Feeding habits of the franciscana dolphin Pontoporia blainvillei (Gervais & d’Orbigny, 1844) in Ilha Grande Bay, southeastern Brazil

This study describes for the first time the diet of the franciscana ( Pontoporia blainvillei ) in Ilha Grande Bay, correlating it with sexual maturity through age estimation. The franciscana is an endangered species endemic to South America. Research and conservation of this species is based on Franciscana Management Areas (FMA). The present study aims to characterize the diet of the franciscana in Ilha Grande Bay, located in FMAIIa. Stomach contents of 28 franciscanas were analyzed from 2017 to 2025 to identify the prey with the highest index of relative importance. The most important prey species were Umbrina canosai , Isopisthus parvipinnis , and Dorytheutis plei . It was only possible to compare the diet between mature males and females. Males had greater species diversity, but both sexes had the same most important prey species, U. canosai and D. plei . Males tended to have a more generalist, opportunistic diet, while females tended to have a more specialized diet. The largest preys were consumed at ages close to the estimated sexual maturity of the franciscanas for both sexes. The 16 prey species found in this study have previously been reported in the FMAIIa, but with different levels of importance. This variation in prey within the FMAs may be considered normal and demonstrates that the franciscana can adapt its diet to the abundance and availability of local prey. Continued studies of franciscana feeding habits in this bay are recommended to understand its behavior and habitat areas, as well as the local availability of resources.