Distribution and habitat use of small cetaceans off Abrolhos Bank, eastern Brazil

Abstract

An eight year summary of opportunistic sightings of small cetaceans in Abrolhos Bank, eastern Brazil, is provided with reference to species distribution, habitat use and group size. Data were gathered from 1997 to 2004 during research cruises (more than 500 days of sampling effort) aiming to study the biology of humpback whales, and were analyzed using a geographic information system (GIS). Dolphin species were identified on 151 sightings: estuarine dolphin, Sotalia guianensis – 49%; roughtoothed dolphin, Steno bredanensis – 16%; and bottlenose dolphin, Tursiops truncatus – 9%. These small cetaceans did not use the area similarly. Distance from coast, distance from nearest river entrance, distance from nearest coral reef, and depth significantly differed among the three species (p < 0.05). Estuarine dolphin distribution was more coastal and concentrated near Caravelas and Doce Rivers. Rough-toothed dolphin distribution was concentrated near the coral reefs in the northern region of the Abrolhos Bank, whereas bottlenose dolphins were widely distributed across the Bank, along various depth ranges. Although the three species coexisted in the northern region of the Abrolhos Bank, our data suggest each showed specific habitat use patterns.