## 4 Discussion  
The purpose of hatchery-based augmentation of a fish population is to ensure the possibility of recruitment each year that it is practiced. Walleye exhibits highly variable recruitment among years and waterbodies [11; 12]. Recruitment of walleye is affected by a large number of biotic and abiotic factors [13]. Previous analyses have identified biotic predictors of walleye recruitment in lakes, including adult stock size [11; 14; 15] as well as predation and competition by other species [16; 17; 18]. Abiotic factors affecting walleye recruitment have been identified, including lake size [19], spring water temperatures [11; 20; 21], a surrogate for regional climate variability [15], and water levels [14; 21]. [PERSON] et al. [22] were able to model recruitment success based on lake surface area, water temperature degree-days, shoreline development factor, and conductivity. Of the variables analyzed by [PERSON] et al. [23], degree-days during the first year of life and first winter severity were the most important for predicting recruitment of lake walleye, with relatively weak year-classes predicted to occur with cold first growing seasons and severe first winters. However, we know of no such explanatory or predictive models for recruitment of walleye for highly variable, large riverine ecosystems, where in addition to thermal variation, there is also variation in flow and water level, all affecting the suitability of habitat available to young-of-year walleye. Hence, variable recruitment of walleye is an uncontrollable factor affecting the year-to-year results and programmatic efficacy of this supplementation approach. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Citation**} & \multicolumn{2}{c}{**Trophy**} \\ \hline \multirow{2}{*}{**Year**} & \multicolumn{2}{c}{**New R/**} & \multirow{2}{*}{**Elsewhere**} & **New R./** & \multirow{2}{*}{**Elsewhere**} \\  & **Claytor Res.** & & & **Claytor Res.** & \\ \hline  
\hline Totals & 418 & 1036 & 53 & 31 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Catches of citation (2.27 kg or 63.5 cm TL) and trophy (4 kg) walleye in waters of Virginia. Although walleye supplementation has been widely practiced, its effectiveness is not well studied, especially in river systems. In this report, we present evidence that hatchery-based augmentation contributed to recruitment of the upper New River walleye stock. We note that two walleye stocks historically occurred in the upper New River [8], the native stock spawning at Fosters Falls and at the foot of Buck Dam, and a mixture of native and introduced genotypes at Allisonia just above Claytor Reservoir. Stocking of walleye sourced from outside the New River ceased in 1997. Lacking augmentation for over 25 years, the spawning assemblage at Allisonia has decreased ([PERSON], personal observation), supporting our inference that augmentation is required to support walleye in the anthropogenically disturbed upper New River. While many freshwater fisheries have been supplemented with hatchery-produced juveniles, few non-salmonid supplementation programs have been evaluated as thoroughly as this one, over 18 years of supplementation, with a pause to assess the impact of its cessation, and then resumption of stocking. Justifications for maintaining native fish populations within riverine ecosystems include maintenance of historical biodiversity and local adaptation [24]. Adaptation to different cation/anion or metal concentrations was inferred for two Georgian Bay, Ontario, walleye populations [25]. Individual choice of spawning habitat (rocky lake shoals or riverine rapids) was shown to be heritable for walleye in Iowa [26]. Walleye show considerable spawning philopatry in the Great Lake region [24; 27]. Native-origin walleye stocked in five Minnesota lakes increased in frequency relative to non-native walleye over time [28], suggesting local adaptation. Upper New River walleye exhibit large ultimate size (over 7 kg), supporting a trophy fishery.