One of the defining characteristics of the Anthropocene is the transfer of species to ecosystems outside of their native range. These non-native species can become invasive and cause ecological and/or economic harm to the ecosystems they invade. Unfortunately, strong evidence of negative influences from invasive species on native biota and ecosystems is rare because Long-term data needed to rigorously test for these effects are rarely available. The invasion of silver carp in the Upper Mississippi River System (UMRS) provides a unique opportunity to assess the influence of this invasive species on native fishes because twenty years of standardized data (including six years preceding the invasion) on fish abundance, water quality, and river stage are available from three reaches that have been invaded by silver carp and three reaches where they are not yet established. The objective of this study was to test for the impacts of silver carp on native sport fishes in this system using these long-term data. We chose to use sport fishes as our indicator because: 1) management with regard to sport fishes is relatively consistent (to increase or maintain sport fishes) across this system, 2) sampling gear developed to assess fish communities often was developed with sport fishes as a focus, 3) monitoring the status and trends of several species of sport fish was a goal for the monitoring data we analyzed, and 4) negative effects of silver carp on native sport fishes would have both an ecological and economic impact.
Results/Conclusions
. Our results provide strong empirical evidence of a negative influence of silver carp on sport fishes in the UMRS. Trends for adult sport fishes were generally increasing in control reaches, whereas reaches with silver carp generally had declining sport fish abundance. The mechanism for this decline appears to be constraint on the recruitment of sport fishes as a result of competition for zooplankton between silver carp and the early life stages of sport fishes.