Morphology and life history strategies of Illex argentinus in the north extreme of species distribution

RAFAEL SCHROEDER; RICHARD SCWARZ; AUGUSTO CÉSAR CRESPI ABRIL

Congreso; Cephalopod International Advisory council symposium; 2015

The present study aimed to differentiate local populations of Illex argentinus from the winter migratory group in Brazilian waters based on geometric morphometrics. Ontogenetic morphological variations were found for both sexes. In spite of the migratory group was composed of larger individuals (with centroid size larger than 0.4), large animals of both groups had similar morphology. These results suggested that the change in shape was related to an adaptation to the environment. On the other hand, the comparison of the reproductive attributes of adult squids, removing the size effect, showed different relationships for total and gonad weight and especially for gutted body weight in advanced maturity stages for males and females of these groups. Residuals of gutted body weight demonstrate that muscular thickness of the mantle of migratory group was thinner. Additionally, the reconstruction of size distributions for 60 days before the capture using daily growth increments deposited in gladius of squids captured in a scientific cruise with short hauls (~30min) allowed the identification of two patterns: (i) growth depensation, in which large individuals of a population tend to get even larger, compared to smaller individuals. This process is enhanced by intra-specific competition when the amount of available food is scarce and non-concentrated; and (ii) the migratory group was negatively skewed distributed, probably induced by the selective removal of smaller squid by cannibalism, which associated to the consumption of mantle would provide the energy needed to fuel the migration into less productive oligotrophic waters.