Ageing Precision and Error Analysis of Whole-view and Sectioned Otoliths in Largemouth Bass and Spotted Bass

The objectives of this study were to quantify ageing precision for largemouth bass (Micropterus salmoides) and spotted bass (M. punctulatus), and to evaluate the effect of ageing errors on the estimation of common fisheries metrics. Sagittal otoliths were extracted from 2164 largemouth bass and 738 spotted bass collected from throughout the Arkansas River, Arkansas. Largemouth bass collections occurred during 2004, 2005, and 2010; spotted bass collections were limited to 2004 and 2005. Annuli were counted by two independent readers from digital images of each whole otolith. For individuals aged greater than 2 yrs from whole views, otoliths were transverse sectioned through the focus and polished, with the cross-sectional surfaces imaged and re-aged. Precision between readers of both whole-view and sectioned otoliths was determined for all ages, whereas precision between ages generated from whole-view and sectioned otoliths also was determined. Precision between readers of whole-view otoliths averaged 95% for largemouth bass and 93% for spotted bass, whereas between-reader precision of sectioned otoliths was 92% for largemouth bass and 94% for spotted bass. Between-method precision of spotted bass ages averaged 91%. Although between-method precision of ages averaged 84% overall for largemouth bass, precision declined noticeably from 89% during 2004 &#45 2005 to 66% in 2010. Between-method precision suggested that the practice of sectioning otoliths from age-3 and age-4 individuals may be overly conservative for black basses in most instances. Sectioning fewer black bass otoliths should translate into a significant time savings for fisheries researchers. Using a pooled largemouth bass dataset, simulated ageing errors produced &#8804 5% differences in von Bertalanffy growth and <10% in catch-curve mortality parameters. Observed differences of this magnitude should be tolerable for basic fisheries assessments and many forms of largemouth bass management, though the error may be too large for certain modeling efforts. Results also indicated that spotted bass may be reliably aged using procedures similar to those recommended for largemouth bass.

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