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Tuesday, January 29 • 6:00pm - 9:00pm
(P42) Comparison of Three Age-estimation Methods Using Scales and Otoliths for Bloater (Coregonus hoyi) in Lake Michigan

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AUTHORS. Kristy Phillips, Timothy O'Brien, Steve Farha – USGS Great Lakes Science Center

ABSTRACT. Bloater (Coregonus hoyi) are valuable as both a commercial species and endemic prey fish in the upper Great Lakes. Reliable age estimates are critical to population models and sound management of bloater stocks. A reference set of 128 bloater were used to compare scale and sagittal otolith methods with the goals to compare age estimates between structures and to increase precision in age estimates within and among readers. Scales were pressed onto acetate slides and read using a microfiche projector, while sagittal otoliths were thin-sectioned using precision saws. Otolith ages were estimated using microscopy and static, 2D images. There was good agreement between microscopy and static 2D image estimates between and among readers and high variability in the average coefficient of variation (ACV) between and among readers with scale reads. In general, scale ages were estimated to be lower overall when compared to the microscope and image estimates across all readers. Otolith microscope reads using transmitted light had the highest percent agreement among the three readers (65.4%, 54.3%, and 61.4%, 3 reads each). The otolith structure had a lower ACV (range = 4.3 – 7.6%) among the three readers when compared to scales (range = 7.4 – 12.1%). When comparing otolith microscope and 2D image estimates, results varied per reader, however ACV remained under the recommended 10% CV for each reader regardless of otolith structure aging method. These results may be influenced by reader experience, but this study has demonstrated that sagittal otoliths are superior to scales for estimating age of Lake Michigan bloater. To achieve higher precision and agreement within and among readers it is recommended that sagittal otoliths be used to estimate bloater ages.

Tuesday January 29, 2019 6:00pm - 9:00pm

Attendees (4)