| Summary: | The species richness, spatial distribution, seasonality and interspecific associations of cetaceans in tropical oceanic waters between the Gulf of Guinea and Angola were examined using 5 905.3 h of dedicated survey effort collected from 13 platforms of opportunity (geophysical vessels) between 2004 and 2009, and from incidental records. Most effort (87.8%) was recorded in waters >1 000 m deep. A total of 1 814 on-effort and 1 496 incidental sightings were recorded, comprising 22 species. Physeter macrocephalus and Megaptera novaeangliae were the most frequently sighted cetacean species, with Globicephala macrorhynchus and Stenella frontalis the most frequently sighted delphinids. Five species occurred in both neritic and oceanic waters, while the remainder had exclusively oceanic distributions. The occurrence of P. macrocephalus and M. novaeangliae differed significantly according to depth category. Most species occurred year-round; however, M. novaeangliae exhibited a strong, significant winter and spring occurrence. There were 65 interspecific groups recorded, involving at least 12 species. Mixed schools of G. macrorhynchus and Tursiops truncatus accounted for 55.4% of recorded associations. This extensive year-round dataset adds considerably to the understanding of cetacean distribution in the eastern tropical Atlantic and provides baseline information on which to base cetacean conservation and management in this poorly studied region.Keywords: eastern tropical Atlantic Ocean, interspecific associations, sighting rate, spatial distribution, species richness, temporal distributionAfrican Journal of Marine Science 2011, 33(1): 1–15
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