Age, growth, and maturity of little tunny, Euthynnus alletteratus (Rafinesque, 1810) in southeastern Brazil

Abstract

This is the first attempt to assess life parameters of little tunny Euthynnus alletteratus in the southwestern Atlantic. Fin spines, liver, and gonad information from 345 fishes (330-780 mm fork length) sampled from artisanal landings between March 2018, and February 2019 were used to analyze age, growth, and sexual maturity. Age was estimated by counting and measuring increments in sectioned spines, and the von Bertalanffy growth function was used to fit length-at-age data. There was no significant difference between male and female size distributions. Gonadosomatic index peaked from November to February in both sexes, associated with the South Atlantic Central Water (SACW) upwelling in temperatures between 15-18°C. Reproduction in cold waters has never been reported before and is possibly related to a richer environment for feeding and growth of larvae. The coefficient of variation among successive readings was 9.2%. The oldest fish was 5 years, and one annual increment for 2 and 3-year-old fish was observed to form associated with SACW. Little tunny growing in southeastern Brazil shows a higher growth rate and smaller asymptotic length when compared to most stocks in Mediterranean waters. Growth was not significantly affected by sex, and the von Bertalanffy growth parameters for all fish were L∞ = 791.9 mm, k = 0.42, and t0 = -0.97 yr-1. Length at first maturity is attained by 1-year-old fish of either sex (423-492 mm), suggesting that a small proportion (8%) of juveniles was recorded from fishery landings.