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Commercial exploitation of the Argentine shortfin squid (Illex argentinus) was virtually nonexistent in Brazilian waters until 2000 when foreign trawlers initiated their operations on slope grounds as part of a government-induced chartering program. Since then, the species has been included among the targets of a developing slope trawl fishing off southeastern and southern Brazil. Biological samples were collected from commercial catches of 25 national and seven foreign (chartered) trawlers between 23°-33°S and 170-740 m depth. These samples represent two periods of the commercial exploitation of Illex argentinus in Brazil: 2001- 2003, when both chartered and national trawlers operated simultaneously, and 2006-2007, when only national vessels continued to exploit I. argentinus along with other slope stocks. Catches contained immature and maturing squid throughout the year, as well as at least two distinct, fully mature, spawning groups: one composed of small-sized males and females present year-round on the shelf-break/ upper slope (< 400 m), and the other consisting of large squid present only in austral winter-spring in southern (26°-29°S) and deep fishing grounds (400-700 m). The latter group has sustained the large winter catches reported since 2000 and the large sizes and concentrations of the specimens sparked the interest of the fishing industry as a potential target of the slope fishery. The reproductive attributes and temporal/ spatial distribution patterns of winter spawners support the hypothesis that relates this group to migrating concentrations of a north Patagonian shelf stock. If confirmed, the present data would underscore the need to consider multinational shared stock management strategies in the SW Atlantic. [ABSTRACT FROM AUTHOR]