Seasonal and interannual variability in growth and maturation of winter-spawning Illex argentinus (Cephalopoda, Ommastrephidae) in the Southwest Atlantic

Abstract

An investigation was carried out during the Illex argentinus trawl fishery (January-July) in the fishery regions of 42 °S and 45-47 °S off the Exclusive Economic Zone of Argentina between 1985 and 1990. Statoliths of 5,232 squid were sampled and processed to study age and growth patterns in squid, hatched in different months. Among squid of similar ages (within an age interval from 180 to 300 days), the May-hatched squid were the smallest while the September-hatched were largest. Growth rates of squid of the same hatching-months were significantly different according to year, but these differences were considerably smaller than those observed between various hatching-months within one year. The largest individuals at a given age were captured in 1990, and the smallest in 1985. Males and females became mature at age 220-320 and 210-360 days respectively. The maturation period lasts 1.5-2.5 months in males and 1 month in females. Early and late-maturing groups were observed within each hatching-month. The peak. of spawning was in July of 1984, 1986, 1987, in June of 1985 and in August of 1989.