Development of a Spatially Balanced Fish Sampling Protocol for Mid-Sized Rivers of Missouri

Despite providing habitat for over 200 fish species in Missouri, mid-sized rivers have been understudied relative to the state’s wadeable streams and great rivers. We developed a standardized fish sampling protocol to estimate site-level richness within mid-sized rivers. The protocol uses six active and passive sampling gears and a unique spatially balanced design to target the diversity of habitats within these systems. To accommodate the breadth of river sizes considered mid-sized (e.g., watershed area 1000 – 39,000 km²), absolute sampling effort was scaled to river width, yet relative effort among gears remained approximately equal across rivers creating a standardized protocol accomplishable within 3-6 days. We completed eight surveys in six mid-sized rivers collecting over 35,000 individuals and 109 species. Site-level richness varied from 62 to 30 species with highest richness observed in the Ozarks (53.8 ± 6.2, n = 4) and in fall (50.8 ± 14.5, n = 4). However, on average, only 33% of detected species at a site were captured with a single gear indicating redundancy among gears. Our protocol provides a scientifically defensible approach for sampling mid-sized rivers that can complement existing stream-monitoring programs to provide a more comprehensive evaluation of biodiversity within the state.