Phenology of Annulus Formation in Walleye and Smallmouth Bass Otoliths

摘要

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 evaluatethe influence of fish age, sex, and sample location (walleye only) on the timing and detection of annulus formation. Timingof 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 acrossanalysis 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 differencesin timing of annulus formation across species-specific strata was surprising given the well-known influences ofage, sex, and water temperature on somatic growth. Nonetheless, results will aid managers in improving the accuracy ofage estimates.