Evaluating the Effects of Asian Carp On Native Fishes

Understanding fish community interactions is a critical component of large river ecology, especially the interactions of nonindigenous fishes on native fauna.  Non-native large bodied planktivores are capable of posing deleterious effects to large river ecosystems. In particular, the effects of silver carp on native planktivorous large river fishes have received little attention despite the apparent relevance. As such, the objective of this study was to determine population level interactions of silver carp with bigmouth buffalo and gizzard shad (i.e., native planktivores). Specifically, we used data collected for the Long Term Resource Monitoring program (LTRM) and Missouri Department of Conservation standard sampling in the free-flowing stretch of the Mississippi River and its associated floodplain from 1992-2012.  We also employed controlled experiments to determine the potential mechansim structuring the relationship between non-native and native planktivores.  Our results suggest that non-native planktivore relative abundance has increased while relative abundance of native planktivorous fishes has declined. Specifically, the gizzard shad and bigmouth buffalo have shown precipitous declines in abundance while silver carp have dramatically increased. As a quantitative measure of a limiting resource, we found that silver carp condition has remained fairly consistent while bigmouth buffalo and gizzard shad condition has declined.  Correspondingly, the results of our controlled mechanistic experiments suggest that silver carp may be able to exclude native fishes via exploitative competition. Based on the results of this study, silver carp are likely negatively influencing native planktivorous fishes (e.g., creating a limiting resource through competition), and because of this management efforts should be directed at reducing silver carp abundance to subsequently rehabilitate native planktivores.