Comparison of Structures Used to Estimate Age and Growth of Yellowstone Cutthroat Trout

Abstract

Understanding age and growth of fishes is critical for making meaningful management decisions. Obtaining useful information is dependent on using the best structure (e.g., scale, otolith). The objective of this study was to evaluate precision and reader confidence in age estimates from sagittal otoliths (i.e., whole, sectioned) and scales for Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri collected from Henrys Lake, Idaho. We also sought to compare growth estimates among structures sampled during annual gill net surveys in May 2019 and 2020. We removed sagittal otoliths and scales from 416 Yellowstone Cutthroat Trout. Two readers without prior knowledge of fish length independently aged scales, whole otoliths, and sectioned otoliths. Each reader also provided a confidence rating of 0 (not confident) to 3 (completely confident). Percent exact agreement between readers was highest for sectioned otoliths (85.3%), followed by scales (68.5%) and whole otoliths (66.1%). Average confidence rating was highest for sectioned (mean ± SD = 2.2 ± 0.6) and whole (1.4 ± 0.5) otoliths and lowest for scales (1.0 ± 0.2). Among structures, percent exact agreement (i.e., consensus age) was highest between whole and sectioned otoliths (66.7%), followed by scales and sectioned otoliths (58.9%). Exact agreement was lowest between scales and whole otoliths (51.2%). Differences in back-calculated length at age estimates between sectioned otoliths and scales were minimal, particularly for ages 1–4. Although sectioned otoliths required more time to prepare than scales or whole otoliths, sectioned otoliths produced the most precise age estimates for Yellowstone Cutthroat Trout, with the highest reader confidence.

Precision of four calcified structures for age estimation of Black Carp

“…Similar to Quist et al. (2022) and Koch et al. (2008), confidence was assigned based on a scale of 0 (no confidence) to 3 (complete confidence).…”

“…We assessed between‐reader precision by percent exact agreement (PA), percent agreement within one annulus (PA ± 1), and the coefficient of variation (CV; Chang 1982) of annuli counts reported on bubble plots following the methods in Quist et al. (2022) to identify which structure produced the most consistent age estimates. We compared the consensus estimated annuli counts between structures with PA and CV to evaluate precision.…”

“…Annuli were counted and not assigned ages based on standard aging conventions to minimize potential discrepancies in reported age, as structures were examined independently by readers without knowledge of capture date for fish collected throughout all seasons. Similar to Quist et al (2022) and Koch et al (2008), confidence was assigned based on a scale of 0 (no confidence) to 3 (complete confidence). After individual counts were made, the two readers conferred to establish consensus annuli counts through simultaneous reexamination of structures and annuli with disagreement.…”

“…2017; Quist et al. 2022). Black Carp Mylopharyngodon piceus is an emerging invasive species in North America with a reproducing population in the Mississippi River represented by several cohorts of wild origin fish (Whitledge et al.…”

“…Precise age estimates are needed for life history characterization, quantifying dynamic rates, and assessing age-specific habitat requirements of fish (Buckmeier et al 2017). Structures including scales, otoliths, vertebrae, fin rays, and spines have been compared for numerous fish species to identify methods of age estimation that reduce processing time and provide consistent or precise results among readers (Sylvester and Berry 2006;Spiegel et al 2010;Seibert and Phelps 2013;Klein et al 2017;Quist et al 2022). Black Carp Mylopharyngodon piceus is an emerging invasive species in North America with a reproducing population in the Mississippi River represented by several cohorts of wild origin fish (Whitledge et al 2022).…”