USING OTOLITH MICROCHEMISTRY TO CLASSIFY YELLOW PERCH AS STOCKED OR NATURALLY PRODUCED

Fisheries managers routinely use stocking to supplement fish populations (Schramm and Piper 1995, Fisher 1996). Stocking eyed-eggs offers substantial cost savings compared to stocking fry and fingerlings (PFBC 2011); however, traditional stocking evaluation using oxytetracycline (OTC) marking of otoliths is ineffective for eyed-eggs of some species (e.g., yellow perch, [Perca fla- vescens]). Thus, there is a need for additional approaches to be able to classify fish as stocked or naturally produced. Fish otoliths are paired calcified structures in the inner ear that permanently deposit trace elements in proportion to water column concentrations (Campana 1999, Campana et al. 2000). Coupled with otolith growth increments (i.e., annuli), elemental accumulation permits retrospective evaluation of environmental history (e.g., natal origins, movement) if water chemistry is spatially heterogeneous and temporally constant (Elsdon et al. 2008). Otolith microchemistry can be used to evaluate stocking contributions (Pracheil et al. 2014) and in the context of eyed-egg stockings, may be useful for classifying fish as stocked or naturally produced. Yellow perch is a popular sport fish species in South Dakota (Gigliotti 2007) and is routinely stocked by fisheries managers to supplement weak year classes (Schoene- beck et al. 2010). The South Dakota Department of Game, Fish and Parks (SDGFP) propagates yellow perch for stocking (e.g., eyed-eggs, fry, fingerlings) and also stocks adult perch through trap and transfer operations (Lott 1991, Fisher 1996). However, the contributions of yellow perch stockings in South Dakota are largely unknown because it is difficult to differentiate stocked fish from resident individuals (Brown and St. Sauver 2002). Our objective was to assess the utility of otolith microchemistry to distinguish hatchery-reared yellow perch stocked at the eyed-egg stage from naturally produced individuals