We studied the relationship between stream discharge and reproductive success for five members of a prairie stream fish assemblage. Based on information obtained from the literature, we constructed seven models relating stream discharge to successful reproduction. To assess the utility of our models, we collected larval and juvenile Arkansas River shiners Notropis girardi, peppered chub Macrhybopsis tetranema, plains minnow Hybognathus placitus, flathead chub Platygobio gracilis, and red shiners Cyprinella lutrensis from the Canadian River, Texas, during 2000-2001. We removed otoliths and counted daily growth increments to determine ages. Models were parameterized by use of age and discharge data. Models were evaluated with the Akaike information criterion likelihood statistic to assess which model(s) best described reproductive success for each species. Of the seven models evaluated, the best overall model predicted that reproductive success was uniform across dates when discharge was present in the river; however, reproduction was predicted to be unsuccessful during periods when the river was confined to isolated pools. These results suggest that the presence of discharge in the river may be more important for successful reproduction of prairie stream cyprinids than the magnitude of discharge.

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We estimated age‐specific fecundity and survival rates for peppered chub Macrhybopsis tetranema from the Canadian River, New Mexico and Texas. We used these estimates to construct a life history matrix model that assumed age‐0 survival was related to river discharge. Model predictions agreed well with the observed abundance of peppered chub for the 6‐year period from 1996 to 2001. Based on the Akaike information criterion, this model received greater support from observed catches of peppered chub than did two alternative null models (one null model assumed a static or fixed population and the other assumed a population with a constant growth rate over the 6‐year study period). Elasticity analysis showed that the peppered chub population growth rate was most sensitive to changes in age‐0 survival (elasticity = 0.48) and age‐1 fecundity (elasticity = 0.44). We performed sensitivity simulations to determine the effect of parameter uncertainty on the observed elasticities. Based on 1,000 simulations, we found that the peppered chub population growth rate was most sensitive to age‐0 survival and age‐1 fecundity and was robust with respect to uncertainty in our estimates of these parameters. Our model accurately predicts changes in peppered chub abundance based on river discharge and provides a mechanistic explanation for previous anecdotal observations indicating that the reproductive success of peppered chub is related to river discharge.

SynopsisStream fishes often exhibit a bet-hedging multiple spawning reproductive strategy. In many species, the reproductive season lasts several months. This exposes young fishes to varying environmental conditions that may differentially affect growth. We studied the effect of hatch date on first-summer growth among members of a prairie-stream fish assemblage. The reproductive season in both years of the study was protracted, lasting from April through August. Due to intermittent stream-discharge, there were two distinct periods during which most species successfully reproduced. In general, growth rate was greater among individuals with an early hatch date than among those with a later hatch date. Multiple regression models indicated that hatch date was related to growth in all study species with one exception (red shiner, Cyprinella lutrensis). The results of this study provide evidence that young-of-the-year of multiple spawning stream-fish species that are spawned late in the season may grow at a slower rate than young spawned earlier in the season.

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