AUTHORS: Greg G. Sass, Wisconsin Department of Natural Resources; Colin Dassow, Wisconsin Department of Natural Resources; Holly Embke, United States Geological Survey; Zachary Feiner, Wisconsin Department of Natural Resources and University of Wisconsin-Madison; Joseph Mrnak, Wisconsin Department of Natural Resources; Stephanie Shaw, Wisconsin Department of Natural Resources
ABSTRACT: Many walleye populations in the Midwestern United States have declined due to inconsistent or failed natural recruitment, with stocking often failing to rehabilitate natural recruitment or sustain quality fisheries for tribal subsistence and angler harvest opportunity. Numerous factors have been implicated in walleye natural recruitment declines including climate change and phenological variability, habitat loss, production overharvest, invasive species, fish community compositional change, and fisher behavior. Walleye populations have also been shown to be prone to depensation. Still, some walleye populations have remained resilient to these disturbances offering hope for continued natural recruitment and population persistence. We discuss several alternative management strategies to maintain walleye population resilience by focusing on the probability of depensation in a walleye population (rather than assuming compensation) and assessment of yield:production ratios. Critical depensation is a positive adult biomass or abundance threshold below which a population collapses. Because the probability of depensation for Wisconsin walleye populations is unrelated to population productivity, resilience to depensation is critically dependent on maintaining sufficient adult densities to avoid crossing this ecological tipping point. Resilience can also be maintained by estimating walleye population adaptive capacity to harvest and ensuring that yield does not exceed annual production. Both strategies suggest an immediate need to reduce exploitation rates and create cultivating conditions for walleye to ensure the greatest probability of not crossing a depensatory threshold. Further, walleye “bright spots” (i.e., populations showing evidence for the greatest resiliency now and in the future) should be managed most conservatively as they are likely to draw the most fisher effort to remaining harvest opportunities. Recognizing walleye fisheries as social-ecological systems, ecosystem-based fisheries management approaches, and challenging traditional fisheries management paradigms will be paramount to ensure the sustainability of walleye populations.
