Habitat‐Related Bioenergetics in a Free‐Flowing River: Implications for Potential Competition Between Native and Invasive Fishes

Large free‐flowing rivers are rare but important ecosystems. Environmental conditions in these systems vary through space and time, resulting in dynamic patterns of habitat quality for aquatic species. Such variability could influence invasive species success by altering habitat quality, thereby supporting native species adapted to these conditions. Our study examined spatial and temporal trends in energetic habitat quality between native gizzard shad ( Dorosoma cepedianum ) and invasive silver carp ( Hypophthalmichthys molitrix ) in the free‐flowing Wabash River, USA. Environmental conditions (water temperature, velocity, prey type and density) were sampled throughout the river and used as input data to a spatially explicit bioenergetics model to predict fish growth rate potential as an index of habitat quality. Seasonal energetic habitat quality varied considerably for both species. Spring habitat quality was poor for both species throughout the river, and only small portions of the river were suitable during summer, mainly in off‐channel habitats. More of the river was suitable for gizzard shad, especially during autumn. During all seasons, spatial overlap in high‐quality habitat was high between species, especially in the highly suitable off‐channel and main‐channel border habitats. Promoting habitats in unregulated rivers that provide combinations of flow, food availability, and temperature unique to native species may be important for supporting native species and deterring invasive species. Dam removals that allow access to diverse off‐channel habitats may promote biodiversity and protect against invasions in riverscapes.