Ecology of marine tucuxi, Sotalia guianensis, and bottlenose dolphin, Tursiops truncatus, in Baía Norte, Santa Catarina state, southern Brazil

The marine tucuxi (Sotalia guianensis) occurs in coastal waters of western Central and South America sympatric to the bottlenose dolphin (Tursiops truncatus) throughout its range. This paper presents information on ecology based on 228 marine tucuxi and 36 bottlenose dolphin sightings collected during 226 boat-based surveys conducted from 1993 to 2002 in Baía Norte (27°30'S and 48°31'W), Santa Catarina state, southern Brazil. Both species were found year round although seasonal occurrence, sighting indices, sightings per unit of effort as well as group size and composition were strongly different. These features were different for marine tucuxis but similar to bottlenose dolphins when compared to other areas. Marine tucuxis were only found in the western part of the bay while bottlenose dolphins occurred mostly in the eastern section. Distances between species' sightings on the same days averaged 6.9km. Observations were made of both dolphin species feeding on the same fish species, of tucuxis being displaced by bottlenose dolphins and of an adult tucuxi bearing tooth rakes likely to have been caused by bottlenose dolphin attacks. Spatial segregation was not clearly explained by the environmental variables analyzed, suggesting that biological features such as aggression or competition may be influencing tucuxi distribution and social structure in Baía Norte