Using passive telemetry and environmental variables to predict Silver Carp (Hypophthalmichthys molitrix) movement cues on the northwestern edge of their invasion front

Silver carp Hypophthalmichthys molitrix, are a highly mobile aquatic invasive species in the United States. The James River, South Dakota, USA, is a tributary of the Missouri River and is considered the northwestern leading edge of their invasion front. Understanding silver carp movement patterns on the cusp of this invasion is key to combatting the northwestward expansion of the species. We used passive telemetry to observe large-scale movement patterns of silver carp in the James River, South Dakota. Fifty silver carp were implanted with acoustic transmitter tags in June 2021, and movement data was recorded over a 1.5-year period. Most individuals exhibited site fidelity and stayed within the James River throughout the duration of the study. We used environmental data (i.e., temperature, dissolved oxygen, daily mean discharge, the change in discharge over 24 h and 48 h) and movement data collected from passive telemetry receivers to understand and predict silver carp movement cues in the James River. Daily mean discharge ("flow") was the most important predictor of silver carp movement in the James River. As flow increased, the probability of movement increased from 59% (95% CrI: 34% to 81%) at 1.5 m3/s to 94% (95% CrI: 80 to 99%) at 100 m3/s. In this study, silver carp exhibited a high propensity for movement within the James River, especially during periods of high flow. To prevent further northwestward expansion of these fish, silver carp movements must continue to be monitored and removal and prevention of further range expansion must be prioritized.