Covariates of age-0 Walleye

Covariates of age-0 Walleye Sander vitreus fall recruitment from stocked populations in six midwestern reservoirs

Jason C. Doll, Thomas E. Lauer, and Sandra Clark-Kolaks

https://doi.org/10.1016/j.fishres.2015.07.034

Abstract

Walleye Sander vitreus are native to central North American freshwater habitats. Introductions within and outside their native range have occurred in all of the lower 48 states. These stockings have occurred due to the increasing popularity of this species, leading to the demand surpassing the supply. Despite the popularity of this species for anglers, and extensive research on the distribution, life history, population dynamics, culture, and stocking strategies, there is disparate information on first year survival of stocked populations. The objective of this study was to test for associations between biotic and abiotic variables for recruitment of age-0 fish in the fall. We tested for the influence of the number of stocking events, moronid stocking density, spring/summer warming rate, and spring/summer maximum discharge on electrofishing catch rates in the fall of age-0 walleye. We used a hierarchical generalized linear model with the Poisson distribution to evaluate these relationships. Parameters of the model were estimated using Bayesian inference. Our model suggested the number of stocking events, moronid stocking density, and maximum discharge/rainfall were the most important factors influencing walleye recruitment. Fall catch rates of age-0 walleye were positively related to stocking events, negatively related to moronid stocking density, and negatively related to maximum discharge/rainfall. However, these relationships were not concordant across all reservoirs. Further, variability we observed across reservoirs support the conclusion that walleye populations must be managed at individual reservoirs. This study will assist managers locally and regionally to determine stocking strategies for walleye to improve recruitment in midwestern reservoirs.

Figure 6. Posterior predicted walleye catch-per-unit-effort (CPUE) at age-0 in the fall based on average walleye stocking events, average maximum spring/summer discharge/rain, and variable moronid stocking density at each reservoir. Moronid stocking density is standardized to a mean 0 and unit standard deviation. Thus, 0 indicates average moronid stocking density for the specific reservoir. Black circles and vertical bars represent medians and 95% credible intervals of the posterior distributions. The width of a violin area represents the probability density of the predicted walleye age-0 CPUE, wider areas indicate a higher probability for that value.