CONICET | Buscador de Institutos y Recursos Humanos

The franciscana dolphin Pontoporia blainvillei is the most endangered small endemic cetacean species of the southwestern South Atlantic Ocean. We assessed intra-specific variation in the diet of franciscana regarding biological parameters (sex, total body length, age class and sexual maturity) and between distinct environments (open marine area vs. an area adjacent to an estuary) from Buenos Aires coast, Argentina, using both stable isotopes and stomach content analysis. We found a significant isotopic enrichment in 15N in neonates and nursing calves, representative of the lactation period. We found differences in the diet of franciscana between dolphins from the marine open area and dolphins living in waters influenced by the estuary. Significant isotope differences were found between the two areas. The lower 15N values in dolphins living in waters adjacent to the estuary could be associated with a major consumption of small sizes of the striped weakfish (Cynoscion guatucupa), which has lower isotope values than the larger sizes consumed in the marine open area. This trophic differentiation between locations is in agreement with the existence of two genetically distinct populations recently found in the study area. This study reveals geographical variations in the diet of franciscana dolphin, supporting the new delineation of distinct franciscana populations in Argentina waters. Considering the small home range and the limited movement pattern of the species, populations living near the estuary would likely need protection due to its low levels of genetic diversity found and feeding specialization. Therefore, the preservation and conservation of that habitat is recommended to ensure the population viability of franciscana in the region.

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