Home ranges of Guiana dolphins (Sotalia guianensis) (Cetacea: Delphinidae) in the Cananeia estuary, Brazil

Abstract

Home ranges of seven Guiana dolphins (Sotalia guianensis) (Van Beneden, 1864) were studied in the Cananeia estuary (similar to 25 degrees 03'S 47 degrees 55'W), south-eastern Brazil. Boat-based observations were conducted from May 2000 to July 2003 in similar to 132 km(2) of protected inner waters. The photo-identification technique was used to follow naturally marked individuals through time and space. From a total of 138 catalogued individuals, five males and two females presented 20+ sightings and were used for home range estimation. Sightings were plotted and analysed in a Geographic Information System (GIS). With the 'Home Range Tools' extension the fixed kernel density estimator with band width (smoothing parameter) chosen via least squares cross-validation was performed for each individual. The fixed kernel method was used to estimate the non-parametric utility distribution of each dolphin, keeping band width (h) constant for a data set. The first polygons created by these parameters had an amoeboid shape and in some cases more than one centre of activity. The 95% home range estimated outlines varied from 1.6 to 22.9 km(2) (7.9 +/- 8.3 km(2)). This large interval shows strong evidences on individual variation in S. guianensis' home ranges. Several individuals showed small home ranges when compared to other cetacean species. An overlap of home ranges of different sizes and shapes were observed for Guiana dolphins with large range movements. Centres of activity were concentrated in the main entrance of the Cananeia estuary. This was a first attempt to understand the way S. guianensis uses the Cananeia estuary and such data are essential for conservation and management purposes.