Effects of Common Carp on Trophic Dynamics of Sport Fishes in Shallow South Dakota Water Bodies

The Common Carp Cyprinus carpio is one of the most common freshwater fish invaders worldwide, creating adverse effects on water quality and impacting ecosystem structure and function. To assess how Common Carp impact food web dynamics, we compared the trophic dynamics of Bluegills Lepomis macrochirus and Largemouth Bass Micropterus salmoides in three lakes containing Common Carp populations with the trophic dynamics in three lakes without Common Carp. All six lakes were located in eastern South Dakota. Stable isotope analysis was used to estimate trophic positions and indicate energy sources utilized by adult and age‐0 fish. Additionally, diets of age‐0 Bluegills were analyzed to assess whether Common Carp were inhibiting ontogenetic diet shifts, and bomb calorimetry was used to evaluate differences in energy density of age‐0 fish prior to winter. Age‐0 fish and adult Bluegills derived significantly more energy from pelagic sources in the systems populated with Common Carp. Adult Bluegills in Common Carp systems remained at a relatively constant trophic position across their entire size range, whereas in non–Common Carp systems, the trophic positions of adult Bluegills tended to increase with size. Even though age‐0 fish relied more heavily on pelagic‐derived energy in the systems with Common Carp, significant differences were not observed in the autumn energy densities of age‐0 fish or in the age‐0 Bluegills’ diet. Given our results, Common Carp are unlikely to impact overwinter survival of age‐0 fish in these shallow systems. The present study illustrates the value of using stable isotopes for food web investigations and demonstrates that Common Carp do alter trophic dynamics of other fishes in the systems they invade, but responses differ depending upon the species and life stage. Received February 11, 2016; accepted November 28, 2016 Published online February 21, 2017