Age and Growth of Gray Redhorse in the South Llano River, Texas

Monday, September 9, 2013
Governor's Hall I (trade show) (Statehouse Convention Center)
Preston Bean , Texas Cooperative Fish and Wildlife Research Unit, Texas Tech University, Lubbock, TX
Timothy B. Grabowski , U.S. Geological Survey, Texas Cooperative Fish and Wildlife Research Unit, Lubbock, TX
Gray Redhorse Moxostoma congestum is native to upland streams from the Brazos River in Texas to the Río Soto La Marina in Tamaulipas, Mexico.  Populations of gray redhorse are stable across much of its range, but habitat degradation associated with dewatering of streams has led to the decline of some populations in the western portion of its range.  We evaluated age structure and growth of a gray redhorse population in the South Llano River, Texas and evaluated the relationship between residuals from a von Bertalanffy growth model and annual streamflow parameters.  Length-frequency histograms revealed a trimodal distribution with the modes representing the first two modes corresponding to age-1 and age-2 fish, respectively, and the third mode corresponding to age-3 and age-4 fish as determined by aging of scales.  These results will aid in predicting responses of native fishes to modifications of streamflow as demand on water resources continues to grow in the region.