An Evaluation of Walleye (Sander vitreus) Spawning Potential in a North Temperate Wisconsin Lake

Abstract

Poor spawning habitat can limit walleye (Sander vitreus) reproduction in north temperate lakes and therefore the need to understand and quantify high quality spawning habitat is essential in managing walleye populations. To address this issue, artificial spawning reefs have been constructed in an attempt to augment recruitment, but with limited success. The objectives of this study were to: 1) quantify physical characteristics of high quality walleye spawning reefs in lakes with high natural recruitment, 2) develop a model that predicts spawning habitat potential in lakes, and 3) use the models to evaluate spawning habitat in a lake with low recruitment and predict the potential success of constructing an artificial spawning reef there. Red Cedar and Big Crooked Lakes, both north-temperate Wisconsin lakes with high natural recruitment of walleye, were used to evaluate habitat characteristics of high quality spawning sites and develop resource selection functions of walleye spawning habitat. The modeling results obtained from both lakes were applied to a third lake, Beaver Dam Lake, Wisconsin, which has low/intermittent recruitment of walleye and a pre-existing artificial spawning reef. Spotlighting and SCUBA surveys were conducted in study lakes immediately after ice-out to determine the extent of egg deposition by walleye in lake littoral zones. Egg collection chambers were also buried in “suitable” substrates just prior to the spawning period to determine egg survival at different locations within Red Cedar and Beaver Dam Lakes. Survey quadrats were placed along transects within egg deposition zones to characterize habitat on spawning reefs and 100 transects were placed randomly in sample lakes to quantify available habitat. Habitat variables measured at each quadrat included depth, distance from shore, substrate, embeddedness and organic material. The best logistic regression models (i.e., best individual model and alternate models) created from Red Cedar and Big Crooked Lakes were chosen based on AIC values and correct classification rates. Final models were evaluated using actual used and available habitat data from each study lake; each model had high accuracy rates when used to classify sites. Models were then used to evaluate relative spawning potential of walleye in the littoral zone habitats of Beaver Dam Lake. Walleye spawned primarily within 2 m from shore in water less than 0.35 m deep, on larger substrates (gravel and cobble) that had low embeddedness values (mean = 1.5). As a result, the best resource selection function from Red Cedar Lake (overall correct classification = 90.5%) predicted that the relative probability of egg deposition increased on sites closer to shore, at shallower depths, with increasing percentages of gravel and cobble and higher embeddedness values. The best resource selection function from Big Crooked Lake (overall correct classification = 97.4%) predicted that the relative probability of egg deposition increased on sites closer to shore, with increasing percentages of gravel and cobble, and on sites with lower embeddedness values. An additional simplified model consisting of gravel and cobble was also created and applied to shallow, near-shore habitat in Beaver Dam Lake. When models were applied to Beaver Dam Lake, the majority of the littoral zone of the lake as well as the artificial spawning reef had a low relative probability of egg deposition (< 0.5) (i.e., habitat that was not suitable). Based on the accuracy of models when tested on data collected from study lakes, models were highly transferable across systems. Therefore, these models can be used to predict the characteristics of high quality spawning sites as well as the use of an artificial spawning reef by walleye, aiding in both the protection of natural spawning sites as well as determining the need for potential habitat restoration.