Seasonal and Diel Movements and Habitat Use of Robust Redhorses in the Lower Savannah River, Georgia and South Carolina

Abstract

AbstractThe robust redhorse Moxostoma robustum is a large riverine catostomid whose distribution is restricted to three Atlantic Slope drainages. Once presumed extinct, this species was rediscovered in 1991. Despite being the focus of conservation and recovery efforts, the robust redhorse's movements and habitat use are virtually unknown. We surgically implanted pulse‐coded radio transmitters into 17 wild adults (460–690 mm total length) below the downstream‐most dam on the Savannah River and into 2 fish above this dam. Individuals were located every 2 weeks from June 2002 to September 2003 and monthly thereafter to May 2005. Additionally, we located 5–10 individuals every 2 h over a 48‐h period during each season. Study fish moved at least 24.7 ± 8.4 river kilometers (rkm; mean ± SE) per season. This movement was generally downstream except during spring. Some individuals moved downstream by as much as 195 rkm from their release sites. Seasonal migrations were correlated to seasonal changes in water temperature. Robust redhorses initiated spring upstream migrations when water temperature reached approximately 12°C. Our diel tracking suggests that robust redhorses occupy small reaches of river (∼1.0 rkm) and are mainly active diurnally. Robust redhorses were consistently found in association with woody debris and gravel streambed sediments along the outer edge of river bends. Fish exhibited a high degree of fidelity to both overwintering and spawning areas. Our observations of long‐distance seasonal migrations suggest that successful robust redhorse conservation efforts may require an ecosystem management approach.