Reproductive parameters of Pontoporia blainvillei (Cetacea, Pontoporiidae), on the coast of São Paulo and Paraná States, Brazil

Abstract

Whereas the reproductive biology of franciscanas (Pontoporia blainvillei) has been relatively well studied in the populations that occur in the southern part of its distribution (southern form), there are few reproduction studies of populations that occur north of 27°S (northern form). In this study, the gonads of 40 individuals of P. blainvillei (22 males and 18 females) which were incidentally caught or stranded on the southern coast of São Paulo State and the coast of Paraná State (25°00'S - 25°58'S) between 1997 and 1999, were analyzed macro- and microscopically. The results revealed that the testes of adult male franciscanas do not exceed 5.5 cm in length and 1.6 cm in width, with a maximum testes weight/body weight ratio of 0.12 %. The relative size of the testes suggests a single-male breeding system, without sperm competition. The maturity of the left and right ovaries seems to occur simultaneously, with both of them being functional. Ovulation apparently occurs only in the austral summer months. Although not confirmed due to the small sample size, the data suggest a reproductive cycle of two years for the species in the study area. The length of sexual maturity was estimated as being between 112 and 116 cm for males, and between 122 and 126 cm for females, at the age for both sexes between 4 and 5 years. The neonatal length was estimated at 71.2 cm, with most births occurring between October and December. Pregnancy was estimated to last 10.6 months, with a lactation period varying from approximately 6.2 to 8.5 months. The fetal growth rate was calculated to be 7.55 cm/month. The absence of polarity in the ovulation and the smaller sizes of sexual maturation of the franciscanas in the study area suggest populational differences when compared with franciscanas from other areas throughout its distribution.