Distribution, abundance and density estimates of franciscanas, Pontoporia blainvillei (Cetacea: Pontoporiidae), in Babitonga bay, southern Brazil

Abstract

Pontoporia blainvillei (Gervais & d'Orbigny, 1844) is threatened throughout its distribution. The species can be found year-round in the Babitonga bay estuary (26º 02'-26º 28'S and 48º28'-48º50'W), in the north coast of the state of Santa Catarina, Brazil. Boat surveys were conducted in order to evaluate its abundance and density between 2000 and 2003. Sampling was random and stratified, with 46 transects in five sub-areas, comprising a total area of 160 km². Data collection was conducted following the linear transect method with distance sampling. A total of 1174.7 km was scanned and 38 groups were observed. Franciscanas were not uniformly distributed in Babitonga bay. Group size ranged from one to 13 animals (mean ± SD = 5.02 ± 3.62). Model 1 (Half-Normal) showed the best fit to the data. The estimated population size was 50 animals and the density was 0.32 individuals km-2. Density estimates evaluated in the sub-areas where franciscanas occurred resulted in a density of 0.46 individuals km-2. Monitoring this population is of considerable importance due to the constant threats that this species faces in this bay.

Tidal and seasonal influences in dolphin habitat use in a southern Brazilian estuary

“…The franciscana is a species that occurs mainly in the coastal region, outside bays, where the sand substrate is predominant, and the Babitonga Bay franciscana population is the only known species that resides year-round in estuarine environment (Cremer and Simões-Lopes 2008). The Guiana dolphin is strongly associated with estuarine environments in southeastern and southern Brazil (Borobia et al 1991), and prefers areas with mud substrate (Lodi 2003).…”

“…The highest frequency of franciscana feeding behaviour in Anegada Bay, Argentina, has been observed at high tide (Bordino et al 1999). However, knowledge of the behavioural ecology of the species is still limited because observation in its natural environment is difficult due to its small body size, discreet behaviour and cryptic colouration (Cremer and Simões-Lopes 2008).…”

Use of carbon and nitrogen stable isotopes to study the feeding ecology of small coastal cetacean populations in southern Brazil

“…In this study, it was presumed that Franciscana dolphins found in estuarine and nearshore areas, respectively, are from distinct populations, and that the estuarine population is probably a resident one (Cremer & Simões-Lopes 2005. In the estuarine area, the Franciscana population was estimated to of approximately fifty individuals (Cremer & Simões-Lopes 2008), while the Guiana dolphin population was estimated to be 208 individuals (Cremer et al 2011). There is no available data on the abundance of the nearshore Franciscana population.…”

Abundance of Conepatus chinga (Carnivora, Mephitidae) and other medium-sized mammals in grasslands of southern Brazil

“…In Brazil, this method has been used in aerial counts of marsh deer Blastocerus dichotomus (Illiger, 1815) (e.g., sChaller & VasConCelos, 1978Pinder, 1997;Mourão et al, 2000;andriolo, 2005), and boat counts for cetaceans (e.g., CreMer & siMões-loPes, 2008;FlaCh et al, 2008). Transect lines on the ground are used basically to estimate densities of primates (e.g., Peres, 1997;González-solís et al, 2001;santana et al, 2008).…”