Systemic features of fisheries of the Upper Mississippi River System Gutreuter, S. 1992. Systemic features of fisheries of the Upper Mississippi River System, 1990 fisheries component annual report. U.S. Fish and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin, October 1992. EMTC 92-T001. 42 pp. (NTIS #PB93126431) ABSTRACT During 1990, the fisheries component of the Long Term Resource Monitoring Program (LTRMP) conducted standardized sampling in Pools 4, 8, 13, and 26 of the Upper Mississippi River and La Grange Pool of the Illinois River. Fixed sampling sites from up to nine habitat classes were surveyed by seining, small "minnow" fyke netting, electrofishing, fyke netting, and hoop netting during two fish community sampling time periods (June 25 to August 3 and August 1 to September 17) and three special efforts to sample black crappie Pomoxis nigromaculatus, channel catfish Ictalurus punctatus, and sauger Stizostedeon canadense. A backwater and impounded habitat species complex characterized by bullhead minnow Pimephales vigilax, centrarchids, yellow perch Perca flavescens, and northern pike Esox lucius was distinguishable from a riverine channel border species complex characterized by redhorses Moxostoma spp., river shiner Notropis blennius, catfish, white bass Morone chrysops, and freshwater drum Aplodinotus grunniens. This pattern is complicated by a longitudinal gradient of decreasing abundance of mesothermal species such as silver redhorse Moxostoma anisurum, shorthead redhorse Moxostoma macrolepidotum, northern pike, pumpkinseed Lepomis gibbosus, yellow perch, and walleye Stizostedeon vitreum. The consistency of significant effects suggests that the LTRMP sampling design can detect real patterns in fish community structure. KEYWORDS rivers, fish, ecology, community structure, length distribution, habitat, monitoring, distribution, relative abundance, Mississippi River