Age structure and biological parameters of southern blue whiting (<i>Micromesistius australis</i>) in its main concentration area in the southwestern Atlantic Ocean in 2019

A comprehensive understanding of a species life history is fundamental for effective fisheries management. This study contributes crucial, up-to-date information by analyzing the age structure and key biological parameters of southern blue whiting (Micromesistius australis) in the area defined by the 52° S-56° S parallels, based on data collected in 2019. It determined the population structure, growth parameters, and natural mortality using data from 2019 commercial bottom trawls and one research cruise. Analyzed specimens ranged from 26 to 59 cm total length (TL) in males and 26 to 64 cm TL in females. Length-frequency distributions were similar between sexes, with a main mode between 45 and 47 cm TL. Age analysis of 2,378 otoliths indicated a minimum age of two years and maximum ages of 20 years old. Significant differences in growth parameters were observed between sexes, primarily due to females having a larger asymptotic length. Von Bertalanffy growth function parameters were: females L∞ = 63.93 cm, K = 0.18 year-1, and t0 = -1.41 years; and males, L∞ = 57.43 cm, K = 0.21 year-1, and t0 = -1.39 years. The length-weight relationship also showed a significant sex difference. Length and age at 50% maturity were estimated at 35.25 cm TL and 2.93 years, respectively, with no significant differences between sexes. Estimates of instantaneous natural mortality ranged from 0.27 to 0.33 year-1. These findings provide valuable insights into M. australis life history in the region, relevant for future stock assessments and sustainable management strategies. The inclusion of Malvinas Islands data significantly enhances the robustness and applicability of these findings across the Southwest Atlantic.