Marcos R. Rossi-Santos

Residence and site fidelity of Sotalia guianensis in the Caravelas River Estuary, eastern Brazil

Between April 2002 and April 2005, 210 estuarine dolphin groups were sighted, with 58 animals individually identified. Fifteen dolphins were photo-identified just once, while only two animals were sighted in 15 different months. Some individuals showed long-term residence (more than 3 y). Residence rates showed heterogeneity in the dolphin’s permanence of the estuary, with 60% of the individuals with low numbers (<10) and only 7% showing high values for residence (maximum=45.9). Continued resightings of some dolphins support the regular use of the study area by the animals, despite some individuals that, after a long time without resightings were registered again. Individual range analysis showed that dolphins shared the same common area, the Caravelas River Estuary. A marked fluctuation in the number of photo-identified dolphins was observed in the study area, revealed by the high number of individuals with just a few resightings. The majority of the dolphins (60%) present a yearly residence pattern, as observed in other areas, suggesting that a few individuals show high fidelity for the area, while many other dolphins move constantly between different areas for unknown reasons.

Evidence of Bottom Contact Behavior by Estuarine Dolphins ( Sotalia guianensis ) on the Eastern Coast of Brazil

We present herein the first records of evidence of bottom contact behavior by Sotalia guianensis. From April 2002 to December 2004, boat cruises were conducted along a 135-km stretch of coast on the Abrolhos Bank, eastern coast of Brazil. Evidence of bottom contact behavior was observed directly or through photographs on 25 occasions during the study period. On 16 occasions, one or more dolphins were observed with mud adhered to their dorsum, flanks, peduncle, head/melon, or dorsal fin. On five occasions, a mud-plume suspended by the movement of the dolphins and their contact with the bottom was observed. During four other occasions, both types of evidence (mud adhered to the body and mud-plume) were observed for the same group of dolphins. Contact by cetaceans with the sea floor is widely reported for several species and seems mainly related to feeding behavior, which probably is also the case for the observation presented here.

Padrões comportamentais e intensidade de movimentos de Sotalia guianensis (P. J. van Bénéden) (Cetacea, Delphinidae) em duas diferentes áreas da costa brasileira

The behavioral patterns of the estuarine dolphin, Sotalia guianensis (P. J. van Beneden, 1864), were compared between two populations along the Brazilian coast: Caravelas (Bahia), along the eastern coast, and Norte Bay (Santa Catarina), along the southern coast. Applying the focal-group sampling in both areas, information such as the geographic position (UTM) of groups and predominant behavioral patterns were obtained. Geographic positions were used to calculate the total distance traveled by estuarine dolphin groups on each observation day. Since the distance traveled varies with time, the daily mean speed of the dolphin’s group was used as an index of movement intensity. Two comparable and easily recognizable behavioral patterns were considered: travelling and foraging. Overall movement intensity and behavioral pattern frequency were similar between both areas. However, a seasonal variation was observed in both parameters in Norte Bay, while in Caravelas these parameters were homogeneous throughout the year. Variation in the behavior of the estuarine dolphin was consistent with variations in environmental factors, such as water temperature.

Interspecific cetacean interactions during the breeding season of humpback whale ( Megaptera novaeangliae ) on the north coast of Bahia State, Brazil

The large majority of cetacean interspecific studies report only on dolphin interactions, while studies on interactions between odontocete and mysticete are less common. The present work aims to report on sightings of cetacean interactions, during the breeding season of humpback whales (Megaptera novaeangliae), along 370 km of the Bahia State, north-eastern Brazil, addressing aspects of cetacean distribution and behaviour. During 7 seasons (2000―2006), a total of 230 research cruises were performed, in which 38 events of interactions among humpback whales and other cetaceans (Tursiops truncatus, Steno bredanensis, Peponocephala electra and Balaenoptera acutorostrata) were observed, plus another 5 encounters without the whales presence, including T. truncatus, S. bredanensis, P. electra, Stenella clymene and Stenella attenuata. Our results confirm the occurrence of multiple cetacean species in the Bahia State, being the first study in the world to report on a large range of interactions involving another 4 cetacean species, grouped with up to 3 mixed species per sighting, with humpback whales in their annual breeding ground.

Notas sobre a distribuição, tamanho de grupo e comportamento do golfinho Tursiops truncatus (Cetacea: Delphinidae) na Ilha de Santa Catarina, sul do Brasil

The ecology of the bottlenose dolphin (Tursiops truncatus) is scarcely documented in Brazil. The objective of this article is to present information about the distribution, group size and behavior of T. truncatus collected oportunistically around the Island of Santa Catarina. Locality, date and time, group size and behavior were registered after each opportunistic sighting. Seventy-one groups were observed between 1989 and 2005, in all months of the year. The species was sighted along all the coast of the island, using a great variety of habitats including protected bays and exposed beaches. Group size varied from 1 to 200 individuals, with a mean group size of approximately 8 individuals (mode = 2). Interactions with three species of sea birds were also documented. Data presented here suggest that the species is common around the Island of Santa Catarina, has a great plasticity in habitat use, and a varied behavior repertoire.

Opportunistic Sightings of Dolphins (MAMMALIA, CETACEA, DELPHINIDAE) in the North Coast of Bahia State, Northeastern Brazil, Between 2001 and 2006

Using opportunistic platforms to study humpback whales (Megaptera novaeangliae) during their breeding season, from July to November, we analyzed the distribution of dolphin sightings in a poorly studied area, the north coast of Bahia State, Brazil. Between 2001 and 2006, more than 500 days of surveys were performed (2360 h of effort), in which 93 groups of dolphins were sighted from Itacare (14° 53′S, 38° 15′W) to Subauma (12° 30′S; 37° 63′W): 58 (62.4%) bottlenose dolphin, Tursiops truncatus; 21 (22.6%) estuarine dolphin, Sotalia guianensis; 7 (7.5%) -toothed dolphin, Steno bredanensis; 3 (3.2%) Clymene’s Dolphin, Stenella clymene; 2 (2.1%) pygmy killer whale, Feresa attenuata; 1 (1.1%) melon-headed dolphin, Peponocephala electra and 1 (1.1%) Atlantic Spotted dolphin, Stenella frontalis. Group size and depth range were: 1–30 for T. truncatus (10–150 m); 1–35 for S. guianensis (4–60 m); 1–6 for S. bredanensis (27–45 m); 1–100 for S. clymene (42–121 m); 5–6 for F. attenuata (97–200 m); 2 for S. frontalis at 51 m and 20 for P. electra at 150 m. The more frequent sightings of Tursiops truncatus and Sotalia guianensis are probably related to their known distribution patterns in Brazilian coastal waters. The sightings reported to S. guianensis add new information in a previously unstudied area. The records of pelagic species such as Stenella clymene, Feresa attenuata and Peponocephala electra, can be related to the narrow continental shelf of the studied region. The sightings presented here confirm the occurrence of two additional species (F. attenuata and S. frontalis) in the Bahia state, and reveal the wide diversity of cetaceans in this area. This study is an initial step to document and collaborate with the knowledge about the dolphin species that occur in the shore of Bahia.