An Age-Structured Production Model is applied to assess the Alfonsino (Beryx splendens) resource in the West and East SIOFA areas of the Southern Indian Ocean. Data limitations restrict these applications to deterministic variants, which assume no variation in annual recruitment about the predictions from a stock-recruitment relationship. The models are fitted to the CPUE series and single year of commercial catch length distribution information available. Both West and East stocks are estimated to be at about 60% of their pre-exploitation spawning stock biomass levels, and well above the levels corresponding to MSY (MSYL). These results are insensitive to all sensitivities explored, except for changes in the value assumed for natural mortality (M). For the Base case assumption of M=0.2, projections under constant annual catches up to 40% above the 2018 levels remain above MSYL for the next two decades. However, if a less productive situation is assumed (M=0.15), there are some cases of spawning biomass dropping below MSYL within 10 years for both areas, including even for continuation of the 2018 catch for the East area.