Evaluation of Otolith Microchemistry for Identifying Walleye Stocked as Fry or Fingerlings

Author

• Joshua Fluur, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2026

Degree Name

Master of Science

Department

Zoology

First Advisor

Whitledge, Greg

Abstract

Walleye (Sander vitreus) is a popular sport fish whose populations are often supported by maintenance or supplemental stocking, with most fish stocked as fry, fingerlings, or advanced fingerlings. Evaluation of stocking efficacy is important to inform decisions regarding fish stocking rates and sizes and allocating hatchery fish to locations where maintenance or supplemental stocking is most needed. Several types of artificial tags or marks have been proven useful in the identification of stocked fish, but they often have various drawbacks. Natural chemical markers in otoliths offer several advantages compared to conventional tags or marks and can be used to identify stocked fish when differences between hatchery-reared and wild fish are present. However, the accuracy of these approaches for identifying Walleye stocked at either fry or fingerling sizes has not been evaluated. Thus, this study aimed to assess identification accuracy for Walleye that were stocked and captured at different life stages using otolith microchemistry. Known stocked fish and fish moved between chemically distinct locations to simulate stocking were obtained from several sources. Results indicated that otolith microchemistry can identify Walleye stocked as fingerlings with high accuracy and that the source hatchery signature can be detected in fish stocked as early as three days post-hatch. Results of this study will provide guidance regarding applications of otolith microchemistry techniques to assess contributions of stocking and natural reproduction to Walleye populations and relative efficacy of stocking fish at varied sizes.