Accuracy and Precision of Age Estimates Obtained from Three Calcified Structures for Known‐Age Kokanee

Kokanee Oncorhynchus nerka growth is often density dependent; thus, proper management of kokanee populations necessitates an understanding of population dynamics using age structure data. To date, no calcified structures have been validated for kokanee. We compared the accuracy (i.e., the percentage of reconciled age estimates that matched the known ages of fish) and precision (i.e., the percentage of fish for which complete agreement was achieved on age estimates among all readers) of aging estimates for scales, sectioned otoliths, and sectioned pectoral fin rays from 455 known‐age kokanee (ages 0–4) collected from five lentic waters in Idaho. Across all waters combined, mean weighted accuracy and precision were similar for scales (86% and 70%, respectively), fin rays (83% and 65%), and otoliths (82% and 65%), with no significant differences between structures. However, among water bodies, accuracy and precision of each calcified structure varied considerably. For example, scales were the most accurate and precise structure and otoliths were the least accurate and precise structure at one water body, while otoliths were the most accurate and precise structure and scales were the least accurate structure at two water bodies. Fin rays were the least precise structure at four of the five study waters, but were the least accurate structure for only one water body. Individual reader accuracy was most affected by fish age and water body, and older fish (age 3 and older) were consistently assigned incorrect ages regardless of the water body or the calcified structure. Taken collectively, all three structures produced satisfactory aging accuracy and precision for kokanee, but no structure was unequivocally best; at any individual water body, annual growth and local environmental conditions appeared to influence the readability of calcified structures. Semelparous kokanee (landlocked Sockeye Salmon Oncorhynchus nerka) are a popular sport fish that generally reach maximum ages of 2–4 years (e.g., Rieman and Myers 1992; Grover 2005; Lepak et al. 2012). Kokanee are endemic to many lentic systems across the western United States and Canada, but state and provincial management agencies commonly use hatchery supplementation to introduce populations and maintain stocks for recreational harvest. In addition to providing high‐yield harvest fisheries, kokanee may also serve as important forage fish for predatory species (e.g., Rainbow Trout O. mykiss, Lake Trout Salvelinus namaycush, and Bull Trout Salvelinus confluentus) in some trophy fisheries (Wydoski and Bennett 1981; Johnson and Martinez 2000; Hansen et al. 2010). In Idaho, kokanee are an integral part of numerous fisheries that generate high angler effort, thus making them a management priority in many waters (IDFG 2019). Kokanee population management goals often seek to balance fish size, catch rates, and abundance. Kokanee populations exhibit strong density‐dependent growth (Rieman and Myers 1992; Buktenica et al. 2007), which poses *Corresponding author: phil.branigan@idfg.idaho. gov Received October 5, 2018; accepted March 26, 2019 North American Journal of Fisheries Management 39:498–508, 2019 © 2019 American Fisheries Society ISSN: 0275-5947 print / 1548-8675 online DOI: 10.1002/nafm.10286