Cooperative Research Units
Education, Research And Technical Assistance For Managing Our Natural Resources
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Statewide evaluation of calcified structures used to estimate ages of largemouth bass and northern pike


July 2012 - June 2017


This project is a continuation of the Wisconsin DNR Fish Age Task Group’s efforts to develop statewide protocols for estimating the age of species of management interest and is similar to the efforts we have completed for bluegills and walleyes. Our objective is to provide guidance to biologists regarding selection and preparation of calcified structures. At this point we have processed and aged scales from more than 200 largemouth bass collected from 7 lakes statewide. We are currently processing northern pike collected during spring 2015. Our initial results suggest that dorsal spines are more effective for replicating otolith ages than scales, if a correction factor is employed.

Research Products and Activities


  • Isermann, D.A., R. Koenigs, and C. Isermann. February 2014. Replicating otolith ages for walleyes in Wisconsin using dorsal spines: development of correction factors. Wisconsin Chapter of the American Fisheries Society. Green Bay, Wisconsin.
  • Isermann, D. A., R. Koenigs, and C. Isermann. 2014. Adjusting Dorsal Spine Ages to Reduce Bias in Estimates of Growth and Mortality for Wisconsin Walleyes. 2014 Annual Meeting of the American Fisheries Society, Quebec City, Quebec, Canada.

Current Staff

Federal Staff: 95

Masters Students: 239

Phd Students: 142

Post Docs: 53

University Staff: 240

5 Year Summary

Students graduated: 701

Scientific Publications: 1936

Presentations: 4260



Funding Agencies

  • Wisconsin Department of Natural Resources


Cooperative Research Units Program Headquarters Cooperators

  1. U.S. Geological Survey