Population assessment of Patagonian toothfish in Subarea 48.4

This paper presents an update of the assessment of toothfish (Dissostichus spp.) in Subarea 48.4. The Subarea is divided into two management regions and assessed using a CASAL assessment of D. eleginoides in the northern region and a simple Petersen biomass estimate derived for D. eleginoides and D. mawsoni in the southern region. The CASAL model structure used to assess the stock in 2011 has been retained although a small number of changes have been made to try to improve the fit of the model and to reduce the dependency on a relatively small amount of data. These changes comprise the addition of catch at age information for 2011, a minor change to the initial parameters of the selection pattern and the inclusion of additional information on size at age. CASAL estimates of stock size, harvest rate and recruitment are similar to those of last year’s assessment. B₀ is estimated at around 1,690 tonnes and B₂₀₁₂/B₀ at around 88%. Sustainable yield, calculated in accordance with the CCAMLR decision rules, is 63 tonnes for D.eleginoides in the northern region whilst sustainable yield calculated from the Petersen biomass estimates of Dissostichus spp. in the southern region and application of the gamma value (0.038) determined for toothfish in Subarea 48.3 was 52 tonnes. Options for the future development of the assessment of toothfish in Subarea 48.4 are considered.