Although sometimes described as a ‘river dolphin’, the Franciscana does not occur in freshwater habitats. The species is generally found in turbid coastal waters, but also inhabits clear waters as well as marine areas associated with islands and rocky shores (Pinedo et al. 1989, Danilewicz et al. 2009). Franciscanas are found mainly in the marine environment and only occasionally in estuaries (Santos et al. 2009) and one inland bay (Cremer and Simões-Lopes 2008). They are relatively common in the Uruguayan part of the La Plata River estuary (Praderi 1986). Franciscanas are primarily coastal, inhabiting waters beyond the surf zone and out to the 30 or 50 m isobath, depending on the region. For example, in FMAs III and IV they occur in waters up to 50 m deep (Crespo et al. 2010, Danilewicz et al. 2010), while in FMAs I and II they appear to be restricted to waters inshore of the 25 or 30 m isobath. Franciscana density decreases with distance from the coast, although the rate and degree of the decrease vary according the width of the continental shelf (Crespo et al. 2010, D. Danilewicz, unpub. data).

Franciscanas apparently do not migrate, although seasonal inshore–offshore movements have been documented in some areas (Bordino et al. 1999, Bordino 2002). Movements of 70-90 km along the coastline have been recorded for satellite-tagged individuals in Argentina (Wells et al. 2013). Predation by both large sharks and Killer Whales (Orcinus orca) has been documented (Praderi 1985, Ott and Danilewicz 1996, Santos and Netto 2005).

Franciscanas feed on several species of shallow-water fish (e.g., sciaenids, engraulids, gadids, batrachoids, trichiurids and carangids), cephalopods, and crustaceans (Brownell 1989, Di Beneditto and Ramos 2001, Rodriguez et al. 2002, Danilewicz et al. 2002, Troina et al. 2016). Their coastal marine habitat is typically characterized by continental run-off with high discharge of high-nutrient river flows (e.g., Patos Lagoon [Lagoa dos Patos] in RS and the La Plata River [Río de la Plata] in Argentina and Uruguay). Juvenile sciaenids, the most important prey of Franciscanas, are typically associated with continental runoff and the influence of subtropical shelf waters (Crespo 2009).

Franciscanas inhabit shallow coastal waters (and they sporadically enter the estuary of the La Plata River [Rio de la Plata]) of subtropical and temperate regions of the western South Atlantic Ocean (Crespo 2009, Secchi 2014). They are found only along the east coast of South America (Brazil, Uruguay, and Argentina), from the northern Golfo San Matias, central Argentina (ca 42°10'S), to Espírito Santo, southeastern Brazil (18°25'S) (Siciliano 1994, Crespo et al. 1998). The species is not distributed continuously throughout its range. Surveys (including beach and aerial surveys, museum specimens, interviews with local people) indicate that Franciscanas are extremely rare or absent in two northern areas: (1) between central and southern Rio de Janeiro State comprising nearly 300 km of coastline and (2) in southern Espírito Santo State comprising approximately 150 km of coastline (Azevedo et al. 2002, Siciliano et al. 2002, Secchi et al. 2003a, Danilewicz et al. 2012). The reasons for these gaps are unclear, but the species’ preference for shallow and productive waters (Brownell 1989, Pinedo et al. 1989, Danilewicz et al. 2009) suggests that depth and the narrowness of the continental shelf influence habitat selection (Siciliano et al. 2002).

The Franciscana is listed in Appendix II of CITES. Measures are needed to reduce the level of bycatch of this species.