Assessing suitable habitat for freshwater mussel reintroductions using 3D-printed subadult replicates

Reintroduction of native freshwater mussels following aquatic habitat restoration is an increasingly used conservation practice to establish self-sustaining populations. Despite the common use of hatchery-grown subadult mussels (< 40 mm) for reintroduction efforts, their physical habitat requirements as well as guidance on identifying suitable release locations for different mussel species and sizes are severely lacking. We addressed this knowledge gap by deploying three-dimensional (3D)-printed subadult mussels equipped with scannable tags in a river as a proxy for hard-to-track live subadult mussels. We tracked mobilization, displacement and resettlement of 3D-printed and live freshwater mussels at five sites in the Mission Reach of the San Antonio River, Texas, USA, over two years. We found mobilization increased at higher discharges, smaller mussels mobilized at lower flows than adult mussels, site-specific geomorphic features reduced displacement distances, and boulder fields, or habitats with large stable roughness elements, resettled mussels at the highest rate. The study methods and results can directly inform freshwater mussel reintroduction efforts and river restoration project designs that include mussel habitats.