Comparisons of precision and bias with two age interpretation techniques for opercular bones of longnose sucker, a long-lived northern fish

Abstract

Two preparations of opercular bones for estimating age of longnose suckers Catastomus catastomus revealed that annuli were obscured by dense bone and undetected when the whole operculum technique was used. By thin-sectioning the opercula, we removed the dense bone, revealing previously obscured annuli. Using opercula collected from older fish in Labrador, Canada, we found that the dense bone overgrowth led to an overall age bias of 1 year. When samples were broken into groups based on sectioned ages, however, there were minimal differences in age between the two techniques for fish age 6 and younger and a 2-year age difference for fish estimated to be age 10 and older. To compare precision in locating annuli between the two techniques, we calculated coefficient of variation values among independent determinations. Both techniques demonstrated low variance, however, age determinations had greater variation with thin-sectioning than with whole opercula interpretations. Therefore, we conclude that care must be taken when making annulus determinations from thin-sectioning. Due to the presence of dense bone overgrowth, associated with the whole operculum technique, we conclude a combination of both techniques would provide the most thorough procedure for interpreting opercular age for such long-lived fish (30-50 years). © American Fisheries Society 2012.