Evaluations of growth and habitat use by Guadalupe bass at a riverscape scale in the South LLANO River, Texas

Abstract

Guadalupe bass Micropterus treculii is a black bass species endemic to central Texas. Its dependence on undisturbed pool and run habitats with sufficient flow and cover renders it sensitive to habitat alteration. The decline of the species due to habitat alteration/loss and introgressive hybridization with introduced smallmouth bass Micropterus dolomieu has prompted efforts to restore Guadalupe bass habitats. However, detailed data on how the species may respond to these efforts are lacking. I assessed age-specific Guadalupe bass habitat associations and habitat specific growth rates at three different scales (fine, intermediate, and coarse) in the South Llano River. Substrates were classified using side-scan sonar. Scales and otoliths were extracted from Guadalupe bass to determine age and growth. Over 65% of captured Guadalupe bass were age-2 or age-3, but individuals ranged from 0-7 years of age. Overlap in habitat associations was exhibited between age classes 1-3+. Age-0 Guadalupe bass tended to associate with greater proportions of pool and run mesohabitats with submerged aquatic substrates. Finally, low discharge rates appeared to have the greatest influence on Guadalupe bass growth rates with growth exhibiting a negative correlation with the proportion of discharge observations falling in the Q90 range in a given year. My results suggest age-specific Guadalupe bass habitat associations that may increase the effectiveness of restoration efforts directed at the species. Further application of these results may allow the use of the Guadalupe bass population trajectories and habitat occupation rates as an indicator of stream health in Edwards Plateau streams or as a predictor of changes in stream condition.