Preliminary analysis of toothfish catch, CPUE, size structure and mark-recapture data from SSRUs 486A and 486G, with comments on the sustainability of different harvest levels

Available catch, effort, catch-at-size and tagging data for Statistical Subarea 48.6 are analysed to provide preliminary assessments for Dissostichus mawsoni and D. eleginoides separately in Subarea 48.6 north of 60°S (the combined SSRUs 48.6A and 48.6G). A preliminary assessment for D. mawsoni in Subarea 48.6 south of 60°S (the combined SSRUs 48.6B through 48.6E) is given in an Appendix. An age-structured production model approach with a deterministic recruitment is applied.  Age is linked to size via a simple von-Bertalanffy equation in which variance in catch-at-length for a given age is proportional to the mean length at that age.  The model makes provision for IUU catches, insofar as this is possible given the available information.  Actual assumptions are set out in this document.  CPUE data are standardised using GLMs prior to their use in the assessments.  A simple accounting equation is used to keep track of the number of tagged animals in the population and to predict the number of recaptures per year.  The method includes recaptures for the year of release.  The tagging likelihood term is based on the Poisson mass distribution function.  The bulk of the model parameters are held constant at levels reported for other better researched toothfish stocks.