This paper presents an updated assessment for Patagonian toothfish (Dissostichus eleginoides) at the Heard and the McDonald Islands (Division 58.5.2) with data until the start of August 2013. Compared to the last assessment in 2011, this assessment updated the growth model and compared the effects of a range of alternative fishery structures and model assumptions for year class strength (YCS) on stock assessment estimates and projected catch limits that satisfy the CCAMLR decision rules. Re-defining the fishery structure was based on a method by Candy et al. (2013) that suggested a simplification of the longline hauls into two sub-fisheries that were depth-stratified but not regionally-explicit. Alternative trawl sub-fisheries were evaluated within the assessment model in different scenarios.
All evaluated scenarios produced similar spawning stock biomass (SSB) patterns and estimates of current status. Across scenarios with YCS estimation, estimates of virgin spawning biomass (B0) ranged from 89 448 - 101 847 tonnes, and SSB status in 2013 ranged from 0.63 - 0.69 of B0. A model scenario that ignored information on YCS variation resulted in an SSB status of 0.58 in 2013, but was considered to be less realistic. The impact of altering the sub-fishery structure for trawl on model estimates was relatively small, however the selectivity functions for the different trawl sub-fisheries varied substantially indicating that a separation of the trawl sub-fisheries is appropriate. The scenario with estimating a YCS from 1992-2009 compared to 1984-2009 was the preferred model, since the estimated YCS pattern was more consistent and did not show an early period with stronger inter-annual fluctuation.
Based on this assessment, we recommend that the catch limit for the 2013/14 and 2014/15 seasons be set at 3005 tonnes.