Quantifying freshwater mussel composition and abundance in two prairie rivers

Freshwater mussels are vital components of healthy aquatic systems, providing water filtration, nutrient cycling, structure for macroinvertebrates, and food for wildlife. Across North America, freshwater mussel populations have experienced severe declines, prompting renewed efforts to evaluate the effectiveness of different survey techniques. Additionally, quantifying environmental relationships for freshwater mussels is crucial for conservation, yet studies addressing freshwater mussel habitat associations in the Great Plains are lacking. During this study, we conducted three distinct surveys (i.e., dead shell, qualitative [snorkeling], and quantitative [quadrat] at each of 10 reaches on the Verdigris River and 16 reaches on the Caney River during the summers of 2023 and 2024 to compare freshwater mussel richness and abundance across different survey methods. Shell surveys on the Verdigris and Caney rivers consistently captured fewer species at the site level compared to snorkel and quadrat surveys. Although snorkeling is faster and comparable to more intensive quadrat surveys regarding species richness, these approaches yielded different results with respect to community composition. For both rivers, excavating ~10 quadrats would achieve the same estimates of richness and relative abundance as the site-level snorkel surveys. Quantitative sampling was also used to determine mussel density and species richness among different mesohabitat types (upper recirculation zone, lower recirculation zone, pool, riffle, run, outerbend, pointbar, shoal). On the Verdigris River, upper recirculation zones, pools, and riffles contained the greatest densities and richness of freshwater mussels; on the Caney River, run mesohabitats harbored the highest mussel densities and richness. We also used a single-season single-species occupancy modeling framework to identify factors influencing detection and occupancy for all mussels, juvenile mussels, and Monkeyface Theliderma metanevra. The most-supported models indicated that detection of all mussels and juvenile mussels was negatively associated with mean flow (m/s) while Monkeyface detection was negatively associated with proportion of gravel. Occupancy of all mussels and juvenile mussels was positively associated with proportion of gravel and cobble, while occupancy of Monkeyface was positively associated with proportion of gravel. Comparing survey methods and understanding habitat associations will help inform conservation efforts and future mussel monitoring.