Daily ages of young-of-year Silver Chub from western Lake Erie, 2017-2018

Daily ages of young-of-year Silver Chub were estimated from counts of rings in lapilli otoliths. Lapilli were mounted to glass slides with thermoplastic cement and sanded to the core with 2000 grit sandpaper to expose daily rings. To improve clarity, sanded otoliths were polished with 0.3 μm alumina powder and a polishing cloth prior to viewing. To estimate daily age, counts of rings in otoliths were made under 100-200 magnification three times by one biologist with more than two decades of experience analyzing daily rings in otoliths. For each round of counts, lapilli were viewed in random order and without knowledge of fish length. For each otolith, we calculated the mean ring count and all pairwise differences. We used the average (rounded up) of the two ring counts that were closest to each other and within 10% of the mean count as the estimated age. If all pairwise differences were greater than 10% of the mean ring count, we estimated ring count a fourth time and calculated the new pairwise differences. If there were no pairs within 10% of the mean ring count after a fourth count, we eliminated the otolith from further analyses.