POPULATIONS ASSESSMENT OF LARGEMOUTH BASS IN THE UPPER MISSISSIPPI RIVER SYSTEM BY THE LONG TERM RESOURCE MONITORING PROGRAM Kevin S. Irons 1, Todd M. Koel 2, T. Matt O'Hara 1, and Michael McClelland 1. 1 Illinois Natural History Survey, Long Term Resource Monitoring Program, Havana Field Station, 704 North Schrader Avenue, Havana, IL 62644; and 2 Minnesota Department of Natural Resources, Mississippi Monitoring Station, 1801 South Oak Street, Lake City, MN 55041. The Long Term Resource Monitoring Program (LTRMP) for the Upper Mississippi River System (UMRS) includes six field stations located in five states. Since the inception of the program in 1989, > 25,000 largemouth bass have been collected and measured from backwaters, side channels, and other aquatic habitats using multiple gear types. Information on the biology and life history of largemouth bass in this system has been documented by several researchers. However, this is one of the first studies regarding this species which has been conducted on a systemic scale. Largemouth bass catches have varied from 1,123 during the flood year of 1993 to a high of 7,028 during 1995, with an average of 62% of age-zero fishes (<100 mm) collected from shorelines of contiguous backwaters. Recruitment and growth in the UMRS was closely associated with the hydrological regime, especially in southern reaches where water levels were highly variable. Length-frequency distributions indicated that cohort size was greater during years with high waters. Largemouth bass also exhibited a flood-pulse advantage, and had improved growth when waters approximate the natural flow regime of the river. Reaches with the most diverse channel and off-channel habitats have the most prolific bass populations in this system. Keywords: Illinois River, Mississippi River, largemouth bass, populations, Long Term Resource Monitoring Program _________________________________________________________________________________ 1