A comparison between otoliths and scales for use in estimating the age of Dissostichus eleginoides from South Georgia

Age composition is fundamental to understanding the population dynamics and productivity of a fish stock. The use of scales to estimate age can result in large errors in age data for long-lived species, usually due to compres sion of scale circuli with age. Patagonian toothfish (Dissostichus eleginoi des) is considered to be a long-lived species whose age has been estimated using both scales and otoliths. We estimated the age of D. eleginoides caught off South Georgia using otoli ths and scales. For scales, we made impressions on acetate slides; for otol iths, we used transverse sections prepared by baking and grinding the poste rior and anterior sides. Using ANOVA, we compared data obtained from the tw o structures to test the hypothesis that otoliths and scales give the same age estimates, and compared the precision of age estimation for both struct ures and between readers. Ages estimated using scales were significantly less than those estimated us ing otoliths. For scales, bias occurred for both readers between readings; for otoliths, only one reader was biased. Residual variances indicated one reader was relatively more precise than the other in estimating age using o toliths, but less precise using scales. This reflected the comparative expe rience of the two readers in estimating the age of D. eleginoides using oto liths and scales.