Use of Daily Growth Increments on Otoliths to Assess Stockings of Hatchery-Reared Kokanees

Abstract

Abstract Hatchery-reared kokanees Oncorhynchus nerka may form discernible “stress” checks on their otoliths when they are stocked into lakes and rivers. We established the reliability of this mark for distinguishing age-0 hatchery fish from wild fish in Lake Pend Oreille, Idaho. Hatchery fish marked with dietary oxytetracycline (OTC) were recaptured 1–3 months after they had been stocked in the lake. All specimens with OTC marks on their bony structures also had a stress check. We also validated daily otolith increments for age-0 kokanees by comparing increment counts external to the stress check with known days between release and recapture of hatchery fish. Then, counts of daily increments allowed us to correctly identify fish from several co-occurring release groups that had been stocked at different times in the same season. Such discrimination will enhance evaluations of alternative stocking strategies. Because some otolith growth increment counts varied slightly from days at large, and because fish ...