Identifying Recruitment Bottlenecks for Age-0 Walleye Sander Vitreus in Northern Wisconsin Lakes

Walleye recruitment has declined in several northern Wisconsin lakes for unknown reasons. Our goal was to identify the timing and potential causes of recruitment bottlenecks for age-0 walleyes in northern Wisconsin lakes.  In 2014 and 2015, we sampled two walleye lakes with declining natural recruitment (D-NR) and two with sustained natural recruitment (S-NR).  Adult walleye were captured in spring using nighttime electrofishing and egg mats were used to verify spawning.  Towed ichthyoplankton nets, light traps, beach seines, micro-mesh gillnets, and electrofishing were used to capture age-0 walleye. Water quality data, zooplankton samples, and panfish diet information were also collected.  Walleye spawning was documented on all lakes, but relatively few eggs were encountered on D-NR lakes.  Age-0 walleyes were not captured in D-NR lakes after the early larval stage, while age-0 walleyes were captured at multiple life stages during both years on S-NR lakes.  Over 800 panfish diets were examined with only five containing larval fish.  Temperature and dissolved oxygen were similar for all lakes.  We identified a recruitment bottleneck for age-0 walleye occurring at or before the larval stage in D-NR lakes.  A sampling protocol has been developed and the project will be expanded to include additional lakes.