Effects of Gizzard Shad Introductions on Aquatic Communities in South Dakota Glacial Lakes

Due to recent climate warming gizzard shad Dorosoma cepedianum (GZD) are experiencing a natural range expansion northward; the impacts of which are not fully understood. South Dakota represents the northwestern edge of the native range of GZD and overwinter survival of GZD has recently been documented in several systems.  To determine potential effects of GZD on aquatic communities we used a before-after-control-impact study design and introduced GZD into two lakes and monitored them, and one control lake during 2007-2011. Gizzard shad successfully reproduced in both lakes, both years and were documented in walleye diets when available. Walleye Sander vitreus growth increased significantly in East Krause but not in Middle Lynn. However, relative abundance of walleye in Middle Lynn increased during years with GZD present.  In the control lake, walleye growth and condition declined when yellow perch Perca flavescens reproduction was limited. Further, walleye consumed a higher percentage of invertebrates in the control lake than in either treatment lake suggesting that prey fish resources were likely limited in this system. Yellow perch dynamics were not impacted by GZD at the levels present during this study; diets of perch were variable, but similar to previous research and no GZD were documented in perch diets. Our results suggest zooplankton was not limiting and that a range expansion of GZD would initially have positive impacts on walleye and little impact on yellow perch populations in South Dakota glacial lakes.