Cooperative Fish and Wildlife Research Units Program: Wisconsin Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Wisconsin Fishery Project

Evaluation of biological performance indicators for monitoring exploitation of walleye populations in northern Wisconsin

January 2013 - June 2015


Participating Agencies

  • Wisconsin Department of Natural Resources

We determined if variation in biological performance indicators (BPIs; ω, mean total length (TL) at age 3, mean age at 50 cm TL, age classes present, age class diversity [H], catch-per-effort [CPE] of age-0 walleyes, coefficient of variation in age-0 CPE, targeting angler catch rate, and the mean TL of the 10 smallest mature females) observed for walleye populations in northern Wisconsin could be explained by exploitation rates while also considering adult density, lake surface area, recruitment category (naturally-reproducing or stocked), latitude, and longitude as additional explanatory variables. We also determined if BPIs could be used to identify walleye populations that have experienced relatively high exploitation rates (i.e., rates ≥ upper quartile values) in each recruitment category. Exploitation was of little importance in explaining observed variation in BPIs and BPIs were not effective in identifying walleye populations with relatively high mean exploitation rates. Biological performance indicators may be effective for assessing changes in exploitation within individual populations, but appear ineffective at a broad spatial scale because relatively high or low BPI values observed for some populations may be the result of factors other than exploitation. Additionally, exploitation rates for walleye populations in northern Wisconsin were generally low (median values ≤ 0.12) and may not be sufficient to elicit measurable changes in BPIs. Lastly, population and fishery data are collected at a temporal scale (sampling interval usually ≥ 3 years) that may not be sufficient to describe relationships between BPIs and exploitation. Our initial results suggest that BPIs do not provide a useful alternative or compliment to the existing system for monitoring walleye exploitation in northern Wisconsin. While we have completed the initial phase of this project, ongoing analyses will attempt to determine the behavior of BPIs in relation to exploitation using data for walleye populations where more frequent estimation of exploitation rates has occurred.