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Estimating Largemouth Bass Age: Precision and Comparisons among Scales, Pectoral Fin Rays, and Dorsal Fin Spines as Nonlethal Methods

Reid L Morehouse, Steven B Donabauer, Angela C Grier

Scales are commonly used to age largemouth bass since the samples are easy to extract and process. Yet, scale annuli are often difficult to interpret among the largest (and presumably oldest) individuals. The goal of this study was to determine whether a more precise nonlethal structure could be used to age largemouth bass. We examined scales, pectoral fin rays, and dorsal fin spines from largemouth bass collected from six glacial lakes in northern Indiana. Collectively, 861 structures were aged by three analysts and post-concert reads concluded with 85%, 94%, and 99% agreement for scales, pectoral fin rays, and dorsal fin spines, respectively. Pre-concert exact (± 0 years) percent agreement among age analysts was highest for dorsal fin spines (27%) followed by pectoral fin rays (23%) and scales (2%). Mean coefficient of variation was lowest among dorsal fin spines (16%) followed by pectoral fin rays (22%) and scales (37%). Scales exhibited the most variability and bias, while dorsal fin spines were the least variable and most unbiased structure. We encourage researchers to use scales for younger fish and dorsal fin spines for larger fish when both: (1) nonlethal methods and (2) a higher standard of precision are sought to evaluate specific management objectives.