Reproduction of female franciscana (<i>Pontoporia blainvillei</i>) in Rio Grande do Sul, southern Brazil

Abstract

In this paper, the reproductive biology of female franciscanas (Pontoporia blainvillei) is described based on a sample of 97 individuals collected in Rio Grande do Sul, southern Brazil. Data were collected from dolphins incidentally by-caught by the commercial fleet of Rio Grande and Tramandaí or stranded in the northern coast of Rio Grande do Sul. Age was estimated by counting the growth layer groups present in the dentin and cementum of the teeth. The female reproductive status was determined through the analysis of the ovaries, mammary glands and uterus. The large majority of the recorded ovulations occurred in the left ovary (88%). There was no evidence that the corpus luteum (CL) increases its size as gestation progresses, and there is a considerable individual variation in CL size in females of different stages of pregnancy. The reproduction of the franciscana is markedly seasonal and the species present a typical birth-pulse pattern in Rio Grande do Sul. Births begin abruptly in October and decrease gradually until February. Length and weight at birth was estimated at 73.4cm and 6.1kg, respectively, and the gestation period lasts 11.2 months. Mating and conception should occur between November and March. Sexual maturity in females is attained between 2 and 5 years. Estimation of mean age at sexual maturity was calculated as 3.7 years (CI 95%=3.0–4.4 years) by the DeMaster method and 3.5 years by the logistic equation. Length and weight at sexual maturity were 138.9cm (CI 95%=132.8-145.1) and 32.8kg (CI 95%=29.9-35.7), respectively. Annual pregnancy rate in Rio Grande do Sul was estimated to be 0.66, with a calving interval of 1.5 years. Due to its low age at sexual maturity, short calving interval and brief lifespan, the franciscana is one of the cetacean species with the fastest life history traits. There is no evidence of reproductive senescence and franciscanas seem to remain reproductively active throughout life.