Reproductive aspects of male franciscana dolphins (Pontoporia blainvillei) off Argentina

As the first study to investigate reproductive aspects of male franciscana dolphin – Pontoporia blainvillei – in Argentine waters, the aim of this paper was to assess sexual maturity by using histological and morphometric methods. P. blainvillei was labeled as “Vulnerable” by the IUCN in 2008. The specimens analyzed were either incidentally caught in artisanal fishing nets (n = 47) or found stranded on the beach (n = 3). Testis weight and testicular index of maturity were reliable indicators of sexual maturity, being their values: MTW: 1.14 ± 0.60–4.49 ± 1.94; IM: 0.03 ± 0.01–0.09 ± 0.03, for immature and mature specimens’ respectively. It was found that the hierarchical cluster analysis (HCA) might be appropriate for establishing sexual maturity stage, based on both the body morphometric measurements and age. The values for age, standard length and total weight at attainment sexual maturity were 2.92–3.54 years, 126.19–126.27 cm and 23.47–23.75 kg. Considering the extremely low relative testis weight, the reversed sexual length dimorphism, the absence of secondary sexual characteristics, and the lack of scars from intrasexual combats in males, the hypothesis that sperm competition does not occur in the species, and male combats for accessing female reproductive may be rare for P. blainvillei is reinforced. All these features fit the species within a serial monogamous mating system.