Rough-toothed dolphins (Steno bredanensis) are regularly present in continental shelf areas of the South-western Atlantic. However, there is little information on the natural history and ecology of these delphinids. This study evaluated the occurrence, habitat use and individual movements of the species in coastal waters off Rio de Janeiro, south-eastern Brazil. Data were obtained from boat surveys between August 2011 and May 2018, during which rough-toothed dolphins were sighted in 21 distinct events, predominantly in autumn and winter. The mean group size was 29 individuals. Rough-toothed dolphins were usually recorded 130 to 2300 m from the coast, between 7.6 and 28 m depths. In total, 115 individuals were catalogued through dorsal fin marks and 61 (53%) were resighted between one (47.5%) and four (9.8%) occasions. The interval between resightings ranged from seven to 2087 days (mean = 268). Agglomerative hierarchical clustering indicated 30 individuals (49.2%) in low degree, 12 (19.7%) in medium degree and 19 (31.1%) in high degree of site fidelity. Dolphins showed a higher frequency of low degree of habitat use, despite the presence of multiyear recaptures, which may be related to the prevalence of dolphin occurrence in autumn and winter, a large home range and/or the abundance and distribution of food resources. Dedicated surveys and regional collaboration are needed to evaluate the home range and population status of this species for their effective conservation. Our findings enhanced knowledge of this little studied species facing increasing anthropogenic threats in coastal waters off Rio de Janeiro.

To verify the movements of the rough-toothed dolphin (Steno bredanensis) on the coast of Rio de Janeiro State, south-eastern Brazil, we performed a photo-identification comparison between the catalogued individuals of Rio de Janeiro City (22°54′10″S–43°12′27″W) (N = 30) during August and September 2011 and the Cabo Frio region (22°52′46″S–42°01′07″W) (N = 41) during March and August 2011. Two photo-identified individuals from Rio de Janeiro City were resighted in the Cabo Frio region, approximately 119.7 km east of the original Rio de Janeiro sighting and two other individuals identified in the Cabo Frio region were resighted in the Rio de Janeiro City area, approximately 117.0 km west of the original sighting. This study reports the first information about the movements of the species in Brazil within these coastal areas.

Information on cetaceans off Gabon in tropical West Africa is summarized from boat-based surveys carried out between 7 March and 7 August 2009. Thirteen cetacean species were positively identified comprising two baleen whale species, one sperm whale species and ten species of delphinid. Bryde's whale (Balaenoptera brydei) and humpback whale (Megaptera novaeangliae) were the most frequently encountered species. Cetaceans were found throughout a range of sea surface temperature between 20.5°C and 27.5°C and a wide range of depths with the majority of effort and sightings occurring seaward of the shelf break. Of particular interest from the study were the following: (1) Gabonese waters have a broad cetacean diversity, especially with a large and diversified delphinid community in the northern part of the study area; (2) the variations in oceanographic conditions within Gabonese waters are likely to result in a temporal variation in species composition; (3) the sightings of Atlantic spotted dolphin (Stenella frontalis) are the first at-sea sightings confirmed for these waters, although not unexpected given their distribution and abundant presence in surrounding waters; and (4) the poorly known Clymene dolphin (Stenella clymene) was sighted on four occasions in deep oceanic waters and was the most abundant cetacean. These are the first confirmed records of Clymene dolphins in Gabonese waters.

In June 2009, a white rough-toothed dolphin (Steno bredanensis) calf was photographed in a group of at least 50 dolphins in the southern Gulf of Guinea, 95 nauticol miles off the Gabon coast (01°45′S 007°29′E), West Africa. Reports of unusually pigmented cetaceans are infrequent and this record represents the first of an all-white rough-toothed dolphin. Furthermore, there is little documentation concerning rough-toothed dolphins and this note contributes to the knowledge of this species in tropical West African waters.

In this note we contribute new evidence of epimeletic behaviour in Steno bredanensis in Brazilian waters. On 2 April 2007 we received information from lifeguards about a dead stranded rough-toothed dolphin at Prainha, Arraial do Cabo, east coast of Rio de Janeiro State, Brazil. The dolphin was a male juvenile, 187 cm in total body length from the tip of the upper jaw to the caudal notch, and it was in a moderate state of decomposition. The results presented here, in addition to previous studies, indicate that rough-toothed dolphins display a highly complex social structure.