Biological Performance Indicators for Evaluating Exploitation of Minnesota's Large-Lake Walleye Fisheries

We examined the potential for using biological performance indicators (BPIs) to detect the overexploitation of populations of walleye Sander vitreus (formerly Stizostedion vitreum) in Minnesota's large lakes. We developed equations to predict growth (i.e., the von Bertalanffy growth parameter and total length at age 3) and female age at 50% maturity from growing season length and female total length at 50% maturity from growth. Indices of spawning stock age diversity and the variation of population abundance were characterized by means of summary statistics. Thresholds for BPIs were determined by adding a measure of variability to the predicted and mean values. We evaluated the sensitivity of each BPI by comparing observed values with the thresholds for an overexploited population in Upper Red Lake. All six BPIs for Upper Red Lake exceeded the thresholds, demonstrating their potential use for monitoring walleye exploitation. However, the magnitude by which each threshold was exceeded differed by BPI, indicating that some may be more sensitive than others. Managers should integrate the performance of a suite of BPIs with time series analysis to identify the onset of overexploitation of large-lake walleye fisheries.