Spatial distribution, stock structure, and biological characteristics of Antarctic toothfish, Dissostichus mawsoni, in Subarea 88.3: Research findings and observations on bycatch species from 2016 to 2023

Antarctic toothfish (Dissostichus mawsoni) were found at depths ranging from 550 to 2000 m throughout Subarea 88.3, with size distributions and catch rates (i.e., abundance) varying by depth and location. Size distributions along the continental slope were typically bimodal, composed of both juvenile and adult fish, indicating the presence of different life stages in close proximity. The highest catch rates were recorded in the central slope region, highlighting this area as a critical habitat for the species. Growth patterns of D. mawsoni differed between sexes, with females being generally larger at a given length than males, consistent with observations from the Ross Sea. Von Bertalanffy growth curves derived for Subarea 88.3 were similar to those observed in other Pacific sectors, suggesting similar biological dynamics across regions. Histological analysis estimated the length at 50% maturity (L₅₀) to be 125.32 cm for females and 124.08 cm for males, with the length at 75% maturity (L₇₅) estimated at 134.62 cm for females and 142.94 cm for males. The age at 50% maturity (A₅₀) was estimated at 12.55 years for females and 13.77 years for males, while the age at 75% maturity (A₇₅) was estimated at 15.01 years for females and 17.98 years for males. However, further sampling is required to validate these maturity parameters due to observed variability in the data. This study suggests a potential need for further investigation into the spatial patterns of the biology and stock structure of Antarctic toothfish, particularly regarding the possible influence of Circumpolar Deep Water (CDW) and bottom currents within Subarea 88.3. The study also highlights the variable catch rates of key bycatch species, such as grenadiers, across research blocks, suggesting the need for detailed species identification and biological sampling to better understand their distribution and impacts. The findings provide important insights into the life history and stock structure of D. mawsoni in Subarea 88.3, underscoring the significance of ongoing monitoring and research to support future stock assessments and sustainable management strategies.