The Relationship between Age-0 Walleye Density and Adult Year-Class Strength across Northern Wisconsin

Abstract

Walleyes Sander vitreus are an important cultural and economic resource in northern Wisconsin, both as a recreational fishery and a tribal subsistence fishery. Understanding the recruitment of age-0 walleyes to the adult population could be of great utility in effectively managing harvest and informing stocking efforts in this mixed-use fishery. Our objective was to determine the relationship between abundance of age-0 walleyes in the fall and the subsequent adult year-class 4 years later and to explain additional residual variation related to environmental variables. Since 1986, fall electrofishing surveys have been conducted to estimate the densities of age-0 walleyes and spring mark–recapture surveys to estimate spawning adult walleyes. We fit a gamma stock–recruitment curve to a data set of 104 paired surveys (age-0 survey with adult survey conducted 4 years later) on 58 lakes and attempted to explain residual variation related to additional environmental variables. Our analysis suggests that the maximum number of age-4 fish (3.36/ha) is not produced by the maximum number of age-0 fish but by a somewhat intermediate density (243/ha) and that this relationship varies with the complexity of the shoreline. This density-dependent relationship should help managers refine models forecasting walleye abundance, as well as optimize stocking rates.

Received December 28, 2011; accepted April 27, 2012

ACKNOWLEDGMENTS

We thank all past and present fisheries biologists and technicians of the Wisconsin Department of Natural Resources and the Great Lakes Indian Fish and Wildlife Commission who painstakingly collected the data analyzed here. We thank Steve Hewett and two anonymous reviewers for providing many useful comments, Dan Hayes for help with some of the coding, and Jon Deroba for discussions regarding model-fitting. We also thank the staff of the Great Lakes Indian Fish and Wildlife Commission staff for their continued collaboration in managing the joint tribal–recreational walleye fisheries in northern Wisconsin. Partial funding for this project was provided by the Federal Aid in Sport Fish Restoration program.