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Tuesday, January 26 • 10:40am - 11:00am
Precision and Bias of Largemouth Bass Ages Estimated From Scales and Otoliths

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AUTHORS: Stephen M. Tyszko*, Ohio Division of Wildlife; Jeremy J. Pritt, Ohio Division of Wildlife

ABSTRACT: Accurate age and growth information is essential to effective fisheries management, yet biases and precision of methods used to estimate Largemouth Bass age are not fully understood. Although counting annuli on sectioned sagittal otoliths has been validated as an accurate method of age estimation for largemouth bass, scales continue to be used without a full understanding of the bias involved and how it can impact management. We collected 1,911 largemouth bass from 17 reservoirs across Ohio during spring in 2013 and 2014 to compare precision of age estimates from scales and otoliths among three readers, and evaluate age-specific bias of age estimates derived from scales. Mean average coefficient of variation (ACV) was 7.9 for otolith age estimates and 53.4 for scale age estimates. It was apparent that age estimates from a few inexperienced personnel contributed considerably to this variation. When only considering age estimates made by experienced personnel (973 largemouth bass), ACV was 1.5 for otolith age estimates and 53.1 for scale age estimates. We analyzed data from experienced readers with an age-bias plot and fitted a non-linear mixed model to test for an aging structure effect on von Bertalanffy model parameter estimates. Age estimates derived from scales were biased high for ages ≤ 4 and were biased low for ages ≥ 7, and aging structure had a significant effect on von Bertalanffy model parameter estimates where K was overestimated an L¥ was underestimated. Scales provide imprecise and biased age and growth information for largemouth bass which reduces the overall power to compare populations. We recommend using otoliths to estimates largemouth bass age and stress the importance of properly trained personnel.

Tuesday January 26, 2016 10:40am - 11:00am EST
Emerald A