A review of tag-based stock assessments of the Antarctic toothfish Dissostichus mawsoni in Subarea 48.4

The stock abundance of Antarctic toothfish in Subarea 48.4 is estimated using tag based mark-recapture analysis. During WG-FSA-14 the recommendation was made that the stock should move from the Petersen estimation method to the use of the Chapman bias corrected estimator; a correction specifically developed to reduce estimation bias in populations with low recaptures, a feature typical of the data available for this species in 48.4. During a review of assessment methodology two main issues have been identified: the appropriate application of the method when applied to estimate low tag recapture rate population abundance, and the mis-identification of species at release. This paper presents a review of assessment data and methods in order to discuss and address the issues.