Cooperative Fish and Wildlife Research Units Program: Texas
Education, Research and Technical Assistance for Managing Our Natural Resources

Flow regime is among the most important environmental factors influencing population dynamics for stream fishes; however, developing direct relationships between flow regime and growth, recruitment, or mortality rates has proven challenging. However without a thorough understanding of these relationships, it is difficult to develop recommendations for instream flows to benefit species of conservation concern, such as Guadalupe Bass Micropterus treculii. Guadalupe Bass is considered to be vulnerable due to its dependence upon intact stream habitats, yet the flow requirements for the species, or even how flow influences its growth, recruitment, or mortality, is not well understood. Therefore, the objectives of this study are to 1) evaluate the influence of flow regime on the growth and recruitment of Guadalupe Bass across its entire range, and to monitor the impact of changing flow regime on the growth and mortality of young-of-year through their first summer. Samples will be collected from locations within the Brazos, Guadalupe, San Antonio, and Nueces River Basins and euthanized. We will remove their sagittal otoliths and determine the age and growth history of each individual. These data will be used to reconstruct the year classes and to estimate recruitment and mean growth rates related to flow conditions.