as they sense the field, creating a non-lethal barrier. Because optimal barrier performance depends on current velocity, temperature, conductivity, etc., we are evaluating the performance of this dispersal barrier by following movements of common carp (a surrogate for the invasive carps) tagged with combined radio/acoustic transmitters in the vicinity of the dispersal barrier. To date, we have tagged 79 fish. We are following the common carp using a combination of fixed receivers immediately upstream and downstream of the dispersal barrier to detect any movement across the barrier, and using mobile tracking by boat. Since November 2002, we have detected 75 of the 79 tagged fish. One tagged fish crossed the barrier on April 3, 2003. This fish likely moved through the electric field at the same time as a commercial barge passed through the electric field. This fish passage may be an indication that commercial navigation traffic can move fish across the field because of the strong propeller thrust from these barges and/or because the large steel hulls change the shape and strength of the electric field.
Since April, no other tagged common carp have passed through the barrier. We will continue to gauge the effectiveness of the dispersal barrier for the next two years. We expect that our work will provide the detailed information to maximize the effectiveness of the dispersal barrier before Asian carps move into close proximity to the dispersal barrier. An effective barrier will close down this avenue of expansion of the Asian carps into the Great Lakes and also keep future invasive fishes from crossing this artificial linkage between the Mississippi and Great Lakes drainage basins. The same technology, if effective in this demanding application, could be applied worldwide.