Habitat use by the Guiana dolphin (Sotalia guianensis) (Cetartiodactyla: Delphinidae) in southeastern Brazil

Abstract

The coastal habit and site fidelity reported for Sotalia guianensis make this species especially vulnerable to human activities. Thus, ecological studies focusing on the habitat use of the populations are essential for S. guianensis protection, as it helps to identify critical areas for conservation. The present study aims to analyze the habitat use by Sotalia guianensis in three bays in southeastern Brazil: Guanabara Bay (GB11Guanabara Bay.), Sepetiba Bay (SB22Sepetiba Bay.) and Ilha Grande Bay (IGB33Ilha Grande Bay.). From 2017 to 2019, four surveys per month were carried out in each bay on board of outboard-powered boats. After locating a group of dolphins, researchers recorded data every five minutes, applying the focal-group method. Information collected included geographical position, time of day, group size and composition, predominant behavioral state, and local depth in meters. The ArcGIS software was selected to create distribution maps and estimate the area use using the fixed Kernel Density method (KDE). The variables collected were statistically compared within and between populations. Feeding was the predominant behavior (frequency of 84.2% in GB, 73.3% in SB and 52.2% in IGB), but behavior frequencies differed between populations (X2=57.622, df=2, p < 0.00001). Group size and composition also varied according to the study area (KWsize: H2,732=68.479, p < 0.0001; KWcomposition: H2,732=85.311, p < 0.001), IGB and SB showing large aggregations with many calves and GB, small groups. In GB, dolphin distribution was restricted to shallow waters of the northeastern region and central channel (K95% = 9.9 km2; K50% = 1.2 km2). Guiana dolphins from SB selected greater depths, concentrating in the central region (K95% = 190.6 km2; K50% = 32.6 km2). In IGB, dolphins occurred in an extensive area (K95% = 264.9 km2; K50% = 42.5 km2), though observed more frequently in shallow waters of the western region. The results described can contribute to a better knowledge of the populations and serve as a basis for conservation strategies.