Comparison of age readings from scales and otoliths of the Patagonian toothfish (Dissostichus eleginoides) from South Georgia
Scale and otolith age readings were compared for 105 specimens of the Patagonian toothfish (Dissostichus eleginoides) from the South Georgia region (Subarea 48.3). In 44% of specimens, age readings from both structures were identical. A Wilcoxon test for paired data (Ts = 0.256, n = 59) conducted on the remaining 56% showed that differences in age estimates between the two methods were not significant. Otoliths frequently appeared totally opaque, making it impossible to read them, while scale images were always clear. The scale method is considered most appropriate for determining the age of D. eleginoides because it does not underestimate age and is the most effective with regard to time and cost. Values of fish growth parameters using the generalised von Bertalanffy equation estimated from 1 000 data records are: Lt = 207.01 cm [1 - e - 0.0748{t + 0.2898}]; where Loo = 207.01 cm, K = +0.0748 and to = -0.2898. The maximum age of D. eleginoides was found to be 24 years. This is very close to the maximum age of 22.8 years calculated from Taylor's formulae which relates maximum observed age to natural mortality. In this case we used M = 0.13, which is the value recommended by CCAMLR.