In order to achieve the milestone “1.5 Update CASAL model” (SC-CAMLR-37 Report, Annex12), the CASAL models for Dissostichus eleginoides at Division 58.4.4b were revised.
We updated CASAL model with data up to 2019/20 fishing season. In this report, the base model (M1 model) is derived from the M4 model of previous report (SC-CAMLR-39/BG/51). We estimated the harvest rate (CAY and MAY) as defined in CASAL manual using each CASAL runs.
A single-sex age structured CASAL model using 5 cm bin for length distribution (M2 model) was built to assess the stock of constructed for D. eleginoides of the research block 1 of Division 58.4.4b. We updated data weighting values with latest data. Similar to the CASAL results reported previously (WG-FSA-2019/62, SC-CAMLR-39/BG/51), the MPD profile look good under both scenarios. It is noted that he MPD estimate values of B0 (M1: 870.54 tonnes, M2: 751.90 tonnes) are smaller than previously estimated in SC-CAMLR-39/BG/51 (ranging from 854 to 940 tonnes).
In both scenarios, estimated MCYs for D. eleginoides are higher than current catch limit 18 tonnes in block 1 at Division 58.4.4b. Harvest rates to achieve CCAMLR management target (50% B0), FCAY, were estimated to be close to 7%, which is higher than current precautionary harvest rate for explanatory fisheries where there is no estimate of B0.