Understanding How Fish React to the Most Powerful Electric Barrier in the World
BY SAM FINNEY, CARTERVILLE FWCO
Bighead and silver carps have been marching toward the Great Lakes via the Mississippi River and its tributaries since the 1970s. Both species of Asian carp are voracious eaters that can cause severe ecological damage. Silver carps pose an additional risk to recreational boaters who can be injured when silver carps become agitated by boat motors and jump out of the water. The impact of some jumping silver carps is great enough to break bones.
Concern about Asian carps invading the Great Lakes was catapulted into the spotlight in 2009 when environmental tests indicated that the leading edge of the population was perhaps farther north, and closer to the Great Lakes, than experts anticipated. Residents of the Great Lakes region are no stranger to aquatic invasive species (zebra mussels!). With local economies and the multibillion dollar Great Lakes commercial fishing industry potentially in jeopardy if a self-sustaining population of Asian carps becomes established in the Great Lakes, the U.S. Fish and Wildlife Service (Service) joined with international, federal and state partners to stop the potential invasion.
Part of the Service’s work involves testing the effectiveness of electric barriers located in the Chicago Sanitary and Ship Canal southwest of Chicago, which are operated by the U.S. Army Corps of Engineers (USACE) to deter the inter-basin establishment of Asian carp and other fish through an electric field in the water. Initially, the focus of the barriers was to keep round gobies from invading the Mississippi River Basin, but the barriers’ focus has shifted to keeping Asian carp out of the Great Lakes. There are currently three electric barriers that began operation in 2002, 2009, and 2011.
Recognizing the important role the electric barriers play in the fight against a potential Asian carp invasion of the Great Lakes, biologists from the Carterville Fish and Wildlife Conservation Office felt it was important to understand how the electric barriers impact fish. Thus began a series of intensive and innovative research projects to study how fish behave around these powerful electric barriers.
Studying how fish react to large electrical barriers in a canal open for navigation required biologists working on the project to be both creative and innovative. During the initial years of testing (2011-2012), biologists used sonic and video cameras to observe how fish in cages lashed to boats, and free swimming fish behaved in and around the barriers. With the exception of a few small fish, almost all of the wild fish observed with the underwater sonars seemed to be repelled by the barriers. Initial test results of fish pulled through the barrier in cages were encouraging as well. Almost all the fish tested in cages by boats were incapacitated by the electricity coming from the barriers. Despite reassuring results, biologists observed that caged fish were not shocked as easily when tested near conductive small metal boats used during research. This got biologists thinking. What about the numerous large metal barges that pass through the barrier every day? And what about the area of high electricity where some small fish failed to be repelled by the barriers during this research?
Biologists with the Service began to put their heads together with USACE to test caged fish around barges, as well as tethered free-swimming fish, as barges moved through the barrier. In some, but not all, of the areas tested around the barges, fish in cages were incapacitated. Tethered free-swimming fish ended up upstream of the barriers during up to eight percent of the trials, and alive, when barges crossed.
Biologists also looked deeper into the fish around the area of highest electricity using crane-mounted sonar cameras, called DIDSON. During these fixed DIDSON studies, it was observed that in the area of highest electricity, 61% of the videos taken showed schools of small fish, estimated to be approximately two to four inches and not thought to be Asian carp, crossing the electrical field. With the Great Lakes potentially at risk, current research and management actions are being explored to better shore up the electrical defenses. Possibilities being explored include regulating barge configurations and speeds, or adding fish-deterring structures to barges to reduce or eliminate fish getting by with barges. A new barrier is being constructed, and this construction will incorporate what biologists have learned about fish and electricity in the canal over the past decade.
Current evidence suggests that Asian carp populations directly adjacent to the barriers are very low or nonexistent. Adult populations of Asian carp are approximately 18 miles downstream of the barriers and 55 miles from Lake Michigan. These populations have not moved upstream for several years. This creates a window of opportunity for additional actions to be taken to keep Asian carp out of the Great Lakes. Research findings have larger implications, as there are thousands of electric barriers around the country and the world. This research, and the techniques developed to study fish behavior around electric barriers, will prove invaluable in the placement and testing of electric barriers designed to stop the spread of aquatic invasive species, like Asian carp.
More details about the studies are available at: http://www.fws.gov/midwest/fisheries/carterville/didson-barge.html.
More details about the ongoing USACE studies and barrier operations can be found at http://www.lrc.usace.army.mil/Missions/CivilWorksProjects/ANSPortal.aspx