A Review Of Artificial Spawning Habitat For Walleye In Wisconsin North Temperate Lakes
Michael A. Bozek, Wisconsin Cooperative Fishery Research Unit, College of Natural Resources, University of Wisconsin-Stevens Point, Stevens Point, WI 54481; (715) 346-4023; mbozek@uwsp.edu
David Neuswanger, Wisconsin Department of Natural Resources, 10220 N. State Hwy 27, Hayward, WI 54843
Terry Margenau, Wisconsin Department of Natural Resources, 810 W. Maple Street, Spooner, WI 54801
Heath Benike, Wisconsin Department of Natural Resources, Brule, WI 54820
Creating or enhancing walleye spawning reefs has been a widespread lake management tool at least since the 1930's in North America and is currently gaining popularity. However, despite widespread application of this technique, specific design criteria and critical evaluation of project success are lacking. We evaluated the success of 20 artificial walleye spawning reef projects from lakes in northern Wisconsin constructed from 1968 through 2003 and evaluated a natural reef. Reef projects were evaluated relative to the ability to discern measurable improvements in walleye numbers post-construction versus pre-construction. Project lakes averaged 304 hectares in surface area and the average rock structure covered 0.008 hectare of sandy lakebed - 0.03% of lake surface area. Most structures were comprised of 5- to 25-cm rock, usually placed on the ice over shallow areas where walleyes were likely to spawn once the rocks fell into place in the spring. Overall, none of the projects conclusively demonstrated improvements in walleye reproduction attributable to construction of spawning reefs to date. Some projects were confounded by management factors unrelated to the rock projects, such as concurrent fingerling stockings and walleye length limit changes. However, despite the lack of a single standardized evaluation protocol employed among projects, only one project showed any measurable increase in young-of-year walleye. But in that case, the increase occurred concurrent with installation of winter aeration and thus causality is unknown. This review clearly suggests that more effort needs to be placed in understanding factors limiting walleye reproduction both at the whole-lake and site scales. Elucidating what creates optimal conditions for natural reproduction and understanding what limits walleye recruitment in lakes would provide the best opportunity for developing future projects that attempt to overcome limitations to walleye recruitment in lakes.