The effects of flow and stream characteristics on the variation in freshwater mussel growth in a Southeast US river basin

Summary The evaluation of the age and growth of animal populations is essential for understanding and predicting how populations will respond to changes in environmental conditions and anthropogenic stressors. We used a novel, von Bertalanffy hierarchical modelling approach to quantify relationships between the growth of three freshwater mussel species and various site‐ and watershed‐level factors including seasonal discharge, land cover and stream size in the lower Flint River Basin, Georgia, U.S.A. Our modelling approach quantified the mussel‐to‐mussel variation in the von Bertalanffy parameters and accounted for biases associated with multiple measurements made on each mussel specimen, which are generally not accounted for as sources of bias in age and growth studies. Modelling results suggested that maximum shell size parameter and the Brody growth coefficient varied across species, on average, 19 and 33%, respectively, among individual mussels within sample sites. The variation was related to short‐term high streamflows during the spring season, stream size, channel geomorphology and land cover in the watershed. This study provides insight to the factors affecting the growth of stream‐dwelling freshwater mussels. Although hierarchical von Bertalanffy growth models are rarely used for freshwater mussel age and growth studies, this approach can provide important information regarding the ecology of freshwater mussels.