Erik W. Dilts and Cecil A. Jennings, Georgia Cooperative
Fish and Wildlife Research Unit, D. B. Warnell School of Forest Resources, University of
Georgia, Athens, Georgia 30602; Voice 706-542-4833
FAX 706- 542-8356; E-Mail: ewd3819@owl.forestry.uga.edu
James L. Shelton, Jr., D. B. Warnell School of Forest Resources,
University of Georgia, Athens, Georgia 30602
Keywords: robust redhorse, Catostomidae, sediment, gravel
quality, survival to emergence
Robust redhorse are large, riverine catostomids that deposit fertilized
eggs in loose gravel. Low larval abundance (<13.4 larvae/1000 m3) and an
absence of juveniles in the Oconee River, Georgia suggest that recent recruitment there
has been minimal. Decreased larval survival to emergence (STE) has been implicated as a
recruitment constraint. Two experiments were devised to test this hypothesis. In the
first, fertilized eggs were incubated in gravel mixtures containing reciprocal ratios of
the two most abundant size classes of gravel found in the Oconee. In the second, eggs were
placed in representative mixtures containing four levels of percent fine sediment (0, 25,
50, and 75). Larval STE was not related to variation in gravel quality (P = 0.71).
However, larval STE was inversely related to percent fine sediment (P < 0.0001).
Reductions in STE from treatments containing 25% fine sediment were related to larval
entrapment. Reduced gravel permeability in treatments containing ~50% fine sediment
depressed dissolved oxygen concentrations to levels that were insufficient (i.e., ~5.0
ppm) for the survival of incubating eggs and larvae. Fine sediment concentrations in the
substrates used by spawning robust redhorse in the Oconee range from 25-50% and may limit
recruitment in these fish.
