Preliminary Findings for a Relationship between Instream Flow and Shoal Chub Recruitment in the Lower Brazos River, Texas

Abstract

Seasonal flow pulses in rivers facilitate spawning, dispersal, and early life stage survival of many fish species. To evaluate the effectiveness of current flow standards to sustain threatened fish populations, we investigated the relationship between hydrology and recruitment of the Shoal Chub Macrhybopsis hyostoma, a broadcast-spawning minnow in the Brazos River, Texas. From March 2013 to March 2014, we collected metalarval and juvenile Shoal Chub bimonthly at night using arrays of stationary drift nets. Otoliths were examined to estimate age, and the relationship between hatch date and discharge was analyzed. Shoal Chub recruited under both base-flow and pulse-flow conditions, including intervals of increasing, decreasing, and stable discharge. However, hatch dates of surviving fish indicated greater levels of recruitment during flow pulses, particularly on the rising limb. Greatest recruitment occurred during flow pulses of a magnitude defined as two per season according to the method of hydrological analysis adopted by the state’s environmental flow program. Our findings imply that the state’s current environmental flow standards for the lower Brazos River may be insufficient to sustain Shoal Chub populations and additional research on this issue is warranted.

Received October 11, 2015; accepted March 30, 2016 Published online July 28, 2016

Acknowledgments

We thank C. Montana, C. Krabbenhoft, D. Lay, A. Vigneaux, M. Lisbon, S. Angel, C. Rivera, D. Saenz, L. Bower, D. Fitzgerald, A. Medellin, K. Mahavadi, N. Smolensky, and D. Kim for assistance with field collections and laboratory work. We thank Dr. K. Conway for assistance in larval cyprinid identification L. Kleinsasser for study design and contract assistance, and K. Aziz for map production. Partial funding for this project was through the Texas State Wildlife Grants program grant T-60-1 in cooperation with the U.S. Fish and Wildlife Service, Wildlife and Sport Fish Restoration Program. Additional financial support was provided by the Texas Water Resources Institute through a Mills Scholarship.