Fish Diversity and Abundance in Relation to Interannual and Lake-Specific Variation in Abiotic Characteristics of Floodplain Lakes of the Lower Kaskaskia River, Illinois

—The importance of floodplain lakes to tropical river systems is well established, but little is known about the function of these habitats in temperate river systems. We examined fish diversity, abundance, and reproduction within six oxbow lakes of the Kaskaskia River, Illinois, over 5 years and their relationship to 11 abiotic environmental variables. The lakes were hydrologically dynamic within and among years, varying in the time connected with the main stem (0–22 weeks/year) and the frequency of low (,0.3m) water (0–23 weeks/year). Differences were found both among years and lakes. All measured limnological variables (dissolved oxygen, Secchi disk depth, conductivity, and temperature) varied temporally, but only conductivity and Secchi disk depth varied among lakes. Fish species differed among lakes and between adjacent lotic habitats, and species-specific abundance varied among years, seasons, and lakes. This variation was related to several environmental variables. Diversity was positively related to the distance between the oxbow lake and the river but not to any variables that had interannual variation. Seine catch per unit effort (CPUE) was negatively related to mean water level and Secchi disk depth. Total electrofishing CPUE was not related to any variables; however, that of bluegills Lepomis macrochirus was positively related to maximum depth and that of warmouths L. gulosus was positively related to vegetated area. Across all lakes, evidence of reproduction was found for five species and was negatively related to the mean water level and frequency of low water and positively related to flood periodicity. The oxbow lakes have the potential to contribute to the fish community of the main river by providing spawning and nursery habitat for several fish species as well as helping maintain several less abundant main-stem species. However, when considering management options to maintain or restore these ecosystem functions, interannual variation in environmental variables, particularly those related to flood periodicity, should be considered. Main river channels, backwater habitats, and oxbow lakes are believed to be highly integrated and interdependent within river ecosystems (Welcomme 1979; Bayley 1995; Sparks 1995; Winemiller et al. 2000; Herwig et al. 2004, 2007). Periodically rivers have variable flood pulses that produce a dynamic edge or ‘‘moving littoral’’ zone (Junk et al. 1989) in the floodplain where the aquatic and terrestrial habitats meet. This moving littoral zone increases nutrient cycling (Junk et al. 1989), enhances growth rates of some species (Wahl and Nielsen 1985; Gutreuter et al. 1999), and provides corridors for fish migration between the main river channel and oxbow lakes (Amoros and Bornette 2002), which in turn, can increase biodiversity. As a result of this periodic connection between oxbow lakes and main river channels, oxbows are thought to provide fish in the main river with important spawning and nursery habitat (Welcomme 1979; Sheaffer and Nickum 1986; Sabo and Kelso 1991; Turner et al. 1994) or overwinter habitat (Dettmers et al. 2001a). However, the importance of oxbow habitats and the resulting fish composition probably varies with the attributes of the individual lakes and rivers. Tropical floodplain systems have been well studied (see review by Welcomme 1979), but little is known about floodplain systems in the north temperate zone (Winemiller et al. 2000). Relative to tropical systems, temperate river systems experience larger seasonal temperature fluctuations, less distinct rainy and dry seasons (leading to less predictable flooding cycles), and more seasonally variable light regimes (Junk 1999; Tockner et al. 2000; Wahl et al. 2008). Temperate rivers also have experienced stronger disturbances in their paleoclimatic history leading to lower species diversity than have tropical river systems (Junk 1999). The interaction between temperature and flooding cycles may also lead to differences in ecosystem processes in temperate systems (Tockner et al. 2000). A few studies have investigated the environmental factors related to larval and juvenile fish abundance in * Corresponding author: [email protected] 1 Present address: Department of Natural Resource Ecology and Management, Oklahoma State University, 008c Ag Hall, Stillwater, Oklahoma 74078, USA. Received December 13, 2007; accepted April 27, 2009 Published online August 13, 2009 1076 Transactions of the American Fisheries Society 138:1076–1092, 2009 Copyright by the American Fisheries Society 2009 DOI: 10.1577/T07-272.1 [Article]