Inventory of Freshwater Mussels at Ozark National Scenic Riverways, 2023–2024

The Ozark National Scenic Riverways (OZAR) is a national park unit located in the Ozarks region of Missouri and encompasses much of the mainstem Jacks Fork and Current River. Past surveys of freshwater mussel populations indicated potential declines for many species in OZAR. We conducted occupancy-based surveys at 60 randomly selected sites during 2023–2024 to update species inventories and establish a repeatable baseline. We also examined fish and mussel records to determine if the absence of host fish should be further investigated as a potential cause of mussel decline. Visual searches detected 13 mussel species, with catch-per-unit-effort (CPUE) and species richness lower than previous surveys, suggesting continued decline. Mean species-level occupancy across the mussel community (i.e., all species detected) was low (<25%), and detection probability for observing a freshwater mussel during a 45-minute person-survey averaged 29%. Mussel occurrence decreased in spring-influenced reaches and riffle habitats but increased in off-channel and glide/race habitats. A host fish linkage index indicated that most mussel species have viable hosts present, though species dependent on few or lentic-associated hosts may face reproductive limitations. These results provide managers with actionable data for conservation planning and outline potential future survey methods, including targeted habitat sampling to sustain mussel diversity in OZAR.