Illex argentinus

The Argentinean short-finned squid, Illex argentinus, is distributed along the shelf and slope in the western South Atlantic from 22° to 54°S. Since 1977 catches by a local and an international fleet increased by two orders of magnitude from c. 7 000 to > 700 000 t y-l. The species is associated with the Subtropical Convergence of the Brazil and Falkland (Malvinas) Currents. Three or four stocks are identified: the summerspawning stock (SSS), the south patagonic stock (SPS), the Bonaerensis-northpatagonic stock (BNS) and the southern Brazil stock (SBS), which may be a northern continuation of the BNS. Surveys of the shelf and adjacent oceanic waters from 29° to 54°S have covered most of the year. Mature and spawned specimens, and rhynchoteuthion paralarvae of I. argentinus, have been found in summer over the northern Patagonian Shelf and in winter and spring from 29° to 38°S, mainly off the Río de la Plata and along southern Brazil. Evidence suggests that the SPS, which supports the major fishery, makes a spawning migration northward to the confluence of the Brazil and Falkland (Malvinas) Currents, and paralarvae are subsequently carried to the confluence. The life span of I. argentinus is c. one year. Females grow faster and reach a larger size than males, and there is evidence that within a cohort, specimens hatching in warmer conditions have higher overall growth rates. Mantle length at maturity ranges from 142 to 250 mm for males and from 195 to 330 for females. Squid from the SSS are the smallest at maturity and those from the SPS are the largest. Potential fecundity could be as high as 750 000 in the largest females if spawning is intermittent and all eggs that attain a major axis of >0.05 mm at first maturity undergo complete vitellogenesis and are released. Crustacea are the major prey of I. argentinus in the southern part of the species range and fish increase in importance towards the north. It is preyed on by the most abundant demersal fishes of the patagonian Shelf. Off Argentina and Uruguay Merluccius hubbsi is a major competitor with I. argentinus for Engraulis anchoita as well as being predator and prey at different ontogenetic stages. In southern Brazil it is preyed upon by various species of tuna and the serranid Polyprion americanus. Future research should focus on the biology of the early ontogenetic stages, on gene flow among stocks and on the impact of the fishery for I. argentinus on other commercial species.

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