Effects of Turbidity and Cover on Prey Selectivity of Adult Smallmouth Bass

—Environmental factors such as turbidity and habitat complexity affect many aspects of aquatic food webs, including predator–prey interactions. We examined the effects of turbidity (0, 5, 10, 20, 40 nephelometric turbidity units [NTU]) and cover (presence or absence) on prey selection by adult smallmouth bass Micropterus dolomieu (mean 6 SD 1⁄4 290 6 41 mm total length) in laboratory pools. Individual predators were given a choice of five northern crayfish Orconectes virilis, five golden shiners Notemigonus crysoleucas (a pelagic fish), or five round goby Neogobius melanostomus (an invasive benthic fish). Smallmouth bass selected round goby at low turbidities (0 and 5 NTU) and golden shiners at the highest turbidity (40 NTU) in trials without cover. With cover, smallmouth bass increased selectivity for golden shiners, particularly at the turbidity extremes (0, 20, and 40 NTU). Northern crayfish were negatively or neutrally selected in all trials across both turbidity and cover treatments. Turbidity had a greater effect than cover on prey consumption rate, which decreased as turbidity increased. Our results suggest that turbidity and cover, two important environmental variables, can influence prey selectivity by smallmouth bass. Predation is an important structuring force for communities in a variety of systems (Connell 1975). This is certainly true for fishes and their prey because population densities (Hixon and Carr 1997) and size structures (Broenmark et al. 1995) of prey can be affected, with results cascading to lower trophic levels (Carpenter and Kitchell 1985). Thus, predator–prey interactions have been studied extensively by aquatic ecologists. Such research has concluded that the outcomes of predator–prey interactions depend on the behaviors of both predators and prey. Fish predators make decisions about where, when, and how to feed (Dill 1983) to optimize foraging success, whereas prey use any number of behaviors to avoid predation (see Endler 1986). Foraging decisions of predators (Dill 1983) and antipredator behaviors of prey (Savino and Stein 1982; Miner and Stein 1996; Shoup et al. 2003) also change with differences in environmental factors, such as water clarity, water temperature, and availability of complex habitat. The effects of environmental variables such as turbidity on interactions between fish predators and their prey have been repeatedly demonstrated. Turbidity levels can be highly variable due to seasonal changes in suspended sediments and algal blooms as well as wind-driven suspension of sediments (Abrahams and Kattenfeld 1997). In streams, sudden changes in water levels can cause extreme changes in turbidity (Larimore 1975), as can strong wind events in lakes with large fetches. As turbidity increases, both *Corresponding author: [email protected] Present address: Federal Energy Regulatory Commission, Washington, D.C., USA. Present address: Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, Oklahoma, USA. Present address: Great Lakes Fishery Commission, Ann Arbor, Michigan, USA. Received August 4, 2008; accepted September 6, 2009 Published online December 31, 2009 353 Transactions of the American Fisheries Society 139:353–361, 2010 Copyright by the American Fisheries Society 2009 DOI: 10.1577/T08-159.1 [Article]