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

Abstract

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.

Natal Contributions of Kokanee Salmon to Flaming Gorge Reservoir, Wyoming–Utah: An Evaluation Using Otolith Microchemistry

“…The source of broodstock coupled with a limited time in the hatchery, may contribute to similarities in growth between natural and hatchery-produced kokanee in the system. In addition to similar growth between natural and hatchery-origin kokanee, it is worth noting that kokanee grew relatively fast in FGR compared to kokanee in other systems (Markevich 2008;Branigan et al 2019). Markevich (2008) reported the fork-length of age-3 kokanee captured from Kronotskoe Lake, Russia, averaged about 190 mm.…”

“…Markevich (2008) reported the fork-length of age-3 kokanee captured from Kronotskoe Lake, Russia, averaged about 190 mm. Additionally, age-3 kokanee sampled from Lake Pend Oreille and Mirror Lake, Idaho, displayed total lengths less than 300 mm (Branigan et al 2019). For comparison, natural and hatcheryorigin kokanee in FGR were greater than 300 mm MEF at age-3.…”

Using seasonal oscillations in fin ray microchemistry to chemically age Lake Sturgeon

“…2018; Branigan et al. 2019). Age estimates provide a way for managers to assess important population dynamics, such as changes in stock size, mortality rate, mature individuals, and possible recruitment, in order to develop policies that protect and enhance stock structure (Campana 2001; Maceina et al.…”

“…In fisheries management, the use of calcified structures for age and growth analysis is commonly practiced (Jackson et al 2007;Koch and Quist 2007;Maceina et al 2007;Rugg et al 2014;Hessenauer et al 2018;Branigan et al 2019). Age estimates provide a way for managers to assess important population dynamics, such as changes in stock size, mortality rate, mature individuals, and possible recruitment, in order to develop policies that protect and enhance stock structure (Campana 2001;Maceina et al 2007).…”

Accuracy and Precision of Otolith‐Derived Age Interpretations for Known‐Age Lake Trout

“…Accuracy of age interpretations, however, is more difficult to measure and can only be determined when known-age fish, rare in natural settings, are available (Beamish and McFarlane 1983). For that reason, accuracy of age interpretations is assessed less often and typically requires the use of mark-recapture methods to obtain true ages of fish (Campana 2001;McNicol and MacLellan 2010;Hanselman et al 2012;Haglund and Mitro 2017;Branigan et al 2019). Due to the rarity of known-age fish, analyses that include assessments of both the precision and accuracy of otolith-derived age interpretations are lacking for many fishes, including Lake Trout.…”