Entrainment, retention, and transport of freely swimming fish in junction gaps between commercial barges operating on the Illinois Waterway Jeremiah J. Davis a, ⁎, P. Ryan Jackson b , Frank L. Engel b , Jessica Z. LeRoy b , Rebecca N. Neeley a , Samuel T. Finney c , Elizabeth A. Murphy b a U.S. Fish and Wildlife Service, Carterville Fish and Wildlife Conservation Office, Wilmington Substation, 30239 S. Route 53, Wilmington, IL 60481, United States b U.S. Geological Survey, Illinois Water Science Center, 405 N. Goodwin Avenue, Urbana, IL 61801, United States c U.S. Fish and Wildlife Service, Carterville Fish and Wildlife Conservation Office, 9052 Route 148, Suite A, Marion, IL 62959, United States abstract article info Article history: Received 23 January 2016 Accepted 15 May 2016 Available online 8 June 2016 Communicated by Edward Rutherford Large Electric Dispersal Barriers were constructed in the Chicago Sanitary and Ship Canal (CSSC) to prevent the transfer of invasive fish species between the Mississippi River Basin and the Great Lakes Basin while simulta- neously allowing the passage of commercial barge traffic. We investigated the potential for entrainment, retention, and transport of freely swimming fish within large gaps (N 50 m 3 ) created at junction points between barges. Modified mark and capture trials were employed to assess fish entrainment, retention, and transport by barge tows. A multi-beam sonar system enabled estimation of fish abundance within barge junction gaps. Barges were also instrumented with acoustic Doppler velocity meters to map the velocity distribution in the water surrounding the barge and in the gap formed at the junction of two barges. Results indicate that the water inside the gap can move upstream with a barge tow at speeds near the barge tow travel speed. Water within 1 m to the side of the barge junction gaps was observed to move upstream with the barge tow. Observed transverse and vertical water velocities suggest pathways by which fish may potentially be entrained into barge junction gaps. Results of mark and capture trials provide direct evidence that small fish can become entrained by barges, retained within junction gaps, and transported over distances of at least 15.5 km. Fish entrained within the barge junction gap were retained in that space as the barge tow transited through locks and the Electric Dispersal Barriers, which would be expected to impede fish movement upstream. Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. Index words: Fish entrainment Asian carp Barge Hydraulics Illinois Waterway Electric Dispersal Barrier Introduction During the last century, introductions of non-indigenous species to the Great Lakes Basin have caused substantial ecological and economic harm (Mills et al., 1994; Pimentel et al., 2005). These introductions have occurred through a variety of mechanisms including accidental release, intentional release, movements through canals, movement along highways and railroads, and ship-related introductions (Mills et al., 1993). The Chicago Area Waterway System (CAWS), including the Chicago Sanitary and Ship Canal (CSSC), is a combination of natural and manmade channels that form an interconnected navigable waterway of approximately 90 miles at the most upstream end of the Illinois Waterway (Duncker and Johnson, 2015)(Fig. 1). As the only navigable connection between the Mississippi River Basin and the Great Lakes Basin (Rasmussen et al., 2011), the CAWS has garnered great attention since the invasion of the Mississippi River Basin by bigheaded carps (Bighead Carp (Page et al., 2013) Hypophthalmichthys nobilis and Silver Carp Hypophthalmichthys molitrix, collectively) in the late 20th century (Kolar et al., 2007). Under authorization of the Invasive Species Act of 1996, the U.S. Army Corps of Engineers (USACE) constructed a large electric fish deter- rent system (Demonstration Barrier) at river mile (RM) 296 of the Illi- nois Waterway near Romeoville, IL. This system was intended to prevent the inter-basin transfer of invasive fish species while simulta- neously preserving continuity of this important shipping route (Moy et al., 2010). The Demonstration Barrier came online in 2002 and produced peak electrical gradients at the surface of the canal of 0.39 V/ cm. Two additional electric barriers came online in 2009 (Barrier IIA) and 2011 (Barrier IIB). The newer barriers are each composed of high voltage narrow electrode arrays and lower voltage wide electrode arrays that were configured so that fish approaching from downstream would be subjected to a gradually increasing electrical field. These barriers produce greater peak electrical gradients (0.79 V/cm–0.91 V/cm over the narrow array) than the Demonstration Barrier, and typically operate in tandem for the purpose of redundancy in case of a mechanical Journal of Great Lakes Research 42 (2016) 837–848 ⁎ Corresponding author. Tel.: +1 815 423 5327. E-mail address: Jeremiah_Davis@fws.gov (J.J. Davis). http://dx.doi.org/10.1016/j.jglr.2016.05.005 0380-1330/Published by Elsevier B.V. on behalf of International Association for Great Lakes Research. Contents lists available at ScienceDirect Journal of Great Lakes Research journal homepage: www.elsevier.com/locate/jglr