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

Abstract

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.

Ecological traits of the franciscana dolphin (Pontoporia blainvillei) from the Late Pleistocene to the present days based on stable isotope analysis

“…The franciscana feeds in marine and estuarine waters, preying upon fish, squid, and crustaceans, following the abundance of prey species (Bassoi et al, 2020(Bassoi et al, , 2021Rodríguez et al, 2002). The current diet of the species varies along its distribution range (Botta et al, 2022;Paso-Viola et al, 2014), as well as within aquatic (marine versus estuarine) habitats (Rodríguez et al, 2002).…”

“…The current diet of the species varies along its distribution range (Botta et al, 2022; Paso‐Viola et al, 2014), as well as within aquatic (marine versus estuarine) habitats (Rodríguez et al, 2002). There appear to be no dietary differences between males and females (Bassoi et al, 2021; Troina et al, 2016). In the coastal waters of southern Brazil, under the influence of the Patos Lagoon estuary, the franciscana dolphin consumes about 23 species of fish, six cephalopods, and four crustaceans (Bassoi et al, 2021).…”

“…There appear to be no dietary differences between males and females (Bassoi et al, 2021; Troina et al, 2016). In the coastal waters of southern Brazil, under the influence of the Patos Lagoon estuary, the franciscana dolphin consumes about 23 species of fish, six cephalopods, and four crustaceans (Bassoi et al, 2021). The squid Doryteuthis sanpaulensis , the benthopelagic fish Cynoscion guatucupa , the shelf‐pelagic fish Anchoa marinii , and the costal‐estuarine fish Paralonchurus brasiliensis are the most important prey items (Bassoi et al, 2021; Troina et al, 2016).…”

Resource partitioning in a cetacean community from Uruguayan waters

“…Previous studies indicate that the franciscana dolphin is a generalist species with opportunistic feeding habits (Bassoi, 2005; Campos et al, 2020; Rodríguez et al, 2002). Nevertheless, dietary differences between sex and age‐class groups and some degree of specialization in the feeding strategy have been reported (Bassoi et al, 2021; Tellechea et al, 2017). Moreover, based on stomach content analysis, differences in diet between franciscana dolphins from estuarine and marine waters were found (Rodríguez et al, 2002).…”

Guidelines to merge stranding databases: the case of franciscana (Pontoporia blainvillei) in the extreme South of Brazil

“…Aerial surveys and data on fisheries bycatch indicate that franciscanas are more common in shallow waters, up to the isobaths of 30 or 50 m depending on the region, and may occur less frequently beyond these depths (Danilewicz et al, 2010;Secchi et al, 2021). The franciscana's habitat and diet overlap with the coastal gillnet fishing area in the southern coast of Rio Grande do Sul state (RS), Southern Brazil, and with the commerciallyvalued species such as whitemouth croaker (Micropogonias furnieri) and striped weakfish (Cynoscion guatucupa) (Secchi et al, 1997;Rodríguez et al, 2002;Danilewicz et al, 2009;Haimovici & Cardoso, 2016;Bassoi et al, 2021), respectively. The spatial overlap results in a very high mortality rate of franciscanas in gillnet fisheries (Prado et al, 2021), and many of these dead dolphins wash ashore on the adjacent coast (Prado et al, 2013).…”