SOUTHEASTERN NATURALIST 2007 6(3):471–478 Effects of Flow Fluctuations on the Spawning Habitat of a Riverine Fish Timothy B. Grabowski 1,2 and J. Jeffrey Isely 3,* Abstract - Shallow-water, lithophilic spawning fishes are among the most vulner- able to anthropogenic fluctuations in water levels. We monitored water levels and environmental conditions at the nest sites of Moxostoma robustum (Robust Red- horse) on a main-channel gravel bar in the Savannah River, GA–SC. During the course of the 2005 spawning season, over 50% of the observed nest sites were either completely dewatered or left in near zero-flow conditions for several days. This occurred on two separate occasions, once early during the spawning season and then again near its conclusion. We hypothesize the habitat preferences of spawning Robust Redhorse leave them vulnerable to water-level fluctuations, and this phenom- enon may be widespread in regulated river systems. Introduction Changes in the flow regime of rivers associated with the construction and operation of hydropower facilities affects the availability and quality of fish habitat, ultimately leading to changes in fish assemblage structure (Bunn and Arthington 2002, Freeman et al. 2005, Pringle et al. 2000). Lithophillic spawning fish deposit eggs on or within the substrate in shallow water (Balon 1975). This is a common reproductive strategy utilized by riverine fishes including Cyprinidae (minnows), Catostomidae (suckers), and Salmonidae (salmonids) and, to a lesser extent, by Acipenseridae (stur- geons) and Polyodontidae (paddlefish). These fishes are arguably among the most vulnerable to fluctuations in water levels. For example, the dewatering of salmonid redds in some Pacific northwest drainages due to hydropeaking has been identified as a potentially significant source of mortality in devel- oping eggs (McMichael et al. 2005, Reiser and White 1983, Stober and Tyler 1982). While the phenomenon of nest-site dewatering has not been docu- mented for other taxa, rapid and significant water-level fluctuations occur frequently in regulated rivers throughout the United States (Baxter 1977, Bowen et al. 1998). Moxostoma robustum Cope (Robust Redhorse) is one example of a species potentially vulnerable to the effects of nest-site dewatering. This 1 Department of Biological Sciences, Clemson University, Clemson, SC 29634-0326. 2 Current address - Institute of Biology, University of Iceland, Askja, Sturlugata 7, Is- 101 Reykjavik, Iceland. 3 US Geological Survey, South Carolina Cooperative Fish and Wildlife Research Unit, Clemson University, Clemson, SC 29634-0372. * Corre- sponding author - jisely@clemson.edu.