Habitat Use and Selection of Silver Carp in the Lower Wabash River System

The spatial ecology of non-native species in invaded systems remains relatively poorly understood despite the importance of suitable habitat in the success of invasion. Silver Carp Hypophthalmichthys molitrix are a highly invasive non-native species with established populations throughout the Midwestern United States. Much research has focused on habitat use of bigheaded carp in large river systems, though invasion risk remains high in smaller systems, such as tributaries of the Great Lakes and the Ohio River. The Wabash River, a unique system in the Midwest, remains largely un-impounded and is comparable to many of the smaller riverine systems at risk of invasion. The objectives of this study are to understand fine-scale habitat use and selection of Silver Carp in the Wabash system and determine if environmental variables can be used to predict Silver Carp habitat use. To understand habitat use, active tracking utilizing acoustic telemetry occurred monthly from 2021-2023 throughout the lower 260 km of the Wabash. Fish position was located via triangulation using a combination of omni-directional and directional hydrophones. Habitats within the study reach were sampled to determine availability and compared to detection locations to understand selection. Analysis of telemetry detections suggested that Silver Carp selected specific habitat types, generally preferring areas of greater depth and lower flow velocity while avoiding the main channel. However, selection varied throughout the study reach, with different patterns in upstream versus downstream areas. Both temperature and discharge were useful predictors of habitat use, with logjams serving as important refuge habitat in high flow conditions and throughout the winter months. Results of this study provide useful targets for large-scale removal events of Silver Carp via commercial fishing. Habitat selection patterns observed in this study provide useful insights into what areas may be important for Silver Carp to become established in a non-channelized system.