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 latest data up to 2018/19 fishing season. In this report, there are no change in model assumptions and scenarios from the previous model (WG-FSA-2019/62) except for removing M3 (without spowning season in CPUE standardization). We estimated the harvest rate (CAY and MAY) as defined in CASAL manual using each CASAL runs.
A single-sex age structured CASAL 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 in WG-FSA-2019/62, the MPD profile look good under all scenarios. It is noted that he MPD estimate values of B0 (ranging 854-940 tonnes) are larger than WG-FSA-2019/62 (ranging 621-683 tonnes).
Putting aside the first recorded CPUE of the time series (2007/2008) decreases the estimate of B0 (M2 compared to M1) and accounting for a higher IUU level increased the B0 estimate (M4 compared to M1). Overall, the B0 estimates in this paper are higher than estimated in 2019.
In all scenarios, estimated MCYs for D. eleginoides are higher than current catch limit 23 tonnes in block 1 at Division 58.4.4b. Harvest rates to achieve CCAMLR management target (50% B0), FCAY, were estimated as 7%, which is higher than current precautionary harvest rate for explanatory fisheries where there is no estimate of B0.