Effects of American Water Willow Establishment on Density, Growth, Diet, and Condition of Age-0 Largemouth Bass in Kansas Reservoirs

—Many Kansas reservoirs are currently experiencing decreased sport fish production as a result of the typical aging processes that occur in impounded systems. American water willow Justicia americana was planted in three Kansas reservoirs (.1,800 ha) for littoral zone habitat enhancement to mitigate sport fish losses and increase the recruitment of age-0 largemouth bass Micropterus salmoides. We investigated whether the density, growth, condition, and diet of age-0 largemouth bass in coves with water willow differed from coves without water willow in these reservoirs. Samples of largemouth bass were collected from 2001 to 2004 in June, July, and August. We found a consistent pattern among reservoirs and sample years; coves with water willow had significantly greater densities of age-0 largemouth bass than control coves, but no significant differences were found in growth, condition, or diet. Water willow beds appeared to buffer wave action, trapping fine sediments and floating debris, which significantly increased the overall habitat complexity. The additional organic material may have augmented littoral productivity, supporting the higher densities without physiologically hindering the age-0 largemouth bass. Overall, our study suggests that water willow establishment is an effective means of enhancing littoral nursery habitat for age-0 largemouth bass. Macrophytes can benefit largemouth bass Micropterus salmoides populations by providing cover, increasing foraging efficiency, and augmenting prey abundance, especially for age-0 largemouth bass (Dibble et al. 1996; Wrenn et al. 1996). Several studies have reported a positive association between largemouth bass abundance and abundance of aquatic macrophytes (Dibble et al. 1996; Parkos and Wahl 2002). Durocher et al. (1984) reported that as submerged vegetation approached 20% of the total lake coverage there was an increase in largemouth bass standing stock. The structural complexity provided by macrophytes is thought to increase largemouth bass densities. For example, macrophytes provide colonizing surfaces for epiphytic bacteria and algae (Dodds 2002), the principal food source of many invertebrates (Baker and Orr 1986) that are consumed by young bass. Macrophyte decomposition also builds organic substrate used by benthic organisms (Beckett et al. 1992). Moreover, shelter from predation and harsh environmental conditions coupled with an increase in food resources can lead to an increase in abundance of zooplankton (Quade 1969; Timms and Moss 1984; Moss et al. 1996), macroinvertebrates (Tolonen et al. 2003), and fish (Dibble et al. 1996; Smart et al. 1996) as well as more diverse fish assemblages (Killgore et al. 1989; Keiper et al. 1998; Pierce et al. 2001). Presumably, high densities of prey in littoral zones with macrophytes would benefit largemouth bass populations, assuming vegetation densities are not sufficiently high to inhibit their foraging success (Wiley et al. 1984). Many reservoirs remain unvegetated because of insufficient native plant propagules and unsuitable conditions for seedling establishment (Smart et al. 1996; Strakosh et al. 2005). These reservoirs are ideal * Corresponding author: [email protected] 1 Present address: Department of Biology, State University of New York–Fredonia, Fredonia, New York 14063, USA. 2 The unit is jointly sponsored by the U.S. Geological Survey; Kansas Department of Wildlife and Parks; Division of Biology, Kansas State University; and the Wildlife Management Institute. 3 The unit is jointly sponsored by the U.S. Geological Survey, Biological Resources Division; Montana Fish, Wildlife and Parks; and Montana State University. Received September 18, 2008; accepted November 3, 2008 Published online February 23, 2009 269 Transactions of the American Fisheries Society 138:269–279, 2009 Copyright by the American Fisheries Society 2009 DOI: 10.1577/T08-186.1 [Article]