Intrapopulation variation in the diet of franciscana dolphin (Pontoporia blainvillei) off southern Brazil

The franciscana dolphin (Pontoporia blainvillei) is a coastal dolphin endemic to the western South Atlantic Ocean. The dolphin is listed as vulnerable in the IUCN Red List, with incidental catches in gillnet fisheries the greatest conservation concern for this species. Insights into the feeding habits of this dolphin are essential to understand its distribution, movements and use of habitat, which are fundamental for effective management of the species. The feeding habits of franciscana dolphins were investigated from analyses of stomach contents of animals incidentally caught by two fishing operations from southern and northern regions of the southern Brazilian coast. In this study we investigate the existence of intrapopulation (sexual maturity and sex-related) variation in the diet of the franciscana dolphin, evaluating the spatial (northern and southern geographic areas) and seasonal influences. The analyses were based on Linear and Generalized Linear Models (LM and GLM). The majority of identified prey species were bottom-dwelling teleosts and the squid Doryteuthis sanpaulensis. The most important prey differed spatially and seasonally between northern and southern regions of the study area, and our results revealed significant differences between sexes and sexual maturity stages, mainly related to prey species sizes. This variation might indicate differences in prey selection, availability or habitat use patterns among these groups. In any case, these dietary differences are likely to minimize intraspecific competition for food resources, and/or indicate spatio-temporal variation in prey availability.

Feeding habits of the franciscana dolphin (Pontoporia blainvillei) in south-eastern Brazil

This study evaluated the feeding habits of the franciscana dolphin (Pontoporia blainvillei) in south-eastern Brazil. Stomach contents were collected from a total of 145 dead specimens found incidentally caught by fishing vessels or stranded between 2005 and 2015. Fish otoliths, cephalopod beaks and whole non-digested prey were used for prey species identification. A total of 9337 prey items were identified, including 26 species of teleost fishes and three species of cephalopods. The most important prey families were Sciaenidae among fish and Loliginidae among cephalopods. Franciscana dolphins tended to feed on small fish (mean = 5.25 cm) and cephalopods (mean = 8.57 cm). The index of relative importance (IRI) showed that Pellona harroweri and Doryteuthis plei were the most important prey for both males and females. The PERMANOVA test confirmed that there is no significant difference between the feeding habits of different sexes, but detected a significant difference among seasons. Overall, our results show that franciscana dolphins are predominantly ichthyophagous and non-selective in relation to the type of prey, feeding on pelagic, demersal and pelagic-demersal prey.

Opportunistic Development and Environmental Disaster Threat Franciscana Dolphins in the Southeast of Brazil

The Franciscana dolphin ( Pontoporia blainvillei), a small cetacean endemic to southwestern Atlantic coastal waters, is the most endangered marine mammal species in the south Atlantic. In the Espírito Santo State, in southeastern Brazil, the Franciscana dolphin distribution overlaps regions suppressed and threatened by an intensive industrial and port development in the coastal zone. Moreover, most of Franciscana’s home range was recently impacted by the collapse of a dam that released millions of iron mining waste into the Atlantic Ocean. Considering the restricted coastal habitat of the species, these impacts can be considered an immediate threat, increasing the probability of local extinction of the species. This research calls attention to the necessity for improvement in the regional Environmental Impact Assessments, Conservation Action Plans, and to the development of an effective zoning for ports and conservation areas in the region. These actions could increase conservation efforts and mitigate the current and expected impacts on the Franciscana population in the Espírito Santo State.