Throughout 1 year, from October 2003 to September 2004, 88 visits to the landing site of a small urban fishery (APREBAN) in Rio de Janeiro city were conducted and 816 specimens of Rhizoprionodon lalandii were analysed. The sample, mostly females, was composed of two cohorts: young-of-the-year were abundant in spring and summer and adults predominated in autumn and winter. Gravid females were most abundant from April to June, whereas post-partum females composed most of the catch in August to September. Adult males were present all year although were more abundant between February and July. No neonates were captured during the study and most embryos collected measured slightly below the reported total length (LT) at time of birth (L0) for the species, suggesting that parturition may occur slightly outside the main fishing grounds or that neonates were not captured in commercial gillnets set at this time of the year. The mean LT at maturity (LT50) for males was 578 mm and females matured between 620 and 660 mm, although a precise estimate of LT50 for females could not be determined. The total length (LT) and total mass (MT) relationship ( M- T = 7 E − L- T 3 · 2597 ) was calculated for both sexes and showed no significant differences. The mean condition factor increased steadily from February to July followed by a steep decrease in values relative to females in August and September, suggesting a pupping season. The present study area can be classified as a coastal juvenile habitat and a probable mating ground for R. lalandii.
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