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 intermittency 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.

Fig. 1

Study area and location of sampling sites on the upper Brazos River, Texas.

Fig. 2

Mean daily streamflow for Brazos River study sites between April 2003 and March 2005.

Fig. 3

Mean daily streamflow for Brazos River study sites in 2003 and 2004 (solid line) and the proportion of all young-of-year N. oxyrhynchus collected that were spawned on each date during the reproductive season (circles). Spawning dates were determined by back-calculating the number of daily growth increments on otoliths. Shaded areas indicate periods during which the river did not flow.

Fig. 4

Mean daily streamflow for Brazos River study sites in 2003 and 2004 (solid line) and the proportion of all young-of-year N. buccula collected that were spawned on each date during the reproductive season (circles). Spawning dates were determined by back-calculating the number of daily growth increments on otoliths. Shaded areas indicate periods during which the river did not flow.

Fig. 5

Mean proportion (±SE) of late vitellogenic oocytes in the ovaries of N. oxyrhynchus from the Brazos River at each site and sampling date plotted with mean daily discharge for Brazos River study sites in 2003 and 2004.

Fig. 6

Mean proportion (±SE) of late vitellogenic oocytes in the ovaries of N. buccula from the Brazos River at each site and sampling date plotted with mean daily discharge for Brazos River study sites in 2003 and 2004.

Contributor Notes

Associate Editor: J. W. Snodgrass.

¹ Department of Biological Sciences, Texas Tech University, Mail Stop 3131, Lubbock, Texas 79409-3131; E-mail: (BWD) bart.durham@lcu.edu; and (GRW) gene.wilde@ttu.edu. Send reprint requests to BWD.

Received: 07 Aug 2007

Accepted: 17 Jun 2008