Bottom trawl surveys were carried out by New Zealand on parts of the continental slope of the Ross Sea region in SSRUs 88.1HIK and 88.2A in 2008, 2015, and 2019. Catches from the three surveys contained a mixture of three species: M. whitsoni, M. caml, and Cynomacrurus piriei, and were combined across years and scaled to the slope area to give a composite biomass estimate.
Indicative estimates of grenadier biomass for the entire Ross Sea region slope ranged from 35 837 t to 44 131 t, depending on whether constant density of CPUE-based scaling assumptions were used, with estimates from VAST as intermediate. Using the biomass estimated under the constant density assumption and species-specific exploitation rates at equilibrium biomass, an estimated catch limit for macrourids on the continental slope would be 418 t. This would result in a decrease to the catch limit in the north of 70 °S management area (14 t), and a slight increase to the south of 70 °S (322 t) and the Special Research Zone (82 t). We recommend that work on estimating biomass of macrourids using different data sources continues and that additional work be continued to determine appropriate approaches for setting catch limits in the different management areas.