Patterns in spatial use and movement of Silver Carp among tributaries and main-stem rivers: insight from otolith microchemistry analysis

Invasive Silver Carp ( Hypophthalmichthys molitrix ) have established populations throughout the Missouri River basin. The main-stem Missouri River has undergone a multitude of alterations, creating a channel with greater mean depths and velocities, limiting optimal habitat for Silver Carp. Tributaries to the Missouri River may provide refuge from the swift flows within the main-stem Missouri River and, therefore, may play a vital role in the life-cycle of Silver Carp throughout the basin. Understanding the spatial extent under which these invasive fish function in this large, open river system is crucial to inform management efforts. Here, we used otolith microchemistry of Silver Carp from the Kansas River, a major tributary to the Missouri River, to reconstruct environmental histories as a means to assess the proportions of resident (individuals who never left the Kansas River system) and transient (individuals who at some point occupied the Missouri River) individuals. Silver Carp within the Kansas River were predominantly residents (adults = 54%; juveniles = 65%) with the majority of reproduction coming from within the Kansas River itself. These results suggest removal efforts in the Kansas River may be effective means of managing this invasive fish species. Transient fish exhibited short durations of signatures indicative of the Missouri River (mean percent of data points for adults = 10% and juveniles = 36%), suggesting movements into the Missouri River were brief. These results highlight the importance of connectivity of tributary habitat among large rivers and provides important information for invasive species management.