Reproductive biology of male franciscanas from Rio Grande do Sul, southern Brazil

Reproductive biology in the franciscana (a small dolphin endemic to coastal waters of the southwestern Atlantic Ocean) was studied because of concerns about this species' vulnerability as bycatch in gill and trammel nets. Some 121 individuals were collected in Rio Grande do Sul, southern Brazil, to evaluate age, length, and weight at attainment of sexual maturity. Indicators used to determine seasonality, sexual maturity, and other measures of reproduction are explained. Sexual maturity was estimated to be attained at 3.6 yr or 3.0 yr, depending on the calculation used. At least some mature males appear to remain reproductively active throughout the year. The absence of secondary sexual characteristics, reversed sexual size dimorphism, and the small number of intrasexual combat scars suggest that male combat for access to females is rare. This species likely forms temporary pairs during the reproductive period.