Abstract
The present work aimed to estimate the population density of Sotalia guianensis in the Bay of Antonina, southern Brazilian coast, by linear transects, distance method. The average group size in the total area was 2.57 individuals/group. The study area is 28.1 km2 and it was divided in two sub-areas, an outer area closer to the sea and another more enclosed with a higher fresh water input. In the Sector I, the one with greater marine influence, the density estimation found was D = 3.01 animals/ km2 (Variation Coefficient, VC 24.67%), whereas in Sector II there was no estuarine dolphin record. Also, during the rainy season a higher density value was found in the bay (D = 4.99 individuals/ km2, VC 15.93%). When the area division was ignored an overestimation of density was found (D = 3.80 animals/km2; VC 15.71%) due to the data extrapolation beyond the sampled area, including areas not much used by the dolphins. This superestimation due to the few estuarine dolphins records in the Bay of Antonina and also to the method used, which was biased by existing of sand banks at low tide which made it impossible to access all transects.
Highlights
The genus Sotalia is found from Honduras, Central America (DA SILVA; BEST, 1996) to Santa Catarina State, Southern Brazil (SIMÕES-LOPES, 1988)
The acknowledgement of the two species for the genus is recent (CABALLERO et al, 2007; CUNHA et al, 2005; MONTEIRO-FILHO et al, 2002) and S. guianensis is reported with data deficient (DD) status by the World Conservation Union (IUCN, 2011)
Groups from 2 to 5 individuals were observed, the most frequent (61.53%) were those formed by 2 individuals
Summary
The genus Sotalia is found from Honduras, Central America (DA SILVA; BEST, 1996) to Santa Catarina State, Southern Brazil (SIMÕES-LOPES, 1988). The acknowledgement of the two species for the genus is recent (CABALLERO et al, 2007; CUNHA et al, 2005; MONTEIRO-FILHO et al, 2002) and S. guianensis is reported with data deficient (DD) status by the World Conservation Union (IUCN, 2011). Density estimation is one of the most relevant population studies because it can show increase, decrease or stability in the species number for an area (KREBS, 1989), and it is evaluated and expressed by individual numbers or population biomass per unity area or volume (ODUM, 1988). The present work was carried out with the marine species S. guianensis, commonly found in tropical, costal and estuary waters (CARVALHO, 1963), but it has been recorded in rivers (NOWAK, 1999). Concerning the population estimation studies for this species it is possible to quote Edwards and Schnell’s work (2001), north of its distribution, in the Cayos Miskito Reserve, Nicaragua. In addition to population estimation, the authors gathered information about behaviour, activity and average group size
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