Evaluating effects of drought and anthropogenic influences on the growth of stream fishes on the Edwards Plateau, Central Texas

Drought and flow regime alteration have the potential to affect fish growth through numerous ecological and physiological mechanisms, and in so doing, can greatly influence demographic processes, such as recruitment and mortality. Changing climate patterns and increasing water demands from a rapidly growing human population has made understanding these effects critical to the conservation and management of stream fishes on the Edwards Plateau in central Texas. My objective was to evaluate the influence of annual flow regime on the growth rates of a suite of stream fishes within a paired river system in central Texas. The North Llano River (NLR) and South Llano River (SLR) are adjacent low-order, spring-fed streams of similar size that differ greatly in their flow regimes due to differences in spring inflows and anthropogenic water withdrawals. I extracted otoliths from eleven stream fish species common to both the NLR and the SLR and used them to back-calculate lengths at age. I used mixed-effect models to evaluate the influence of annual flow metrics on growth. Response to annual flow metrics, particularly during drought conditions, was species-specific, and varied between the two river systems. In general, the North Llano River was influenced by the extent and duration of flow events, and the South Llano River was influenced by monthly flows and can be seen in species such as Redbreast Sunfish and Guadalupe Bass. My results will provide a better understanding of how drought, coupled with anthropogenic alterations, affects the growth rate of stream fishes. Results from this study can provide guidance for the management and conservation of stream fishes relative to water use and instream flows.