An Evaluation of Precision in Age Assessment of Thin-Sectioned and Whole Otoliths and the Efficacy of Using Oxytetracycline as an Aid in Validating Otolith Annuli in Burbot
Abstract.—Precision of estimated ages within and between three readers was examined and compared for thin-sectioned and whole burbot Lota lota sagittal otolith pairs (n = 47) collected between November 1995 and May 2000. In addition to estimated total ages, for thin-sectioned burbot otoliths, age past a discernable oxytetracycline (OTC) mark, incorporated in May 1995, was discerned and mark intensity was rated. The average proportion of correctly aged annuli past the OTC mark varied from 0.74 to 0.81 for the three readers. Average total age assigned to whole otoliths was significantly less than that of thin-sectioned otoliths. Average mean percent error was generally less than 10% and was lower for thin-sectioned than for whole otoliths. The OTC mark was easily detected for 42 of the 47 thin-sectioned otoliths, but was not as intense as when examined in 2000. The results of this study suggested that precise and repeatable age assignments can be obtained from thin-sectioned burbot otoliths and that whole otoliths likely underestimate true age. In addition, oxytetracycline can be used effectively to validate ages of burbot otoliths. Oxytetracycline marks were detectable on burbot otoliths when stored between sampling efforts from 1995 to 2005, although the intensity of the mark faded with time and exposure.