Effects of streamflow and intermittency on the reproductive success of two broadcast-spawning cyprinid fishes

We studied daily growth-increment formation in the otoliths of early life history stages of Sharpnose Shiner, Notropis oxyrhynchus, and Smalleye Shiner, Notropis buccula, in the Brazos River, Texas to investigate the influence of streamflow and intermlttency on the production of young. Both species successfully produced offspring throughout a four- to five-month period. Successful reproduction occurred over a longer period in 2004 than in 2003. The results of our study revealed that recruitment by N. oxyrhynchus and N. buccula populations in the Brazos River, Texas are related to streamflow in two principal ways. First, the greatest proportion of young-of-year produced during the reproductive season is associated with elevated streamflow events. Second, no young-of-year are successfully produced during periods of intermittency when the river is not flowing. Our results suggest that the focus of conservation efforts, which to date have primarily concentrated on creating proper streamflow conditions for spawning, should also be focused toward ensuring proper conditions for survival of ova and young larvae.