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

Abstract

The 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 6 8.4 river kilometers (rkm; mean 6 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 128C. 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.

Post‐release movements and habitat use of robust redhorse transplanted to the Ocmulgee River, Georgia

“…Occasionally, individuals left the main channel during high water events. This movement and habitat-use pattern is similar to the habitat preferences previously described for this species (Jennings and Shepard, 2003;Grabowski and Isely, 2006; R. Heise, North Carolina Wildlife Resources Commission, personal communication). In the Ocmulgee River, robust redhorse seem to be able to find suitable non-spawning habitat in both piedmont and coastal plain habitats that meet species-specific minimum standards of cover, depth, current velocity, and water quality.…”

“…Although the upstream-downstream differences seen in habitat use by radio-tagged robust redhorse probably are an artefact of differences of habitat quality and availability, the observed seasonal differences in movement and habitat use were consistent with those described for wild radio-tagged robust redhorse in other systems (Grabowski and Isely, 2006;R. Heise, North Carolina Wildlife Resources Commission, personal communication).…”

“…Radio-tagged fish transplanted to the Ocmulgee River adopted behavioural patterns that were consistent with those reported for wild fish (Grabowski and Isely, 2006) within 90-120 days of their release. Before they were fully acclimatized to the Ocmulgee River, the radio-tagged fish exhibited an exploratory pattern of movement and behaviour, mostly in the downstream direction.…”

“…Below Juliette Dam particularly downstream of Macon, Georgia, the Ocmulgee River becomes a coastal plain river and has a relatively low gradient, a meandering channel, predominantly sand and mud substrate, and frequent sand bars and deep pools that are typical of coastal plain rivers. A similar pattern was observed in the Savannah River where fish exhibited different habitat selection depending upon their position relative to a dam that served as a division between the piedmont and coastal plain regions of the river (Grabowski and Isely, 2006). Regardless of their position relative to Juliette Dam, radio-tagged robust redhorse were consistently found in the main channel associated with current, deep water, and physical structure, particularly woody debris.…”

“…However, there has been little assessment of the post-release dispersal, movements, and habitat use of robust redhorse at this time, and there has not yet been long-term monitoring of these populations. Wild adults are potadromous and make long-distance upstream migrations (>100 km) to spawning habitat in spring (Grabowski and Isely, 2006). Adult robust redhorse also demonstrate a high degree of fidelity and specificity to both spawning sites and home ranges Isely, 2006, 2007).…”