Effects of Regulated River Flows on Habitat Suitability for the Robust Redhorse

Abstract

The Robust Redhorse Moxostoma robustum is a rare and imperiled fish, with wild populations occurring in three drainages from North Carolina to Georgia. Hydroelectric dams have altered the species' habitat and restricted its range. An augmented minimum-flow regime that will affect Robust Redhorse habitat was recently prescribed for Blewett Falls Dam, a hydroelectric facility on the Pee Dee River, North Carolina. Our objective was to quantify suitable spawning and nonspawning habitat under current and proposed minimum-flow regimes. We implanted radio transmitters into 27 adult Robust Redhorses and relocated the fish from spring 2008 to summer 2009, and we described habitat at 15 spawning capture locations. Nonspawning habitat consisted of deep, slow-moving pools (mean depth = 2.3 m; mean velocity = 0.23 m/s), bedrock and sand substrates, and boulders or coarse woody debris as cover. Spawning habitat was characterized as shallower, faster-moving water (mean depth = 0.84 m; mean velocity = 0.61 m/s) with gravel and cobble as substrates and boulders as cover associated with shoals. Telemetry relocations revealed two behavioral subgroups: a resident subgroup (linear range [mean ± SE] = 7.9 ± 3.7 river kilometers [rkm]) that remained near spawning areas in the Piedmont region throughout the year; and a migratory subgroup (linear range = 64.3 ± 8.4 rkm) that migrated extensively downstream into the Coastal Plain region. Spawning and nonspawning habitat suitability indices were developed based on field microhabitat measurements and were applied to model suitable available habitat (weighted usable area) for current and proposed augmented minimum flows. Suitable habitat (both spawning and nonspawning) increased for each proposed seasonal minimum flow relative to former minimum flows, with substantial increases for spawning sites. Our results contribute to an understanding of how regulated flows affect available habitats for imperiled species. Flow managers can use these findings to regulate discharge more effectively and to create and maintain important habitats during critical periods for priority species.

Received December 12, 2014; accepted April 13, 2015

ACKNOWLEDGMENTS

Funding was provided by the North Carolina Wildlife Resources Commission's State Wildlife Grants Program and by Duke Energy. This research was enhanced by the ongoing efforts of the Robust Redhorse Yadkin–Pee Dee River Technical Working Group. John Crutchfield graciously provided Pee Dee River habitat data and helped to procure funding. Christin Brown, Patrick Cooney, Scott Favrot, Angel Hammers, Tracy McCulloch, Mills Reagon, Andrew Rominger, Ben Wallace, and Dan Weaver assisted with field work. Bud Freeman, Chris Goudreau, and Kevin Whalen provided constructive manuscript reviews. The North Carolina Cooperative Fish and Wildlife Research Unit is jointly supported by North Carolina State University, North Carolina Wildlife Resources Commission, USGS, U.S. Fish and Wildlife Service, and Wildlife Management Institute. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.