About Pontoporia blainvillei (Gervais & d'Orbigny, 1844)
Pontoporia blainvillei, known as the La Plata dolphin, has the longest beak proportionate to body size of any living cetacean, reaching up to 15% of total body length in older adults. Males grow to 1.6 metres (5.2 ft) in length, while females reach 1.8 metres (5.9 ft), and the species weighs up to 50 kilograms (110 lb) and lives up to 20 years. Its body is greyish brown with a lighter underside. Flippers are large and broad relative to body size, narrow at the point where they attach to the body, giving them an almost triangular shape with serrated trailing edges. Its crescent-shaped blowhole sits just in front of a crease in the neck, creating the impression the dolphin’s head is permanently tilted upward. The dorsal fin has a long base and a rounded tip. The species has homodont dentition of conical teeth, with 48 to 61 teeth on each side of both the upper and lower jaw. Both sexes reach sexual maturity between two and three years of age, though some populations record maturity as late as five years. Females have a two-year reproductive cycle. Gestation lasts 10 to 11 months, and newborn calves are 70 to 75 cm long at birth. Calves are weaned at one year old, and females may give birth for the first time by age five. Research on a population near Brazil found most births occur between September and February, during the austral spring and summer, with an average gestation period of 11 months. La Plata dolphins generally have small testes, which indicates sperm competition plays a minor role in their mating strategy. Testis size varies seasonally, matching their breeding season, but further research is needed to confirm this observation. Relative to body mass, testis size suggests La Plata dolphins primarily practice serial monogamy, meaning individuals stay with one partner for a breeding season or part of a breeding season, rather than being strictly monogamous. While evidence points to a two-year reproductive cycle, more data is needed to confirm this conclusion. The La Plata dolphin occurs in coastal Atlantic waters of southeastern South America, including the RÃo de la Plata estuary. Its distribution ranges from the Tropic of Capricorn near Ubatuba, Brazil, south to PenÃnsula Valdés, Argentina; its full reported range extends from the mouth of the Doce River in Regência, EspÃrito Santo, Brazil, to PenÃnsula Valdés in Chubut Province, Argentina. It is the only member of the river dolphin group that lives in the ocean and saltwater estuaries rather than freshwater. While some individuals spend part of their lives outside river systems, many live their entire lives within rivers and never enter the open ocean. The species has been observed swimming in small groups in Miramar, Buenos Aires Province, Rio Negro Province, and BahÃa Rosas. Along the Brazilian coast, it is most commonly found in depths of 8 to 30 meters, with accidental captures recorded up to 35 meters, but a small number of individuals have been sighted further from shore.
