FALL ASSESSMENT WORK
As September rolls around and water temperatures begin dropping below 70°F, we begin our annual fall electrofishing season. The focus of the fall assessments is to get an idea of how strong of a year class was produced in the spring. Small, 3 to 6 inch, young-of-year (YOY) walleyes are captured in the shallows, measured, and scale samples are taken for aging and growth analysis. The fish are then released. Unlike spring sampling, each lake is only sampled on one night per year. The goal is not to establish a population estimate, but rather to develop an index (catch of YOY/hour of shocking time) of year class strength. By conducting annual monitoring, fishery managers can better predict what the future fishery of a lake may look like as young fish grow into older, larger fish more desirable to anglers.
We also sample slightly larger, age-1 walleyes at the same time in the fall and compare their catch rates from year to year. Our ultimate goal is to determine which index (YOY or age-1) is most useful in predicting how strong of a spawning stock will be available 4-5 years in the future when those fish have reached sexual maturity. After ten plus years of cooperative data collection with the Fond du Lac Band on nearly 2 dozen lakes, it appears that walleyes are often subject to substantial mortality during their first winter and that monitoring those that have survived to age-1 may be the best method of predicting strong spawning populations down the road.
While we generally work on lakes that rely upon natural reproduction to sustain the walleye population, we occasionally conduct assessments on lakes where periodic stocking is used to augment walleye numbers. In those cases, our fall assessments are useful in documenting stocking success, or alternatively, failure. Should the surveys show a continued lack of recruitment, local fisheries managers may choose to reevaluate their lake management strategy.