In order to achieve the milestone “1.1 Update biological parameters”(SC-CAMLR-37 Report, Annex12), biological parameters (length-weight relationship, growth curve, Age Length Key, and maturity ogice) of Dissostichus eleginoides for Division 58.4.4b were updated based on the data gathered up to the 2017/18 fishing season by France and Japan. Furthermore, the updated CASAL models were developed to conduct an exploration of the impact of different scenarios of depredation and IUU in order to evaluate the uncertainties associated with these factors as achievements of milestones “1.2 Updated estimation of IUU catch” and “1.5 Update CASAL model” (SC-CAMLR-37 Report, Annex12).
A single-sex age structured CASAL model was built to assess the stock of D. eleginoides at the research block 1 of Division 58.4.4b. The base model (M1) did not explicitly consider either IUU catch and depredation; those were explored within sensitivity runs in the three alternative models (M2~M4). Compared to the CASAL results previously reported in WG-FSA-15/23, the MPD profile become better under all scenarios.
Comparing the MPD profile between M1 (base model without depredation) and M2 (4.8% depredation model), depredation would not have large impact on estimated B0 at the block 1 of Division 58.4.4b. On the other hands, the degree of IUU estimation potentially has large impact on the CASAL B0 estimation. The results of MCMC indicates future predictions of toothfish biomass under current catch level (19 tonnes) with/without depredation and IUU catch.