the population structure and reproductive biology of mustelus schmitti was analysed during autumn (1994, 1995) and spring (1994) in the rio de la plata oceanic front. the samples consisted mainly of adult males and immature females, indicating that nursery areas are situated elsewhere. in autumn, the highest female densities occurred between 36°s and 35°s, with densities decreasing further south, and high male densities occurred over all latitudes of the study area. in spring, both sexes occurred north of latitude 36°30′s. males attained maturity at 59 cm total length (tl), and females at 72 cm tl. litter size varied from one to ten in spring and two to nine in autumn, with embryos ranging from 9 to 26 cm and 7 to 26 cm tl respectively. the mean tl of embryos was significantly higher in spring (22 cm), suggesting that parturition occurs in late spring and summer. litter size was found to increase with female tl.