Live fast and die young: accelerated life histories of walleye populations in degraded boreal lakes

Abstract

Despite their widespread distribution in North America, many walleye (Sander vitreus) populations have declined, primarily due to anthropogenic activities (e.g., mining, agriculture, municipal wastewater, aquatic invasive species, and overfishing) that degrade lakes. We compared population structure and dietary composition of walleye in two historically stocked degraded lakes and two naturally recruiting non-degraded lakes in the Abitibi-Témiscamingue region, Québec, Canada. Food resources were assessed for larvae, young-of-the-year (YOY), juveniles, and adults by sampling zooplankton, macroinvertebrates, and prey fish. Growth and relative abundance were quantified via electrofishing for YOY, gillnets for older fish, and otolith age reading. YOY were more abundant and grew faster in degraded lakes, benefiting from high spring zooplankton availability. Simplified food webs in degraded lakes lacked pollution-sensitive macroinvertebrates, making walleye diets more fish-dominated. Although juveniles and adults were equally or more abundant in degraded lakes, premature adult mortality compromised population stability. We recommend improving adult habitat, managing prey species, and reviewing fishing regulations to enhance survival of mature walleye and support sustainable populations.