Phenology of Annulus Formation in Walleye and Smallmouth Bass Otoliths

Brianna J. Graff, Daniel J. Dembkowski*, Melissa R. Wuellner
Department of Natural Resource Management, South Dakota State University, Box 2140B, Brookings, SD 57007, USA.

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© 2014 Graff et al.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Natural Resource Management, South Dakota State University, Box 2140B, Brookings, SD 57007, USA; Tel: 605 688 6577; Email:


Walleye Sander vitreus and smallmouth bass Micropterus dolomieu were sampled monthly (May-October) from Lake Sharpe, South Dakota during 2006 and 2007 to estimate the timing of otolith annulus formation and to evaluate the influence of fish age, sex, and sample location (walleye only) on the timing and detection of annulus formation. Timing of annulus formation was evaluated using marginal increment analysis. Walleye samples were stratified by age, sex, and sample location (i.e., upper and lower Lake Sharpe) and smallmouth bass samples were stratified by age and sex. Monthly mean marginal increment measurements for both species generally increased from May to June, declined in July, and slowly increased from August to October. Although monthly differences in marginal increment measurements across analysis strata were rarely consistent, July generally had the lowest mean marginal increment across species and strata, suggesting that annulus formation in walleye and smallmouth bass in Lake Sharpe likely occurs in July. The lack of differences in timing of annulus formation across species-specific strata was surprising given the well-known influences of age, sex, and water temperature on somatic growth. Nonetheless, results will aid managers in improving the accuracy of age estimates.

Keywords: Age, growth, marginal increment analysis, otolith, smallmouth bass, walleye.