Habitat preferences of Guiana dolphins, Sotalia guianensis (Cetacea: Delphinidae), in Norte Bay, southern Brazil

Abstract

Habitat preference and spatial distribution of Guiana dolphins (Sotalia guianensis) in Norte Bay, southern Brazil, was studied from 2001 to 2005. Boat surveys (N = 91) were made to evaluate the spatial distribution of the dolphins. Seven habitat variables were integrated into a geographical information system, and habitat preference was tested using the ‘Neu method’ and a habitat index. The Guiana dolphins did not use all habitat types in the same proportion as were available. Areas used more intensively included, in order of importance: (1) areas with a steep sloping sea-floor; (2) areas further from urban areas; (3) areas further from mangroves; (4) areas near the mouth of the bay; (5) shallow water areas; (6) areas of clayey-silt sediments; and (7) areas close to shore. From 2001 to 2005 there was a shift in spatial distribution and habitat use by the dolphins. The low frequency of use of areas close to urban encroachment and its related impacts to the marine environment raises concern about the coastal habitat destruction. The Guiana dolphin may be considered a habitat specialist, despite its wide latitudinal distribution in the western Atlantic Ocean. The ecological niche of the species may be defined by a narrow strip of shallow coastal waters (mostly < 30 m) bordering the coastline. The shift in the spatial use was probably linked with changes in the abundance of important prey of the species and possibly was caused by the collapse of a fish stock in the study area region. Different habitats may favour different assemblages of prey and consequently different foraging strategies by the dolphins. Human-related habitat alterations throughout the range of this species are likely to affect dolphins' ecology in many ways and, thus, must be evaluated and mitigated to conserve their critical habitats. © 2010, Marine Biological Association of the United Kingdom. All rights reserved.