ABSTRACT: Walleye (Sander vitreus) is a popular sportfish 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 can potentially be used to identify stocked fish, but many have various drawbacks. Natural chemical markers in otoliths or eye lenses 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, the objectives of this study are to assess identification accuracy for Walleye stocked as fry or fingerlings using otolith microchemistry and eye lens stable isotope analysis. Known stocked fish and fish moved between chemically distinct locations to simulate stocking were obtained from several sources. Results to date indicate 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 and eye lens chemistry techniques to assess contributions of stocking and natural reproduction to Walleye populations and relative efficacy of stocking fish at varied sizes.
