Delphinid Mixed-Species Associations in the Oceanic Waters of the Western South Atlantic

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Abstract: Dolphins are highly social animals usually reported in large groups comprised of individuals of a single species, although they are often reported associating with other species as well. The drivers for the formation of these mixed-species associations (MSAs) are poorly understood, and records in Brazilian waters are scarce. To better understand their occurrence in the region, we assessed seasonal and spatial distribution of MSAs in waters over the outer continental shelf and slope off Brazil (22° to 33° S). Data were collected during spring and autumn between 2009 and 2014. From a total of 187 Delphinidae sightings, 28 consisted of MSAs. Tursiops truncatus was the most frequently sighted species in an MSA (n = 22 sightings) and was mostly found in lower numbers than its associated counterparts: Globicephala melas, Stenella frontalis, Grampus griseus, and Pseudorca crassidens. MSAs between Stenella attenuata and Stenella longirostris or Delphinus delphis and S. frontalis were also reported. Our data did not show any seasonal or spatial trends in overall MSA frequency; nevertheless, the widely distributed T. truncatus appears to shift its associates according to their local abundance (e.g., associating with G. melas in the southern region of the study area and with S. frontalis in the southeastern region). Although a lot remains to be investigated regarding the ecological drivers for such associations between sympatric dolphins in Brazilian waters, this was the first effort to describe their occurrence and distribution patterns using cetacean dedicated surveys.
Key Words: Brazil, odontocetes, distribution, interspecific associations, cetaceans
Page Numbers: 53-62

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