This paper explores the recruitment assumptions used in integrated assessments of toothfish stocks within the CAMLR Convention Area, conducted using Casal2. Current CCAMLR decision rules require projecting stock assessments forward for 35 years to determine precautionary catch limits. The current methods for estimating future recruitment vary among the four stocks: Patagonian toothfish (Dissostichus eleginoides) in Subarea 48.3, Division 58.5.1, and Division 58.5.2, and Antarctic toothfish (Dissostichus mawsoni) in Subarea 88.1 and SSRUs 88.2AB (Ross Sea region). This paper reviews the approaches taken to projecting recruitment in stock assessments presented to WG-FSA-IMAF-2024.
Among the four stock assessments, there were areas of concordance which form general principles for estimating future recruitment. These general principles include:
- Assumptions about future recruitment levels and variability should be informed by past estimates.
- Where available, time series of standardised surveys provide valuable fishery-independent indices of recruitment trends.
- Where there is evidence of a change in recruitment which is not included in the Casal2 model, a more recent time period should be used to forward project recruitment.
From these general principles, we give the following recommendations for the four integrated stock assessments:
- Projections using the entire assessment time series are presented in all assessments as a baseline.
- Where there is evidence of a change in recruitment, either positive or negative, a recent time period (~10 years) should be used to project future recruitment.
- Where fishery-independent surveys are available, these should be used to compare indices of recruitment to those in the model.