ROUND GOBY (Neogobius melanostomus) DISTRIBUTION IN THE ILLINOIS WATERWAY SYSTEM OF METROPOLITAN CHICAGO. Mark T. Steingraeber, Ann L. Runstrom, and Pamella A. Thiel U.S. Fish and Wildlife Service, Fishery Resources Office, 555 Lester Avenue, Onalaska, WI 54650 There is concern that the range of the round goby (Neogobius melanostomus), a nonindigenous fish recently introduced to the Great Lakes drainage basin from Eurasia, may expand to other drainage basins with adverse ecologic consequences. The Illinois Waterway System (IWS) connects the Great Lakes and Mississippi River basins and facilitated the spread of another exotic nuisance species, the zebra mussel (Dreissena polymorpha), to several environmentally sensitive drainages of interior North America earlier this decade. We surveyed the distribution of round goby in a portion of the IWS near metropolitan Chicago in autumn 1996 with traps, seines, trawls, set lines, and by angling. A total of 61 round goby were captured in the Little Calumet River in south Chicago at locations upstream of river mile 321.4 (12 miles inland from Lake Michigan). No round goby were captured at sites in connecting channels downstream (i.e., further inland) of this point as far away as Joliet (river mile 283). Bottom trawling, particularly over rocky substrates, was the most successful means of capturing round goby and accounted for 87% of the total catch. Goby captured by trawling were significantly smaller than those captured by other gears and significantly smaller goby were captured at the sampling site furthest upstream. The length frequency distribution of the round goby we captured suggested the presence of fish from the three most recent year classes (1994-1996). The rocky substrate preferred by round goby may be less common in a short reach of the Little Calumet River downstream of river mile 321. Despite this potential habitat deficiency, population growth and human interventions are soon likely to expand the range of the round goby in the IWS. Keywords: aquatic nuisance species, round goby, Neogobius melanostomus, Illinois Waterway System, Mississippi River Mark Steingraeber U.S. Fish and Wildlife Service 555 Lester Avenue Onalaska, WI 54650 Telephone: (608) 783-8436 Facsimile: (608) 783-8450 E-mail: Mark_Steingraeber@mail.fws.gov Poster presentation preferred (willing to convert) Presenting author is not a student