Relations between Walleye (Sander vitreus) Recruitment and Spawning Habitat in Northeastern Wisconsin Lakes
Rammer, Gina M.
University of Wisconsin-Stevens Point, College of Natural Resources
MetadataShow full item record
The addition of spawning habitat to increase walleye (Sander vitreus) recruitment has been used as a management tool in many north temperate lakes for decades. However, a previous assessment of 20 artificial spawning habitat projects in northern Wisconsin showed that few projects were successful in increasing abundance of age-0 walleyes. Poor reef design or the existence of recruitment-limiting factors unrelated to spawning habitat such as stock size, species composition, prey availability, and spring weather patterns are likely more important factors in these systems. The objectives of my study were to: 1) develop an accurate and efficient standardized method to measure walleye spawning habitat in lakes without conducting a time consuming assessment of all nearshore habitat and 2) determine if a relation between walleye recruitment, defined by fall age-0 walleye abundance, and spawning habitat exists in naturally recruiting north temperate lakes. Twenty study lakes with varying amounts of walleye spawning habitat and recruitment patterns in northeastern Wisconsin were chosen to be measured for spawning habitat and walleye recruitment. To develop a standardized sampling method, walleye spawning habitat was measured using three experimental methods: 1) littoral zone habitat was measured along 250 random transects, 2) visible gravel/cobble segments were measured from a boat at the shoreline-water interface, and 3) the length of actual spawning habitat, defined by criteria developed from previous resource selection functions as ≥ 50% gravel and/or cobble substrate with low embeddedness, was measured along shoreline areas. When compared to the criterion-based, direct habitat measurement, a random transects method yielded the most accurate index of walleye spawning habitat. The boat measure of spawning habitat, however, was only weakly correlated with the direct measure, suggesting that this method should only be used, at best, as a crude index of total spawning habitat. Average age-0 walleye abundance was weakly related to total spawning habitat (m2), although no relation was found when data were corrected for lake size. Average adult walleye abundance was found to be related to total spawning habitat (m2), as was average adult abundance/ha and spawning habitat (m2)/ha. Substrate variable analysis showed that age-0 walleye abundance was weakly negatively correlated with fine organic matter and adult walleye abundance was related to the percent gravel substrate present, as was adult walleye abundance/ha. Lake size was weakly related to adult abundance and total spawning habitat (m2) but was not related to age-0 abundance. This study increases our understanding of how critical habitat may limit walleye populations and could be used in the development of spawning habitat protection strategies. It does not appear that the addition of spawning habitat to a poorly recruiting system will likely increase age-0 walleye. The weak correlations between age- 0 walleye abundance and available spawning habitat and limited study lakes (N=20) also suggest future research be done, utilizing the same methods, to increase the sample size. Future spawning habitat studies should also include an evaluation of other important recruitment-limiting factors, like fish community structure and water quality.