Prey selectivity of common predators on Silver carp (Hypophthalmichthys molitrix): controlled laboratory experiments support field observations

Silver Carp Hypophthalmicthys molitrix (Valenciennes, 1844) are an invasive species in the Mississippi River Basin and their current role in this novel ecosystem is not fully understood. Juvenile Silver Carp can and do occur in great numbers after a successful spawn. These massive schools of small Silver Carp seem to be an obvious prey source for the common predators of the Mississippi River system. The level to which native piscivores are consuming this novel prey item is unclear. Therefore, the goal of this research was to assess the diets of native piscivores collected in Pool 26 and the Open River reach of the Mississippi River. Using diet contents and catch rates of small fishes, selection or avoidance could be determined for predator prey interactions. Then a controlled laboratory experiment was conducted to determine if common predators [White Bass Morone chrysops and Largemouth Bass Micropterus salmoides (Lacepede, 1802)] would select for or against this novel prey in the presence of two native prey fish [Gizzard Shad Dorosoma cepedianum (Lesueur, 1818) and Emerald Shiner Notropis atherinoides]. Understanding how predator-prey interactions occur in a controlled laboratory experiment may provide insight to trends observed in the field. The majority of native piscivores appeared to be avoiding Silver Carp in both reaches and selecting native prey fishes. The order in which prey fish were consumed by both predators showed significant avoidance of Silver Carp. It appears that the trends observed in the field were supported by our controlled laboratory experiment. The effectiveness of different native piscivores to consume Silver Carp may have impacts on future management decisions.