Growth model identification of short-finned squid Illex argentinus (Cephalopoda: Ommastrephidae) off southern Brazil using statoliths

Statoliths of 689 Illex argentinus specimens collected by national and foreign trawlers in Brazilian waters were analyzed. Catches occurred between 2001 and 2008, from 23° to 32° S and at depths of 80–730 m. Exponential, Power, Gompertz and Schnute models were fitted to size-at-age data and the logistic model was used for maturity modeling. Fitting procedures used the maximum log-likelihood and Akaike criteria for identification of best models. Total age estimates ranged between 56 and 320 days for squid between 35 and 376 mm mantle lengths. Gompertz and Schnute models, which suggest the positive acceleration of growth in the early stages of ontogeny followed by a decrease in the second phase, provided the best fit to the size-at-age dispersion in this study. The inflection point in the maturity curve was 137 days for males and 143 days for females. The age range for post-spawning squid was 116–250 (average 187) days for males and 133–280 (average 201) days for females showing a life cycle close to six months. None of the examined individuals reached one year of age. The wide range of sizes-at-age implied that catches of I. argentinus off southern Brazil probably include mixed micro-cohorts and different population units.