Calf chronology of the Franciscana dolphin (Pontoporia blainvillei): birth, onset of feeding, and duration of lactation in coastal waters of Argentina

Abstract

Information of birth and early life history of cetaceans is scarce and generally estimated indirectly from pregnant females. Based on 91 calves of Franciscana dolphins (Pontoporia blainvillei) stranded or by-caught in artisanal fisheries from the northern coast of Argentina, it was possible to characterize the calving season and the lactation period in the Franciscana dolphins, based in the evidence of milk into their stomach contents. The calving season is extended during four months, with a high frequency in November. The mean size at birth was 64 cm, a lower size than estimated in other areas of the species geographical distribution. The lactation have duration of at least 7 months with two stages: (a) strict lactation period with calves with exclusively traces of milk in its stomach contents and with high occurrence during November and a mean body length of 70.8 cm, and (b) beginning of predation, specimens with a mix milk-solid food and a mean body length of 87.8cm, with high individuals incidence in February. Our results show a short exclusive lactation with an early feeding predation evidences. The lactation pattern of the Franciscana dolphins found in this work is common in short lifespan small and coastal cetacean.