The Amundsen Sea region toothfish fishery has been operating since 2003. In 2015, a research plan was developed to estimate the toothfish biomass the area, particularly in the South.

The biological characterisation of the fishery shows a truncation of the right-hand limb of the age distribution between 2004 and 2014. No age data are currently available after 2014. We recommend that further ageing of toothfish in the ASR be made a priority to develop annual age-length keys and age frequencies. We further recommend that catch limits in the ASR be calculated following the trend analysis rules developed by WG-FSA for research blocks (CAMLR-XXXVI 2017, Annex 7, paragraph 4.33). However, the calculations are slightly different as the effective tag release and recaptures (to account for different levels of tag survival and tag detection by individual vessels) can be applied:

• 882H: 177 t based on a one-year Chapman estimate using effective tagging survival and tag detection rates and allowing a maximum of 20% change in the catch limit from 200 t.
• Research block 882_1: 240 t based on CPUE by seabed area and allowing a maximum of 20% change in the catch limit from 200 t.
• Research block 882_2: 240 t based on a one-year Chapman estimate using effective tagging survival and tag detection rates and allowing a maximum of 20% change in the catch limit from 200 t.
• Research block 882_3: 160 t based on CPUE by seabed area and allowing a maximum of 20% change in the catch limit from 200 t.
• Research block 882_4: 214 t based on CPUE by seabed area and allowing a maximum of 20% change in the catch limit from 200 t.

We note that research blocks 882_1, 3 and 4 use CPUE by seabed area analogy and can also be calculated by CCAMLR Secretariat using the agreed method for research blocks in other areas. As 882H and research blocks 882_2 use effective tagging survival and effective tag detection rates, we have presented Chapman estimates for these research blocks.

We note that consideration of the spatial overlap of tag releases and subsequent effort to recapture tagged fish remains an issue for tag-based estimations of biomass and we note that improved analytical methods need to be developed. Individual research block catch limits (rather than an overall catch limit for all southern research blocks) should improve the ability for information to be obtained from these research blocks, especially blocks 1 and 4, where sea ice dynamics can prevent access early in the season.