Differentiation of the argentine short-finned squid (Illex argentinus) (CEPHALOPODA: TEUTHIDA) populations off southern Brazil using morphology and morphometry of the statolith.

Abstract

The population structure of the Argentine shortfin squid Illex argentinus Castellanos, 1960, an emergent deep-water resource off southern Brazil, was studied from morphology and morphometry of the statolith. A total of 315 mature males and females caught by trawlers between July and September 2002 between 23o S and 33o S, had their statoltihs examined for distinctive morphological features and measured in eight different dimensions. Statolith measurements variability was analyzed by both univariate and multivariate techniques and tested for the effect of two hypothetical population groups defined by previous size-at-maturity patterns: summer-autumn spawners (group 1) and winter-spring spawners (group 2). These analyses were preceded by similar tests for the effect of sexes and maturity stages, as to assess additional significant effects of these factors on statolith morphometry. General morphology was consistent with patterns previously described for mature animals, with some occasional anomalies. Five out of eight statolith measurements differed significantly between population groups in both sexes indicating that statoliths of group 2 were generally less elongated and more robust that those individuals from group 1. The same pattern was observed although less conspicuously in the multivariate analysis. Results reinforce previous hypotheses that commercial concentrations of I. Argentinus exploited off Brazil are largely composed of maturing squid that migrate from the coast of Argentina and Uruguay into their winter spawning grounds in southern Brazilian waters.