Assessment models for Antarctic toothfish (Dissostichus mawsoni) in Subarea 88.2 SSRU 88.2E for the years 2002–03 to 2010–11

We provide an update of the Bayesian sex and age structured population stock assessment model for Antarctic toothfish (Dissostichus mawsoni) in the SSRU 88.2E, using revised catch, catch-at-age and tag-recapture data from selected trips and all vessel trips. The 2011 reference case model resulted in a 30% higher estimate of initial biomass than for the 2009 base case. The main reason for this increase was likely to be because of the increase in the proportion of selected trips in the 2011 assessment.



Model fits to the data were adequate, with the tag-release and recapture data providing the most information on stock size, although there were conflicts between information in the recapture data from different years. Monte-Carlo Markov Chain (MCMC) diagnostics suggested no evidence of non-convergence in any of the models. The selected trips model run using the revised maturity ogive MCMC estimated initial (equilibrium) spawning stock abundance B0 d at 10 100 t (95% credible intervals 8 720–11 770 t), and current (B2011) biomass estimated at 82.7% B0 (95% credible intervals 80.0–85.1%). Estimated yields from this model were 484 t.



SSRU 88.2E has historically been assessed and managed as a separate area because it is geographically separated from the Ross Sea fishery and little fishing had been carried out in the other parts of Subarea 88.2. Furthermore, it is generally considered more conservative to manage small fisheries separately to avoid potential problems with localised stock depletion. However, over the past 2–3 years there has been an increase in fishing in SSRUs 88.2CDFG and it may now be more appropriate to carry out a combined stock assessment based on SSRUs 88.2C–G. This combined stock assessment is developed in a separate paper.