Comparison of direct and image-based viewing methods for estimating age in Antarctic toothfish Dissostichus mawsoni

Abstract Precise and accurate age and growth information is critical to the development of Antarctic toothfish ( Dissostichus mawsoni ) fisheries management. Currently, age and growth labs use direct view and image view methods to age Antarctic toothfish, but only the direct view method has been validated (Brooks et al., Polar Biol 34:329–338, 2011), and the statistical robustness of the image view method compared to the direct view method for aging toothfish has not been evaluated. This study compared age estimates derived from the two viewing methods from three readers, testing for precision and bias, using a validated reference set of 185 Antarctic toothfish otoliths. Consensus image view age estimates showed high precision values compared with consensus direct view age estimates: CV of 4.50%, APE of 3.18% and 96% agreement within ± 2 years. Evans-Hoenig symmetry test suggested no systematic bias, χ 2 = 1.82, df = 4, P = 0.77. Within-reader precision and bias values also suggested the two methods produce similar age estimates. Between-reader values showed lower precision, but the comparison of the two most precise readers in the study did not significantly differ between methods. This study suggests that the image view aging method produces comparable age estimates to the direct view method.