LIFE HISTORY AND ECOLOGY OF FRANCISCANA, PONTOPORIA BLAINVILLEI (CETACEA, PONTOPORIIDAE) - Biology, Evolution and Conservation of River Dolphins Within South America and Asia - page 304

(2002) reported that there are two areas in its northern range where franciscana are extremely
rare or absent. One of these is situated between Maca￩ (circa 22º25'S) (southern Rio de
Janeiro State) and Ubatuba ( ca 23º18'S) (northern São Paulo State); the other occurs between
southern Espírito Santo (circa 19º40'S) and northern Rio de Janeiro States ( ca 21º37'S)
(Figure 2). Although unusual records of stranded franciscanas have been documented by
Azevedo et al., (2002) within one of these gaps (in southern Rio de Janeiro State), the
hypothesis that the species is rare in this area remains valid, due to a marked genetic
difference between samples collected from northern Rio de Janeiro and from São Paulo State
southward (Secchi et al., 1998; Ott, 2002). This suggests the existence of two isolated
populations, one small in northern Espírito Santo and, possibly, another in northern Rio de
Janeiro. The reason for these hiatuses is still unclear, but, due to the species' preference for
turbid waters less than 30-35 m deep (Pinedo et al., 1989; Secchi & Ott, 2000; Danilewicz et
al., 2009), water transparency and depth may be among the factors (Siciliano et al., 2002).
The species is restricted to coastal waters and two criteria have been suggested as
offshore limits to its distribution: a) the area between the shoreline and the 30 m isobaths and
b) the area between the shoreline and 30 nautical miles (NM, 1.853 kilometers) from the coast
(Pinedo et al., 1989). Nevertheless, based on the depth distribution of incidentally caught
dolphins (Moreno et al., 1997; Secchi et al., 1997), it was considered that the 30 m isobath
best fits as the outer distribution limit of the species in southern Brazil (Secchi & Ott, 2000),
though a few animals have been incidentally caught or sighted in deeper waters ( e.g. Secchi et
al., 1997; Crespo et al., 2009; Danilewicz et al., 2009). In its northern range, the species
seems to occur in relatively deeper water (Di Beneditto & Ramos, 2001). No size, age or sex-
related difference in habitat use patterns in relation to depth have been observed in southern
Brazil (Denilewicz et al., 2009).
Figure 2. The franciscana distribution is restricted to coastal waters of the western South Atlantic, from
Itaúnas, southeastern Brazil to Golfo San Matias, Argentina.